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The adoption of dicamba-tolerant soybean varieties has increased the concern and demand for new drift and volatility reduction technologies. Potential spray nozzles and adjuvants should be studied to determine its effects on drift and volatility of dicamba tank-mixtures. The objective of this study was to evaluate physicochemical characteristics of spray solutions containing dicamba; to analyze droplet size effect with air induction nozzles; and to assess dicamba volatilization on soybean plants with a proposed methodology. Treatments included dicamba only and mixtures with herbicides and adjuvants. Dicamba mixed with lecithin + methyl soybean oil + ethoxylated alcohol adjuvant had the greatest efficacy potential among treatments considering tank-mixture pH, surface tension, contact angle and droplet size. The MUG11003 nozzle produced the coarsest droplet size and was better suited for drift management among nozzle types. The proposed volatilization methodology successfully indicated dicamba volatilization in exposed soybean plants and among the evaluated treatments, it showed greater volatilization for dicamba with glyphosate + lecithin + propionic acid adjuvant.

BACKGROUND: Unlike post-emergence herbicides (POSTs), little is known about droplet size effect on pre-emergence herbicide (PRE) efficacy. Four nozzle types were used to apply different PRE herbicides on eight soybean fields in Missouri and Mississippi in 2017 and 2018, respectively. Pendimethalin, metribuzin, clomazone, imazethapyr and pyroxasulfone were selected based on their physicochemical characteristics (adsorption, volatility and solubility) and were sprayed using XR11002, ULD12002, TTI6011002, and TTI11002 nozzles. RESULTS:The XR nozzle produced the smallest droplet size (D V0.5 ), 204 m, followed by the ULD, TTI60 and TTI with D V0.5 of 468, 646, and 794 m, respectively. Droplet size, spray coverage, nozzle type or physicochemical characteristics showed no effect on PRE herbicide efficacy, except in the Monroe County, MS, field, with pendimethalin. The TTI60 twin fan nozzle enhanced pendimethalin weed control (up to 91%) in comparison with pendimethalin sprayed with the TTI nozzle (64%), in a high organic matter (OM) soil composed of large soil clods and high weed pressure. It was hypothesized that improved herbicide penetration assisted by the TTI60 dual fan pattern increased herbicide-moisture contact and clod coverage by the herbicide. Under soils with higher OM content (>2%) pendimethalin weed control was reduced. In soils with low OM (<0.7%), low cation exchange capacity (CEC) (<13.1%) and rainfall of 12.2 mm within 3 days after application, metribuzin also resulted in reduced weed control. CONCLUSION:The results indicate that droplet size does not affect PRE herbicide efficacy regardless of physicochemical herbicide properties including adsorption, volatility and solubility.

No abstract

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Sphenophorus levis is a difficult to control pest in sugarcane that causes great damage to the subterranean part of the plant. Low insect control has been a result of the pesticide application technology adopted but also because of the lack of studies regarding the pest’s behavior. This research aimed to examine the repellency of insecticides to S. levis adults and to evaluate the activity and location behavior of S. levis adults under 24 hour-observations. Repellency studies were conducted in free-choice tests providing treated soil with lambda-cyhalothrin + thiamethoxam and untreated soil as choice options to S. levis adults. Insect activity and location behavior studies were assessed by hourly observations of S. levis adults in containers with soil and sugarcane plant. Results indicated S. levis adults were not repelled nor attracted to soil treated with lambda-cyhalothrin + thiamethoxam. Additionally, insects presented nocturnal behavior with most activities (walking, digging and mating) starting at 18:00 pm until 2:00 am. An average of 20.7% of insects were out of the soil at night while the majority, 79.3%, remained inside the soil. During the day most insects, 95%, remained hidden in the soil. Exposed insects were primarily located on soil surface. According to these results, nocturnal insecticide applications may improve S. levis adult control due to greater insect activity and exposure at night.

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Sphenophorus levis Vaurie, 1978 (Coleoptera: Curculionidae). is a difficult to control pest in sugarcane that causes great damage to the subterranean part of the plant. Low insect control is the result of the pesticide application technology adopted but also a consequence of the lack of studies regarding the pest’s behavior. This research aimed to examine the attractiveness and repellency of one labelled insecticide dose to S. levis adults and to evaluate the activity and location behavior of S. levis adults under hourly observations over 24 h. Repellency and attractiveness studies were conducted in free-choice tests with treated soil with an insecticide product composed of lambda-cyhalothrin + thiamethoxam active ingredients and untreated soil. Insect activity and location behavior studies were assessed by conducting hourly observations of S. levis adults in containers with soil and sugarcane plant. The results indicate that S. levis adults are not repelled nor attracted to soil treated with the labelled dose of lambda-cyhalothrin + thiamethoxam in sugarcane. Additionally, insects presented nocturnal behavior for most activities (walking, digging and mating) starting at 6:00 p.m. until 2:00 a.m. An average of 21% of insects were out of the soil at night while the majority, 79%, remained inside the soil. During the day, most insects, 95%, remained hidden in the soil. Exposed insects were primarily located on the soil surface. According to these results, nocturnal insecticide applications may improve S. levis adult control due to greater insect activity and exposure at night.