Systemic Insecticide Applications at Planting and First Square in Bt Cotton for Early Season Insect Control - La Paz and Mohave Counties
Tim C. Knowles, La Paz County Cooperative Extension
Temik 15G (6 lbs/acre) and Thimet 20G (7.5 lbs/acre) granular insecticides were applied in furrow at planting and compared to an untreated check in two experiments in Parker Valley and Mohave Valley, AZ. At first square each of these main plots was split in half and either Temik 15G or DiSyston 8L was sidedressed to each subplot and compared to an untreated strip. Thrips and lygus counts were taken at weekly or biweekly intervals and plant response measured from the 2 or 3 leaf stage through layby. Under the thrips pressure experienced in these two experiments (0.5-1.5/plant), Temik and Thimet at planting provided similar and adequate protection from thrips for up to 7 weeks following application. Temik 15G sidressed at 14 lbs/acre at first square provided lygus bug control for up to 42 days following application under light lygus bug pressure (5-15/100 sweeps). Di-Syston 8L sidedressed at 1 qt/acre at first square provided lygus bug control for 35 days following application under moderate lygus bug pressure (15-20/100 sweeps). Under the conditions of this study, systemic insecticide applications at planting and first square did not increase cotton lint yields of insecticide treated Bt cotton plots, compared to the untreated control plots.
Temik 15G (aldicarb) and Thimet 20G (phorate) have been widely used in furrow at planting serving as a systemic insecticide for thrip, spider mite, lygus bug, and nematode control. These granular insecticides are water soluble, mobile with soil water, and are generally expected to provide insect control for a period of 4 to 6 weeks post application (planting through first square). Systemic insecticides are used at planting as a preventative measure against potential future thrips, spider mite, or lygus bug pressures. The actual economic return on systemic insecticides applied at planting depends on actual insect pest pressure during the 4 to 6 week post application period. Comparatively, the approximate cost of Temik 15G applied at 6 lbs/acre is $21.00, and Thimet 20G applied at 7.5 lbs/acre is $16.50, both plus the cost of application. Although the Thimet application is cheaper, there is no return on the investment if insect pests are not present in damaging numbers, or if cotton plants compensate for early season square shedding caused by feeding insects.
Temik 15G and Di-Syston 8 (disulfoton) are occasionally used side-dressed in season at first square serving as systemic insecticides for Lygus bug control. These materials can be used 4 to 6 weeks post application of an at planting in furrow granular insecticide application for early season insect control through layby. Temik can be applied with a granular sidedress rig and Di-Syston can be applied sidedress combined with liquid fertilizer solutions. Again, economic return on the investment is based on actual future lygus bug pressure from first square through layby. Comparatively, the approximate cost of Temik sidedressed at 14 lbs/acre is $49.00, and Di-Syston 8 applied at 1 qt/acre is $17.50, both plus the cost of application.
With the commercial introduction of Bt cotton in 1996, pink bollworm control became a fixed cost of approximately $40/acre (technology fee plus seed premium). However, Bt does not control whitefly, thrips, or lygus bugs, so the following has been suggested for season long insect pest control: application of the two insect growth regulators (IGR) would provide adequate whitefly control in most fields. Thes sequential applications of Knack (pyriproxyfen) at 8 oz/acre ($42.75) and Applaud (buprofezin) at 8 oz/acre ($32.25) cost $75.00/acre. For thrips and lygus bug control from planting through first square, 7.5 lbs Thimet 20 G/acre applied in furrow at planting costs $16.50. Temik 15G would be sidedressed at first square at 14 lbs/acre for a $49.00/acre expense to provide lygus bug control form first square through layby. This Bt cotton insect control program assumes secondary insect pest pressures remain low for a minimum fixed total cost of $180.50/acre. This insect control program is expensive, and uncertainty exists concerning the consistency of return on input investments in preventative insecticide applications.
With current cotton prices falling at or below $0.70/lb, cotton producers are less likely to apply preventative measures as a good insurance policy. Preventative granular insecticide applications are expensive, and actual returns on this investment are only realized under heavy early season insect pest pressures. Field studies need to be conducted to develop information on return on investment over time with these systemic insecticides, since treatment is anticipatory.
A field experiment was conducted to evaluate the effect of Temik and Thimet applied in furrow at planting on thrips and Lygus bug control in and plant responses of Bt cotton through first square. At first square, each of the main plots was split to include a check and either a sidedress application of Temik or Di-Syston to evaluate lygus bug control and plant responses from first square through layby.
Materials and Methods
Two field experiments were conducted during 1997 in Parker Valley (located in southwestern La Paz County) and Mohave Valley (located in western Mohave County) to determine the effect of Temik and Thimet applied in furrow at planting compared to an untreated check on thrips and Lygus bug control in and plant responses of Bt cotton through first square. At first square, each of the main plots was split to include a check and either a sidedress application of Temik or Di-Syston to evaluate lygus bug control and plant responses from first square through layby.
Mike Keavy, farm manager of King Ranch was the Parker Valley cooperator. Deltapine NuCotn 35B was planted wet on 38 inch rows on April 8. The field was adjacent to onions and cotton. In furrow at planting systemic insecticide treatments included a check plot, Thimet 20G applied at 7.7 lbs/acre, and Temik 15G applied at 6.3 lbs/acre. Each treatment was replicated four times in a randomized complete block experimental design. Individual plots were 8 rows wide by the length of the irrigation run (1250 feet long). At first square (May 28), each main plot was split in half to compare Temik 15G sidedressed at 14 lbs/acre to an untreated check. Each resulting subplot was 4 rows wide by the length of the irrigation run.
