A2088

MMaannaaggiinngg iinnsseeccttss iinn tthhee hhoommee vveeggeettaabbllee ggaarrddeennJ.A. Wyman and P.J. Pellitteri

— 11 —

B CCoonntteennttss BInsect pest identification. . . . . . . . . . . . . . . 2

Insects as pests . . . . . . . . . . . . . . . . . . . 3

Immature key . . . . . . . . . . . . . . . . . . . . 4

Adult key. . . . . . . . . . . . . . . . . . . . . . . 6

Cultural control . . . . . . . . . . . . . . . . . . . 8

Mechanical control . . . . . . . . . . . . . . . . . 9

Pest exclusion . . . . . . . . . . . . . . . . . . . . 9

Chemical control . . . . . . . . . . . . . . . . . . 10

Miscellaneous products . . . . . . . . . . . . . . 11

Insecticide toxicity . . . . . . . . . . . . . . . . . 11

Insecticide application . . . . . . . . . . . . . . . 12

Guidelines for insecticide use . . . . . . . . . . . 12

Development of insect management strategies . . 13

Insect management of vegetable crops . . . . . . 14

General pests . . . . . . . . . . . . . . . . . . . 18

Timetable of pest abundance and damage . . . . 20

IInnttrroodduuccttiioonn

Although insects frequently become pests in thehome vegetable garden, pest insectsrepresent only a small portion of the total

insect fauna. Over 7,000 insect species have beenrecorded in Wisconsin, but of these less than 100 aregarden pests. In fact, many insects are directlybeneficial as predators or parasites of pest insects, oras pollinators or decomposers of plant and animalmaterial. The vast majority of insects have no directimpact, either positive or negative, and are importantonly indirectly as components in food chains.

Control or management of the insects which dobecome pests can take many directions dependingon personal choice and the characteristics of theindividual pest. Our objective should not be toeradicate the pest entirely but to manipulate it or theenvironment in which it lives, so as to maintainpopulations below levels which cause unacceptabledamage.

Proper identification of insect pests is an essentialfirst step in insect management. After an insect isidentified, it is possible to examine its life cycle,biology and behavior and identify weak links whichcan be exploited to reduce its effects. The greater theknowledge of a pest, the greater the number ofmanagement options that are available to homegardeners.

This publication contains illustrated keys anddetailed narrative to assist in identifying pests. Itdiscusses different styles and types of pest controland suggests a variety of methods. Also included is aseasonal timetable that shows what time of the yearspecific pests are most active.

IInnsseecctt ppeessttiiddeennttiiffiiccaattiioonn

Insects are members of a group of animals calledArthropoda (jointed-feet) this group contains over75 percent of all described animal species on

earth. There are several classes within the arthropodswhich are not true insects but are closely related. Themost common relatives are the Crustacea (lobsters,shrimp, crabs), which are primarily aquatic but can beland dwellers (sow bugs). The Arachnida are alsorelated, and include two important categories in thehome garden, the mites and the spiders. TheDiplopoda group include centipedes and millipedes.Centipedes are usually predaceous, insect feeders,while the millipedes are plant feeders that usually feedon decaying organic matter.

The insects are the largest group of arthropods andthus are most frequently encountered as pests. Ananimal can be identified as an insect if you answeryes to all the following characteristics.

Is the body divided into three regions whichare specialized for different tasks? (Head witheyes and antennae for sensory perception andmouth parts for feeding, thorax with legs andoften wings for locomotion, and the abdomen.)

Does it have three pairs of jointed legs? (Thesemay be reduced or lost in very specializedinsects or in some larval insects.)

Does it have one pair of antennae (feelers)located on the head?

Are there two pairs of wings in the adult stage?(These may be highly modified or lostaltogether.)

Most insects change from the time they hatch fromeggs until they are full grown. This change in form iscalled metamorphosis. It may be a gradual change,involving little more than an increase in size, to a verydramatic difference between the young and the old.

There are several ways of characterizing the typesof metamorphosis, but the most common method is todivide them into incomplete (or simple) and completemetamorphosis.

— 22 —

B B

In the incomplete metamorphosis, insects whichhatch from eggs are called nymphs. As they feed andgrow they shed their skins, or molt. In the wingedspecies, wings first appear as pad-like buds on thenymphs. Each stage between molts is referred to asan instar. There is no prolonged “resting” periodbefore the adult stage is reached. The commonorders of insects which have incomplete or simplemetamorphosis are listed in the chart accompanyingfigure 1.

The complete metamorphosis involves a very majorchange in form between the young and the adult. Inthe winged forms the wings develop internally insteadof externally. The typical development involves theegg, larva, pupa and adult. The larvae may gothrough a number of instars and molts as they grow.The pupae may take several forms; they may beexposed or contained in a capsule-like puparium or ina silken cocoon. Some common orders having thistype of development are listed in the chartaccompanying figure 1.

To assist identification of common insect pests ofvegetable gardens, a pictorial key is included in thispublication (see pages 4–7). If you cannot identify aninsect, take it to your county Extension office.

IInnsseeccttss aass ppeessttss

Insects become pests more frequently than otheranimals because of the large number of speciesand their unparalleled ability to increase

populations very rapidly. Their reproductive capacitystems from the large number of offspring and from theshort life span of the insect. A complete life cycle canbe as fast as 7–10 days from egg to adult.

Many controlling factors in the environmentcombine to prevent insects from reaching theirreproductive potential. These factors can be bothbiological (parasites, predators, food availability) orphysical (rain, frost, pesticides). The biological factorsare most important in long-term control of insectnumbers, with physical factors exerting short-livedreductions.

Home gardeners should try to manipulate thenaturally occurring control factors and add new ones,where appropriate, to maintain insect pest populationsat non-damaging levels. The following discussionsuggests factors which can be important in pestmanagement.

— 33 —

B M A N A G I N G I N S E C T S I N T H E H O M E V E G E T A B L E G A R D E N B

Examples Orders

Lacewing Neuroptera

Beetles Coleoptera

Scorpion fly Mecoptera

Caddisfly Trichoptera

Moths, butterflies Lepidoptera

Flies, mosquitoes Diptera

Fleas Siphonaptera

Wasps, bees, ants Hymenoptera

Examples Orders

Grasshoppers Orthoptera

Termites Isoptera

Booklice Corrodentia

Thrips Thysanoptera

True bugs Hemiptera

Aphids Homoptera

Earwigs Dermaptera

Incomplete metamorphosis

Figure 1. Metamorphosis of various insects

Complete metamorphosis

egg larvae pupa adult

egg nymphs adult

— 44 —

IImmmmaattuurree kkeeyyNymphs

Not worm-shaped (without wings)

No tail pipe extendingfrom rear of body

Six true legs (three pairs),prolegs present; caterpillars

Tail pipes

* Beneficial insect

Green, brown or black larvaewithout horn at rear of body

Plant lice (aphids) Tail pipes extending fromrear of body.Onion thrips

About the size and shape of the exclamationmark “!”; yellowto brown in color.

