sweet corn management

7/30/2019 sweet corn management

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WW-07061-GO 1995

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Copyright 2002 Regents of the University of Minnesota. All rights reserved.

Vince Fritz

Horticultural ScienceSouthern Experiment Station, Waseca

Cindy B. TongHorticultural Science

Carl J. RosenSoil, Water, and Climate

Jerry A. WrightBiosystems and Agricultural Engineering

West Central Experiment Station, Morris

Sweetness in corn is genetically determined. Sweet corn is a recessive mutant of field corn, and

some of its sweetness is due to recessive mutants of the starchy gene found in field corn (Su).Other modifiers and genes affecting sweetness include the sugary-extender gene (se) and the

supersweet or shrunken gene (sh2).
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Main Genetic Types

Normal sugary (su) corn is the standard corn grown for processing and the fresh market. The

seed germinates well at 55-60F.

Sugary enhanced (se) corn results in slightly increased sugar levels and slower conversion of

sugars to starch after harvest. Kernels are very tender with good "corn" flavor. Seed germinateswell at temperatures of 55-60F.

Supersweet or shrunken-2 (sh2) corn produces kernels with two to three times the complex

sugars of the standard corn varieties. Texture is crispy rather than creamy as with the normal and

sugary enhanced varieties. Fresh market shelf life is extended due to the ability of the kernels toretain moisture and sweetness. Seeds are smaller,lighter in weight, and shrunken in appearance

(giving the genetic type the name "shrunken").

Recommended Varieties

Yellow Kernels

Sugary (su)

early season (62-72 days): Northern Vee, Earlivee, Seneca Horizon main season (73-83 days): Jubilee, NK 199 late season (> 83 days): Jubilee RR, Cornocopia, Arrestor

Sugary enhanced (se)

early season (62-72 days): Sugar Buns, Bodacious, MapleSweet, SpringTreat, Tuxedo,Seneca Daybreak

main season (73-83 days): Incredible, Miracle, Kandy King late season (> 83 days): Tendertreat, Kandy Korn

Supersweet (sh2)


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early season (62-72 days): Northern X-tra Sweet, X-tra Sweet 82 main season (73-83 days): Sweetie 82, SuperSweet Jubilee late season (> 83 days): Illini X-tra Sweet, Paradise

White Kernels (must be isolated from yellow or bicolor types)

Sugary (su)

late season (>83 days): Silver Queen


early season (62-72 days): Sugar Snow, Divinity main season (73-83 days): Alpine late season (> 83 days): Argent

Supersweet (sh2)

late season (> 83 days): How Sweet It Is, Snowbird, Pegasus

Bicolor Kernels

Sugary (su)

early season (62-72 days): Quickie late season (> 83 days): Honey n Frost


early season (62-72 days): Athos, Ambrosia, D'Artagnan, Kiss n Tell, Seneca Dawn main season (73-83 days): Calico Belle, Delectable, Lancelot


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Supersweet (sh2)

early season (62-72 days): Snowy Sun, Sweet-Green bi-70 main season (73-83 days): Honey n Pearl, Monte Carlo late season (> 83 days): Phenomenal, Hudson

Ornamental Corn

Standard cob size: Chinook, Indian Ornamental, Seneca Red Stalker, Fiesta Miniature cob size: Wampum, Indian Fingers, Strawberry Popcorn

Baby Corn

All baby corn is hand harvested and hand husked from immature corn at or within one to twodays after silking. The main varieties used are either prolific (multiple-eared) starchy field corn

types (Su) or supersweet (sh2). Research indicates the quality (sweetness and crispness) is

equally good for all genotypes, but that yields are higher with prolific (multi-eared) starchytypes. Varieties with small kernels and long ears are particularly suited for this purpose. The

pickled baby corn (imported from Taiwan and Thailand) is produced from special field corn (Su)varieties developed there for that purpose.

