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Soybean yield response to dicamba exposure

Xtendimax drift
Figure 1: Xtendimax drift onto non dicamba-tolerant soybean. Photo: Liz Stahl.

Due to non-Xtend soybeans’ sensitivity to dicamba, injury symptoms aren’t reliable indicators of yield loss.

Slight dicamba injury doesn’t always result in significant yield loss, according to published research. However, yield losses from dicamba exposure can be dramatic.

The level of yield loss depends on several factors. These include:

  • Soybean growth stage at the time of exposure.

  • Exposure dose.

  • Growing conditions for the remainder of the growing season.

Soybean growth stage

Research suggests that if minor exposure occurs during early vegetative development, yield loss is less likely compared to when soybean has entered reproductive development.

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Table 1: Losses of non-tolerant soybean exposed to dicamba

Shows average yield and percent yield losses after researchers applied 1/10 of the labeled Engenia rate at different growth stages. Source: University of Nebraska.

Table 1

Growth stage at application Average yield Average yield loss
Check (no dicamba) 59 bushels per acre 0%
Early vegetative (V2) 24 bushels per acre 59%
Late vegetative/early flowering (V7/R1) 3 bushels per acre 95%
Full flowering (R2) 19 bushels per acre 68%

Dicamba exposure dose

Similar to injury symptoms, the impact on yield increases with the level of dicamba exposure.

Research: Nebraska

Findings from the Nebraska study include:

  • Even very small concentrations of dicamba (1/1000 of the labeled rate) at V2 reduced yields by an average of three bushels per acre.

  • As the exposure increased to 1/10 of the labeled rate, yield losses approached 60 percent (Figure 2).

Percent yield loss
Figure 2: Percent yield loss of non-tolerant soybean at V2 to varying micro-rates of dicamba. Source: University of Nebraska.

Research: Purdue

Similar research at Purdue in 2009 and 2010 studied eight dicamba rates ranging from 1/10,000 to 1/25 of the labeled rate.

They found dicamba reduced yields of non-tolerant soybeans by 10 percent with exposures as low as 1/1064 to 1/510 of the labeled rate. Keep in mind, a 1/1000 rate is equivalent to 1/10 of one teaspoon per acre.

These studies looked at single exposures of dicamba at different rates and soybean growth stages. To date, no data describe yield effects on soybean exposed more than once.

Environmental effects

Drought conditions during reproductive growth stages can influence yield.

In the Purdue study, one of the site-years received only 2.75 inches of rain from July through September. The drought stress amplified dicamba exposure’s impact on yield. Even at an extremely low rate of 1/3333 of the labeled rate, yields were reduced by 10 percent.

Jeffrey Gunsolus, Extension weed scientist

Reviewed in 2018

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