Leafhopper 1⁄8 inch, green,wedge-shapednymph. Like adultsbut smaller.

Squash bug and leaf-footed bugOblong, greenishbrown body, 1⁄2 inchlong; often has twoblack spots onabdomen.

Cabbage looperTwo pairs of prolegs.Light-green larvaeup to 11⁄2 incheslong, body makes alooping motion whilemoving.

European corn borerWithout cross stripes; notbrown at each end; flesh-colored caterpillars up to1 inch long with smalldonut-shaped brownspots over the body.

Common stalk borerBrown and white stripesrun lengthwise on body.Yellow head. Bores intostems of manyvegetables.

Diamond mothcaterpillarThree pairs of prolegs.Light green, cigar-shaped larvae lessthan 3⁄4 inch long.

HornwormsRed or black horn atrear of body.

White grubFat, soft, C-shaped, whitegrubworms.

Four pairs of prolegs

➞

— 55 —

Worm-shaped larvae

ProlegsTrue legs

WirewormSlender, white or brown,hard-shelled worms.

Smooth-skinned larvae

Without cross stripes; not brown at each end;without donut-shaped spots.

Found on leavesFound in soil

Larval skin with warts or spines

Six true legs (three pairs), no prolegs No legs present

Root maggot1⁄2 inch long or less,white transparentbody, tapered at oneend.

Slugs“Snail-like,” gray tobrown, up to 1 inchlong. Leave shinytrials on leaf surface.

Colorado potatobeetle larva Reddish brown, hump-backed smooth-skinnedgrubs.

CutwormsGray, brown, white or black;smooth skinned. Markingsindistinct. Curl up in C-shape when disturbed.

Corn earwormLight green to nearly black larvaeup to 2 inches long with coarseblack hairs and alternating light anddark stripes running lengthwise onbody.

Imported cabbage worm Leaf green, velvety-skinnedlarvae, up to 11⁄4 inch long.

Asparagus beetleDark-gray, slug-likelarvae with soft, plump,non-hairy skin; blackhead and legs.

Lacewing*Spindle-shaped larvaewith long sharppointed jaws.

Lady beetle*Carrot shaped.Flattened, graduallytapering body with awarty back; does nothave long sharp-pointedjaws; colored withpatches of blue, blackand orange.

— 66 —

AAdduulltt kkeeyy

Spider mitesBarely visible—aboutthe size of a period.Adults have eight legs.

Aphids1⁄8–1⁄10 inch long,small, soft bodied, two tail pipes,usually no wings,pear-shaped bodies.

Lacewing* Front wings entirelymembrane-like.Finely netted, heldtent-like over body.Green in color. Hair-like antennae.

Leafhopper1⁄8 inch long, wedgeshaped. Hop whendisturbed.

AsparagusbeetleMetallic blue toback, orange toyellow marking.

Flea beetleAbout 1⁄8–1⁄4 inch long.

Ground beetle* 1⁄4 inch or longer.

Usually entirely one color—black, brown, blue or green

Plant bug1⁄4 inch long,actively fly.

Squash bug1 inch long,dark brown.

Antennae longer than lengthof head and thorax

Wings overlap on back, baseof front wing may be leathery;not hard shelled

* Beneficial insect

— 77 —

Moths and butterflies Wing covered with finepowder-like scales.Various sizes.

White flyTiny (1⁄8 inch), moth-likeinsects. Wings coveredwith whitish dust. Wingsoverlap when resting.

Lady beetle* Usually yellow, orange, orred beetles; usually withone or more spots perfront wing—but not eight.

Spotted cucumber beetle Yellow-green with six blackspots on each front wing.

Striped cucumber beetle Yellow with two blackstripes on each frontwing, elongate body.

Colorado potato beetle Yellow with four blackstripes on each frontwing; fat, round body.

Mexican beanbeetle Yellow to copper brown;eight black spots oneach front wing.

Picnic beetle Dark brown-blackwith four orange-yellow spots on back.

Larger than a period;adults have six legs

Wings present; notail pipes

Two pairs ofwings present

Spots or stripes onfront wings

Antennae shorter thanlength of head and thorax

Beetles Front wings entirelyhard shelled, meetingdown the middle instraight line.

True flies androot maggotadultsOnly one pair ofwings present.

Front wings withstripes

CClliimmaatteeInsects are cold-blooded and thus drastically

affected by temperature extremes. Extreme cold andheat reduce insect numbers. Insect development isslow or non-existent at low temperatures and speedsup at higher temperatures. Although temperaturecannot be manipulated, it can serve as a useful guideto the rate at which insects reach damaging levels.With some insects temperature can be used to predictthe occurrence of important life stages (seecalculating degree days on page 13).

Some pests need humid conditions to thrive(cutworms, slugs) while others may be successfulunder hot dry conditions (thrips, mites). Rainfall oftenprovides control by washing insects (such as aphids)from plants.

BBiioollooggiiccaall ccoonnttrroollNaturally occurring biological controls can play an

extremely important role in limiting insect populations.Insect predators including lady beetle larvae andadults, lacewing larvae, predacious sucking bugs(such as the assassin bug) and many others arealways present in a vegetable garden. Together withthe less obvious parasitic insects they can contributegreatly to a healthy garden. These biological controlsfrequently prevent pest populations from reachingdamaging levels. These effects are seldomspectacular and often go unnoticed. Remember thateven when biological controls are functioningeffectively there will still be a residual population ofpests. Removing all pests, particularly with aninsecticide, will disrupt biological control. To promotethe natural activities of predators and parasites, useinsecticides only when absolutely necessary and asselectively as possible. Introducing parasites andpredators by releasing commercially purchasedinsects such as lady beetle or praying mantis haslimited value in Wisconsin.

Naturally occurring insect diseases can beextremely effective in reducing populations. Bothfungal and viral diseases are common in someinsects. Whenever the conditions are optimal fordisease development and a large population ofinsects occurs at the same time, a disease epidemicusually breaks out. This phenomenon is most oftenseen in aphids and caterpillars. Unfortunately, it is noteasy to manipulate such disease occurrence.However, collecting sick or dying insects andspraying their crushed and diluted body parts onplants is occasionally successful. This approach has

no effect unless the insects are infected with adisease. You can identify a diseased population byseeing an increased number of insect carcasseswhere some of the carcasses are moldy, discolored,or decomposing into liquid tissue.

CCuullttuurraall ccoonnttrrooll

Cultural control is an area of insect managementwhere gardeners can utilize a wide array ofcrop management approaches to effectively

disrupt or adversely affect insect pests.

