Cotton Report 1997
ABOUT THE COLLECTION
The Cotton Report is one of several commodity-based agricultural research reports published by the University of Arizona.
This report, along with the Forage and Grain Report, was established by Hank Brubaker, Extension Agronomist, after seeing a similar report published by Texas A&M University in the mid-1970’s.
The purpose of the report is to provide an annual research update to farmers, researchers, and those in the agricultural industry. The research is conducted by University of Arizona and USDA-ARS scientists.
Both historical and current Cotton Reports have been made available in the UA Campus Repository as part of a collaboration between the College of Agriculture and Life Sciences and the University Libraries.
Contents for Cotton Report 1997
- 1996 Weather Conditions
- The 1997 Arizona Cotton Advisory Program
- Agronomic Evaluations of Bt Cotton
- Evaluation of Planting and Dating Effects on Crop Growth and Yield for Upland and Pima Cotton, Marana, 1995
- Evaluation of Planting Date Effects on Crop Growth and Yield for Upland and Pima Cotton, 1996
- Date of Planting by Long Staple Variety Trial, Safford Agricultural Center, 1996
- Defoliation Tests with Ginstar at the Maricopa Agricultural Center in 1996
- Cotton Defoliation Evaluations, 1996
- Defoliation of Pima and Upland Cotton at the Safford Agricultural Center, 1996
- Cotton Heat Stress
- Development of a Yield Projection Technique for Arizona Cotton
- Evaluation of a Feedback Approach to Nitrogen and Pix Application
- Evaluation of Late Season Pix™ Applications
- 1996 Low Desert Upland Cotton Advanced Strains Testing
- Arizona Upland Cotton Variety Testing Program, 1996
- Short Staple Cotton Advanced Strains Trial, Safford Agricultural Center, 1996
- Upland Advanced Strains Cotton Variety Test at the Maricopa Agricultural Center, 1996
- Short Staple Variety Trials in Cochise County, 1996
- Short Staple Variety Demonstrations, Graham County, 1996
- Short Staple Variety Trial, Greenlee County, 1996
- Short Staple Regional Cotton Variety Trial, Safford Agricultural Center, 1996
- Upland Regional Cotton Variety Test at the Maricopa Agricultural Center, 1996
- Pima Regional Variety Test at the Maricopa Agricultural Center, 1996
- Pima Cotton Regional Variety Trial, Safford Agricultural Center, 1996
- Field Determination of Permanent Wilting Point
- Review of Irrigation Timing Stufies Conducted in 1995 and 1996
- Lint Yield Response to Varied Levels of Water Stress and Consumptive Water Use Requirements of Upland Cotton
- Irrigation Efficiencies and Lint Yields of Two Upland Cotton Varieties Grown at the Maricopa Agricultural Center, 1996
- Using Drainage Lysimeters to Evaluate Irrigation and Nitrogen Interactions in Cotton Production
- Evaluation of Irrigation Termination Management on Yield of Upland Cotton
- Gila Basin Voluntary Pest Management Project, 1995 and 1996
- Status of Whitefly Resistance to Insecticides in Arizona Cotton
- Silverleaf Whitefly on Cotton
- Monitoring Whitefly Susceptibility to Applaud
- Whitefly Growth Regulators: A Field Sampling Protocal for Nymphs
- Whitefly Control Using Insect Growth Regulators
- Whitefly Growth Regulators: Large-Scale Evaluation
- Commercial Field Performance of KNACK™ on Cotton in the Yuma Valley
- Management of Pyrethoid-Resistant Whiteflies in Arizona Cotton: Selection, Cross-Resistance, and Dynamics
- Conservation of Natural Enemies Relative to Use of Insect Growth Regulators for Control of Sweetpotato Whitefly
- Upland and Pima Cotton Demonstration Using IGR's Knack and Applaud to Control Silverleaf Whitefly at the Yuma Valley Ag Center in 1996
- Silverleaf Whitefly and Cotton Lint Stickiness
- Seasonal Infestation by Pink Bollworm of Transgenic Cotton, NuCOTN 33, and Parental Cultivar DPL-5415 in Commercial Fields: the Second Season
- Demonstration to Manage Pink Bollworm with BT Cottons, Yuma Valley Ag Center, 1996
- Control of Pink Bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae) with Biocontrol and Biorational Agents
- Steinernematid Nematode Infections of Pink Bollworm Larvae in Field Tests
- Lygus Bugs in Arizona Regain Susceptibility to Key Insecticides
- Side-Dress Temik® Effects on Lint Yields
- Nitrogen Management Experiments for Upland and Pima Cotton, 1996
- Fertilizer Nitrogen Recovery in Irrigated Upland Cotton
- Evaluation of Calcium Soil Conditioners in an Irrigated Cotton Production System
- 1996 Seed Treatment Evaluations
- Aflatoxin Contamination of Bt Cottonseed
- Telone II® Following Grain Rotation for Nematode Control?