Starchy (Su)

Tainan No. 5, Tainan No. 11, Tainan No. 351, Baby Corn

Supersweet (sh2)

Florida Staysweet, How Sweet It Is (white), Stylesweet

Sugary (su)


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Silver Queen (white)

Seed

Each ounce contains approximately 120-180 sweet corn seeds. About 10-15 pounds are used per

acre. Seed sizing has been widely used in the seed industry to improve uniformity of emergenceand stand establishment. In general, flat seed performs better than round seed and heavier seed

performs better than lighter seed.

Large differences in seed vigor may occur between varieties, particularly under cool, wet, or

compacted soil conditions. The difference in performance is not apparent from germinationinformation on the identification tags because germination tests are frequently conducted underideal conditions. Personal experience with a particular variety is often the only way to know its

potential and limitations.

Use only seed that has been properly treated with fungicides and insecticides for maximum

germination and stand establishment. Seed companies are now offering supersweet varieties that

are specially coated with a polymer after being treated with pesticides. The polymer coatingreduces user exposure and reduces the amount of pesticide used.

Isolation

Isolation is necessary for two reasons: color and kernel quality (sugars and texture). Two ways to

achieve isolation are distance and time. If effective isolation is not achieved, significantoutcrossing can occur, which can render a significant amount of product unsalable (up to 10

adjacent rows of each variety!).

By Distance

Locate the variety most affected by outcrossing upwind from other varieties. Plant varieties with the same genetic type together in a block -- at least 250 feet away

from other genetic types.


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Since colored kernels in white varieties are very obvious, use an isolation distance of 500feet or more between white and colored varieties.

By Time of Pollination

If the two- to three-week pollination time difference is to be used as a means of isolationbetween genetic types, and plantings of different genetic types are adjacent, several things needto be considered:

The later planting must not be planted based o n calendar day difference but rather ongrowth stage or heat units. Obtain specifics regarding the variety from the individual seed

company. The maturity difference between the two types of corn also needs to be figured

into the planting date difference. Assuming the standard sweet (su) and supersweet (sh2)varieties have the same maturity (days from seeding to pollination), delay planting the

second variety until the first planting has eight or more leaves, or until 300 or more heat

units (base 50F) have elapsed.

To obtain an effective two- to three-week spread at pollination, the early planting mustgerminate uniformly. If germination is not uniform, late-germinating plants may causeproblems.

By Blocking

Fresh market growers who have a use for, or a market for, ensilage may also choose to "block"

plantings that have not been isolated by distance or pollination time. This practice consists ofwalking progressively further from the boundary of the two plantings, examining a sample of

ears in each row visually until a row is found where the outcrossing incidence is acceptable, and

abandoning the intervening rows (and using them for silage).

Seeding and Spacing

For early fresh market sugary varieties (su), seeding may start as soon as soil temperatures reach

50F and after the danger of spring frost has passed. Use 10-15 pounds/acre of seed, depending

on the variety and seed size. Seeding at a depth of l2 inches is generally satisfactory. Shallowplanting ( inch) and maintenance of high soil moisture are recommended where head smut may

be a problem and for supersweet (sh2) types. For processing, recommended stands are 26,000 to

27,000/A if irrigated or 20,000 to 24,000/A if not irrigated while for fresh market, where large

ear size and good husk color are important, stands should be between 20,000 and 25,000 peracre.

For a rough planting schedule that will provide about 10-14 days between mid-season peakharvests between plantings, wait until most of the plants in the previous planting have three


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leaves before planting again.

Plant fast-growing, small-stature varieties in rows approximately 30 inches apart, with 6-8 inchesbetween plants. Grow vigorous, tall-growing varieties in rows 30-36 inches apart, with 9-12

inches between plants. Plant processing varieties according to the row spacing and rate

recommended by the processor.