SSeelleeccttiioonn ooff ccrrooppssCrops vary widely in the number of insect pests

associated with them. Asparagus, beets, green or waxbeans, carrots, peas and tomatoes have relatively fewserious insect problems. Cole crops (cabbage,broccoli, brussels sprouts, cauliflower, radish,rutabaga, turnip) and potatoes have many insectpests and are extremely difficult to grow withoutsustaining some losses. When choosing crop types,also remember to consider plant disease problems.Extension publication Disease-Resistant Vegetablesfor the Home Garden (A3110) will help you selectcultivars with resistance to many disease problems.

TTiimmiinngg ooff ppllaannttiinnggBecause insect pest development is dependent on

temperature, insects are present in damagingnumbers for relatively short and predictable periodsduring the growing season (see the timetable of pestabundance and damage on page 20). By delaying oradvancing planting dates, gardeners can frequentlyavoid periods of high pest activity and drasticallyreduce damage. Examples of these controls arediscussed later under the specific crop sections.

When avoidance of insects is difficult, it is importantto keep the time that plants are most susceptible to aminimum. For example, many plants are particularlysusceptible to injury in the seed or seedling stages.Gardeners can reduce injury by planting only duringgood growing conditions, when germination is mostrapid, or by using plastic mulches to hasten growth.

— 88 —

B B

SSaanniittaattiioonn aanndd cclleeaann ccuullttiivvaattiioonn

Insect pests can often overwinter in plant debris.Good sanitation and removal of crop residues in thefall reduces or delays infestations the following spring.Working the soil in the fall and spring exposes insectswhich live or overwinter in the soil and can cause highmortality. Pests such as slugs and cutworms are moreof a problem in mulched gardens.

Weed control is important particularly with grassyweeds because several common garden pests(cutworms, grubs, wireworms) are attracted tograsses to lay their eggs.

CCrroopp rroottaattiioonnThe effectiveness of crop rotation in a garden is

limited to insects which have only one generation anddo not migrate readily. In such cases, rotation can beextremely effective. For example, corn rootwormadults lay eggs only in corn, and these eggsoverwinter. If corn is planted in the same spot, theresulting larvae cause damage, but if it is rotated evena short distance from the original site, damage isavoided.

Soil insects which are associated primarily withgrass and sod (grubs, wireworms) can be severeproblems if the garden is rotated into an area whichwas previously sod.

CCoommppaanniioonn ppllaannttiinnggResearch has demonstrated that plants such as

marigolds, basil and nasturtiums do not provideprotection when planted next to most vegetables. Infact, they often attract and support many of a garden’scommon pests. Diversifying a garden by interplantingdifferent plant types can help reduce problems butrequires a thorough understanding of the insectswhich attack each plant. In general, the fewer peststwo plants have in common, the better companionsthey are.

FFeerrttiilliizzeerr aanndd wwaatteerrIn general, plants which are healthy and growing

vigorously are able to contend with higher insectpopulations than plants which are weak or stressed.Thus, proper amounts of fertilizer and water and goodgrowing practices usually aid in reducing insectdamage.

RReessiissttaanntt vvaarriieettiieessAlthough most vegetable cultivars exhibit

differences in resistance to insect attack, theseattributes have not been exploited by commercialbreeders. Personal experience with varieties can oftenbe used to select the more insect-tolerant cultivars.

MMeecchhaanniiccaall ccoonnttrrooll

Home vegetable gardens are frequently of smallsize, so gardeners can physically preventcertain insects from attacking plants or can

remove the insects when they are present.Gardeners can use a number of approaches to

prevent insects from attacking plants. Crawlinginsects such as cutworms can be excluded with aphysical barrier such as a tin can around the bases ofplants. Paper discs can prevent access to plant basesto control cabbage maggot. Flying insects can beexcluded by placing a netting over the plants duringperiods of intense pest activity. Reflective mulch(aluminum foil or white plastic) effectively repelsaphids. Colored traps such as yellow bowls filled withsoapy water can attract insects away from plants anddrown them. These controls are given as examples.Gardeners often successfully devise new mechanicalcontrols or adapt existing ones to suit individualpreferences and situations.

When insects are on plants, gardeners canphysically remove and destroy them. This hands-onapproach is most effective with large, easily detectedpests such as hornworms and Colorado potatobeetles. Using an insect net to catch andremove day-flying insects like theimported cabbage worm or the squashvine borer can also reduce egg laying.

PPeesstt eexxcclluussiioonn

Because Wisconsin has extremely harsh winters,insects must hibernate in the state or migrate infrom states with milder climates each year. For

this reason, most insect infestations do not becomesevere until well into the growing season.Commercially purchased transplants, however, areproduced in greenhouses or southern states whereinsects are active year-round and may be infestedwhen purchased. Careful inspection of transplantsand removal of pests can effectively prevent earlybuildups of pests on these plants.

— 99 —

B M A N A G I N G I N S E C T S I N T H E H O M E V E G E T A B L E G A R D E N B

CChheemmiiccaall ccoonnttrrooll

Insecticides represent an artificial means ofreducing insect populations. They have theadvantage of being relatively simple to use and

quick to reduce populations which are at damaginglevels. Gardeners should use insecticides as only onepart of a carefully designed management strategy. Inthis way, the benefits of such materials can berealized and the adverse impacts on other naturalfactors can be avoided.

TTyyppeess ooff ffoorrmmuullaattiioonnssMany different insecticidal products are available

commercially, but these represent relatively few activeingredients which are formulated into many differentproducts. The most common formulations are:

Emulsifiable concentrates (EC)—Theseinsecticides are purchased as liquids whichare not soluble in water but form a whiteemulsion when mixed with water. They must bediluted with water prior to application.

Wettable powders (WP)—These are dryformulations (finely divided powders) where theinsecticide is mixed with inert material whicheasily disperses in water to form a suspension.They must be diluted before application, andoccasional agitation is recommended toensure that the suspension remains evenlymixed.

Dusts—Dusts are dry formulations with smallpercentages (2–5 percent) of insecticidesmixed with inert dust. They are applied drywithout dilution.

Baits—These are dry insecticide formulationsmixed with a material which is attractive topests as a food (bran, apple pomace) andformed into pellets. Baits are sprinkled on thesoil and must be eaten by pests to be effective.

TTyyppeess ooff iinnsseeccttiicciiddeessInsecticides can be manufactured chemically or

can be extracted from certain plants. The mostcommon insecticides available for home garden useare:

Botanical insecticides (extracted fromplants)

Ryania, Rotenone: Derived from the roots oftropical plants and need to be ingested to actas stomach poisons. These are normally usedagainst chewing insects.

Pyrethrin: Derived from the flowers of certainchrysanthemum plants. Pyrethrin causes rapidparalysis and apparent death, but insects maysubsequently recover. It is used primarily as afly spray additive or against soft-bodiedinsects. Mixtures with piperonyl butoxideprovide greater control.

Nicotine: Derived from the tobacco plant and iseffective against some soft-bodied insects.

Manufactured insecticides

Carbaryl (Sevin): A widely used insecticidewith several trade names. Effective on beetlesand some caterpillars but does not kill aphids.Persistent on plants for 4–5 days. Available asliquid, dust, wettable powder and baits.

