Efficacy of Experimental Insecticides for Insect Control in Cotton Grown in the Low Desert Region of Arizona, 1997
David L. Kerns, Yuma Agricultural Center
Experimental insecticides were evaluated for control of lygus bugs relative to commercial standards in cotton. These products were also evaluated for activity towards whiteflies and pink bollworms. CGA293343 was not effective when used as a side-dress material at layby, but was effective toward whiteflies, and towards lygus at higher foliar rates. Regent, Vydate and Mustang + Thiodan were highly effective for lygus control, while EXP61096A and Mustang alone performed poorly. Against whiteflies, CGA293343, Acetamiprid, and Mustang + Thiodan were most efficacious, while Mustang alone and with Thiodan were most effective towards pink bollworms.
Lygus bug, Lygus hesperus Knight, sweet potato whitefly, Bemisia tabaci (Gennadius) and pink bollworm, Pectinophora gossypiella (Saunders) are all key pests of cotton grown in Arizona. Lygus is primarily a pest form the beginning of squaring until mid-plant boll maturity after which damage is usually of little economic concern. Currently, lygus is controlled using broad-spectrum insecticides such as pyrethroids, organophosphates or carbamates. Insecticide resistance in much of Arizona has led to much interest in alternative insecticides such as the chloronicotynl, Provado. Sweet potato whitefly usually begins to infest cotton when nearby hosts, such as melons, begin senescence, usually around the beginning of squaring. Prior to 1996, growers relied heavily on organophosphate / pyrethroid mixtures for whitefly control. Insecticide resistance and subsequent difficulty controlling whiteflies resulted in much interest in alternative insecticides. In 1996-97, a Section 18 emergency use permit was issued in Arizona for the use of Knack and Applaud. Use of these products appeared to greatly enhance whitefly control over previous years experiences, and set the standard for whitefly control in cotton. Pink bollworm can usually be detected early in the cotton's fruiting stage but normally reaches damaging levels in mid-July through August. Pink bollworms are controlled by planting B.t. cotton or using broad-spectrum insecticides, often in conjunction with pheromone to disrupt mating. Because these pests overlap in their occurrence, there is interest cross efficacy to these pests.
This study was setup to primarily evaluate insecticides for lygus control, but also collect some information on their efficacy towards whitefly and pink bollworm. Thus, insecticides applied for lygus control were evaluated for their impact on whiteflies and pink bollworms. However, once the lygus populations declined, insecticides targeting lygus would be dropped from the treatment list and replaced with whitefly materials. The following products were evaluated: CGA293343, EXP61096A, Regent, Mustang, Mustang + Thiodan, and Vydate C-LV for efficacy toward lygus; CGA293343, EXP61096A, Regent, Mustang, Mustang + Thiodan, Acetamiprid, Nexter, Applaud and Knack for efficacy toward sweet potato whitefly; and CGA293343, Regent, Mustang, Mustang + Thiodan and Vydate C-LV for efficacy towards pink bollworm.
CGA293343 is being developed by Novartis, and Acetamiprid by Rhone Poulenc act at the nicotinic receptor similar to Provado and Admire (imidacloprid). These material are thought to have good potential against whiteflies and lygus. Regent (fipronil) and EXP61096A, are being developed by Rhone Poulenc, they unique and chemically similar, acting at the GABA receptor. These products are thought to have potential against lygus. Nexter (pyridaben) is a unique chemistry being developed by BASF and acts by disrupting oxidative phosphorylation. It has demonstrated activity towards whitefly in several crops.
Materials and Methods
This trial was conducted at the Yuma Valley Agricultural Center. Cotton, 'DPL 5461', was planted on 40 in beds on March 19, 1996. The test was a randomized complete block design, with 4 replicates. Plots were 4 rows X 50 ft, bordered on each side by 2 blank rows and on each end by 10 ft alleys. Applications were made on 21 May (side dress), 18 and 25 June, 01, 08, 15, 22 and 30 Jul, and 12 Aug (Table 1). Two rates of CGA293343 were evaluated as side-dress applications at layby, and if they proved ineffective towards lygus or whitefly would to applied foliarily. EXP61096A would be applied for lygus control at two rates, and if they proved ineffective would be replaced by two rates of Regent. Towards the end of the season when lygus were of little concern several products would be replaced by whitefly materials. The low rate EXP61096A / Regent plots would be treated with Acetamiprid while the high rate would treated with Nexter. Applaud and CGA293343 would be substituted for Mustang and Mustang + Thiodan respectively, and Knack would replace Vydate. All foliar treatments included Kinetic spreader sticker at 0.1% v/v.
The side-dress application was applied using a tractor driven side dress fertilizer applicator designed to deliver 10 gallons per acre about 8 inches from the plants on the middle of the side of the bed. The material was injected about 3 inches beneath the soil surface. Foliar treatments were sprayed using a tractor mounted sprayer. The boom covered 4 rows, with 3 hollow-cone D-2 nozzles per row, one centered over each row and two on 18 in drops on each side. The sprayer was calibrated to deliver 20 gallons per acre at 40 psi. The tractor traveled at 3 mph.
