BACKGROUND: Crops genetically engineered to make insect-killing proteins from Bacillus thuringiensis (Bt) have revolutionized management of some pests. However, the benefits of such transgenic crops are reduced when pests evolve resistance to Bt toxins. We evaluated resistance to Bt toxins and Bt cotton plants using laboratory bioassays and complementary field trials focusing on Helicoverpa zea, one of the most economically important pests of cotton and other crops in the United States. RESULTS:The data from 235 laboratory bioassays demonstrate resistance to Cry1Ac, Cry1Fa, and Cry2Ab occurred in most of the 95 strains of H. zea derived from Arkansas, Louisiana, Mississippi, Tennessee, and Texas during 2016 to 2021. Complementary field data show efficacy decreased for Bt cotton producing Cry1Ac + Cry1Fa or Cry1Ac + Cry2Ab, but not Cry1Ac + Cry1Fa + Vip3Aa. Moreover, analysis of data paired by field site and year shows higher survival in bioassays was generally associated with lower efficacy of Bt cotton. CONCLUSIONS:The results confirm and extend previous evidence showing widespread practical resistance of H. zea in the United States to the Cry toxins produced by Bt cotton and corn, but not to Vip3Aa. Despite deployment in combination with Cry toxins in Bt crops, Vip3Aa effectively acts as a single toxin against H. zea larvae that are highly resistant to Cry toxins. Furthermore, Vip3Aa adoption is increasing and previous work provided an early warning of field-evolved resistance. Thus, rigorous resistance management measures are needed to preserve the efficacy of Vip3Aa against this highly adaptable pest.

Recent increases in the prevalence of glyphosate-resistant (GR) Palmer amaranth mandate that new control strategies be developed to optimize weed control and crop performance. A field study was conducted in 2012 and 2013 in Jackson, TN, and in 2013 in Knoxville, TN, to evaluate POST weed management programs applied after harvest (POST-harvest) for prevention of seed production from GR Palmer amaranth and to evaluate herbicide carryover to winter wheat. Treatments were applied POST-harvest to corn stubble, with three applications followed by a PRE herbicide applied at wheat planting. Paraquat alone or mixed with S-metolachlor controlled 91% of existing Palmer amaranth 14 d after treatment but did not control regrowth. Paraquat tank-mixed with a residual herbicide of metribuzin, pyroxasulfone, saflufenacil, flumioxazin, pyroxasulfone plus flumioxazin, or pyroxasulfone plus fluthiacet improved control of regrowth or new emergence compared with paraquat alone. All residual herbicide treatments provided similar GR Palmer amaranth control. Through implementation of POST-harvest herbicide applications, the addition of 1,200 seed m À2 or approximately 12 million seed ha À1 to the soil seedbank was prevented. Overall, the addition of a residual herbicide provided only 4 to 7% more GR Palmer amaranth control than paraquat alone. Wheat injury was evident (, 10%) in 2012 from the PRE applications, but not in 2013. Wheat grain yield was not adversely affected by any herbicide application. Nomenclature: Pyroxasulfone, 5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl)pyrazol-4-ylmethyl 4,5-dihydro-5,5-dimethyl-1,2-oxazol-3-yl sulfone; Palmer amaranth, Amaranthus palmeri S. Wats; corn, Zea mays L.; wheat, Triticum aestivum L. Key words: Glyphosate resistance, herbicide resistance, weed control.Aumentos recientes en la prevalencia de Amaranthus palmeri resistente a glyphosate (GR) requiere que nuevas estrategias de control sean desarrolladas para optimizar el control de malezas y el desempeño de los cultivos. Se realizó un estudio de campo en 2012 y 2013, en Jackson, Tennessee, y en 2013 en Knoxville, Tennessee, para evaluar programas de manejo de malezas POST aplicados después de la cosecha (POST-cosecha) para la prevención de la producción de semilla de A. palmeri GR y para evaluar la residualidad de los herbicidas durante el trigo de invierno. Los tratamientos fueron aplicados POST-cosecha a campos después de la cosecha del maíz, con tres aplicaciones seguidas por un herbicida PRE aplicado al momento de la siembra del trigo. Paraquat solo o en mezcla con S-metolachlor controló 91% del A. palmeri existente 14 d después del tratamiento, pero no controló el rebrote de la maleza. La mezcla en tanque de paraquat con un herbicida residual ya sea metribuzin, pyroxasulfone, saflufenacil, flumioxazin, pyroxasulfone más flumioxazin, o pyroxasulfone más fluthiacet mejoró el control de rebrotes o nueva emergencia de plántulas al compararse con paraquat solo. Mediante la implementación de aplicaciones de herbicidas POST-cosecha se previno ...

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), (Hemiptera: Miridae) is considered the most damaging pest of cotton (Gossypium hirsutum L.) in the mid-southern United States, although it is established throughout the United States, southern Canada, and northern Mexico. The introduction of transgenic crops for the control of moths in the Heliothine complex and eradication of the boll weevil, Anthonomus grandis, from much of the United States led to greatly reduced pesticide use in cotton fields, which allowed L. lineolaris to emerge as a new primary pest of cotton in the mid-southern United States. Since the publication of a review by Layton (2000) on damage caused by Lygus lineolaris, many new studies have been published on the changes in host range, population dynamics, sampling methods and thresholds, cultural practices, sex pheromones and attractant blends, novel pesticides and insecticide resistance mechanisms, olfactory and feeding behaviors, introduction of biological control agents, host-plant resistance mechanisms, and new molecular and genetic tools for integrated pest management of Lygus species in cotton and other important crops. Here, we review and discuss the latest developments in L. lineolaris research in the last two decades.

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), is an important pest of cotton in many areas of the southern United States. An experiment was conducted at two locations in Mississippi during 2016 and 2017 to evaluate action thresholds for tarnished plant bug on a novel Bacillus thuringiensis cotton that expresses the Cry51Aa2.834_16 toxin. Treatments included the current action threshold, a 2× threshold, and treatments where insecticides were only applied during the early season (preflower) or only during late season (during flowering) based on the current action thresholds. These were compared to an untreated control and a weekly insecticide use regime that received weekly insecticide sprays. All treatments were imposed on both Bt Cry1Aa2.834_16 cotton and a nontraited cotton. The Bt Cry1Aa2.834_16 trait reduced the number of tarnished plant bugs and injury, and improved yields compared to nontraited cotton. For all spray treatments except the weekly insecticide use regime, yields were greater for the Bt Cry51Aa2.834_16 cotton than the nontraited cotton. In terms of thresholds, Bt Cry1Aa2.834_16 cotton sprayed based on current action thresholds resulted in similar yields to the weekly insecticide use regime of both cotton types. In contrast, the 2× threshold resulted in lower yields than the current threshold for both cotton types. Though thresholds intermediate to the currently recommended action threshold and the 2× threshold were not tested, these data suggest that currently recommended action thresholds appear appropriate for Bt Cry51Aa2.834_16 cotton. These results suggest that this trait will be an important component of current IPM programs in cotton where tarnished plant bug is an important pest.