Malathion: Moderately effective on a widerange of insects. Persistent on plants for2–3 days. Available as liquid, dust andwettable powder.

Diazinon: Moderately effective on a wide rangeof insects and can be applied to the soil.Persistent for 4–5 days. Available as wettablepowder, liquid and granular.

Methoxychlor: A longer lasting material usedprimarily on chewing insects.

Inorganic insecticides

Oils and soaps: Both oils and mild soap(1–2 percent by volume) or detergent solutionswill kill insects. Oils and soaps kill only insectscontacted with the spray and have littleresidual effect. Many oils will burn certaintissues if applied to actively growing plants.Some soaps have greater insecticidal activitythan others and specific “insecticidal soaps”are now available which are very effectiveagainst soft-bodied insects such as aphids,scales and mealybugs. Pure unscented soaps

— 1100 —

B B

are less likely to burn. If you are not familiarwith these treatments, test spray a smallnumber of plant leaves and allow 2–3 days forsigns of burning. Summer oils can be usedduring the growing season.

Microbial insecticides

Bacillus thuringiensis (Bt) (Dipel, Thuricide): Thistype of insecticide is a bacterium derived from amicrobe and is the only product available forhome garden use. Marketed under several tradenames, this product is actually a formulation ofbacterial spores which contain a toxin. Bt is astomach poison which causes gut paralysiswhen consumed by certain insects. Its action isextremely specific, being effective only againsttrue caterpillars (lepidopterous larvae). Adifferent strain can be used to control beetlessuch as the Colorado potato beetle. It isextremely safe for other organisms.

MMiisscceellllaanneeoouuss pprroodduuccttss

Various products such as salt, red and blackpepper, garlic and flour have been reported tokill insects or discourage feeding. There is no

scientific evidence to support these claims and theiruse should be approached with caution. Insects havemarkedly different sensory perception systems fromhumans and do not respond to the same things. Innature there are numerous insects which feed onplants which produce pepper, garlic and othernoxious odors. For example, the insects attracted tocabbage are attracted to mustard oils which humansutilize for tear gas.

IInnsseeccttiicciiddee ttooxxiicciittyy

Insecticides which are registered for use in homevegetable gardens need to be used properly.Materials which are classified as “slightly toxic” will

bear a “CAUTION” statement on the label. Thosewhich are “moderately toxic” bear a “WARNING,” andthose which are “highly toxic” will bear a “DANGER”statement and will also be identified by a skull andcrossbones symbol on the label. As a measure ofrelative toxicity to humans it is estimated that thefollowing doses would need to be ingested to causedeath in an average 160-pound adult:

| slightly toxic—1 pint to 1 quart

| moderately toxic—1 ounce to 1 pint

| highly toxic—1 drop to 1 ounce

Table 1 compares the relative toxicities ofinsecticides registered for home garden use. Forcomparative purposes, table salt (LD50—3,750mg/kg) and aspirin (LD50—1,750 mg/kg) would beclassified as “slightly toxic” if used as insecticides.

— 1111 —

B M A N A G I N G I N S E C T S I N T H E H O M E V E G E T A B L E G A R D E N B

Table 1. Relative toxicities of insecticides registered for home garden use

Common name Trade name Oral LD50, rata (mg/kg) Mammalian toxicityCarbaryl Sevin 650 Moderate

Diazinon Diazinon, Spectracide 108 High

Malathion Malathion 1375 Moderate

Methoxychlor Marlate, Methoxychlor 5000 Low

Nicotine Various trade names 83 High

Rotenone Rotenone 75 High

Bacillus thuringiensis Thuricide, Dipel, M-One 4000 Low

Pyrethrin Various names in combination 1870 Moderate

with other insecticides.1 LD50 is a term used to describe the toxicity of a pesticide to various test animals. The oral LD50 for rats is the

amount of pesticide in mg/kg of body weight required to kill 50 percent of a test population of rats when takenorally. These values should be used only as comparative values to indicate the relative degree of toxicity sincethey can vary among test animals.

IInnsseeccttiicciiddee aapppplliiccaattiioonn

Most garden insecticides are applied to thefoliage as liquid sprays. Dust and granularformulations are the exception. To prepare a

spray, use the amounts listed in table 2 of insecticidesto each gallon of water. Mix only enough for the plantswhich require treatment, and use the mixture as soonas possible after mixing.

Table 2. Insecticide spray mixes

Insecticidea Rate/gallon of watercarbaryl (Sevin) 50% WP 2 tablespoons

diazinon (Spectracide) 25% WP 2 tablespoons

diazinon (Spectracide) 25% LC 2 teaspoons

malathion 25% WP 4 tablespoons

malathion 50–57% LC 2 teaspoons

methoxychlor 50% WP 2 tablespoons

methoxychlor EC 2 tablespoons

rotenone 5% WP 4 tablespoonsa WP=wettable powder, LC=liquid concentrate,

EC=emulsifiable concentrate

Some insecticides are available in small packagesas dusts. Apply a light coating of dust at the rate of 1ounce per 50 feet of row.

Complete plant coverage of upper and lower leafsurfaces is important. This is because manyinsecticides must contact the insects or be eaten bythem to provide control. On plants which areextremely hairy or waxy, adding a drop of householddetergent per gallon will improve coverage.

GGuuiiddeelliinneess ffoorriinnsseeccttiicciiddee uussee

Always consider the following when usinginsecticides:

Correct timing and treatmentthresholds—Insects infest plants at definitetimes and should only be treated when presentin threatening numbers. Individual gardenersshould make judgments as to how much insectdamage they are prepared to tolerate. Often bytolerating minimal damage, which can easilybe trimmed or discarded, the need forinsecticides is greatly reduced and naturalcontrols build up to regulate the pestpopulation.

Protection of beneficial insects—Bydefinition insecticides kill insects;indiscriminate use will harm the pollinators,predators and parasites which keep a gardenhealthy.

Safety—Insecticides are relatively safe to usewhen properly handled, and only relativelynontoxic materials are registered for homegarden use. Nevertheless, all chemicals canbe toxic if used improperly. Always readproduct labels thoroughly, and followdirections exactly. It is illegal to changecontainers for pesticides. Pesticides should bestored in a locked cabinet out of the reach ofchildren. Check the label for pre-harvestperiods after treatment. Pre-harvest periodsdefine how long you must wait to harvest thevegetable to ensure that there are not toxiclevels of residue of the insecticide left on theplant. If the crop is not on the label, it is illegalto use the product on that particular vegetable.

— 1122 —

B B

DDeevveellooppmmeenntt ooff iinnsseecctt mmaannaaggeemmeennttssttrraatteeggiieess

Two schools of thought are most commonlyencountered in insect management in the homegarden. One school has relied primarily on

insecticide use, while the other—the organicapproach—has shunned all insecticide use exceptthat which is considered “organic” in nature. Anotherapproach is integrated pest management (IPM). WithIPM, all possible approaches to insect managementare utilized in a unified strategy to maintain insectpopulations at nondamaging levels, while avoidingadverse environmental effects.

