Cotton fields were treated with the entomopathogenic nematode Steinernema riobravis (Cabanillas, Poinar and Raulston) for the control of Pectinophora gossypiella (Saunders). Pima S-7 cotton situated at V & C farms Queen Creek Arizona, was treated at a rate of 1 billion nematodes per acre. The nematodes were applied using a spray rig with dropped nozzles, immediately after application the field was irrigated. Pima S-6 cotton situated in Texas A & M research center El Paso Texas, was treated at a rate of 1.3 billion nematodes per acre. In this case the nematodes were applied to the irrigation channel during field irrigation.

Both application methods resulted in excellent distribution of the nematodes over the treated areas as indicated by extraction of nematodes from soil samples. Nematodes applied in Arizona persisted for 19 days in large numbers, and could still be recovered from furrows after 75 days. The number of cotton bolls infested with P. gossypiella was significantly reduced by the application of S. riobravis, and cotton yields from treated plots were 19% higher relative to cotton yields from untreated plots.

In Texas the nematodes persisted for 16 days in large numbers, and could still be recovered from row and furrow bases after 50 days. The nematodes moved rapidly from the furrow soil into the cotton beds. Ten days after application, nematode distribution became fairly even, although the number of nematodes recovered from furrows was significantly higher than bed tops. The mortality of P. gossypiella larvae caged in biopsy cassettes was optimized on field irrigation 17 days after nematode application, when the nematodes had redistributed themselves within the rows and furrows. At this point 100% of caged P. gossypiella larvae were infected and killed by S. riobravis.