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Project description

Improved Irrigated Management of Cotton Aphids in California through an Understanding of Cotton Aphid Biology and Response to Nitrogen Fertilization. (98CC012)
Program UC IPM competitive research grants program
Principal
investigators 		L.D. Godfrey, Entomology, UC Davis
R. Hutmacher, Agronomy and Range Science, UC Davis/Cooperative Extension, Shafter Field Station
Host/habitat Cotton
Pest Cotton Aphid Aphis gossypii
Disciplines Entomology, Plant Sciences
Review
panel 		Cultural Controls
 Start year (duration)  1998 (Three Years)
Objectives Study the life history of cotton aphids in California, including host plants/weeds utilized, population buildup in crops other than cotton, overwintering strategy, presence of a sexual stage, and other aspects of the life cycle.

Study the influence of early-season cotton management (nitrogen fertilization regime and lygus bug management) on cotton aphid population dynamics and seasonal buildup in cotton.

Final report The cotton aphid (Aphis gossypii Glover) escalated from an occasional pest to an annual, severe pest of San Joaquin Valley cotton during the 1990s. Although the cotton aphid is not a new insect in the area, the change in the bionomics of this pest dictated that new research efforts be directed toward the biology, damage thresholds, and management. Cotton aphid outbreaks peaked in severity during the 1995 and 1997 cotton growing seasons with an estimated economic impact of over $65 million in 1997. Reasons for the "emergence" of cotton aphid as a key pest may be linked to changes in cotton production practices and in insecticide use patterns. Specifically, the impact of highest nitrogen application rates and nitrogen-rich cotton plants on aphid reproduction was examined. In addition, the shift to new chemical classes, specifically pyrethroid incesticides, to control other cotton arthropod pests may have enhanced cotton aphid population build-up and this was examined. In large plot studies conducted in grower fields, aphid populations were similar in the 50 and 100 lbs. Nitrogen per A treatments and over two times higher in the 200 lbs. Nitrogen per A treatment. Aphid populations from the 150 lbs. Treatment were not consistent (low and high in the first and second study years, respectively). Detailed studies showed that aphids reared on cotton plants fertilized with 200 and 250 lbs. Nitrogen per A produced significantly offspring and had shorter generation times than aphids from a 20 lbs. Nitrogen per A treatment. A pyrethroid insecticide application (bifenthrin) acted synergistically with nitrogen level in that the aphid population with low nitrogen levels (20 to 100 lbs. Nitrogen per A) was 50 to 75% higher in the bifenthrin-treated plots compared with untreated plots and at 150 to 200 lbs. Nitrogen per A, there were three and four times, respectively, more aphids in the bifenthrin-treated plots compared with the untreated. The final aspect of this study was to study the cotton aphid seasonal life history; a knowledge of cotton aphid biology during the winter may be important in designing alternative management plans. Studies concentrating on the winter and early spring periods showed that the sexual phase of the cotton aphid seasonal life history occurred on pomegranates.

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