In the following section, the major insect pests ofgarden vegetables are discussed together withvarious control approaches. From this, gardenersshould be able to design an insect managementstrategy tailored to suit individual preferences. Thepest keys (pages 4–7) enable each insect to beidentified, and the timetable (page 20) indicates thetime and duration of probable infestations.

— 1133 —

B M A N A G I N G I N S E C T S I N T H E H O M E V E G E T A B L E G A R D E N B

Calculating degree days

Temperature plays an important role in controlling the rate of development of crop plants andinsects. Cold weather slows development while warm weather accelerates it. To monitor cropdevelopment and predict pest behavior, you can use a system that takes into account the

accumulation of heat with passing time. This system is based on degree days (DD).

A degree day (DD) is a unit of measure that occurs for each degree above a base temperatureduring a 24-hour period. The base temperature is the temperature below which there is no plant orinsect development. Specific insects have specific base temperatures. To monitor plant and insectdevelopment using degree days, you will need a maximum/minimum thermometer to obtain thedaily high and low temperatures. Begin calculating degree day accumulations on March 1 using thefollowing equations:

(daily higha+ daily lowb) ÷ 2 = daily average temperature

daily average temperature – base temperature = 24-hour degree day accumulationaUse 86°F if the high temperature for the day is more than 86°F.bSubstitute the base temperature if the daily low is less than the base temperature.

Example: First-generation cabbage maggot emergence peaks at 300 degree days. This pest has abase temperature of 43°F. If the high for one day was 66°F and the low was 44°F, calculating thedegree days would look like this:

(66 + 44) ÷ 2 = 55 (daily average temperature)

55 – 43 = 12 (degree day accumulation)

Record the degree days for each day and continue adding them together. When the total nears300 degree days, take steps to prevent plant damage.

IInnsseecctt mmaannaaggeemmeenntt oonn vveeggeettaabbllee ccrrooppssAAssppaarraagguuss

Asparagus beetles and aphids are two types ofinsects that attack asparagus. Both do most of theirdamage in the spring.

Adult asparagus beetles are 1⁄4-inch long andmay be orange with black spots, or have yellowishsquares on a dark green background. Larvae areplump grayish worms with black heads. Activitybegins in spring as the plants emerge. Both adultsand larvae chew on the shoots and foliage, but somedamage can be tolerated. Eggs are cigar-shaped andblack and often are placed on the foliage in rows.Destruction of crop residues and trash eliminates adultoverwintering sites, and adults can be hand pickedearly in spring before egg laying. Carbaryl, rotenone ormalathion may be used if damage is severe.

Asparagus aphids damage young shoots, stuntgrowth and cause parts of the plant to take on abushy rosette appearance. Normally only one or twoplants in a patch are affected. Soapy water ormalathion can be used as a spot treatment.

BBeeaannss ((ggrreeeenn,, wwaaxx,, bbrrooaadd,, lliimmaa))Beans are a very good choice for people who prefer

to grow vegetables without chemicals, because mostinsect pest damage can be tolerated without treatment.

Seedcorn maggot is by far the most serious pestto all beans. The white legless maggot burrows intothe seed or seedling, causing very poor seedgermination and emergence, and/or stems withoutleaves (snake heads). The adult is a small grayish flywhich looks identical to the cabbage maggot. Thisinsect overwinters in the pupal stage in the soil andbecomes active early in the spring. Heaviest plantdamage occurs during cool damp weather, in heavyorganic soils and after peak adult flights. There arefive generations per year, but most severe damageoccurs in May and June. Peak activity of eachgeneration can be predicted using degree days (200,600 and 1000 degree days with a base temperature of39°F for first, second and third generations,respectively). But since damage is severe for each ofthe first three generations, it is seldom possible toavoid activity periods. Yellow pans (their bright colorattracts insects) filled with water and placed in thegarden are helpful in monitoring and reducing adultnumbers. Damage can be reduced by planting seeds

during good germinating weather, using seed treatedwith insecticide or sowing seed in higher than normalnumbers. Planting seeds too early or directly into richorganic matter, like manure, frequently increasesproblems with this insect. Other crops attackedinclude peas, corn, all vine crops and crucifers, butbeans are the preferred host.

Black bean aphids may cluster on the undersidesof succulent leaves, and large populations can causeyellowish foliage and poor growth. Both winged andwingless forms of this dark black aphid will be foundon the plant. In general aphids are susceptible tomany diseases and are frequently controlled bybeneficial insects. Soapy sprays or malathion can beused if high populations are observed.

Flea beetles can cause occasional problemswhen plants first emerge by chewing numerous smallholes in the leaves. Established plants can toleratesuch feeding. Flea beetles will be most severe inweedy gardens. If a problem does exist, cover theplants with cheesecloth or spray them with carbaryl.

Potato leafhoppers are an annual pest of thefoliage of bean plants. Adults are 1⁄8-inch, wedge-shaped, bright green insects which fly off plantsbefore gardeners can observe them. Nymphs hide onthe undersides of the leaves and move sidewayswhen disturbed. They feed by inserting needle-likemouth parts into the plant and extracting plant sap.Their saliva causes the plant to become stunted andthe outer margins of the leaves to turn yellow orbrown. This damage is called “hopperburn” and isoften mistaken for a disease. There are no effectivenatural enemies of this insect. Potato leafhoppers arefrequently found in large numbers in alfalfa. Gardensclose to alfalfa fields are often inundated when thealfalfa is cut. Hairy-leafed bean varieties have someresistance. Leafhopper feeding may reduce yields,but the average gardener can tolerate this damage.

BBeeeettss aanndd ssppiinnaacchhSpinach leafminers are very small flies. They lay

their eggs inside the leaves of a number of vegetables(spinach is particularly susceptible), where their smallmaggots develop within the leaf tissue. Numerous tanor white trails or blotches appear on the leaves, andgardeners may see small, pepper-like fecal pelletsinside the leafmines. To control this pest, remove anddestroy infested leaves and weeds at the first sign ofactivity. Sprays are largely ineffective becauseinsecticides have long harvest restrictions and pestactivity often coincides with maturation of the crop.Sprays will not kill larvae already in the leaves.

— 1144 —

B B

Green peach aphids (small, 1⁄8-inch, greenishaphids) may build to large populations on theundersides of the leaves. They can stunt the plant’sgrowth or cause it to wilt. The lush growth of spinachand beets makes spray coverage difficult, but forcefulstreams of water, a mild soap solution or malathioncan be used if populations are very high. Late-seasonpopulations are often controlled by naturally occurringfungal diseases.

