Efficacy, application distribution, and concentration by stemflow of Steinernema carpocapsae (Rhabditida: Steinernematidae) suspensions applied with a lateral-move irrigation system for corn rootworm (Coleoptera: Chrysomelidae) control in maize

Efficacy of the 'Mexican' and 'All' strains of Steinernema carpocapsae (Weiser) was determined after application through a lateral-move irrigation system when rootworms were in the 2nd-3rd instars. Control of rootworms by nematodes applied through the irrigation system was compared with control by hand-applied nematode preparations in the row and with terbufos and chlorpyrifos applied just after planting. Root injury ratings were highest in both years for plants from untreated control plots and were significantly lower in the terbufos treatments compared with all other treatments. In 1992, hand application of the All and Mexican strains resulted in significantly lower root injury than did application of the All strain through the irrigation system. Uniformity of nematode application through the irrigation system was characterized over time and distance using the Christiansen uniformity coefficient, which ranged from 68 to 87% within the zone of nematode application. Partitioning of water the corn canopy, particularly by stemflow, increased the concentration and total numbers nematodes delivered to the target area at the base of the corn plant. Total numbers of nematodes in stemflow water collected at the plant base were greater by approximate to 3.1 and 4.6 times than total numbers of nematodes collected at ground or canopy levels, respectively. Total volume of water reaching the soil by stem flow also was approximate to 3.9 times greater than the amounts applied above the canopy.