Chemical Control of the Sweetpotato Whitefly in Cotton

Both registered and experimental insecticides were evaluated for effectiveness against the sweetpotato whitefly in several field expreiments at Yuma, Arizona. Best results were obtained with combinations of two insecticides, particularly a pyrethriod and an organophosphate, rather than with individual materials. Results of these experiments indicate that unusually heavy infestations can be currently controlled even though sustained use of these insecticides would probably lead quickly to the development of resistance. Introduction Five field experiments were conducted at Yuma, Arizona in an effort to find satisfactory controls for the sweetpotato whitefly. Three of these experiments were conducted on cotton planted in March and two on cotton planted beyond the normal planting period, planting date of May 28, 1992. Several of the insecticides in these trials were included primarily for evaulation of efficacy against the pink bollworm. Therefore, their lack of efficacy against the sweetpotato whitefly should not reflect adversely on their overall potential as useful cotton insects insecticides. Materials and Methods The methods utilized were the same for all experiments except the one with NTN33893. For these four experiments, plot size was 4 rows of cotton 60 ft. long with a 10' alley separating plots lengthwise down the row and two fallow rows separating sets of 4 -row plots. Applications were made using a tractor -mounted, CO2powered sprayer with three nozzles per row. Spray was applied at 40 psi to deliver 20 gal. of total spray per acre. The NTN33893 test was conducted in solid -planted cotton with whole plots consisting of 4 rows by field length (280') with subplots 90' long. Treatments consisted of untreated, or 4 and 8 oz. rates of NTN33893, applied as; seed treatment only, seed treatment plus side -dress, and seed treatment plus side -dress plus foliar spray. Sampling for whitefly infestations was done weekly by using the oilcoated pan method for the adult and 1 -inch diameter leaf -disc method for egg and immature populations. Results Results are presented in both tabular and graphic form. The tables present infestation counts on a weekly basis whereas the graphs present yield data. For most of the tests individual tables are presented for each whitefly stage, adult, egg and immatures. Results are referenced on the tables and graphs by both a test number and letter. The test number was used to