Lygus bug evaluations were made on 26 Jun, 02, 08, 17 and 30 Jul, and 09 and 20 Aug, which equated to 2 and 6 days after each treatment. Lygus were sampled using a 15 inch sweep net, swung in a 180 degree arc. Twenty-five sweeps were taken per plot, adults and nymphs were counted. On 28 July and 4 August, lygus damage ratings were taken by collecting 25 medium-sized bolls from each plot and counting the number of damaged carpals from each boll. The percentage of damaged carpals was estimated and a damage rating was calculated using a 1 to 5 scale where 1 = no damage, 2 = one carpal damaged, 3 = two carpals damaged, 4 = three carpals damaged, 5 = four carpals damaged.
Whiteflies were sampled on 16, 24 and 30 June, 7, 14, 21 and 28 July, 4, 11, 18 and 25 August. Ten leaves were collected from 10 plants. Leaves were taken from the 5th node from the top, and the numbers of eggs, small nymphs, red-eyed nymphs and eclosed pupae from 1 cm2 leaf discs were counted. The leaf discs were taken from the area between the mid and secondary veins of the cotton leaves. Sooty mold / honey dew accumulation was evaluated on ten plants within each plot near harvest on 26 Sept. A subjective 1-5 rating scale was used where; 1 = no contamination, 2 = foliar contamination only, 3 = light contamination of lint, 4 = moderate lint contamination and 5 = heavy contamination of the lint.
Pink bollworm damage was evaluated on 22 July and 4 August by counting the number of infested bolls from a 25 bolls per plot sample. All data were analyzed using a analysis of variance, and an F protected (P < 0.05) LSD for means separation.
Results and Discussion
The lygus precount evaluation was made on 16 June, 26 days following the side dress applications of CGA293343. There were no significant differences among treatments, and lygus averaged approximately 9 lygus per 100 sweeps (Table 1). Two days following application 2 (first foliar application), nymph populations were low, but differences among treatments in the number of adults was evident. The high rate of EXP61096A, Mustang, Mustang + Thiodan and Vydate all had fewer adults than the untreated. After application 3, adult lygus populations were increasing but there were no clear cut differences among the treatments and the untreated check. On 1 July, application 4 was applied and since the side-dress application did not appear efficacious, CGA293343 was applied foliarily over the side-dressed plots (Table 3). Two days after treatment (DAT), all insecticides had fewer adults than the untreated, but by seven DAT there were no significant differences. Nymph populations did not reach high level until the 14 July evaluation (7 DAT), where the CGA293343, Mustang, Mustang + Thiodan and Vydate treatments were significantly different from the untreated. At this time all treatments contained fewer adults than the untreated. For applications 7 and 8, Regent was substituted for the EXP6196A treatments (Table 4). Regent, the higher rate of CGA293343, Mustang + Thiodan and Vydate were all efficacious towards lygus nymphs and adults, while Mustang alone appeared to result in higher lygus nymph populations. Based on carpal damage, Mustang + Thiodan and Vydate, followed closely by Regent and the high rate of CGA293343 were most effective in protecting cotton bolls from lygus damage (Table 5). Overall, Mustang + Thiodan, Vydate and Regent appeared most efficacious towards lygus. The high rate of CGA293343 appear slightly less efficacious.
Whitefly densities were low in this trial and not much useful information was generated. There were no significant differences detected among treatments until 14 July (Table 6 and Table 7). On 14 and 21 July, all treatments appeared to have whitefly activity. However, Mustang + Thiodan and CGA293343 appeared most efficacious. A similar trend in the activity of CGA293343 and Mustang + Thiodan occurred following applications 7 and 8 (Table 8). Regent was applied in place of EXP61096A, and did not appear to provide any significant whitefly control. Likewise, Vydate did not appear to offer much whitefly suppression at this time. On 12 August insecticides better suited for whitefly control were substituted for Regent, Mustang, and Vydate (Table 9). Also, Mustang + Thiodan was replaced with CGA293343. By 6 DAT, all treatments contained fewer small nymphs than the untreated, but much of this activity was no doubt carried over for previous treatments, especially for Applaud and Knack which are not quick acting materials. By 13 DAT, distinct differences occurred in the egg counts; as expected neither Applaud nor Knack exhibited adulticidal activity (high egg counts). Acetamiprid appeared highly effective towards adults. Applaud, Knack and probably Nexter were not given the amount of time needed to really see any notable response. Honeydew / sooty mold ratings appeared to be more indicative of efficacy of insecticides applied prior to 12 August. Treatments sprayed with Regent followed by Acetamiprid or Nexter, and Vydate followed by Knack did not differ from the untreated. Overall, Acetamiprid, CGA293343 and Mustang + Thiodan all appeared efficacious towards sweet potato whitefly.
Significant differences among treatments in the number of bolls infested with pink bollworms was observed on 4 August (Table 10). Mustang and Mustang + Thiodan were highly effective towards pink bollworm. The high rate of CGA293343, Vydate and Regent appeared to offer some pink bollworm suppression.
This is a part of publication
AZ1006: "Cotton: A College
of Agriculture Report," 1998, College of
Agriculture, The University of Arizona, Tucson, Arizona,
85721. Any products, services, or organizations that are
mentioned, shown, or indirectly implied in this
publication do not imply endorsement by The University of
Arizona. The University is an Equal
Opportunity/Affirmative Action Employer.