Consider fall weed control on perennial crops

Applying residual and systemic herbicides in the fall greatly enhances season-long weed control the following year.

Fall application of residual herbicides is an effective method of use where the label allows it. Fall application is most effective on established perennial crops, such as tree fruit and small fruit. It may be possible to apply fall herbicides on perennial vegetables, such as asparagus, rhubarbs and strawberries. Herbicide label language may allow fall and spring application, or may limit application to spring only.

Asparagus

Some herbicide labels for asparagus require application after mowing fern in the spring. Some labels allow application before emergence in the spring or after harvest. This could be interpreted to allow fall application. Obviously, fern has to be mowed in the fall if herbicides are to be applied. Where rye is interseeded with asparagus fern in the fall, it is difficult to apply a fall herbicide without injuring the rye. In some situations, weed problems are a more serious concern than the cover crop. For instance, to clean up fields with many perennial weeds, it may be necessary to apply glyphosate or 2,4-D in the fall. They can be applied safely to asparagus fields after frost has killed the fern. The Solicam label allows for fall application after mowing fern. Karmex, Dual Magnum, Sencor and Callisto may be applied in spring or after harvest. These herbicides appear to have good weed control activity in the spring with no loss of residual period.

Rhubarb

For rhubarbs, there are only a few herbicides registered. The Kerb label specifically mentions fall application, with a 218-day (seven months) pre-harvest interval (PHI). The Dual Magnum label allows application in the spring before emergence and after harvest. Application of glyphosate in the fall will kill many perennials, and also fall-germinating and winter annuals. Horseweed can be controlled relatively well with fall applications of glyphosate.

Strawberries

In strawberries, Sinbar may be applied after renovation or in late fall. It is a very effective herbicide and controls most annual weeds and some perennials when applied at 4 to 8 oz. product per acre. Spartan was labeled for strawberries in 2011. It may be applied after renovation or to dormant berries in late fall. It gives good control the following year of pigweeds and several composites when applied in fall. Prowl H2O may be applied to established strawberries during dormancy, which includes late fall. It will give good residual control of most annual grasses in the spring if applied in late fall. Ultra Blazer may be applied in late fall for broadleaf control the next spring.

All of these residual herbicides can stunt strawberries if applied at a rate too high for the soil type. Check labels for correct rate for your soil type. In most cases, do not apply fall herbicides on soils with less than 1 percent organic matter. Apply fall herbicides before mulching.

It is often difficult to apply herbicides in the spring before strawberries begin to green up, especially on wet soils. Growers may try treating an area this fall to see if the practice is suitable for their operation.

Weed control is a year-long activity. Many perennials, biennials and winter annuals germinate or remain alive in the fall. It is a good opportunity to control these weeds and to provide some insurance against wet fields in the spring.

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

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