No. 8 — May 13, 2019

Be Alert for Herbicide Drift

With this window of dry weather this week a lot of corn likely will be planted prior to the weekend rains. As of May 12, only 52 percent of the corn has been planted compared to the five-year average (2014-2018) of 87 percent. I suspect that a lot of the corn being planted is no-till which will result in a lot of burndown herbicides being applied in the next 5 to 10 days. There is anecdotal evidence that corn likely will be planted for some period of time since soybean seed is in very short supply.

Close-up of grape leaf showing herbicide drift damage around edges
Photo: 2,4-D herbicide drift damage in 2018. Photo credit: D. S. Volenberg

As the latter part of the month of May nears many row crop farmers make the switch from planting corn to planting soybeans. With short seed supplies of soybeans this year, many farmers likely will not be able to make the switch from corn to soybeans. I suspect there will be a lot of no-till corn planted into some very weedy fields and this will be followed by a barrage of burndown herbicides. What does this mean for grape growers?

Herbicide drift should be a real concern especially since the grapevines are at a stage of development in which phenoxy herbicides can be very detrimental to grape production. Many grape cultivars will be at or nearing the beginning of flowering in the next week. At this stage of development the grapevine inflorescence/flowers are the most sensitive to synthetic auxins (Bezoic acids, phenoxycarboxylic acids, pyridine carboxylic acids, and quinolone carboxylic acids) herbicides. Some typical synthetic auxin herbicides include the active ingredients of 2,4-D, dicamba, or triclopyr and others (Table 1).

Table 1. The chemical families of synthetic auxins and the active ingredients of each chemical family.

Chemical family Active ingredient
Phenoxy-carboxylic-acid clomeprop, 2,4-D, 2,4-DB, dichlorprop=2,4-DP, MCPA, MCPB,mecoprop=MCPP, CMPP
Benzoic acid chloramben, dicamba, TBA
Pyridine carboxylic acid clopyralid, fluroxypyr, picloram, triclopyr
Quinoline carboxylic acid quinclorac, quinmerac
Other benazolin-ethyl

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