Several species of thrips are known to infest cotton seedlings in the United States and constitute one of the most common insect pest challenges for growers. The species complex, species abundance, extent of crop injury, and impact on lint yield varies widely across the cotton states. Cotton seedlings are most susceptible to thrips injury during the first 4 to 5 weeks after plant emergence. Feeding by thrips results in distortion, malformation and tearing of seedling leaves, reduced leaf area and plant height, reduced root growth, and injury to or death of the apical meristem, the latter of which leads to excessive vegetative branching. Plant maturity (i.e., fruit production) can be delayed and in extreme cases, losses of as much a 30 -50% of lint yield potential have been reported. To date, no varieties of cotton have resistance to thrips, so controls are based solely on insecticide applications. Treatment thresholds and control practices (e.g., insecticide seed treatments, in-furrow or foliar applied insecticides) vary widely across cotton states. This article provides a brief summary of the various species of thrips present in U.S. cotton, their plant host range and injury to cotton, a general description of thrips biology, and management practices currently available to growers.

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae), has become the primary target of foliar insecticides in cotton, Gossypium hirsutum L., throughout the Midsouth over the past several years. This prompted a reevaluation of existing action thresholds for flowering cotton under current production practices and economics. A trial was conducted at 19 locations throughout the Midsouth during 2006 and 2007. Threshold treatments ranged from a weekly automatic insecticide application to a very high threshold of 10 tarnished plant bugs per 1.5 row-m on a black drop cloth. Individually, all locations reached the lowest threshold, and eight locations had a significant yield loss from tarnished plant bugs. Across all locations, lint yield decreased 0.85 to 1.72% for each threshold increase of one tarnished plant bug per 1.5 row-m. Yield loss was most closely correlated to pest density during the latter half of the flowering period. The relationship between plant bug density or damage and yield was similar for drop cloth, sweep net, and dirty square sampling methods, but the correlations among these sampling methods were not high. Incorporating actual insecticide application data from the trial and average production and economic factors for Midsouth cotton, the economic threshold, if monitoring once per week, should be between 1.6 and 2.6 tarnished plant bugs per 1.5 row-m during the flowering period. More frequent monitoring or situations where insecticide applications are more efficacious may alter this threshold.

Insecticide applications to control tarnished plant bug, Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae), during cotton, Gossypium hirsutum L., bud formation are common throughout the Midsouth of the United States. Cultivation practices and the pest complex have changed since action thresholds were established for this pest. A trial was conducted at 33 locations over 3 yr throughout the Midsouth to evaluate tarnished plant bug damage to cotton during the prebloom period. There was no consistent yield response to action thresholds, but average tarnished plant bug density and average square loss were both significant factors impacting lint yield. Based on the yield responses and application frequency of the various action thresholds, the best economic scenario occurred when tarnished plant bug density during the prebloom period averaged eight per 100 sweeps and square retention averaged 90%. The action thresholds required to achieve these averages are expected to be higher than these levels because pest pressure is not normally constant during the prebloom period. When insecticides are required, an application interval shorter than one week may be needed to obtain satisfactory control.

Field studies were conducted to evaluate the effects of glyphosate and conventional herbicides on purple and yellow nutsedges. Tubers collected from the field were counted and tested for viability via growth chamber or triphenyl tetrazolium chloride test to determine the effect of herbicides on tuber density and viability. With purple nutsedge, herbicide treatments containing glyphosate at 0.84 kg/ha followed by (fb) glyphosate at 0.56 kg/ha reduced viable and total tuber density. Among conventional herbicides, treatments containing metolachlor at 2.2 kg/ha plus sulfentrazone at 0.26 kg/ha plus chlorimuron at 0.05 kg/ha applied preemergence (PRE) and metolachlor at 2.2 kg/ha plus imazaquin at 0.14 kg/ha applied PRE fb bentazon at 0.84 kg/ha applied postemergence (POST) reduced total and viable tuber density compared to the nontreated. Metolachlor at 2.2 kg/ha plus sulfentrazone at 0.26 kg/ha plus chlorimuron at 0.05 kg/ha applied PRE fb bentazon applied POST also reduced viable tuber density of purple nutsedge. With yellow nutsedge, all herbicide treatments reduced total and viable tuber density over the nontreated check.

Fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae); corn earworm, Helicoverpa zea Boddie (Lepidoptera: Noctuidae); southwestern corn borer, Diatraea grandiosella Dyar (Lepidoptera: Crambidae); sugarcane borer, Diatraea saccharalis F. (Lepidoptera: Crambidae); and lesser cornstalk borer, Elasmopalpus lignosellus Zeller (Lepidoptera: Pyralidae), are lepidopteran pests of corn, Zea mays L., in the southern United States. Blended refuge for transgenic plants expressing the insecticidal protein derivative from Bacillus thuringiensis (Bt) has recently been approved as an alternative resistance management strategy in the northern United States. We conducted a two-year study with 39 experiments across 12 states in the southern United States to evaluate plant injury from these five species of Lepidoptera to corn expressing Cry1F and Cry1Ab, as both single and pyramided traits, a pyramid of Cry1Ab×Vip3Aa20, and a pyramid of Cry1F×Cry1Ab plus non-Bt in a blended refuge. Leaf injury and kernel damage from corn earworm and fall armyworm, and stalking tunneling by southwestern corn borer, were similar in Cry1F×Cry1Ab plants compared with the Cry1F×Cry1Ab plus non-Bt blended refuge averaged across five-plant clusters. When measured on an individual plant basis, leaf injury, kernel damage, stalk tunneling (southwestern corn borer), and dead or injured plants (lesser cornstalk borer) were greater in the blended non-Bt refuge plants compared to Cry1F×Cry1Ab plants in the non-Bt and pyramided Cry1F×Cry1Ab blended refuge treatment. When non-Bt blended refuge plants were compared to a structured refuge of non-Bt plants, no significant difference was detected in leaf injury, kernel damage, or stalk tunneling (southwestern corn borer). Plant stands in the non-Bt and pyramided Cry1F×Cry1Ab blended refuge treatment had more stalk tunneling from sugarcane borer and plant death from lesser cornstalk borer compared to a pyramided Cry1F×Cry1Ab structured refuge treatment. Hybrid plants containing Cry1F×Cry1Ab within the pyramided Cry1F×Cry1Ab blended refuge treatment had significantly less kernel damage than non-Bt structured refuge treatments. Both single and pyramided Bt traits were effective against southwestern corn borer, sugarcane borer, and lesser cornstalk borer.