Evaluating Insect Pest Management Tools for Cotton with Adaptive Insect Populations in a Semi-Arid Environment

Numerous reports of insect resistance to Bt cotton are a growing concern. (Taillon et al 2018, Kerns et al 2018) The high cost of Bt cotton and variable pressure in New Mexico from year to year makes justification of this expense questionable if resistance levels are high, particularly when there are other options for control and most importantly since pink bollworm is now no longer a concern (Pierce et al 2013, Anon 2018). Insecticide rescue treatments are still an option. Predation is a typically a source of control of approximately 40-60% of bollworm eggs. Some cultural methods of control have been investigated by our program. Row orientation and row spacing had an impact on bollworm survival (Pierce and Monk 2010). However, these cultural control management options can be a hard sell to growers particularly when there is a demonstrable, but not dramatic impact.

Okra leaf cotton was found to have some impact on pink bollworm and boll weevil survival due to lower relative humidity in canopy. (Pieters and Bird 1977, Wilson 1986). This lower relative humidity would likely reduce bollworm survival. (Pierce and Monk 2010) A number of okra leaf cotton varieties were recently registered which can be evaluated for impact on bollworm survival (Zhang, Cantrell, Hughes and Jones 2019). Okra leaf cotton could be a particularly good fit in West Texas and New Mexico due to our low ambient relative humidity. Relative humidity is often in the range of 15-20% which combined with moderately high temperatures, 95o F, can cause extremely high mortality in bollworm eggs and larvae, with less than 1% survival under laboratory conditions. (Pierce and Yates 2001). Relative humidity in canopy for conventional varieties late season is much higher and is part of the reason we have issues with bollworm late season. Lower bollworm damage combined with high yields and good quality lint from Acala1517 genes would give growers additional varietal options and provide higher profits. When there is no need to use insecticides, growers will retain the dollars now used for the Bt technology fee. If there is sufficient demand perhaps we could revisit the grower-University cooperative that produced A1517 seed for growers in New Mexico and West Texas.

Prior testing in Artesia, NM indicated yields of non Bt cultivars were frequently equal to transgenic cultivars in SE New Mexico without insecticide applications (Pierce, Flynn, Kirk and French 2001). Bollworm is a key pest but frequently higher pressure is late in the season when there is little to no impact on yield. In typical years most cotton acreage needs no insecticides for bollworm. Some acres would need one application. Some aggressive growers make two applications, but it likely does not increase yields. Growers seem to be satisfied with profits despite the technology fee, but will be less satisfied with paying for both the tech fee and over the top applications for bollworm.

In 2018-2019, we conducted a field trials in conjunction with Texas A&M University. Results in Texas and New Mexico indicated that there was resistance in both 2 and 3 gene Bt cotton varieties (Pierce et al. 2019, Biles et al 2019). In 2018 resistance seemed to be associated with the Bt product more than the number of genes, with the WideStrike varieties having the highest amount of damage. In 2019 there was extremely low damage so we need to look at another year in the field.

Comparing potential resistance to seed treatments for thrips in the Mesilla Valley

Early-season pest management in cotton was primarily achieved with an in-furrow treatment of aldicarb (Temik®). In 2010, the Environmental Protection agency and Bayer CropScience reached an agreement to terminate production and use of aldicarb in the United States (EPA Newsroom, 2010). Consequently, to achieve cotton production goals growers had to adopt alternative practices for early-season pest management. Neonicotinoid insecticide seed treatments have become the primary solution to managing early-season pests of cotton. Thiamethoxam and imidacloprid are two common systemic insecticide seed treatments applied to commercial cotton seed. Although the two insecticides belong to the same insecticide group, their physical and chemical properties vary and may affect mortality among target pests. Resistance to neonicotinoid seed treatments has been reported, particularly in the Southeastern US, thus it is important to evaluate efficacy in New Mexico. Evaluations in Artesia with low thrip pressure (Figure 1) have suggested that the seed treatments are effective there but we don’t now if they are effective in the Mesilla Valley. A one year field trial in 2018 with state support was not definitive.. The proposed research will fund further research te determine if seed treatments are effective in the Mesilla Valley where Valley where there tends to be higher thrip pressure.