ISSUE 12 July 21, 2005
PRE-HARVEST HERBICIDES IN SMALL GRAINS
Winter-wheat and some of the earliest fields of spring wheat and barley are starting to mature in the southern part of the state. Several herbicides are labeled for pre-harvest weed control and as harvest aids in barley and wheat. Pre-harvest herbicides can aid in the control of perennial weeds and other green weeds that hinder the harvest operation. Weed control with pre-harvest herbicides, however, is generally disappointing as weeds at this time are tall, nearing maturity and slow growing. Furthermore, green weeds can take a week or more to dry down even with an effective treatment.
Glyphosate, in addition to controlling weeds, is labeled for use in aiding the dry down of the crop itself (as opposed to controlling and drying down weeds in the crop). Glyphosate is a systemic herbicide and takes from 7 to 10 days to effectively kill the growing parts of the crop so the dry down process is not immediately visible. Traditionally, fields that had excessive green material were swathed. Swathing enables faster dry down than pre-harvest glyphosate if significant levels of green material are present in the crop. A standing crop that has been treated with glyphosate, however, will dry faster than a swathed field after a rain.
Glyphosate should only be applied after the crop has reached physiological maturity which for most varieties occurs at a grain moisture content of about 30%. At this moisture content the grain is in the hard dough stage and if you run your thumb nail across the kernel, the indentation will remain. Applying glyphosate before physiological maturity can reduce yield, test weight and seed germination. Because germination can be affected when applied too early, glyphosate should not be used in fields that will be used for seed or on barley intended for malt. Pre-harvest applications of glyphosate must be made at least 7 days before harvest.
For addition information about pre-harvest applications of herbicides refer to the 2005 Weed Control Guide and the labels of approved products.
DIRECT COMBINING OATS?
I have had a few questions about direct combining oats. Because of the morphological structure of the panicle, oats are more prone to scattering than other small grains. Therefore, it is difficult to have a standing crop dry enough to direct combine without significant shattering losses occurring. If direct combining is absolutely essential, harvest the crop when the grain is in the 15 to 18% moisture range and use an air drying system to reduce the moisture content level down to a level that is safe for long term storage.
NDSU Extension Agronomist