- Suppression of Plant Parasitic Nematodes in Cotton Using the Antomopathogenic Nematode Steinernema Riobravis (Cabanillas, Poinar, and Raulston) (Rhabditida: Steinernematidae)
Suppression of Plant Parasitic Nematodes in Cotton Using the Antomopathogenic Nematode Steinernema Riobravis (Cabanillas, Poinar, and Raulston) (Rhabditida: Steinernematidae)Cotton fields were treated with the entomopathogenic nematode, Steinernema riobravis, and Vydate® L for the control of plant parasitic nematodes. Short staple cotton grown near Coolidge, Arizona, was treated at a rate of 1 billion and 2 billion S. riobravis nematodes per acre, and 0.5 lb a.i. Vydate® L per acre. Untreated cotton received an application of water only. Treatments were applied through a subterranean drip system with 12 inch spaced outlets. Applications were made in the daily irrigation cycle of 0.33 inches of water, normal irrigation cycles followed Products were uniformly distributed over the treated fields. Entomopathogenic nematodes persisted throughout the 6 week experimental period at the 1 billion per acre rate. However, nematodes applied at 2 billion per acre rate disappeared rapidly. Populations of various plant parasitic nematode species were monitored subsequent to treatment application. Nematodes were extracted using a standard sugar flotation technique and counted in I ml slide samples. Both Meloidogyne incognita and Tylenchorhynchus spp. populations were reduced by S. riobravis applied at 1 billion per acre rate. Phytoparasitic nematodes were reduced following application of Vydate® L, but control was not sustained beyond one week.
Telone II® Following Grain Rotation for Nematode Control?Six field trials were conducted between 1994 and 1996 in Buckeye and Gila Bend, Arizona to determine the effect of soil fumigation with Telone II on the yield of cotton following rotation with Durham wheat. Telone was shank injected at two or more rates (0, 3, or 5 gal/acre) in fields previously maintained with a cotton-wheat-summer/winter fallow rotation. Five fields were planted to Upland and one field to Pima cotton. Four of the six trials resulted in an average lint yield increase of 180 lint lbs/ac compared to the untreated controls. In one trial where all three rates were compared, yield at the 5 gallon rate was increased 141 lint lbs/ac compared to the 3 gallon rate and the control. In two of the trials none of the treatments differed significantly.
Aflatoxin Contamination of Bt CottonseedTransgenic Bt cotton may have reduced susceptibility to aflatoxin contamination as a result of pink bollworm resistance. During 1995 and 1996, Bt cottonseed from several commercial fields in Arizona contained aflatoxin levels unacceptable for dairy use. Comparison of cottonseed with and without BGYF (bright-green-yellow fluorescence) from one highly contaminated (> 6,000 ppb aflatoxin Bj) Bt seed lot indicated that most contamination probably resulted from exposure of mature cotton to high humidity. Seed exhibiting BGYF was repeatedly detected in Bt cottonseed lots but, pink bollworm exit holes were not observed in the field. A field plot test in 1996 demonstrated high resistance among Bt cultivars to both pink bollworm damage and formation of BGYF seed cotton. These observations suggest that resistance to pink bollworm will result in reduced aflaaoxin contamination when pink bollworm pressure coincides with conditions conducive to Aspergillus flavus infection. However, Bt cultivars are not resistant to aflatoxin increases occurring after boll opening and large quantities aflatoxin can form during this period. If insect control provided by Bt cultivars leads growers to hold crops in the field longer, most advantages of Bt cotton in aflatoxin management may be lost. Combined use of Bt cultivars and atoxigenic strains of A. flavus may result in the most reliable control of aflatoxin contamination.