For baby corn two systems are used. One system uses standard populations of about 23,000

plants per acre, where the top ear is left on the plant for grain corn or sweet corn and subsequentears are harvested for baby corn. The second system uses high plant populations of between

34,000 and 44,000 plants per acre where all ears are harvested for baby corn. Row spacings

range from 24 to 36 inches apart. The standard plant populations produce yields of about 4,000pounds of unhusked ears (400 pounds of husked ears) per acre, while the high populations

produce yields of about 8,000-10,000 pounds of unhusked ears (800-1,000 pounds of husked

ears) per acre.

Seed Companies/Distributors

Abbott & Cobb Inc., POB F307, Feasterville, PA 19047 Asgrow Seed Company, POB 5038, Salinas, CA 93915 Crookham Co., Caldwell, ID 83606 Green Barn Seed Co., 18855 Park Ave., Deephaven, MN 55391 FerryMorse Seed Co., POB 4938, 555 Codoni Ave., Modesto, CA 95352 Harris Seeds, 60 Saginaw Dr., POB 22960, Rochester, NY 14692-2960 Harris Moran Seed Co., 3670 Buffalo Rd., Rochester, NY 14624 Illinois Foundation Seeds Inc., POB 722, Champaign, IL 61820 Jordan Seeds, Inc., 6400 Upper Afton Rd., Woodbury, MN 55125 Rogers NK Seed Co., POB 4727, Boise, ID 83711-4727 Seedway, Inc., POB 1333, Syracuse, NY 13201 Stokes Seeds Inc., POB 548, Buffalo, NY 14240 Sunseeds, 2320 Technology Pkwy., Hollister, CA 95023 W. Osborne Seed Co. Int'l., 1679 Highway 99 South, Mount Vernon, WA 98273 Zenner Bros. Seed Co., Inc.,1311 S.E. Gideon St., Portland, OR 97202

Soil


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A wide variety of soils is suitable. It is important that the soil be well drained and well suppliedwith organic matter. The optimum pH range is 5.8 to 7.0.

Soil Temperature

The minimum soil temperature for germination is 50F. Temperatures should reach 60F for the

supersweet and improved supersweet varieties because germination is drastically reduced undercooler soil conditions. Generally, sweet corn takes about 14 days to emerge from 50F soils, but

only about 5 days to emerge at 70F. Soil temperature is a key factor to consider when

scheduling plantings.

Fertilizer Recommendations

A soil test is the most accurate guide in determining fertilizer requirements. Follow

recommended soil sampling to estimate fertilizer needs. Your Minnesota Extension Service

county extension educator can provide you with soil sampling instructions, soil sample bags, andinformation sheets.

Good management practices are essential if optimum fertilizer responses are to be realized.These practices include use of recommended varieties, selection of adapted soils, weed control,

disease and insect control, good seed bed preparation, proper seeding methods, and timely

harvest.

Primary Nutrients

Nitrogen (N)

Eastern Minnesota and All Irrigated Sweet Corn

Because of the mobility of nitrate in soils and the complex transformations from organic matter,

soil tests for N are not reliable for predicting N fertilizer needs in the eastern half of Minnesota,

particularly on sandy irrigated soils. Therefore, N recommendations are based on yield goal,

previous crop, and soil organic matter content. Refer toNutrient Management for Commercial
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Fruit & Vegetable Crops in Minnesota (BU-5886), pg. 9, for more information and referencemap. The soil nitrate test has not been calibrated for sweet corn in eastern Minnesota and is

therefore not used for making N recommendations.

Table 1. Nitrogen Recommendations

Previous Crop and Organic Mater (O.M.) Level

Alfalfa(good stand)

-O.M.-

SoybeansField Peas

-O.M.-

Any Cropin Group 11

-O.M.-

Any Cropin Group 22

-O.M.-

Organic

Soil3

Yield Goal low4,5

medium

to highlow

medium

to highlow

medium

to highlow

medium

to high

tons/A N to apply {lb/A}


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Soil Test Is Used (Western Minnesota)

Yield Goal (ton/A)Soil Nitrate-N (0-2 ft.)

