Fall weed control on asparagus, rhubarbs and strawberries

Herbicides applied to these perennial crops in fall improve weed control in spring.

Application of residual herbicides in the fall on perennial vegetable crops is an effective method to improve overall weed control. Some herbicide labels mention fall application and others only mention spring application. Several labels include after-harvest applications that could include a fall application. Asparagus, rhubarbs and strawberries are perennial vegetable crops that present opportunities for fall herbicide application.

Asparagus

Some residual herbicide labels for asparagus require application after mowing fern in the spring. Other labels allow application before emergence in the spring or after harvest. An after-harvest application could be interpreted to allow fall dormant application. Fern must be mowed before herbicides are applied in both fall and spring to allow the herbicides to contact the soil. In fields with many perennial weeds, it may be necessary to apply glyphosate, 2,4-D or dicamba (Clarity) in the fall. Where rye is inter-seeded with asparagus fern as an over-winter cover crop, glyphosate will kill rye. However, 2,4-D and dicamba cause less rye injury. These herbicides may be applied to asparagus fields after frost has killed the fern without risk of crop injury. They will be effective only against broadleaved weeds that have survived frost.

The Solicam label for asparagus allows for fall application after chopping fern. It may be applied to suppress yellow nutsedge and annual grasses the following year. Karmex and Chateau may be applied in spring or after harvest. Both have low solubility so they tend to stay on the soil surface, and they persist for several months in the soil. If applied in late fall, they will help control winter annuals and early-emerging annual weeds in the spring.

Rhubarb

Only a few herbicides are registered for rhubarb. The Kerb (pronamide) label requires fall application with a 218-day (seven months) preharvest interval (PHI). The Dual Magnum (s-metolachlor) label allows application in the spring before emergence and after harvest. Callisto (mesotrione) must be applied to dormant rhubarb to avoid crop injury. It may be easier to apply herbicides in late fall when rhubarb is dormant than in the spring because rhubarb leaves emerge very early after a few warm days and wet soil may preclude spraying. Application of glyphosate in the fall will kill many perennials, fall-germinating annual weeds and winter annuals. Fall application of glyphosate will help control dandelion, horseweed, fleabane, white campion (cockle) and wild carrot.

Strawberries

In strawberries, Sinbar (terbacil) is labeled for application after renovation or in late fall. It is a very broad spectrum and long-lasting herbicide that controls most annual weeds and some perennials when applied at 4 to 8 oz product per acre. Spartan (sulfentrazone) may be applied after renovation or to dormant strawberries. It gives good control of pigweeds, common lambsquarters, common chickweed, common purslane and other broadleaves. Prowl H2O may be applied to established strawberry during dormancy, which includes late fall, but it probably is more effective if applied in the spring.

Ultra Blazer (acifluorfen) may be applied to strawberry in late fall for broadleaf weed control the next spring. Residual herbicides can stunt strawberry if applied at a rate too high for the soil type. Check labels for correct rate for your soil. In most cases, do not apply fall herbicides on soils with less than 1 percent organic matter. Apply fall herbicides before mulching and after a hard freeze.

It is often difficult to apply herbicides to strawberries in the spring before they begin to grow again. The plants are covered with straw mulch and the leaves emerge and green up during warm, sunny spring days. The mulch acts like a small hothouse over each row. If the herbicides are applied over the straw, most of the chemical is tied up on the straw. Wet soils often make it difficult to get into the fields. Fall application overcomes many of these problems.

Stinger (clopyralid) is effective when applied post-emergence in the fall for control of composites (dandelion, fleabane, horseweed, common groundsel, ragweed, Canada thistle), legumes (clovers, alfalfa, trefoil), smartweeds (ladysthumb, prostrate knotweed,wild buckwheat) and plantains. It can be applied in a tank-mix with Poast (sethoxydim) or Select Max (clethodim) for quackgrass control. These herbicides can be applied safely over the top of the strawberries.

Weed control is a year-round activity. Many perennial, biennial, and winter annual weeds germinate or remain alive in the fall. Some annual weeds (e.g. horseweed) may germinate in fall and overwinter as small seedlings. Fall is a good time to control these weeds as part of a weed-control program.

Dr. Zandstra’s work is funded in part by MSU‘s AgBioResearch.

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