1996 Seed Treatment EvaluationsCottonseed was treated with several fungicide treatments in an effort to protect the seed and seedling from disease. Seed germination and vigor was evaluated in two Arizona locations; Maricopa and Marana. Stand counts were taken on two separate dates after emergence at both Maricopa and Marana and percent emergence was calculated. Significant differences in percent emergence due to treatment were observed in the first sample date at Marana with the treatment combination of NuFlow ND and Maxim having the highest percent emergence. Results from the second sample date at Marana were statistically significant but similar treatment ranking was observed. Results at Maricopa showed no statistically significant differences due to treatment for either sample date.
Evaluation of Calcium Soil Conditioners in an Irrigated Cotton Production SystemIn 1996 a single field experiment was conducted at Paloma Ranch, west of Gila Bend in Maricopa County Arizona. Nucoton 33B was dry planted and watered -up on 15 April. Treatments consisted of various rates and times of application of nitrogen (N) and calcium (Ca) from two sources (N-Carm and CAN-17), as well as a standard N source, UAN-32, along with a Calcium (Ca) check which received no Ca. Treatments], 2, and 3 each received a total of 280 lbs. N/acre. Treatment 4 received a total of 210 lbs. N/acre while treatment 5 received a total of 301 lbs. N/acre. Treatment 1 was a check plot and received only standard applications of UAN-32. Treatments 2 and 4 each received a total of 72 lbs. of Ca/acre. Treatment 5 received a total of 79 lbs. Ca/acre while treatment 4 received a total of 300 lbs. Ca/acre. No significant differences were found among the various treatments in terms of plant growth, soil water content, ECₑ values, and sodium absorption ratios. Lint yields were significantly different (P < 0.07).
Fertilizer Nitrogen Recovery in Irrigated Upland CottonField studies were carried out for the purpose of evaluating fertilizer nitrogen (N) recovery of upland cotton by use of the difference technique. The treatments under study included : i) check (no fertilizer N applied), ii) standard approach (preplant and sidedress), iii) feedback approach (based upon soil and plant factors), and iv) 2X feedback approach. The studies were carried out at two locations Maricopa (MAC) and Marana (MAR). MAC is a low elevation location with a coarser textured soil compared to the MAR location. 'DPL-20' was the variety used in both locations, except for the early years at MAC where 'DPL-90' was used. The sources of fertilizer N were urea and ammonium sulphate, which were sidedress and split applied. In general, for the MAC location the final N fertilizer rates (NFR) applied were higher than for MAR due to higher yield potentials. The total N uptake increased as the NFR increased. The N use efficiency (NUE) values were reduced as NFR increased. The N fertilizer uptake (NFU) showed a decreasing pattern in the first years, and then an increasing trend; which was coupled with rather high amounts of N taken up in the check plot (soil N mineralized). When the N uptake in the check plot was high, NFU values were low, and vice versa. At MAC the N uptake in the check plot, apparently due to mineralized soil N revealed a slight increasing trend during the first years and then, after the fourth year, a rapid reduction of the mineralized soil N (check plot). A similar pattern was observed for MAR, although the total amount of N taken up was smaller compared to the MAC location.
Nitrogen Management Experiments for Upland and Pima Cotton, 1996Three field experiments were conducted in Arizona in 1996 at three locations (Maricopa, Marana, and Safford). The Maricopa and Safford experiments have been conducted for seven consecutive seasons, the Marana site was initiated in 1994. The purposes of the experiments were to validate and refine nitrogen (N) fertilization recommendations for both Upland and Pima cotton. The experiments each utilized N management tools such as pre-season soil tests for NO₃⁻-N, in- season plant tissue testing (petioles) for N fertility status, and crop monitoring to ascertain crop fruiting patterns and crop N needs. At each location, treatments varied from a conservative to a more aggressive approach of N management. Results at each location revealed a strong relationship between the crop fruit retention levels and N needs for the crop. This pattern was further reflected in final yield analysis as a response to the N fertilization regimes used. The higher, more aggressive, N application regimes did not benefit yields at any location.
