Alternaria helianthiand Imazaquin for Control of Imazaquin Susceptible and Resistant Cocklebur (Xanthium strumarium) Biotypes

Abstract

The efficacy ofAlternaria helianthion imazaquin-susceptible and -resistant biotypes of common cocklebur was evaluated with and without imazaquin.A. helianthicaused severe damage to both biotypes when applied at 80,000 conidia ml−1at the five- to six-leaf stage. Symptoms included necrotic lesions, stunting, and mortality. Mortality from imazaquin at 140 g ai ha−1was 0 and 100% and mortality fromA. helianthiat 80,000 conidia ml−1was 33 to 75% and 67 to 100% for resistant and susceptible biotypes, respectively, and surviving plants showed reduction in height, dry weight, and number of new leaves. The combination of imazaquin at 18 g ai ha−1andA. helianthiat 40,000 conidia ml−1was not synergistic or antagonistic in killing common cocklebur.