CCaarrrroottss,, cceelleerryy aanndd lleettttuucceeAster leafhoppers carry a disease called aster

yellows, which is the main problem for these crops.Infestation in May and June results from leafhoppersmigrating into Wisconsin, but because of its migrationpattern, the severity of the disease varies yearly. Wellover 100 species of flowers, weeds and vegetablesare attacked. Once symptoms (stunting, yellowing, ordistorted growth) appear, gardeners should pull upand destroy infested plants to slow the spread of thedisease. Some varieties of carrots such as ‘ScarletNantes’ and ‘Gold King’ are more tolerant of thedisease.

CCrruucciiffeerrss ((bbrrooccccoollii,, ccaauulliifflloowweerr,,ccaabbbbaaggee,, bbrruusssseellss sspprroouuttss,,rraaddiisshh,, rruuttaabbaaggaa,, ttuurrnniipp))

Crucifers include a wide range of closely relatedvegetable species, all of which are extremelysusceptible to insect attack and generally have thesame complex of insects.

Cabbage maggot is the first insect to attack thesecrops. The adult cabbage maggot is a small gray flywhich lays its eggs at the base of crop plants in thecabbage family. The small cylindrical and white eggshatch into legless white maggots which feed on theroots. Seedling plants can be killed rapidly, whiletransplants tend to wilt and die slowly. Root cruciferssuch as radish and turnip show surface tunnelingwhich is often accompanied by soft rots.

The cabbage maggot has three generations inWisconsin. The first emergence of adults fromoverwintering pupae is the largest and mostdamaging. This emergence and theegg laying peak may be predictedaccurately byaccumulating thedegree days (seesidebar). Cabbagemaggots do not

develop below 43°F (base temperature), and theirdevelopment above 43°F is directly proportional totemperature, (the warmer it gets the fastercabbage maggots will develop).

Chemical controls require either soil applicationof diazinon to seed furrows or transplantdrenches. However, these treatments are oftennot effective since they last for only 4–5 days andneed to be applied when the adults are activelylaying eggs.

Knowledge of the emergence enablesgrowers to avoid planting during this time, thusavoiding damage. If planting is necessary, thendiazinon soil treatment should be effective. Duringthis time the adult maggot can also be excluded byplacing a netting over the plants or surrounding thebase with a protective collar.

Flea beetles are frequently a pest of earlyplantings. These small, shiny black beetles, whichjump when approached, chew small circular holes inthe leaves. This damage is insignificant on largeplants, but young seedlings can be rapidly killed.Usually, beetles are present for only a short time andcan be excluded with netting or controlled with acarbaryl spray.

Caterpillars (lepidopterous larvae) which chewholes in the leaves and heads of leafy crucifers posethe greatest insect problem. Three caterpillars arepresent in Wisconsin: the diamondback moth, theimported cabbageworm and the cabbage looper. Thediamondback moth and imported cabbagewormoverwinter in Wisconsin as pupae and are the first toappear on crucifers with a larval generation in June.Diamondback moth adults are small nocturnal mothswith a distinctive diamond pattern on the wings butare rarely seen by the gardener. Larvae are small(1⁄2 inch), cigar-shaped green caterpillars whichwiggle rapidly when touched. Their feeding damage isusually not severe enough to warrant treatment. In theabsence of pesticides this pest is heavily parasitized,and numbers do not exceed damaging levels.

Imported cabbageworms are day-flying whitebutterflies which lay cigar-shaped yellow eggs on theundersides of leaves. Adult flights are easily detected.Gardeners can remove eggs on small plants by hand.Seven to ten days after the eggs are laid, smallvelvety-green caterpillars begin feeding on the leaves.These increase to over 1 inch in length and causeconsiderable damage if large numbers are present.Two damaging larval generations normally occur, withthe first in June and the second in July and August.

— 1155 —

B M A N A G I N G I N S E C T S I N T H E H O M E V E G E T A B L E G A R D E N B

Cabbage loopers do not overwinter in Wisconsin.The adults are mottled brown nocturnal moths withwhite hourglass markings on the wings who migrateinto the state in June. The small, round white eggs areeasily detected on the undersides of leaves. Thelarvae are light green and characteristically move bylooping the body. They reach 11⁄2 inches in length andcause considerable feeding injury. Second generationlarval infestations occur in late August and Septemberand are most severe.

Bacillus thuringiensis sprays are an effective controlof imported cabbageworm and cabbage looper sinceBt is very specific and does not affect helpful parasites.Sprays are most effective if timed to coincide with thepresence of small larvae. These periods can beexpected to occur 1–2 weeks after egg laying andbefore damage is severe. Bacillus thuringiensis is lesseffective against larger caterpillars.

Two aphid species attack crucifers. The greenpeach aphid is a small, light green aphid which mayreach large numbers on the older leaves of leafycrucifers. Gardeners can treat these with soapy wateror malathion, but they cause little damage and may beleft to natural control by parasites and predators. Thecabbage aphid is a gray aphid which lives in closelypacked groups and secretes a copious gray wax.Heavy infestations cause leaf distortion and canprevent head formation. Early detection and removalwith soap or malathion sprays are most effective. Boththe green peach aphid and cabbage aphid can infestthe heads of broccoli and the sprouts of brusselssprouts, where they are extremely difficult to remove.Treat these plants prior to head formation if aphidpopulations are heavy.

OOnniioonnssOnion maggots are small whitish larvae found in

the bulbs of onions. The adult is a grayish fly whichresembles the cabbage maggot. This insect isextremely difficult to control with the options availableto the home gardener. To prevent increasingproblems, gardeners occasionally need to rotate outof plants in the onion family.

Thrips are small 1⁄25-inch insects which causewhitish scratches and brownish blotches on theleaves. They are often associated with weedy gardensand are more severe in hot dry summers. Damage issuperficial and can often be tolerated. Whenpopulations are very high, diazinon can be used as aspray treatment. The insect hides under leaf sheaths,and sprays must be applied with enough water toensure penetration to these areas. Two or threetreatments may be needed.

PPeeaassPeas are normally an early-season crop which has

few insect problems. Seedcorn maggots mayreduce plant stands during poor germinating weatherand can be controlled as described under beans.

Three species of aphid can be found on peas.Although they transmit virus diseases, aphids normallydo not need to be controlled in the home garden.However, gardeners can use soapy water ormalathion if populations become extremely large.

PPeeppppeerrssGreen peach aphids are a common pest of

peppers and often infest transplants as they comefrom the greenhouse. Large numbers of thesegreenish aphids will cluster on the undersides ofleaves, causing a sticky, shiny sap-like residue calledhoneydew which accumulates on lower leaves. Ablack sooty mold fungus frequently flourishes on thehoneydew, and its presence indicates high aphidpopulations. Growth may be distorted, and the plantmay wilt. Green peach aphids are subject to a numberof natural control factors. Gardeners also can controlthem with soapy water, malathion or diazinon.

Flea beetles may cause small shot holes in theleaves. This damage is insignificant on all but thesmallest plants. If needed, carbaryl or rotenone canbe used.