Side-Dress Temik® Effects on Lint YieldsTemik 15G was side -dressed at a rate of 7 lb./acre and 14 lb./acre and compared to an untreated check in two experiments in Buckeye, Az.. Treatments were made prior to the second in- season irrigation (June 3 and June 5) which was just prior to early bloom. Lygus counts were taken using a sweep net on weekly intervals for six weeks post application. The first experiment resulted in a significant increase of 123 lb. and 1241b. lint in both the 7 and 14 lb. rate treatment respectively over the untreated check. The second experiment resulted in a significant 102 lb. lint increase for the 7 lb. treatment with no significant difference for the 14 lb. treatment to the check.
Lygus Bugs in Arizona Regain Susceptibility to Key InsecticidesAdult lygus bugs, Lygus hesperus (Knight), were collected from alfalfa fields in 22 different cotton producing areas of Arizona. A standardized, glass vial method was used to estimate susceptibility of the collected populations to the pyrethroid insecticide Captures (bifenthrin) and the organophosphate Orthene® (acephate). Large differences were recorded in susceptibility of Arizona populations to both insecticides. The most susceptible lygus populations continue to be found in the eastern areas of the state and the least susceptible in central Arizona. Lygus from throughout the state were substantially more susceptible to Capture and Orthene in 1996 than in 1995. Lygus bioassayed repeatedly from the same locations in 1996 exhibited moderate-to-small seasonal variability in susceptibility to Capture. However, some of the same populations varied widely in susceptibility to Orthene in 1996. The large changes in susceptibility to Orthene were attributed to episodic movements of lygus from other hosts. Eleven insecticides were evaluated against populations most and least susceptible to Capture and Orthene to identify promising candidates for future lygus field trials. A Safford population was substantially more susceptible than a Maricopa population to Admire®, Curacron®, Cygon®, Malathion® and Vydate®. Most surprising was the greatly reduced susceptibility to Admire of the Maricopa population. The older insecticides Bidrin®, Lannate®, Monitor ®, Naled®, Ovasyn® and Thiodan® were quite similar in toxicity to both the Safford and Maricopa populations and therefore are good candidates for further field evaluations to judge their merit for inclusion in lygus insecticide rotations. Bioassay results were related to field performance of four insecticides in a field trial conducted in Central Arizona. Findings showed that the two insecticides that caused the lowest mortality in vial bioassays, Orthene and Vydate, resulted in the greatest suppression of lygus in the field. These findings underscore that the absolute level of mortality observed in bioassays should not be assumed to reflect relative efficacy in the field. It also confirms that Orthene and Vydate continue to be good choices for lygus control, even in Central Arizona where populations are decidedly less susceptible to these insecticides. We have demonstrated that the adult vial bioassay provides a reliable method for measuring differences between Arizona lygus populations in susceptibility to a broad range of conventional insecticides. We found the method sufficiently sensitive to repeatedly detect significant within-season and regional differences in lygus susceptibility. These new insights will allow us to better manage the insecticides used in Arizona to control this important pest.
Steinernematid Nematode Infections of Pink Bollworm Larvae in Field TestsUnder field conditions, pink bollworm (PBW), Pectinophora gossvpiella (Saunders), larvae were exposed to soil samples from plots treated with Steinernema riobravis at the rate of 5 nematodes per cm² of soil surface. Larval mortalities were 50% on the day of treatment and 2.5% on day 90 following treatment with irrigations about every 14 to 21 days,. Larval mortality percentages after exposure to soil samples from plots treated with S. carpocapsae at the rate of 5 per cm2 of soil surface were 32.5, 15.3, 5.3 and 2.5 for the day of treatment and day 1, 7, and 15 following treatment, respectively. No further mortality occurred in bioassays conducted up to 90 days following treatment. With plots treated with 25 nematodes per cm² of soil surface, PBW larval mortalities ranged from 100% on the day of treatment to 7.5% on day 63 following treatment with S. riobravis and 92.5% on the day of treatment to 5% on day 7 following treatment with S. carpocapsae. Percentages of larval mortality after exposure to soil samples from plots treated with S. riobravis increased after each irrigation, but did not increase after exposure to soil samples from plots treated with S. carpocapsae.
