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| Photo: A few sporadic weeds in a fall strawberry patch are normal, even with excellent weed control. Photo: Annie Klodd |
Author: Annie
Klodd, Extension Educator - Fruit Production. Reviewed by Emily Hoover and Jim Luby
Four useful tactics to reduce next year's weed management demand include:
● Removing weeds before they shed seeds
● Cultivating between rows
● Carefully applying certain pre-emergent herbicides
● Mulching in the late fall, for winter protection, also provides significant weed suppression the following season
Remove weeds before they shed seeds
Invest time this fall to remove large weeds before they drop their seeds. This is a worthy use of time in the busy fall season. Here’s why:
One Palmer amaranth plant can produce between 100,000 to 1,000,000 seeds (source). One lambsquarter plant produces 72,500 seeds on average (source), and one Eastern black nightshade plant produces up to 825,000 seeds (source). Removing even a portion of your weeds now can make a big difference next year.
Weeds that already have seeds on them must be taken out of the field. If they haven't produced seeds yet, they can be dropped in place.
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| A strawberry field with a heavy infestation of smartweed or knotweed. The plants have produced seed that will reproduce next year unless the plants are removed for the field. Photo: A.K. |
What to do with removed weeds: Composting can kill the seeds if the pile is turned properly, and if the temperature gets high enough for a long enough time period. SARE has a nice guide on how to create proper compost. Burning weed seeds at prolonged extreme heat can kill them. This requires dense, dry piles, as well as a burn permit is some places. At Virginia Tech in 2017, Dr. Michael Flessner's research group killed Palmer amaranth seeds by piling the plants in narrow (3-ft wide) windrows and burning them at extreme temperatures. In the report, they write, "the windrow needs to reach 750-930 F for 10-30 seconds to kill most weed species, but some weeds such as crabgrass will be killed when exposed to 185 F for 20 seconds." I recall that this tactic worked when the piles were dry, but struggled after a brief rainfall (read the report here).
Canada thistle and quackgrass are two of the toughest weeds for fruit growers in Minnesota. They spread rapidly via rhizomes and have few safe and effective herbicide remedies. Early fall is the best time to hand-remove or spray them with labeled systemic herbicides. Their root systems are relatively depleted of energy in the fall, and herbicides will be translocated to the root/rhizome system.
Cultivate between rows
Small weeds between strawberry rows can be terminated in the fall via cultivation, spot-spraying with herbicides, or to some extent, low mowing. Keep the strawberry rows 12-18 inches wide.
Avoid cultivation if the problem is Canada thistle or quackgrass, and instead opt for hand-removal and mowing. Their roots can produce new plants if they are torn up and re-buried, spreading the weed.
Fertilizers or compost can also be incorporated during fall cultivation.
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| The nutsedge infestation in this otherwise productive field is too large to hand-pull. It would benefit from careful application of a pre-emergent herbicide for the following season. |
Example for controlling nutsedge (based on Midwest Fruit Pest Management Guide; MFPMG):
- For a fallow field that will be planted into strawberries next spring: You may spray Sinbar WDG pre-emergent herbicide this fall after the plants are dormant and before spreading straw. Apply Spartan in the spring right before planting. If the field is currently in another crop, wait until the crop is harvested before spraying.
- If a field is currently in
strawberries and those strawberries will be overwintered: Apply Sinbar WDG this
fall after the plants are dormant and before spreading straw. Do not use Spartan in this scenario, because
it is intended for pre-plant only; it can cause severe injury if used after planting.
- Some varieties of strawberries are sensitive to Spartan. Stay within labeled application rates and read all label instructions.
- Glyphosate can be spot-sprayed between rows to kill emerged nutsedge. Do not spray it over the rows.
- Hand-remove nutsedge plants over 6 inches tall that escape herbicide control.
- Sinbar and Spartan have "fair" efficacy on nutsedge (source: MFPMG)
Read this article from University of Massechusetts Extension for more strawberry herbicide options and other important information on their application.
Severe strawberry injury can result from mis-timing or mis-applying these products. Use spray guides and consult the labels for more information before spraying any of these products. The label is the law. This article is not meant to provide all of the information needed, but rather to introduce options for further consideratino.
CAUTION: Mention of a pesticide or use of a pesticide label is for educational purposes only. Always follow the pesticide label directions attached to the pesticide container you are using. Be sure that the plant you wish to treat is listed on the label of the pesticide you intend to use. And observe the number of days between pesticide application and when you can harvest your crop. Remember, the label is the law.
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