Preharvest spraying is done either for perennial weed control or to desiccate the crop prior to harvest.
Glyphosate products are primarily used for perennial weed control and the timing of the application is very important. Some excellent tips on the spray timing of glyphosate products can be found at: www.roundup.ca/preharvest . Preharvest glyphosate application may help even out a crop and is an excellent way to control canada thistle and quackgrass in a reduced tillage environment. Do not apply glyphosate to crops being kept for seed as it may adversely affect germination.
Desiccants are products that dry the crop and weeds more quickly than glyphosate but do not offer any perennial weed control. Weeds and crops may green up again after a few weeks because they were just dried down and not necessarily killed. Using desiccants can be an excellent way to harvest peas earlier and may reduce bleaching and earth tag. Desiccants are often used to spray potato crops and also cereal crops that are being kept for seed.
Our agronomists can help with the selection of products and the timing of application, both of which are important elements of successful preharvest spraying.