Preharvest glyphosate treatment on sorghum in a no-till system

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There are always questions this fall on effective ways to manage grain sorghum to improve the performance of winter wheat planted into no-till sorghum residue following fall harvest. The technique most often asked about is applying glyphosate to the sorghum crop prior to harvest. Most glyphosate labels require that applications be made to the sorghum crop when grain moisture is at 30% or less to minimize any possible yield reductions, and there is a seven-day period between time of application and harvest. 

We have tested the effect of a pre-harvest treatment of glyphosate on grain sorghum and wheat yields. These tests are continuing, and we will report on new results as they are analyzed. But the data we have so far gives you a good idea of what we found in our tests.

Below are two figures comparing grain yield and moisture of sorghum treated with glyphosate and untreated sorghum. 

Figure 1. Yields of sorghum treated with preharvest glyphosate compared to sorghum not treated with glyphosate.


Figure 2. Yields of sorghum treated with preharvest glyphosate compared to sorghum not treated with glyphosate.


Glyphosate was applied to the above sorghum crop when grain moisture was approximately 18-21%, and the grain was harvested 7-10 days following the application. Average yield reduction to the sorghum crop when sprayed with glyphosate was about 2-3 bushels or roughly 2% less than untreated.

Wheat had positive yield responses to preharvest glyphosate applications at all three locations.  Grain protein was also increased at two of the three locations. Figure 3 shows yield results from the 2012 wheat crop.

Figure 3. 2012 wheat yields follow grain sorghum treated with glyphosate and sorghum with no glyphosate treatment.


When glyphosate was applied to the sorghum preharvest, wheat yielded 12-13% more on average than wheat following untreated sorghum. That is equivalent to an average increase of about 5-6 bushels for the wheat crop.

Applications of glyphosate to grain sorghum prior to fall harvest can help improve the performance of the following wheat crop. It is important to follow the glyphosate label for application recommendations. Glyphosate applied at low rates or when temperatures are not adequate may reduce the effectiveness of the product. 

The sorghum field should also be inspected for stalk issues prior to applying the glyphosate. If stalk rots are present, applying glyphosate may increase the chance of plant lodging if it is not harvested in a timely manner.

Josh Jennings, CCA – Graduate Research Assistant, Agronomy

Kraig Roozeboom, Cropping Systems Agronomist