Harvest aids often needed, sometimes overused
Sep 9, 2008 12:49 PM,
By Bob Scott
Extension Weed Specialist
University of Arkansas
It is the time of year when farmers are applying harvest aids. One of the more difficult questions I get asked is, “How much will this dry down my crop and bring the moisture content down so that I can harvest quicker?” Most of the time folks don’t like my answer.
The truth is that there is not much data that supports that harvest aids will bring the moisture content of grain or soybeans down. Unlike boll openers and defoliants in cotton, harvest aids really do little to speed the crop along.
The purpose of most harvest aid applications is to decrease the amount of green material that runs through the combine. This may be weed material or it may be green leaves on the crop.
These situations usually arise from weed control failures or where fungicides have been used, or simply under good growing conditions and favorable moisture that have prolonged the natural desiccation of weeds and crop foliage.
As a general rule, glyphosate is not the best harvest aid, although it does have labeling for that use in many crops. It usually takes between 10 and 14 days for glyphosate to work — a long time in the harvest aid market where treatments often go out only a few days prior to harvest.
One problem is that you typically cannot plan a harvest aid treatment 14 days prior to harvest. If you apply glyphosate to a crop like grain sorghum, you may have stalks breaking over if you are forced to delay harvest due to rainfall.
Standard harvest aid herbicides are Gramoxone or paraquat, sodium chlorate and Aim.
Aim is typically used where morningglories are a big concern. Aim alone will not desiccate other large weeds like jointvetch and grasses. The rates for Aim in various crops as a harvest aid are as follows: corn (all types) and small grains, 2 ounces per acre; sorghum, 1 ounce per acre; and rice and soybean, 1.5 ounces per acre. All these crops have a three-day pre-harvest interval. It is a good idea to add 1 percent volume per volume of crop oil concentrate and 2.5 pounds per acre of ammonium sulfate to Aim.
Gramoxone (paraquat) is labeled as a harvest aid in soybeans at 1 pint per acre. This treatment should be applied only after half the soybean leaves have dropped and the other half are yellow. This also applies to sodium chlorate in soybeans.
For soybeans, I often recommend a combination of sodium chlorate plus paraquat for really grown-up fields. You can substitute Aim with sodium chlorate if morningglories are a primary concern.
Sodium chlorate is labeled for corn, grain sorghum, soybeans, and rice at up to 6 pounds of active ingredient per acre (2 gallons of a 3-pound-per-gallon formula or 1 gallon of a 6-pound-per-gallon formula). Most recommendations are that this treatment goes out about five days prior to harvest when grain is below 25 percent moisture.
Harvest aids can increase combine efficiency. They can also improve the quality of harvested grain. They can get you in the field sooner by eliminating green leaves and weed material.
However, grain moisture should be monitored and harvest aids applied only when you are the proper number of days out from harvest. Do not shorten this interval based on the belief the grain will dry down following a harvest aid application.
Applying harvest aids too soon may result in the crop lodging or failing to mature correctly.
e-mail: bscott@uaex.edu