— 1166 —

B B

European corn borers can be a pest of peppers.Egg masses are laid on the leaves in August, and thedirty white caterpillars with dark heads can be foundburrowing in the fruits which often rot after infestation.This insect is only active for short periods of time, andthe injured areas are easily cut out of damagedpeppers. Because of this, chemical control is notsuggested.

PPoottaattooeessPotatoes are one of the most difficult crops to grow

in the home garden on an economical basis. Much ofthe insect damage is subtle but often responsible forkilling vines 3–4 weeks early, substantially reducingyields. The insect pests of potatoes are hard tomonitor and often missed by the average gardener.

Potato leafhoppers are small (1⁄8 inch), wedge-shaped, bright green insects which migrate into thestate every spring. Their saliva is toxic to the plant andcauses the leaf edges to curl, turn yellow andeventually brown, and die. This “hopperburn” is themost commonly missed insect injury in the Wisconsingarden. There are no good cultural controls, and thepotato leafhopper is without effective natural enemies.To control, spray with carbaryl or malathion at the firstsign of hopperburn. In severe years, more than onetreatment may be necessary. This insect builds tolarge numbers in alfalfa, and large infestations canoccur following the first cutting of alfalfa.

Potato flea beetles are small blackish insectswhich cause numerous 1⁄8-inch holes in potato leaves.This damage is insignificant on established plants andcan be ignored.

Two species of aphids attack potatoes. The potatoaphid is a large (1⁄8 inch), green or red aphid seen onthe succulent new growth of the plant. The greenpeach aphid is a smaller greenish aphid most oftenseen on the lower leaves. They both are responsible forspreading virus diseases. These aphids rarely needcontrol unless plants are grown for seed stock orinfestations are exceedingly heavy. Because many ofthe viruses are carried in the tubers, plant only certifiedseed stock, and do not replant home-grown tubers.

Colorado potato beetles are the most distinctivepest of potatoes. Both the yellow and black stripedadults and the brick-red humped larvae feed on thefoliage. They normally feed on new growth anddamage can be severe. Adults overwinter and moveto emerging potatoes early in the spring (May). Theadults lay bright yellow egg masses, and larvae feedfor several weeks in the summer before pupating inthe soil. Emerging adults then continue feeding

throughout the season until no vines remain.Gardeners can successfully hand pick them toachieve control. Colorado potato beetle is highlyresistant to most garden insecticides. Use the beetlestrain of Bt (M-One) or plant resistant (geneticallyengineered) potatoes. See Extension bulletinColorado Potato Beetle (A3678) for more information.

SSwweeeett ccoorrnn Early-planted sweet corn normally has few serious

problems. This is because most of the corn pests donot become abundant until mid-August. Always rotatesweet corn plantings within the garden to preventcorn rootworm larval problems.

A number of caterpillars can attack the ear tips. Theadults are night-flying moths which first appear in lateJune. The European corn borer, the cornearworm and the fall armyworm are all morecommon in late-planted corn. They usually lay theireggs on leaves or in the developing corn silks.Because the damaged portion of the ear is so easilyremoved, treatment is rarely justified. Gardeners canspray carbaryl while the silks are still green.

Seedcorn maggots can reduce the stand if cornis planted during cool germinating weather. Forcontrol of this pest, see the discussion in this sectionregarding beans.

TToommaattooeess A variety of aphids may affect tomatoes.

However, plants can tolerate large numbers,and natural enemies will eventually controltheir populations. In extreme cases,gardeners may use a forceful stream ofwater, soapy water or malathion for control.

Two caterpillars can be found on tomatoes. Thetomato fruitworm is a brownish to green caterpillarwhich bores into ripening fruit. It is a late-season pest(late August–September) which rarely needstreatment because the infested fruits are easilydetected and discarded.

The tomato hornworm is a very large greenishworm (up to 3 inches) with a spine on the posteriorend and white side stripes. The larva feeds on bothfoliage and fruit, and because each larva eats three tofour times its weight in food daily, the damageappears dramatic. The adult stage of this insect is agrayish hawk moth which is often mistaken for ahummingbird as it feeds on flowers. Because of itslarge size and small numbers, gardeners can geteffective control by hand picking and destroying thelarvae.

— 1177 —

B M A N A G I N G I N S E C T S I N T H E H O M E V E G E T A B L E G A R D E N B

Whiteflies are tropical insects which do not surviveWisconsin winters but often accompany greenhouse-grown transplants. Populations will build throughoutthe summer so that clouds of 1⁄8-inch adults fly upwhen the plants are disturbed. The nymphs (immatureinsects) are scale-like creatures found on theundersides of leaves. This is a very difficult insect tocontrol, but tomatoes can tolerate large numbers ofthese insects. A minimum of three insecticidaltreatments at 5-day intervals must be used to achievecontrol. Diazinon or insecticidal soap can be used. Ifone treatment is missed, the program must be startedagain from the beginning. Thorough coverage on theundersides of the leaves is needed.

VViinnee ccrrooppss ((ccuuccuummbbeerrss,, mmeelloonnss,, ppuummppkkiinnss,, ssqquuaasshh))Seedcorn maggots will attack the seeds of all

of the vine crops. Damage is most severe when plantsare planted before the recommended date or duringcool springs. For control, see the information listed inthe discussion of beans in this section.

The squash bug (an occasional pest) is a 1-inch,dark brown insect which becomes active as plantsemerge. It sucks the plant juices and causes wilting.Because insects are usually present in small numbers,they can be hand picked. Soapy water or carbaryltreatment also provides some control.

Striped or spotted cucumber beetles are 1⁄4-inch, yellow-green beetles which become active invery early spring. Adults feed on developing fruit andfoliage and, more importantly, transmit bacteria whichcause wilt disease. Small numbers of beetles candevastate a planting if they carry the disease, andthey must be controlled before the disease appears.Hand pick and destroy adults, or treat plants withrotenone or carbaryl as seedlings emerge and beetleactivity is noted. In the fall, adults of these beetles canchew holes in the developing fruit.

Melon aphids occasionally build up on theundersides of leaves. They are 1⁄10-inch blackishinsects which may cause stunting or wilting of theplant. Malathion or soapy water may be used asneeded.

Squash vine borers are a very serious and hard-to-control problem of summer and winter squash.Plants begin wilting in late July, and gardeners mayfind plump whitish caterpillars burrowing in the vines.There is only one generation per year and the mothoverwinters as a pupa in the soil. Gardeners muststart control procedures before injury is noted. In mostof the state, adults begin to lay eggs during the last

week of June. Adults are 1-inch, orange and green,day-flying moths. Eggs are brown, button-shaped and1⁄16 inch in diameter and are most often found at thebase of the plant. Gardeners may remove the eggs byhand, cover the plants with cheesecloth or net anddestroy the adults. Apply carbaryl to plant bases as aweekly spray for the 3-week egg laying period. Othertreatments, especially dusts, tend to provideinsufficient coverage. Cucumbers are highly resistantto borer attack, while summer squashes are verysusceptible.

