Early planted soybeans promise higher yields. A pre-harvest desiccant can turn that promise into bushels in the bin with minimal dockage.
The potential yield advantage when you plant soybeans in early May is well documented. But pushing planting dates earlier can lead to increased incidence of green stem and delayed senescence. And soybean leaves might hang on through pod maturity if you applied a fungicide to get your crop through those hot, humid summer days. That green matter can lead to staining and dockage.
A pre-harvest desiccant can kill green tissue (leaves, stems, pods) on soybean plants and green weeds. This can even out a variable crop so that the whole field reaches maturity at the same time allowing you to reduce loss by harvesting earlier. It can also take care of green matter in low spots in the field where soybean plants might lag behind in maturity. Green matter can cause dockage.
When you’re scouting, monitor seed development, not leaf colour. That means you’ll have to wade into the crop canopy to see where things really stand.
It’s important to get a good read on the soybean crop’s maturity because a desiccant won’t change the maturity of the crop, it only enhances dry down. You’ll want to spray a desiccant in a field of mostly mature soybeans.
Timing your spray is critical. Spray when soybean pods have reached physiological maturity at stage R6.5. A soybean plant has reached R6 when the pod cavity on pods in the upper four nodes of the plant are full. Plants reach stage R6.5 when the membrane attaching the seed to the pod wall begins to separate. Once you reach R7, where soybean leaves begin to fall and at least one pod in the upper four nodes of the plant is mature, you’re past the ideal timing for desiccation.
Hot, humid conditions in August might slow down crop maturity. It takes wading into the crop to get an accurate picture of where things are at. From a distance, soybeans may not appear mature enough until it is too late to help.
Mature beans in green pods might not dry down efficiently when it’s warm and wet. And if we get wet and humid conditions into September, seeds can begin to sprout, reducing the quality of the entire crop.
Easier combining is another reason to use a desiccant. Spray a desiccant when the crop has lost 80 per cent of its leaves and 80 per cent of the pods are yellow. If you don’t spray the desiccant until the majority of the pods in the field are brown then you risk harvest loss and shatter, especially since some desiccants have a 15-day pre-harvest interval. This pre-harvest interval pushes back harvest even further.
Desiccants are contact herbicides. They even-up the drydown of plant material across a field within one to three days. Use higher water volumes to get proper crop coverage and drydown.
The environmental conditions at time of spraying will affect the speed at which you see the product work. In warm and dry conditions the green plant material and weeds will drydown quickly. If the weather is cool and wet or if there is high humidity, drydown might take longer. The size of the weeds matters, of course, with larger weeds taking longer to dry.
Dry edible bean growers are familiar with harvest aid treatments. A desiccant will provide more even dry down of the crop and control any escaped weeds, just like in commercial soybeans. But controlling weed escapes can reduce seed staining which is particularly important in dry edibles. A clean, bright sample will grade better.
A side benefit to desiccation is the control of perennial weeds and winter annuals. In the fall, these weeds move sugars down into their roots. Spray a herbicide in the fall and it piggybacks on this natural phenomena to translocate directly into the roots, which means more effective control of weeds than in the spring.
Plus, by cleaning up weed problems in the fall you can seed your winter wheat into a clean field and give the crop a jump on weed pressure.
Consult with the buyer to confirm which products are acceptable to tank-mix. Always check labels or talk to your retailer to make sure you’re using the correct rates, surfactants, water volumes, and timing. Talk to your P&H crop advisor to help choose the right product.
