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Herbicides As Harvest Aids

September 8, 2000
As crops across Illinois reach maturity and harvest approaches, weeds remaining in fields could potentially present harvest difficulties. A very few herbicides exist that could be used as harvest aids, helping to dry down existing weed vegetation prior to

We are often asked if any of these harvest-aid herbicides cause nightshade plants to drop their berries, especially in soybean fields. Although the herbicides labeled for preharvest applications in soybeans can cause the nightshade leaves to dry and drop, they will not cause the berries to drop from the plant.

Preharvest applications of translocated herbicides may also help suppress weed-seed production, but caution must be used, as application of these herbicides too soon (with respect to crop developmental stage) may allow some herbicide to move into the developing seeds. Additionally, translocated herbicides may also provide some suppression of perennial weed species if enough leaf surface is available for herbicide absorption.

Preharvest Herbicides for Corn

Some formulations of 2,4-D may be applied as preharvest treatments. Applications, generally 1 to 2 pints per acre, should be made after the hard-dough stage, and some formulations are labeled for aerial application. 2,4-D controls certain broadleaf species only and provides no control of grass species. Be cautious about off-target movement of 2,4-D, especially when sensitive plants are growing nearby.

Roundup Ultra or UltraMax (glypho-sate) may be used as preharvest treatments in corn. Application rates for Roundup Ultra range from a maximum of 1 quart per acre for aerial applications to 3 quarts per acre for ground applications. For Roundup UltraMax, maximum application rates are 26 fluid ounces and 2.4 quarts for aerial and ground applications, respectively. Grain moisture should be at 35% or less, and plants should be physiologically mature (black layer fully formed). Allow at least 7 days between application and harvest. Applications to seed-production fields are not recommended.

Preharvest Herbicides for Soybeans

Clarity (dicamba) may be applied as a preharvest treatment at 8 to 64 fluid ounces per acre. Applications should be made after soybean pods have reached mature brown color and at least 75% leaf drop has occurred. Allow at least 14 days between application and soybean harvest. Do not use preharvest-treated soybeans for seed unless a germination test is performed on the seed with an acceptable result of 95% germination or better.

Gramoxone Extra (paraquat) may be applied as a preharvest treatment at 12.8 fluid ounces per acre. Include one quart of NIS per 100 gallons of spray solution. Applications should be made after 65% of soybean pods have turned brown or when seed moisture is 30% or less. Allow at least 15 days between application and soybean harvest.

Several glyphosate formulations may be used as a preharvest treatment in Roundup Ready and conventional (nonresistant) soybeans. Application rates will vary according to the formulation. Applications should be made after pods have set and lost all green color. Allow a minimum of 7 days between application and soybean harvest. Do not apply to soybeans grown for seed, as a reduction in germination or vigor may occur.--Aaron Hager and Christy Sprague

Author: Aaron Hager Christy Sprague

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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