GGeenneerraall ppeessttssThe following insects are potential problems on a

wide variety of vegetables.

CCoommmmoonn ssttaallkk bboorreerrCommon stalk borers lay their eggs in grassy

weeds in September. From late May through July thebrown and white striped caterpillars migrate into thegarden and burrow into the stems of tomatoes,potatoes, beans and other thick-stemmed plants.Once inside the stem, the insect cannot be controlled.Fall grass control or mowing will prevent egg layingand is the best control method for common stalk borer.

CCuuttwwoorrmmssCutworms are the larval stage or caterpillar of night-

flying moths. They are whitish gray to brown worms,ranging from 1⁄2 to 2 inches long. They feed almostexclusively at night and hide in the soil during the day.All cutworms curl to a characteristic tight ball whenexposed, making them easy to identify. Mostcutworms cut plants off at or slightly below the soilsurface, making recent transplants especiallysusceptible. Eventually, plants become too thick andtough for cutworms to feed. Adult females areattracted to tall grasses for egg laying, and cutwormnumbers tend to be higher in weedy gardens orgardens bordered by weeds.

To prevent cutworm damage on valuabletransplants, place small paper cups or tin cans withthe bottoms removed at least 11⁄2 inches into the soilaround the base of each plant. Commercial cutwormbaits containing carbaryl are available but must beused before damage begins.

The variegated cutworm climbs susceptible plantsand feeds on foliage. The larger stages do most of thedamage, but because they pupate in 7–10 days, it isusually too late to treat after noticing damage. Earliertreatments with carbaryl or Bt are partially effective.

— 1188 —

B B

PPiiccnniicc bbeeeettlleess ((ssaapp bbeeeettlleess))Picnic beetles are 1⁄4-inch, dark brown to black

beetles with four distinct yellowish orange spots ontheir backs. They do not damage fruit directly but areattracted to overly ripe or damaged fruits orvegetables. Melons, tomatoes, strawberries andraspberries are commonly infested. Because thesebeetles migrate into the garden and are attracted tofermenting fruit and vegetables, the first step incontrolling picnic beetles is to remove and destroyoverly ripe fruit. In most cases, spraying is ineffective.Beetles will continue to migrate into the garden anddelays in harvesting ripe fruit and vegetables due tothe waiting period after spraying will increaseproblems. Place a mixture of one-half water, one-halfdark corn syrup, one cake of yeast, and spoonful ofvinegar in a container outside the garden. It willattract, trap, and drown adult picnic beetles.

PPllaanntt bbuuggssPlant bugs are 1⁄4-inch, tan to dark brown oval

insects with piercing sucking mouthparts. They attackmore than 50 different economic crops but are mostdamaging to strawberries, peppers and snap beans inthe home garden. Feeding by this insect causes poorfruit set, and distorted gnarled fruit due to the toxicsaliva they inject into the plant. Populations aregreatest in rural gardens. This is a highly mobileinsect which overwinters in debris left in the field.Large numbers of adult plant bugs migrate out ofalfalfa fields when hay is cut. To control plant bugs,remove weeds and debris to prevent overwintering. Inproblem areas, sprays of malathion or carbaryl can beused as flower buds start to form.

SSlluuggssSlugs are closely related to snails and can be

common pests in gardens, especially during wetseasons. Slugs feed at night and are especiallytroublesome on tomatoes, strawberries and low-lyingplants. Reducing daytime hiding places such asboards, rubbish, unused pots and rocks will help.Placing pie tins baited with a beer and water mixtureat ground level will attract and drown slugs. Chemicalbaits containing metaldehyde are also available forslug control. See Extension publication General PlantDisorder: Slugs (A3186) for more information on slugsand their control.

WWhhiittee ggrruubbssThe white grub, which is the larval stage of the June

bug, has up to a 3-year life cycle. Because the adultslay eggs in grassy sodded areas, only newlyestablished gardens (1–3 years old) and weedygardens have significant problems. The characteristicC-shaped grubs feed on the roots of most plants.They are most damaging to root crops such as carrotsor potatoes. Tilling the soil to expose the larvae duringthe spring and fall helps reduce numbers. Granularinsecticides such as diazinon can be worked in thesoil before planting in areas where damage isexpected. Established gardens should have fewproblems.

WWiirreewwoorrmmssThe wireworm is the larval stage of the click beetle

and, like the white grub, lays eggs in grassy areas.Wireworms are also troublesome in low, poorlydrained areas. Weed control is the best preventativemeasure. Control procedures for white grubs will alsocontrol wireworms.

FFuurrtthheerr rreeaaddiinnggOrganic Gardening Magazine

Common Sense Pest Control

— 1199 —

B M A N A G I N G I N S E C T S I N T H E H O M E V E G E T A B L E G A R D E N B

References to pesticide products in thispublication are for your convenience arenot an endorsement or criticism of oneproduct over other similar products. Youare responsible for using pesticidesaccording to the manufacturer’s currentlabel directions. Follow directionsexactly to protect the environment andpeople from pesticide exposure. Failureto do so violates the law.

seed corn maggot

cabbage maggot

onion maggot

asparagus beetle

flea beetle

cucumber beetle

colorado potato beetle—adult

—larva

diamondback moth

imported cabbageworm

cabbage looper

European corn borer

corn earworm

squash vine borer

cutworms (various species)

common stalk borer

potato leafhopper

aphids

tarnished plant bug

thrips

Damaging stage may be present Period of most probable damage

April May June July August September

TTiimmeettaabbllee ooff ppeesstt aabbuunnddaannccee aanndd ddaammaaggee

© 1998 by the Board of Regents of the University of Wisconsin System doing business as the division ofCooperative Extension of the University of Wisconsin-Extension. Send inquiries about copyright permission to:Director, Cooperative Extension Publications, 201 Hiram Smith Hall, 1545 Observatory Dr., Madison, WI53706.

Authors: J.A. Wyman is a professor of entomology and P.J. Pellitteri is a distinguished outreach specialist inentomology, College of Agricultural and Life Sciences, University of Wisconsin-Madison and University ofWisconsin-Extension, Cooperative Extension. Produced by Cooperative Extension Publications, University ofWisconsin-Extension.

University of Wisconsin-Extension, Cooperative Extension, in cooperation with the U.S. Department ofAgriculture and Wisconsin counties, publishes this information to further the purpose of the May 8 and June30,1914 Acts of Congress; and provides equal opportunities and affirmative action in employment andprogramming. If you need this material in an alternative format, contact the Office of Equal Opportunity andDiversity Programs or call Cooperative Extension Publications at 608-262-2655.

This publication is available from your Wisconsin county Extension office or from Cooperative ExtensionPublications, Rm. 170, 630 W. Mifflin St., Madison, Wisconsin 53703, Phone 608-262-3346.

A2088 Managing Insects in the Home Vegetable Garden SR-07-98-4M-250