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Pre-Harvest Weed Control and Desiccant Timing (PCN Summer 2014) JUL 9 2014 | Consumers and Producers | Pulse Crop News

This article appeared in the Summer 2014 issue of Pulse Crop News.

It may seem early to be thinking about pre-harvest management of your pulse crops, however understanding a few key things will make harvest go a lot more smoothly.

When a crop reaches maturity, there are a few options to get it ready for harvest, such as swathing or the use of pre-harvest chemicals for straight cutting the crop. Options for pre-harvest spraying on pulses include glyphosate (RoundUp), saflufenacil (Heat) and the desiccant, diquat (Reglone). Perennial weeds, weather, crop stage and maximum residue limits (MRLs) are factors to consider when choosing pre-harvest options.

“Keep in mind that glyphosate is a weed control measure and not registered as a desiccant,” said Mark Olson, Pulse Crops Unit Head with Alberta Agriculture and Rural Development. “If you spray pulse crops with glyphosate in the fall, seed can’t be used because germination is reduced.”

Olson also notes that growers should watch for cool, cloudy weather when spraying glyphosate, since it takes longer to work under low light conditions and the crop can shatter if waiting for extended periods for dry down. Field pea desiccation with approved products can speed up dry down when crop maturity is uneven, but a desiccant will not assist in maturing immature seed. Field pea desiccation will usually eliminate the need for swathing, avoiding potential problems with wind-blown swaths, rain-soaked swaths, and pickup losses.

The crop should be at physiological maturity, when seeds inside the pods are detached and the pods rattle on the lower portion of the plant. Yield losses and smaller seed sizes are possible if the crop has not reached proper maturity. Apply desiccant as the field pea crop is approaching physiological maturity.

The application can be made when the bottom and mid-area pods have turned tan to yellow color, and top pods are pitted and starting to turn yellow. Going in too early can cause “wrinkling” of seeds and the plant may not properly break down the chemical, which can cause issues with pre-harvest intervals and MRLs. Weather conditions at the time of spraying can significantly impact the effectiveness of the drying down process and speed of the plants.

Check the label to ensure the product is registered for the intended crop and use the recommended water rates and volumes. Using the recommended water volume is something that often gets missed and, in general, higher water volumes are needed to get adequate coverage with the products being used.

Check with your dealer or exporter on MRLs and the Alberta Pulse Growers website for up-to-date information this fall.