Many questions about crop desiccation centre on time of application, what results can be expected and how spraying compares to swathing.
The answers to many of the questions depend on what the farmer is trying to achieve.
“Whether swathing, or truly doing a desiccation job, the main objective in drying a crop is probably the same,” said Ron Hockridge, a crop specialist with Alberta Agriculture.
Drying down a crop stops growth in green spots and limits the amount of moisture provided to the seeds.
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Either job can be done after plants are physiologically mature and all that is needed is crop dry down.
There is an advantage to leaving crops standing, because standing crops have more space for air movement, which helps dry the crop out after a rain.
However, an early snowfall will normally do less damage to a swathed crop.
Varieties that tend to shell out, lodge or suffer from neck break are better off swathed.
Equipment is often the deciding factor, since many farms only have a pick-up header on the combines.
For those who want to spray their crops before harvest, there are further decisions to be made.
The product chosen will depend on where priorities are placed between crop dry down and fall weed control.
Any of the preharvest sprays will do a decent job on annual weeds. For hard-to-control perennials, a herbicide with systemic action is a good choice.
Systemics need to be applied at a later stage of crop development to avoid seed injury. The tradeoff is that dry down will be much slower.
Some products have a combination of desiccation and systemic herbicides. It is important to know the product’s strength to anticipate how each action will affect the plants.
“The other factor to consider when choosing a product is the effect frost will have on their action,” Hockridge said.
“For the most part, hard-to-kill perennials will withstand enough frost to keep growing throughout September. They are able to translocate systemic herbicides and the result wanted should be achievable.”
However, they still need some time between application and a heavy frost to be effective.