Plus Fertilizer N to Apply (lb/A)

4 70

6 110

8 145

10 180

Timing of N Application

For coarse-textured and irrigated soils, apply N in two to three applications. At planting, apply

10-20 pounds N per acre with P and K fertilizers as a band (refer to section on starter fertilizers).Apply additional N in two equal applications at the 4-6 leaf stage and again at the 10-12 leaf

stage. For nonirrigated, fine-textured soils, timing of N application during the season is not asimportant. In wet years, broadcast application prior to planting is sufficient to meet crop needs,particularly if anhydrous ammonia or urea is used. Splitting N applications after planting works

well provided that timely rainfall moves the applied N to the root zone.

Nitrogen Source

From a practical standpoint, the source of N to use for sweet corn production should be based on

cost. At equal N rates, N source has little impact on sweet corn provided the N fertilizer isapplied properly and that differential nitrate leaching or ammonia volatilization losses do not

occur. To prevent excessive nitrate leaching, avoid early application of nitrate-based fertilizer

such as ammonium nitrate. If urea is used, be sure that the fertilizer is incorporated or irrigated inwithin 24 hours after application. Ammonia volatilization can be substantial from surface-

applied urea. If anhydrous ammonia is used, do not sidedress too close to young seedlings as

injury can result. The use of a nitrification inhibitor such as N-Serve (with early-appliedanhydrous ammonia) is a best management practice to reduce nitrate leaching.

Phosphorus (P)

Phosphorus requirements for sweet corn are based on soil test P level and yield goal. Banding of

P at planning increases P use efficiency compared to broadcast application and substantially

reduces the recommended P application rates.

Table 3. Phosphate Recommendations

Soil Test P (ppm)

Yield GoalBray-P1 0-5 6-10 11-15 16-20 21+

Olsen-P 0-3 4-7 8-11 12-15 16+

Bcst/Row Bcst/Row Bcst/Row Bcst/Row Bcst/Row


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tons/A P(2)O(5) to Apply (lb/A)

less than 6 70/40 40/25 30/20 10/10-15 0/10-15

6-7 80/40 50/30 30/20 10/10-15 0/10-15

8-9 90/40 60/35 40/25 10/10-15 0/10-15

10 or more 100/40 70/40 40/25 20/10-15 0/10-15

If soil pH is 7.4 or greater, use the Olsen P test to determine P needs. If soil pH is less than 7.4,use the Bray P-1 test. For low P testing soils, a combination of broadcast and band applications is

suggested. For high P testing soils, only banded applications are needed. Testing P levels is

particularly useful for early-planted sweet corn where where soils may be cool and wet.

Potassium (K)

Potassium requirements for sweet corn are based on soil test K level and yield goal. On low Ktesting soils, a combination of broadcast and banded applications of K is suggested. On high K

testing soils, all K fertilizer can be banded.

Table 4. Potassium Recommendations

Soil Test K (ppm)

Yield Goal 0-40 40-80 81-120 121-160 161+

Bcst/Row Bcst/Row Bcst/Row Bcst/Row Bcst/Row

tons/A -K(2)0 to Apply (lb/A) -

less than 6 120/40 60/30 40/10-15 40/10-15 0/10-15

6-7 140/40 80/30 40/10-15 40/10-15 0/10-15

8-9 160/40 100/40 60/25 40/10-15 0/10-15

10 or more 180/40 120/40 80/30 60/25 0/10-15

Secondary Nutrients

Calcium (Ca)

Most soils in Minnesota are well supplied with Ca. In acid soils where Ca levels may be low, Ca

requirements are met through a proper liming program. On acid soils where sweet corn is inrotation with potatoes and liming is not practiced, some supplemental Ca may be needed. Soil

test Ca levels less than 300 ppm are considered low. In this situation, low rates (1,000 pounds per

acre) of a fine lime should be applied during the year that potatoes are not grown.


