When is Wheat No Longer Vulnerable to Herbicide Injury

Substantial wheat acreage, prevalence of poor conditions for application of herbicides throughout this spring, and those considering harvest aids to enhance grain ripening prior to floodwater are prompting specific information regarding wheat vulnerability to herbicides.   Wheat is generally not sensitive to herbicide injury after the hard dough stage of maturity.  Wheat grain reaches its maximum kernel weight and physiological maturity at the hard dough stage.  This is the primarily basis for addressing many of the questions noted previously. 

Since wheat is an annual plant (in contrast to cotton and sorghum which are perennials), its vegetation rapidly senesces or dies when hard dough stage or physiological maturity occurs and high temperatures promote ripening and drydown.   This is why a harvest aid will likely have very little, if any effect on grain drydown and harvest timing, unless weed vegetation is present which could hinder combine harvest.  For more information regarding â€œpromoting wheat harvest timing” using a desiccant, or other more effective means see https://www.mississippi-crops.com/2011/05/04/trying-to-promote-wheat-harvest-prior-to-floodwater/.

Identification of the hard dough stage of wheat plants is relatively easy, but may take considerable sampling because maturity of individual stems normally varies considerably.  The hard dough stage can be visually identified by the transition of kernels from green to brown color and the stem or peduncle immediately below the head turning from green to yellow. 

Hard dough stage can be identified by yellowing of the peduncle or upper stem just below the head. This shows the progression of maturity shortly prior to the hard dough stage. The plant on the right has reached hard dough.

Hard dough stage can also be identified by kernels turning from green to brown and attaining hard consistency. This shows the progression of maturity shortly prior to the hard dough stage. The kernel on the right has reached hard dough.