Effects of low dose applications of 2,4-D and dicamba on Cucurbitaceae and Solanaceae vegetables

David Patrick Hynes, Purdue University

Abstract

Glyphosate is a broad-spectrum herbicide used post-emergence. Since the introduction of the first glyphosate-tolerant crops in 1996, glyphosate has grown to become the most widely used agricultural herbicide. Widespread use of this herbicide as the primary or only chemical mode of action for weed control has driven evolution of twenty-two resistant weed species throughout the world. In response, chemical companies like Dow AgroSciences and Monsanto are developing genetically modified crops that have stacked resistance to 2,4-D or dicamba plus other herbicides, with the thinking that tolerance to extra modes of action will give growers another tool to use to combat glyphosate resistant weeds, both in an extra mode of action and in an expanded application window. However, having potentially millions of hectares planted in crops tolerant to auxinic herbicides raises concerns about drift of these herbicides on to sensitive horticultural crops. In 2010 and 2011, three experiments were established near Lafayette, IN, to determine the effects of low dose applications of 2,4-D and dicamba on watermelon (Citrullus lanatus (Thunb.) Matsumura & Nakai), muskmelon (Cucumis melo L.), fresh market tomato (Solanum lycopersicum L.) and bell pepper (Capsicum annuum L.). Plants were treated with full and partial rates of 2,4-D and dicamba alone and with mixes partial rates of these herbicides plus glyphosate. Measurements included estimated plant injury at 3, 7, 14 and 21 days after treatment (DAT), yield by harvest date and total yield over the season. The potential economic impact of drift was calculated as part of the analysis. Results showed that all application rates of 2,4-D and dicamba caused plant foliar injury to all species tested. Injury generally increased over the rating period, but plants treated with the partial rates recovered over the growing season and produced fruit. Muskmelon plants treated with 2,4-D or dicamba displayed delayed fruit maturity and lower total yield than untreated plants. Potential total economic losses for muskmelon exposed to 2,4-D were as high as $8357 per hectare (ha), and potential losses for muskmelon exposed to dicamba were as high as $5541 ha-1 over the season. Total yields for watermelon plants exposed to 2,4-D or dicamba were not different from untreated plants in any experiment. Fruit maturity was delayed for plants exposed to 2,4-D in all experiments and plants exposed to dicamba in 2011, but plants exposed to dicamba in 2010 did not experience fruit maturity delay. Untreated watermelon plants produced the most total income only when compared to 2,4-D treated plants in 2011, when the potential income loss was $4554 ha-1. Pepper plants exposed to both 2,4-D and dicamba experienced delayed fruit maturity compared to untreated plants, although total yield over the season was not different among the treated and untreated plants. Potential economic losses for peppers exposed to 2,4-D were as high as $2017 ha-1 over the season, and total potential losses from dicamba exposure were as high as $2466 ha-1. Tomato plants exposed to 2,4-D or dicamba experienced some fruit maturity delay, but total harvests for both years were not different among treated and untreated plants. Untreated plants did not produce the most potential total income in either year or for either herbicide, although untreated plants did generate the most income at the first harvest for all experiments. This data shows that companies like Dow AgroSciences and Monsanto who produce crops with stacked herbicide tolerance that includes tolerance to 2,4-D or dicamba need to be aware of the potential for income reductions for crops exposed to drift of these herbicides. Growers of sensitive crops exposed to drift of auxinic herbicides can experience a delay or reduction in early season income and in some cases reduced total income for the season. It is vital that these companies have plans in place to help growers reduce drift potential and be prepared to effectively deal with drift complaints.

Degree

M.S.

Advisors

Weller, Purdue University.

Subject Area

Horticulture

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