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Soybean Seed Quality from Dicmaba(08/17/17)

Most phone calls and emails received are about how much yield loss may occur from dicamba affected soybean.

Soybean Seed Quality from Dicmaba

Most phone calls and emails received are about how much yield loss may occur from dicamba affected soybean. The boiler plate response has been to wait until harvest. I have wanted to do a literature search to see what previous research has been done to determine what to expect regarding soybean seed quality and quantity. The University of Arkansas researchers have conducted a literature search on this issue, and also included results from their research. The following information is a Fact Sheet FSA2181 – Dicamba in Arkansas – Frequently Asked Questions.

https://www.uaex.edu/publications/pdf/FSA-2181.pdf

Dicamba and soybean

University of Arkansas System Division of Agriculture researchers have conducted considerable field research involving control of resistant pigweed and herbicides containing dicamba.

 

Research has shown that yield reduction in non- traited soybean from dicamba injury depends on four factors:

•Growth stage of the plants

•Rate of dicamba exposure

•Number of times the plants come in contact with dicamba

•Environmental conditions following exposure

 

In testing soybean without the dicamba ­resistant trait, Division of Agriculture researchers found the following:

•Dicamba symptoms on soybean may be most visible during vegetative growth stages, but yield loss from one exposure will be minimal unless rate of exposure is ¹/64 X (1.8 ounces per acre or 8.75 grams acid equivalent per hectare) or higher.

 

•Yield loss from dicamba exposure is most likely to occur between late vegetative stages through R3.

 

•Application at ¹/64 X of the recommended rate on R1 soybean can cause greater than or equal to 20 percent yield loss. This rate contains ¹/8 ounce of dicamba spread over one acre.

 

•Application at ¹/1,000 of the recommended rate can cause 10 percent yield loss at the R1 growth stage – the appearance of first blooms. This rate contains 0.008 ounce of dicamba dispersed over one acre.

 

•Application at ¹/100,000 of the recommended rate can cause visible symptoms during vegetative growth but is unlikely to cause yield loss. This rate contains 0.00008 ounce of dicamba dispersed over one acre.

 

Consequences of dicamba drift on soybean without the dicamba­ resistant trait include:

•Lower seed weight (Wax et al. 1969; Kelley et al. 2005; Lyon and Wilson 1986)

•Lowered seed quality (Wax et al. 1969; McCown et al. 2016)

•Delayed maturity (Wax et al. 1969; Kelley et al.2005; Lyon and Wilson 1986)

•Pod malformation (Weidenhamer et al. 1989; Anderson et al. 2004; McCown et al. 2016)

•Reduced seed germination or lower rates of emergence of progeny from seed planted the following growing season (Wax et al. 1969; Thompson and Egli 1973; Auch and Arnold 1978; Lyon and Wilson 1986; McCown et al. 2016)

•Malformed seedlings from affected seed planted the next spring (Thompson and Egli 1973; McCown et al. 2016)

 

Based on these data, soybean seed production fields exposed to dicamba during later reproductive development would likely have dicamba­ like symp­toms on emerging seedlings after planting as well as reduced seed quality, vigor and germination.

Rich Zollinger

Extension Weed Specialist

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