By
khardi J Mukuyu
If you’re a soybean farmer in the Mid-South wondering how much dicamba drift will ding your yields come harvest, hold on. Several factors determine the degree of yield loss that will occur, if any.
The off-target movement of dicamba that has pocked thousands of soybean acres in the bootheel of Missouri, Arkansas, and Tennessee is rooted in Monsanto’s Roundup Ready 2 Xtend Soybeans that tolerate dicamba. Following Chinese approval last February, Monsanto went ahead and released Xtend varieties for planting in 2016.
However, a critical link of this system — new dicamba formulations low in off-target potential — were not approved and could not be used on Xtend soybeans in 2016.http://www.noatz.com
The result has been that existing formulations of dicamba not lableled for use on Xtend soybeans — such as Banvel and Clarity — have injured neighboring non-Xtend soybeans and vegetable crops.
How Injury Occurs
Larry Steckel, University of Tennessee Extension weed specialist, says dicamba injury can occur through:
Drift
Volatility
Temperature
Spray tank and line contamination
Just how much soybeans are damaged, though, hinges on several factors, says Steckel. They include:
Growth stage. Generally, soybeans in vegetative stages have more time to recover. Little yield loss will result if good growing conditions, as most areas are experiencing so far, occur the rest of the season.
Not so with soybeans in the reproductive stage. These soybeans can suffer significant yield loss. However, much hinges on factors like soybean maturity. Steckel says group 3 soybeans have less time to recover than a late group 4 variety.
Soybean stand. A thick stand of soybeans can also tolerate more dicamba injury than can a thin stand.
Weather. Prolonged hot and dry weather can aggravate dicamba injury.
Rate of exposure. University of Missouri scientists note that Banvel rates even as low as 0.001 pounds per acre (1/100th of the use rate) can cause visual crop injury.
University of Arkansas tests show R1 (beginning flowering) is one of the most sensitive stages for dicamba injury: 10% yield losses from dicamba on soybeans have been observed from dicamba contamination at rates as low as 1/1,024 of the labeled rate.
Steckel notes that no hard and fast rule exists on yield loss, though. He says the best way to determine yield loss is with a weigh wagon or yield monitor at harvest if some areas of the same field are not affected by dicamba injury.
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