Control of Pink Bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae) with Biocontrol and Biorational AgentsAt pre- sowing irrigation (mid-March), cotton fields were treated with two entomopathogenic nematode species; Steinernema riobravis and S. carpocapsae for control of diapausing Pectinophora gossypiella larvae. Pima S-6 cotton fields situated in Fort Hancock, Texas were treated at a rate of one billion nematodes per acre. Caged, diapausing larvae were buried in fields at a depth of one inch, in row tops and furrow bases. Nematodes were applied with a spray rig, fixed winged aircraft, or in furrow irrigation via a constant flow, battery box. Fields were irrigated after ground application, prior to aerial spraying and during furrow application. Caged larvae were recovered 48 hours after nematode application. All application methods resulted in uniform distribution of nematodes over the treated fields. No significant differences ir. larval mortality between nematode species or application method could be determined. However, aerial and furrow application methods gave consistently better parasitism of larvae compared to ground rig delivery. Larval mortality in cassettes buried in furrow bases was significantly higher than in row tops. Larval mortality ranged from 53.26-79.14 %. Both nematode species could be recovered 50 days post application. At pin-head square Frustrate® PBW pheromone bands (biosys, Inc.) were applied at 100 bands per acre placement rate (16 g a. i./acre), giving a target release of 115 mg gossyplure/acre/day. Capillary gas chromatography was used to analyze bands throughout the growing season. A uniform release profile indicated sufficient release of pheromone for 144 days after placement. Pink bollworm mating disruption was monitored in three ways: 1. Delta 2 traps were positioned throughout the farm, forming a continuous trap line. Significantly larger numbers of moths were recovered form untreated zones. 2. Virgin female moths were placed in mating stations at dusk. At sun rise moths were collected and later dissected for spermatophores. Significantly higher mating activity occurred in untreated fields (p= 0.000). 3. Green bolls were collected at random and examined for larvae. Significantly higher infestation levels existed in untreated zones. At harvest (November), seed cotton yields were weighed using trailer scales. Higher yields were recovered from pheromone (1,864 lb/acre), and pheromone + nematode fields (1,712 lb/acre), than control fields (1,450 lb/acre). However, due to large variations between fields, the differences were not statistically significant (p = 0.436).
Demonstration to Manage Pink Bollworm with BT Cottons, Yuma Valley Ag Center, 1996Transgenic cotton with the Bollgard™ gene inserted has shown great promise in controlling pink bollworm infestations in cotton. This trial was superimposed over a variety trial. Evaluations of pbw infestation indicated remarkable control even though the bolls became infested. Yields were increased in this trial when almost 100% infestation of pbw was allowed to occur. It appears that the trangenic cottons containing Bollgard™ may be an effective method of pbw control.
Seasonal Infestation by Pink Bollworm of Transgenic Cotton, NuCOTN 33, and Parental Cultivar DPL-5415 in Commercial Fields: the Second SeasonBolls from transgenic cotton, NuCOTN 33 (Delta and Pine Land Co.) containing the Bollgard™ gene (Monsanto Co.) and from the parental cultivar DPL-5415 were examined for mature larvae of the pink bollworm (78,240 total bolls). Bolls from paired fields were collected in the Queen Creek, Buckeye, Maricopa, and Marana, AZ, areas. Equal numbers of bolls were collected from the edges of each field each week July - October except for Marana where a single collection was made 30 October. Bolls were incubated for 2 weeks and/or dissected from 1 September onward. Numbers of pink bollworm larvae were very low in all fields through August and increased to extremely high levels (up to 3.4 larvae/boll at Marana) in some control fields in October. Numbers of pink bollworm found in NuCOTN 33 were extremely low or nonexistent, even in fields immediately adjacent to heavily infested control fields. The overall numbers of larvae found in NuCOTN 33 were comparable to those found in 1995. In 1995, the percent worms of bolls were: NuCOTN 33 = 0.0003 (13 larvae /38320 bolls) compared to 11.80% for DPL -5415 (4711 larvae /39920 bolls). Overall percent worms of bolls for 1996 were: NuCOTN 33 = 0.0004% (14 larvae/33350 bolls) compared to 34.19% (11572 larvae/33850 bolls) in DPL-5415.