Victor Wakimoto, farm manager of V&K Wakimoto Farms was the Mohave Valley cooperator. Paymaster 1244 BGRR was planted wet on 40 inch rows on April 10. The field was adjacent to alfalfa and cotton. In furrow at planting systemic insecticide treatments included a check plot, Thimet 20G applied at 7.5 lbs/acre, and Temik 15G applied at 5.0 lbs/acre, and Temik 15G applied at 6 lbs/acre. Each treatment was replicated four times in a randomized complete block experimental design. Individual plots were 24 rows wide by the length of the irrigation run (800 feet long). At first square (June 4), each main plot was split in half to compare Di-Syston 8L sidedressed with UAN 32 fertilizer at 1 qt/acre to an untreated check. Each resulting subplot was 12 rows wide by the length of the irrigation run.
Thrips were counted on ten whole plants by placing the cotton plants in a tight plastic container with a wick saturated with methyl ethyl ketone to displace thrips from the plants to the bottom of the plastic container. Thrips collection began and followed at weekly intervals after cotton seedlings reached the 2-3 leaf stage (May2-6) and continued through the 10-12 leaf stage (May 30-June 3) when thrips populations had declined. In season lygus bug counts were made weekly using a 100 sweep net count for both nymphs and adults starting at the 5 to 6 leaf stage (May 16-20) and continued through peak bloom or layby (July 11-15). A complete set of plant measurements were collected in July and August. Measurements taken included: plant population, plant height, number of mainstem nodes, first fruiting branch, total number of aborted sites (1st and 2nd position), and the number of nodes above the uppermost white bloom.
The middle eight rows of each plot were harvested with a commercial two row picker on December 18 at the Mohave Valley site. Seed cotton from each plot was dumped into trailers which were weighed on certified scales. A lint turnout of 34% was assumed for the Paymaster 1244 BG RR variety grown at this site.
Results and Discussion
Light to moderate thrips pressure (0.5-1.5/plant) was encountered during 1997 in the test plots Figure 1. Thrips populations never exceeded the suggested economic thresholds of 1/plant prior to the 4 to 5 true leaf stage and 2/plant thereafter (Figure 2). Thrips populations had no significant effect on plant population, plant height, and fruit retention at the Parker Valley site (Table 1). In contrast, thrips pressure exceeded 1.4/plant at the 2 to 3 true leaf stage (May 6) at the Mohave Valley site. Thrips pressure was heaviest on May 2-6 coinciding with 21 days after at planting insecticide application (DAA), then declined to 0/plant by May 30-June 3 (49 DAA). Thrips pressure at the Mohave Valley site seemed to result in a 5% lower plant population, generally a first fruiting branch that was 1 node higher, and approximately 20% lower fruit retention (Table 2).
Under the thrips pressure experienced in these two experiments, Temik and Thimet provided similar and adequate thrips control for up to 7 weeks after the at planting application. However, the duration of thrips protection provided by 5 lb Temik 15G/acre application rate was approximately 2 weeks shorter compared to the 6 lb Temik 15G/acre at planting application rate. Furthermore, granular insecticides applied at planting helped maintain large numbers of thrips and lygus bug predators including minute pirate bugs, ladybeetles, lacewings, damselbugs, and crab spiders.
Light to moderate lygus bug pressure (5-20/100 sweeps) was encountered during 1997 in the test plots (Figure 1). Lygus bug populations did not exceed the suggested economic threshold of 15/100 sweeps until July 11 in Parker Valley and June 24 in Mohave Valley. Thus, lygus bug control was not necessary until first square when the systemic insecticide sidedess applications were made. Temik 15G applied sidedress at 14 lbs/acre 47 days after planting (first square) at the Parker Valley site provided adequate Lygus control out to 42 days after application under light lygus bug pressure (5-15/100 sweeps). Di-Syston 8L applied sidedress at 1 qt/acre 50 days after planting (first square) at the Mohave Valley site provided adequate Lygus control out to 35 days after application under moderate lygus bug pressure (15-20/100 sweeps). Insecticidal control of Lygus from early square through peak bloom resulted in approximately 5% higher fruit retention, compared to untreated control plots (Table 3 and Table 4).
Since insect pest pressure was heaviest at the Mohave Valley site, yhe middle eight rows of each plot were harvested to determine seed cotton yields (Table 5). Systemic insecticide applications at planting and first square had no significant effect on Paymaster 1244 BGRR cotton grown at this site. Cotton lint yields of insecticide treated plots were not significantly different from those observed in untreated control plots. For most of the season insect pest populations remained below currently defined economic thresholds, thus cotton lint yields did not respond to insecticide applications. Cotton lint yields were also relatively low at this site, indicating that yield was probably limited by factors other than cotton insect pest pressure.
The valuable cooperation, land, and resources provided by Mike Keavy of Parker Valley King Ranch and Victor Wakimoto of V&K Wakimoto Farms is highly appreciated. The support and cooperation provided by American Cyanimid Company is gratefully acknowledged.
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.