Fall Spraying Helps Control Perennial Weeds

Actively growing weeds, varying herbicide modes of action and the level of residue are all key factors in fall weed-management programs.

Many no-tillers are considering fall weed control to help reduce competition from perennials like dandelions and perennial grasses and late-emerging annuals.

Annuals that emerge late can produce weed seeds that create problems in next year’s crop.

Controlling weeds in the fall is especially important in the southern Corn Belt where actively growing weeds rob moisture and nutrients from the soil. Further north, perennials can be controlled if they are actively growing.

Weeds generally move nutrients to their roots in the fall to prepare for winter. Translocation provides a mechanism for getting herbicides to the roots of weeds.

Fall spraying can provide some of the best perennial weed control of any season, but it won’t be consistent unless you follow some basic management practices.

Several sound management practices will help control perennials.

Actively Growing Weeds.

Make sure weeds are actively growing after harvest so they take up herbicides.

After combining, check to see that there is enough new growth exposed for good herbicide absorption. Growth should not be drought-stressed or freeze-damaged

New shoots should still be emerging from the roots. Leaves from old cut-off stems are less effectively treated.

It’s best to have 6 to 8 inches of growth to ensure adequate herbicide coverage. Results are best if a high percentage of the potential shoots have emerged.

Monitor Temperatures.

If the temperature falls below 26 to 28 F, wait at least 24 hours to evaluate the foliage to make sure the plant is still actively growing.

Try to spray when the…

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Jim Leverich

Jim Leverich no-tills near Sparta, Wis., and serves as an onfarm research coordinator for the University of Wisconsin.

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