Friday, June 12, 2015

Tank mix different herbicides to control herbicide-resistant weeds

Herbicide-resistant weeds are a big concern for growers.  Not only does it necessitate a re-evaluation of the herbicides that are effective, but it is also a potentially drastic change in other management strategies.  With the adoption of herbicide resistant crops, growers were able to also adopt conservation tillage practices, such as strip-till and no-till, which are better for soil quality and health.  Conservation tillage practices tend to shift the dominant weed species to small seeded species that are shallowly buried, including palmer amaranth.  With the increasing spread of herbicide resistant species, especially glyphosate-resistant palmer amaranth, growers are now faced with the challenge of managing their crop sustainably without undoing the positive effects of the conservation tillage.

One of the best options has been to tank-mix herbicides with different mechanisms of action (MOAs) to control susceptible and resistant populations of weeds.  Tan mixes can allow for control of multiple weed types, such as grasses, sedges, broad-leaved weeds, etc., depending on the chemicals chosen.  Using multiple MOAs in an application reduces the frequency of resistance, as compared to rotating herbicide MOAs seasonally.  Weeds with multiple MOA resistance do exist, so the mixes sprayed need to include herbicides with multiple and different MOAs that are effective on any herbicide-resistant weeds present.

Stanley Culpepper conducting an herbicide application in a trial to determine the levels of herbicide resistance in Palmer amaranth. Image by Joseph LaForest, University of Georgia,