WEED MANAGEMENT APPROACHES FOR SMALL FRUITS

Reid J. Smeda Weed Scientist University of Missouri

Small fruit production:

Blueberries, raspberries, cranberries, grapes, and strawberries

Distribution varies with climate and soil conditions

Individual farm acreage of individual crops is low compared to agricultural crops

Challenges for weed management in small fruits

1) Few herbicides registered How do we get new herbicides?

Corn acreage estimated at 95,900,000 acres in 2012 Grape acreage (bearing) in 2010 was <950,000

2) Many varieties and environmental conditions Grapes Red, white Table, wine More than 50 varieties in US alone

Strawberry More than 10 varieties alone in Missouri

3) FQPA – need to re-register herbicides every 10 years

4) Perennial crops make it difficult to “rotate”

5) Special conditions for production

6) Weeds mimic the crop Growth habit

Appearance

7) Weed control may be necessary for safety concerns:

Weeds:

• Life cycles; annuals (summer and winter), biennials, and perennials

• Time of emergence -- spring (summer annuals, biennials, perennials) -- fall (winter annuals) • Regeneration (annuals and biennials only

reproduce by seed; perennials by seed and reproductive parts)

• Adaptation; the species present are the result of weed species in adjacent areas and your practices

Perennials are difficult to eradicate Field bindweed has creeping roots (up to 20’)

Annuals contribute many seeds to soil bank

Why do weeds exist in crop fields? Weeds are part of nature’s method to cover

soil (prevent erosion) Weeds are part of initial succession stage They compete for resources in disturbed

areas Weeds respond to our control practices Use of mowing selects for low-growing perennials Use of same herbicide program selects for

tolerant or resistant species

Weeds develop in a natural progression of plant succession stages

Weeds adapt to our herbicide programs

Giant foxtail on roadsides and guardrails

Continual emergence of pigweed

Glyphosate 3 lbs ae/A, 0.5”

Glyphosate 3 lbs ae/A, 3”

Glyphosate 3 lbs ae/A, 10”

Stanley Culpepper, UGA

Palmer pigweed

Negative impact of weeds:

Competition for available resources Water, nutrients, light

Competition can impact synthesis of aromatics, polyphenols (anthocyanin), and sugars Pose health risks Poison ivy

Attract other pests Legumes such as clover attract deer

Restrict air flow, increasing probability for development of disease

Deer or vole damage

Where do weeds come from?

Already present (they were there before the small fruit crop was established) Some seeds viable in soil up to 75 years Perennial parts viable up to 5 years

Some weeds transported by wind: development of herbicides selected for specific weed populations and weeds resistant to herbicides

Nature’s response

Crockett County, TN, 2002 Photo -Chism Craig

Marestail

Weeds that used to die no longer all do

RR soybeans

Weeds can be directly transported by wind

Gly-R kochia in Colorado Courtesy: Dr. Phil Westra, CSU

Methods for weed control: Mechanical: Mowing vegetation between rows Specialized cultivation underneath rows Some root pruning may occur (entry point for

crown gall on grapes)

Hoeing

Bare ground areas encourage erosion

Mulches Watch C:N ratio Introduction of new weeds Not effective on perennials

Organic “herbicides” Most are POST materials (no residual activity) Vinegar (acetic acid) Citric acid Plant extracts (mint, d-limonene, cinnamon oil, clove oil,

lemongrass oil

Mode of action is desiccation after stripping of cuticle Contact activity; need to be POST-directed More effective on broadleaves than grasses Best applied at higher spray volumes (50 – 100 gpa)

Herbicides

Crop # PREs # POSTs Total Different MOA

Raspberry (brambles)

8 8 16 11

Blueberry 12 9 21 12

Strawberry 6 10 16 11

Grapes 13 11 24 12

Some applied prior to weed emergence (PRE) and have residual Some applied after weeds emerge (POST); many have little residual Important to READ THE LABEL Pay attention to the PHI (pre-harvest interval) and if labeled for bearing and/or non-bearing crops

What’s missing from your herbicide arsenal? Plant growth regulators (2,4-D, dicamba) Effective on broadleaf perennials High risk for damage to fruit crops

Why is mode of action important?

Helps to minimize selection for resistance Broadens the weed spectrum controlled

Confirmed Glyphosate Resistant Weeds in the U.S.

Italian Ryegrass Rigid Ryegrass

Horseweed (Marestail) Common Ragweed Giant Ragweed Palmer Amaranth Common Waterhemp Hairy Fleabane

Source: Adopted from Chris Boerboom, Univ. Wisconsin

Johnsongrass

Annual bluegrass (MO only)

Kochia

Continued use of POST herbicides with limited residual activity

Use of same MOA ensures selection for tolerant weeds: Glufosinate (Rely) Polygonaceae weeds

increase

Summary:

Site preparation is a key step: get rid of unwanted or tough-to-control weeds Crop health is important to limit weed impact Know your weeds (identification) Prevention is better and cheaper than

reaction to established weeds Integrate tools for weed control

Weed management in small fruits may not have simple answers!

Continued use of the same practice for weed control is like using a bird deterrent; if birds can figure it out, so can weeds!