Silverleaf Whitefly and Cotton Lint StickinessCotton plant densities of 10 or 40 thousand plants/acre had no effect on numbers of silverleaf whitefly, Bemisia argentifolii Bellows and Perring, adults, eggs, nymphs, extracted sugars from lint samples or thermodetector sticky cotton counts. Higher numbers of whitejlies occurred in early-season in Pima S-7 cotton than in DPL 50 or DPL 5415 cotton. Seasonal averages for sugars, percentages of total reducing sugars and thermodetector counts were higher for DPL 50 compared with Pima S-7 but not DPL 5415. Insecticide treatments reduced thermodetector counts and associated sugars extracted from lint.
Upland and Pima Cotton Demonstration Using IGR's Knack and Applaud to Control Silverleaf Whitefly at the Yuma Valley Ag Center in 1996The section 18 granted for the use of insect growth regulators in 1996 in Arizona provided an excellent opportunity to demonstrate the efficacy of the materials. Knack® (Pyriproxyfen) and Applaud® (Buprofezin) both demonstrated excellent control of whitefly in this demonstration. Efficacy of the insect growth regulators was monitored by using the "Ellsworth-Naranjo" methods of measuring adult and nymph whitefly numbers. This method provided good tracking of the populations throughout the period monitored. The areas treated were cotton variety trials both pima and upland. On the upland trial whitefly infestation data was collected on each variety. Hairy leaf varieties tended to have higher whitefly numbers of both adults and nymphs.
Conservation of Natural Enemies Relative to Use of Insect Growth Regulators for Control of Sweetpotato WhiteflyAs part of a large-scale, multi-institutional experiment in 1996 to examine and demonstrate strategies for management of Bemisia tabaci involving the use of two insect growth regulators (IGRs), we evaluated effects on the abundance and activity of native natural enemies. For parasitoids there were significant differences between insecticides regimes on 4 of 10 sampling dates. In general, parasitoid abundance and rates of parasitism were depressed in treatment plots receiving a rotation of conventional chemistry in comparison with those receiving IGRs. There was no apparent effect of any of the treatment variables on parasitoid emergence (immature survival). Results for arthropod predators are still preliminary, but densities were generally depressed in plots receiving a rotation of conventional insecticides in comparison with those receiving IGRs. These preliminary results suggest that use of IGRs for suppression of B. tabaci may help conserve populations of important natural enemies.
Management of Pyrethoid-Resistant Whiteflies in Arizona Cotton: Selection, Cross-Resistance, and DynamicsIn 1995, silverleaf whitefly, Bemisia argentifolii Bellows and Perring, resistance to the widely -used mixture of Danitol® (fenpropathrin) + Orthene® (acephate) was shown to be severe and widespread in Central Arizona cotton. Thereafter, laboratory experiments were undertaken to identify the other major insecticides that were affected by this resistance. Whiteflies were collected in November of 1995 from Maricopa (highly resistant) and Yuma (relatively susceptible) County locations in Arizona. A composite colony was established by combining Yuma and Maricopa whiteflies in a 4:1 ratio. After six generations of adult selection of this population with Danitol + Orthene, appreciable shifts in the concentration responses for pyrethroid, organophosphate, and carbamate insecticides were observed, indicating heritable variation for resistance in the source populations. From this we obtained definitive proof that resistance to Danitol + Orthene confers cross-resistance to Asana® (esfenvalerate), Capture® (bifenthrin), Danitol, Decis® (deltamethrin), Decis + Orthene, and Karate® (lambda-cyhalothrin). Additionally, selection with Danitol + Orthene resulted in statistically significant reductions in susceptibility to Curacron® (profenofos), Lannate® (methomyl), Monitor® (methamidaphos), and Ovasyn® (amitraz). Studies were performed to assess tolerance of Maricopa (pyrethroid- resistant) and Yuma (pyrethroid-susceptible) populations to a diversity of conventional insecticides currently registered for use in Arizona cotton, with the intention of finding compounds that showed promise for overcoming pyrethroid resistance. Of the materials evaluated, Curacron, Lannate, Lorsban® (chlorpyrifos), Ovasyn, Supracide® (methidathion), and Vydate® (oxamyl) were most promising. To determine to what degree pyrethroid resistance in cotton influenced resistance in winter vegetables and melons, and vice versa, whitefly populations were collected from a succession of these crops in Western and Central Arizona regions. In most instances, the whiteflies in Western Arizona were significantly more susceptible to Danitol + Orthene than those in Central Arizona. Significant decreases were found in susceptibility to Danitol + Orthene during the 1996 season at three of the four locations in which multiple crops were monitored. This emphasizes that pyrethroid resistance levels can be increased in whitefly populations from any of the cotton, melons, or other winter vegetable crops evaluated. Therefore, management of pyrethroid resistance in Arizona cotton will require harmonizing resistance management efforts and specifically limiting pyrethroid use in the entire crop complex.
