Effect of tillage on cotton aphids (Homoptera: Aphididae), pathogenic fungi, and predators in south central Georgia cotton fields

Abstract

Two species of fungi, Neozygites fresenii Nowakowski (Batko) and Pandora neoaphidis Remaudiere and Hennebert (Humber), pathogens of the cotton aphid, Aphis gossypii Glover, were studied in 12 south central Georgia cotton fields under conservation or conventional tillage in 2003 and 2004. Aphids and ants on cotton plants were enumerated in both years, and aphid predators (coccinellids, lacewings, and spiders) were counted in 2004. Plant sampling began the first week of June and continued for 16 wks in 2003 and for 14 wks in 2004. Numbers of aphids on cotton plants increased until the first week of July and declined thereafter. More aphids were present on plants in 2004 than in 2003 for the first 9 wks of sampling, but did not differ thereafter. More aphids were present on plants under conservation tillage than under conventional tillage only between weeks 3-8. Pandora neoaphidis was detected in aphids in midMarch by monitoring with pan traps on field margins. Neozygites fresenii, in contrast, was not observed until 18 June 2003 and 16 June 2004, and peaked simultaneously with the aphid population and then declined. The incidence of P. neoaphidis was less than that of N. fresenii, but peaked simultaneously with it in the first week of July. Ants, primarily the red imported fire ant, Solenopsis invicta Buren, occurred in larger numbers in fields under conservation tillage than under conventional tillage, apparently because of greater disruption of soil and weed habitat under conventional tillage. In both tillage types, coccinellids peaked early in the season and lacewings late in the season, with larger numbers of coccinellids present in fields under conservation tillage. Although there was a sharp peak in lacewing numbers late in the season under conservation tillage, overall lacewing numbers were not different under the 2 types of management. Spider numbers increased gradually throughout the growing season, with only slightly higher numbers present under conservation tillage. The effects of different tillage methods were more evident on the aphids and their predators than on the fungal pathogens.