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Magnesium (Mg)

As with Ca, most soils in Minnesota are well supplied with Mg. In acid soils, where Mg levels

may be low, Mg requirements are met through a liming program using dolomitic limestone. Ifliming is not used in the rotation, for example with potato production, some supplemental Mgmay be needed. Mg needs based on a soil test are provided in table 5.

Table 5. Magnesium Recommendations

Magnesium Relative Magnesium to Apply

Soil Test Level Broadcast Row

---(ppm)--- -------(lb/A)------

0-49 low 100 20

50-99 medium 50 10100+ high 0 0

Common sources of Mg fertilizer include potassium-magnesium sulfate (10 percent Mg) andEpsom salts (10 percent Mg). Finely ground dolomitic limestone can also be used to supply Mg.

Sulfur (S)

Sulfur may be needed for sweet corn production on sandy soils. Soil tests for S are only reliablefor low organic matter soils. Needs for S based on a soil test are provided in table 6.

Table 6. Sulfur Recommendations

Sulfur Relative Sulfur to Apply

Soil Test Level Broadcast Row

-(ppm)- --(lb/A)--

0-6 low 20-30 10-15

7-12 medium trial only

12+ high 0 0

For sweet corn, the need for S occurs early in the season. Therefore, a banded application of S in

the sulfate form is suggested.


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Micronutrients

Zinc (Zn)

Of all the micronutrients, Zn is the one most likely to be needed in a fertilizer program for sweetcorn. The need for Zn fertilizer should be based on a soil test.

Table 7. Zinc Recommendations

Zn Soil Test(ppm) Relative Level Zn to Apply(lb/A)

Broadcast Row

0-0.5 low 10 2

0.6-1.0 marginal 5 1

1+ adequate 0 0

If Zn is required, application of Zn in a starter fertilizer is suggested to meet crop needs.However, carryover to succeeding years will be better with broadcast applications. Several

fertilizer products can be used to supply Zn. Except for large particles of Zn oxides, all are

equally effective. Base product selection on cost.

Boron (B)

No consistent responses of sweet corn to B application have been observed in Minnesota. Where

the soil test value for B is below 0.25 ppm, a trial broadcast application of two pounds B per acreis suggested.

Too much B fertilizer can be highly toxic; do not exceed suggested application rates. Fertilizer

containing B should not be in contact with the seed.

Low rates of B (1/8 lb per acre) can be used in a starter fertilizer if the fertilizer is placed two to

three inches below and two to three inches to the side of the seed.

Copper, Manganese, and Iron

Sweet corn responses to copper, manganese, and iron have not been observed in Minnesota and

are therefore not recommended in a sweet corn fertilizer program.


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Lime

The optimum pH for sweet corn production is 5.8-7. Lime is generally recommended if soil pH

is less than 5.8. The need for lime can be determined from a routine soil test. Lime should be

applied before planting and incorporated to a depth of six inches.

For further information on lime-lime application rates, lime sources, and reference map, refer toMinnesota Extension Service bulletin,Nutrient Management for Commercial Fruit & Vegetable

Crops in Minnesota (BU-5886), pgs. 2-4.

Using Manure

The amount of plant nutrients in a fertilizer program can be reduced if manure is used. Thenutrient content of manure varies with type of livestock and methods used in storage, handling,

and application. Many laboratories will measure the nutrient concentrations in manure. Manure

analysis is strongly recommended if routine applications are made for crop production. The

results of such an analysis will give a more precise measurement of the nutrient value of manure.

Using Starter Fertilizer

The use of a starter fertilizer at planting is an excellent management tool for corn production in

Minnesota especially when soil conditions are cold and wet at planting. Yield increases are not

always achieved with starter fertilizer, but this management practice is good insurance. For sweet

corn, fertilizer should be banded two to three inches to the side and two to three inches below theseed. Banding fertilizer too close to the seed or at too high a rate can cause seedling injury due to

high salt concentrations. In general, the N plus K 2 O application in a band should not exceed 90pounds of nutrients per acre. Urea or diammonium phosphate forms of N may cause seedling

injury if banded too close to the seed at planting, especially where the soil pH exceeds 7. In

addition, urea, ammonium thiosulfate (12-0-0-16) or fertilizer containing boron can cause

significant injury if placed in contact with the seed.