Commercial Field Performance of KNACK™ on Cotton in the Yuma ValleyThe insect growth regulator, Knack was evaluated for efficacy against sweetpotato whitefly in paired plots within three commercial cotton fields near Somerton, Arizona. A single application of Knack and Danitol/Orthene was made in July and the impact on whitefly populations, natural enemies and secondary pests was measured for 40 d. Knack appeared to act slowly during the first 2 weeks, but after 21 days nymph populations were greatly reduced. Populations of nymphs and adults began to return to their pre-test levels after 40 d. The Danitol/Orthene application resulted in a significant decrease in adult numbers. Initially nymph densities declined, but after 14 d densities appeared to increase at a much greater rate than was observed in the Knack plots. Under the conditions experienced in this study, a single application of Knack in early July provided protection against sweetpotato whitefly as good, or better than experienced with Danitol/Orthene. Reductions in yields or lint quality attributable to whitefly were not observed in either treatment regime. Although beneficial predators were measured throughout the season, insecticide sprays for lygus control prevented significant buildup of populations. However, the numbers of Liriomyza leafminer adults captured on sticky traps were significantly lower in Knack-treated plots.
Whitefly Growth Regulators: Large-Scale EvaluationTwo insect growth regulators (IGRs) that are selective against whiteflies (Aleyrodidae) became available for the first time in 1996 to Arizona cotton growers under emergency exemption. These IGRs were studied in a commercial -scale whitefly management trial (178 acres) in 1996. The trial was designed to evaluate provisional whitefly recommendations. Three sets of factors were tested in a 48 plot factorial design: application methods, thresholds for initiating IGR use, and insecticide regimes. Ground (broadcast at 15 gallons/acre) and aerial applications (5 gallons/acre) were roughly equivalent over a wide range of variables examined (whitefly populations, number of sprays, cost, and yield). Under the higher population densities, ground applications sometimes suppressed whiteflies to a greater extent than aerial applications. The rapid advance of the population resulted in the initial triggering of all thresholds within just five days. No consistent trend in population suppression was seen for the thresholds tested (0.5, 1.0 and 1.5 large, visible nymphs per 3.88 sq cm leaf disk located between the major and first, left lateral vein of the fifth main stem node leaf below the terminal). The control cost for the highest threshold was significantly less than for the middle threshold, but not for the lower threshold. Under emergency exemption, each IGR may be used only once per season. The sequence of use did not result in any consistent advantage in population suppression, cost, number of sprays needed, or yield. The IGR regimes were in general more efficacious, less disruptive, and less costly than the conventional insecticide regime. There were significantly fewer sprays needed by the IGR regimes compared to the conventional regime. All regimes successfully controlled whitefly populations for a 12 week period and cost significantly less than conventional programs tested in 1995 (Ellsworth et al. 1996a). IGRs are effective, long-lasting, and less environmentally disruptive alternatives to conventional insecticides. They reduce the risk of secondary pest outbreaks and pest resistance, and increase the opportunity of natural enemy conservation.
Whitefly Control Using Insect Growth RegulatorsManagement of whiteflies with two insect growth regulators was compared with standard practices in grower managed cotton near Gila Bend, AZ. The IGRs, Knack (pyriproxyfen) and Applaud (buprofezin) were tested in a randomized complete block experiment with seven replicates. University ofArizona recommendations were followed to time insecticide applications. Following IGR applications, the nymphal populations remained near or below action thresholds (≤ 0.5-1.0 large nymphs per 3.88 cm² disk) from early August through early October. The standard practices treatments maintained the nymphal population through only early September, when populations sharply increased IGR treatments resulted in adult populations below University of Arizona action thresholds nearly as long as the nymphs. There was an adult population peak that followed a nymphal peak near the middle of September.