Herbicide Effects on Parasitism of Tomato by Hemp Broomrape

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Abstract
Thirteen soil-incorporated herbicides, mainly of the dinitroaniline and carbamate groups, were evaluated in the greenhouse for selective control of hemp broomrape (Orobanche ramosaL.) in tomato (Lycopersicon esculentumMill. ‘Rutgers’). Hemp broomrape readily parasitized tomato roots and competed vigorously with the host. Shoots of the parasite emerged within 6 weeks after inoculation. Herbicides at 0.1 to 10.0 ppmw, with one exception, significantly reduced shoot dry weight of tomato measured at 10 weeks after treatment, in comparison with untreated, noninoculated controls. Generally, the degree of inhibition of establishment of the parasite was correlated with herbicidal injury to tomato. None of the treatments prevented the establishment of the parasite without causing severe crop injury. However,N-n-propyl-N-tetrahydrofurfuryl-4-trifluoromethyl-2,6-dinitroaniline (CGA-14397, ER-9063) at 3.3 and 6.6 ppmw exhibited some degree of selectivity as indicated by relative shoot dry weights of the host and parasite. Activated charcoal applied as a root dip on tomato or in soil admixtures prior to transplanting had no effect on parasitism and growth of hemp broomrape.