Neither herbicides nor Aphthona spp. biological control agents provide satisfactory leafy spurge control in all environments where the weed is found. Open-release and caged field studies were conducted to determine the effect of herbicides used in combination with Aphthona spp. flea beetles on both the leafy spurge control and the biological control agent populations. Leafy spurge density was reduced more rapidly when A. nigriscutis or a mixture of A. czwalinae and A. lacertosa was combined with a fall-applied treatment of picloram plus 2,4-D than when either method was used alone. The combination treatment reduced leafy spurge density 3 to 5 yr earlier than did either the herbicides or the biocontrol agents alone and once reduced, the Aphthona flea beetles maintained acceptable control for at least 7 yr. Spring-applied herbicides eliminated the adult food source and negatively affected the flea beetle establishment, but fall-applied treatments did not reduce the flea beetle establishment or its reproduction. The combination treatment was most successful when used with established Aphthona spp. populations that were not increasing in size or reducing leafy spurge density. Land managers could realize a three- to fivefold cost savings with the combination treatment compared with herbicides alone.
Nomenclature: Picloram; 2,4-D; Aphthona nigriscutis Foudras; Aphthona czwalinae Weise; Aphthona lacertosa Rosenhauer; leafy spurge, Euphorbia esula L. EPHES.