Tissue Analysis

Tissue analysis can be used during the growing season to monitor the nutrient status of the plant

and help diagnose nutritional problems. Table 8 shows sufficiency levels in whole plant samples

taken when plants are 12 inches high and in ear leaf samples taken during silking.
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Table 8. Sufficiency Levels

Stage of

Growth

Plant Part

Sampled% ppm

N P K Ca Mg S Fe B Cu Zn Mn Mo

12" height Whole plant 3.5 0.6 3.0 2.5 0.3 0.2 60 50 7 20 50 0.3

Silking Ear leaf 2.8 0.25 1.5 1.5 0.25 0.2 50 40 6 20 25 0.3

Irrigation Management

Water management of irrigated sweet corn is an essential production practice to produceoptimum yields and quality ears. Yield and quality of ears are significantly reduced if moisture

stress occurs during tasseling, silking, and kernel fill. Short periods of moisture stress earlier in

crop development usually will not affect yield unless poor germination occurs. However, it maydelay harvest date. To manage the soil's moisture effectively, a regular in-field soil/water

monitoring program should be established to assist in irrigation scheduling.

Establishment of an effective irrigation scheduling program involves being knowledgeable of

several factors and then putting them into practice. The following discussion briefly outlines

those factors.

Crop Water Use

Water use by the crop is referred to as evapotranspiration (ET). Sweet corn will use four to six

inches less total water than field corn in a season, but generally will use similar daily amounts for

the same conditions. Daily ET is dependent on several factors such as stage of growth, air

temperature, and solar radiation. Table 9, taken from the Minnesota Extension Service bulletin

Irrigation Scheduling (FO-1322), gives estimated daily crop water use in inches for different

corn growth stages and several maximum daily air temperature ranges.

Table 9. Estimated Daily Crop Water Use

Week After Emergence (growth stage)

2 6 8 10 12

(4 Leaf) (12 Leaf) (Tassel) (Pollination) (Milk)

Air Temperature ( F) --inches of ET per day--


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50-59 .02 .06 .09 .10 .10

60-69 .03 .09 .12 .15 .14

70-79 .04 .12 .16 .19 .18

80-89 .05 .15 .20 .24 .22

90-99 .06 .18 .24 .28 .26

The greatest daily water use will usually occur from tassel to harvest. It is not uncommon forsweet corn to use .25 inch per day or more for several days. To keep up with this use, your

irrigation system must have a similar capability. For sandy soils, a system capacity of .25 inch or

greater per day is generally recommended. The following table gives the system gallon perminute (GPM) capacity needed for each acre, irrigated for various pumping periods per day and

crop water use rates. To determine the total system capacity needed to adequately meet the crop

water needs for a given system, simply find the appropriate capacity and multiply it by your total

corn acres (table 10).

Table 10. System Gallon Per Minute (GPM) Capacity

GPM/ACRE at 75% ApplicationEfficiency

Crop Water Use(inches/day)

12 hr/day 18 hr/day 24 hr/day

0.15 7.6 5.0 3.8

0.20 10.1 6.7 5.0

0.25 12.6 8.4 6.3

0.30 5.1 10.1 7.6

Rooting Depth

Sweet corn has a relatively shallow rooting depth compared to field corn. Most literaturesuggests that under irrigation, only soil moisture in the top 18 to 24 inches of the rooting zone

should be managed. If the soil is shallower or a restrictive layer prevents root growth, the root

zone to be managed must be reduced.

