Blog: The Wheat Sheaf

Pre-Harvest Considerations for Variable Maturity Conditions

Heat waves and drought stress that occurred in Alberta this past July and early August, have created issues of pre-mature “ripening”. These stresses elicit hormone responses that cause vegetative plant material to simply shut down and dry down suddenly. Wheat in southern sections are for the most part well past this point but for the remainder of the province, one should be aware of this issue.

Under these drought stresses, the colour change in plant tissues does not truly represent the actual seed maturity. This in-turn creates an enticement to either swath too early (for those planning to swath as a dry-down tool) or to apply glyphosate too early for pre-harvest weed control as these decisions were based on the “visual appearance” of the wheat field rather than the actual “seed maturity”. 

 

Premature ripening
Pictured above: A ripening field may look like it has reached maturity, but looks can be deceiving. Be sure to check the seeds and perform fingernail test (explained below) before applying pre-harvest herbicides such as glyphosate. 

When one shells out some of the wheat seed in such affected fields, often a significant portion of the seed shelled is only at the soft dough stage still (higher than 30% moisture content usually). This stage is simply too early to swath or to spray a pre-harvest glyphosate application for weed control if we wish to prevent unintended shrinkage of any immature seed not quite at the physiological maturity stage. It also may cause possible pesticide residues in our grains. Therefore, at the very least this has a direct negative effect on quality and yield for the individual producer, but at its worst it could affect the industry as a whole if residues of glyphosate or its metabolites persist in our grain above the maximum residue limits (MRL) allowed.

In fields with rolling topography, perhaps with knoll tops and/or low spots, this illusion with maturity can be that much more exaggerated. To prevent issues on these fields with unintended shrinkage and/or unacceptable glyphosate residues, one should manage the crop as based on the latest maturing areas (via a look at the seed), and not based on the earliest maturing areas even if such areas are the majority.

Determining 30% moisture – The fingernail test

Wheat seed is physiologically mature when the seed is about 30% moisture content, a stage when input into the seed by the plant (grain filling) has halted and moisture starts to be removed from the seed (dry down or desiccation phase). For anyone following AWC’s newsletter, “Wheat’s Up” you’ve seen we have discussed how to identify this important stage back in June, but to reiterate, the “fingernail dent test” works in determining this 30% moisture point.

Press your fingernail into the seed across its width, and you should leave a dent mark behind, but it should not break the surface of the seed. However, if while doing this you deform the original shape of the seed, then it is likely not quite there yet. It is at this 30% stage or later when swathing should occur if to be swathed, or when glyphosate products are registered for use for a pre-harvest weed control method when chances of it getting into the grain is least.

Pictured above – seed after performing the fingernail test. You can see that the dent remains, meaning that it is still too early for pre-harvest herbicide application.

Point being in a year like this with many fields experiencing, or which will experience rapid dry-down of plant tissue ahead of seed maturity, one needs to base their decisions on the actual maturity of the seed itself and not just on appearance of the crop.

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