Available Soil Water

Available soil water is the water stored in the soil that roots can extract. The amount of soil water

available to a plant is dependent on both the rooting depth potential and the soil's available


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water-holding capacity (AWHC). The AWHC for a given soil is expressed in inches of water perinch of soil and is dependent on the soil's texture and organic matter. The AWHC for your fields

can be estimated by SCS personnel or others having access to area soil maps. To determine the

total available water capacity in a field, simply take the soil's AWHC times its rooting depthpotential. For example, a sandy loam textured having an AWHC of .12 inch per inch and a 24-

inch rooting depth will store a total of 2.88 inches for the sweet corn plants.

Knowing the amount of available water the soil is storing at any time is very important. It

governs the amount of water that can effectively be applied at each irrigation without over-

irrigating. Several tools are available to assist in monitoring the available water. A discussion ofthe typical monitoring methods can be found in Minnesota Extension Service bulletinsIrrigationWater Management Considerations for Sandy Soil in Minnesota(FO-3875) andIrrigation

Scheduling--Checkbook Method(FO-1322).

Irrigation Timing

Generally, optimum sweet corn growth will occur if the soil moisture level is maintained at about

85 percent of the available water capacity, although symptoms of moisture stress usually do notappear until the soil moisture has been reduced to 40-50 percent of capacity. Cycles of extremewet versus dry conditions should be avoided as it may reduce ear quality. Sweet corn is most

sensitive to moisture stress during pollination and ear formation.

Irrigation start-up should generally occur when the soil moisture level is between a -inch

deficit and 60 percent of field capacity. During the critical growth stages, keep the soil moisture

as high as possible at all times. At germination time it is also important to start out with a fullprofile, but then allow the soil to dry down to possibly 50-60 percent of field capacity up to the

10-11 leaf stage to ensure a rapid and complete root development. Timing of irrigation may also

be influenced by other factors, such as nitrogen application, insecticide spraying, diseasesuppression, forecasted rain, and harvesting.

Harvesting and HandlingOptimum processing quality and returns for normal sweet and sugary-enhanced (su and se)

varieties occur when kernel moisture is about 73 percent and 76 percent for supersweet (sh2)

varieties. Kernel moisture drops approximately 0.5 percent per day in normal sweet and sugary-enhanced corn varieties with considerable variation depending on season and variety. Kernel

moisture of supersweet (sh2) varieties changes at a considerably slower rate. Fresh market corn
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usually reaches peak maturity from 21 to 25 days after silking.

Self-propelled and tractor-pulled harvesters are available from several manufacturers. Thesecome in single-row or multiple-row units of up to eight rows. For fresh market corn harvest,

some of the harvesters have to be slightly modified so that they do not damage the butt portion of

the ear. These modifications are generally made easily and are usually offered as options fromthe manufacturer.

Corn for processing is generally machine harvested in Minnesota between July 25 and October10. Harvest begins when kernels of standard varieties reach 70-74 percent moisture. Corn should

be protected from overheating (kept in shade) and delivered to the processor as soon as possible.

Supersweet and sugary enhanced varieties (grown for fresh market) maintain their sugar contentlonger after harvest than standard varieties but still require immediate cooling and refrigerated

transport and handling. They are usually harvested at 76-78 percent moisture.

Baby Corn

Baby corn has to be hand picked at, or within, one to two days after silks emerge from the ear

tip. Field corn varieties are harvested at silking, while supersweet varieties may be harvested upto the time silks are about two inches long but still fresh. Determine suitability of ears for picking

by sampling for size. Market requirements limit size to 2.5-4 inches in length and 0.25-1 inch in

diameter. Ears quickly become too long and tough. Carefully remove and husk the ear so as notto break or damage it.

Fresh Market

For fresh market, ears are generally sold unhusked. They are very perishable and must be kept

crisp. Refrigerate to protect sugar levels that are important in corn flavor quality.

Processing

Ears intended for processing must be carefully husked and desilked. Process immediately by

canning or freezing.


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Storage

Excerpt fromUSDAAgricultural Handbook #66:

"Hold sweet corn at 32F and 95 to 98 percent relative humidity. Sweet corn is seldom stored,

although occasionally it may be desirable to store an excess supply temporarily. However,storage for more than a few days results in serious deterioration and loss of tenderness and

sweetness. The sugar content, which so largely determines quality in corn and which decreases

rapidly at ordinary temperatures, decreases less rapidly if the corn is kept at about 32F. The lossof sugar is about four times as rapid at 50F as at 32F. At 85F, 60 percent of the sugars may be

converted to starch in a single day as compared with only 6 percent at 32F. However, corn loses

sweetness or desirable flavor fairly rapidly, even when iced and held at 32F. Long shanks andflag leaves should be trimmed before marketing, as they induce denting of the kernels by

drawing moisture from them. Denting is an indication of loss of quality. A loss of 2 percentmoisture from sweet corn may result in objectionable kernel denting.

"Rapid removal of field heat from sweet corn, when at 86F or higher, is especially critical to

retard deterioration. Maximum quality retention can be obtained by precooling corn to near 32Fwithin an hour after harvest and holding ears at 32F during marketing. In practice cooling to this

extent is rarely achieved. However, cooling is the first step in a good temperature management

program. Sweet corn has a high respiration rate, which results in a high rate of heat evolution.

"Sweet corn can be precooled adequately by vacuum cooling, but it must be wetted first (and top

iced after vacuum cooling). Crated corn can be vacuum cooled from about 85 to 40F in a halfhour. Hydrocooling by spraying, showering, or immersion in water at 32 to 38F is effective,

although it takes longer than vacuum cooling for the same temperature reduction if the corn is

packed before it is cooled.

"Crated corn would take over an hour in a hydrocooler to cool to 40F, and few if any, operators

leave it that long. It is important to check cob temperatures during hydrocooling to determine iftemperatures are being lowered to at least 50F. Hydrocooling nomographs for bulk and crated

sweet corn are available. Many hydrocoolers now handle palletized crates, with crates four or

five layers high. These coolers, with overhead spray nozzles, can be effective if they use a largevolume of water and allow an hour or more of operation. After hydrocooling, icing is desirable

during transport or holding to hasten continued cooling, remove the heat of respiration, and keep

the husks fresh. When precooling facilities are not available, corn can be cooled with package ice

and top ice.

"Sweet corn should not be handled in bulk unless copiously iced, because it tends to heatthroughout the pile. Corn should not be expected to keep in marketable condition even in cold

storage at 32F for more than 5 to 8 days. The storage life at 40F is about 3 to 5 days and at

50F about 2 days. Corn brought to Farmers markets is often not packaged and brought to marketin bulk piles. It should be iced as the morning progresses to prevent deterioration.
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"Some corn is prepackaged in moisture-retentive film, with the husks removed after precooling.The film should be perforated to prevent development of offodors or offflavors. This product is

very perishable and must be marketed with continuous refrigeration.

"Use of controlled atmospheres to extend storage offers little promise. Research has shown that

injurious atmospheres contain less than 2 percent oxygen or more than 20 percent carbondioxide. In an atmosphere with 2 percent oxygen, the sucrose content of sweet corn remainedhigher than in other atmospheres tested.

"Some of the new, highsugar sweet corn cultivars should improve consumer satisfaction. As

compared with standard cultivars, which contain 3 to 5 percent sugar at harvest, the new

cultivars contain 7-10 percent sugar and also lose their sweetness more slowly during marketing.Thus, consumers purchasing the sweeter cultivars after several days' storage should get corn with

5-6 percent sugar as compared with standard cultivars containing only 2-3 percent sugar after

similar postharvest handling."

Packaging

Wirebound crates, 42-50 pounds, are commonly used as containers for corn. Corn is packed 4 or5 dozen per crate. It is also sold in waxed cardboard boxes.

AcknowledgmentGratitude is expressed to Dr. Bill Mansour of Oregon State University for providing the

initial template of information from which this publication was developed.

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