Managing the entomopathogenic fungus Conidiobolus thromboides in Russian wheat aphid cultures

Six fungicides were evaluated in vitro for their efficacy in inhibiting veg etative growth and sporulation of the entomopathogenic fungus, Conidiobolus thromboides Drechsler, a contaminant in greenhouse cultures of the Russian wheat aphid, Diuraphis noxia (Kurdjumov). The fungicides copper oxychlorid e (Cupravit), mancozeb + oxadixyl (Sandofan), captab + metalaxyl (Apron C), bitertanol (Baycor), iprodione (Rovral Dip), and mancozeb (Sancozeb) at a rate of 0.1% active ingredient moderately to strongly inhibited C. thromboi des (mean inhibition 81.1%). No true fungicidal activity was observed with any of the fungicides during the test period (7 d at 20 degrees C). Amount of sporulation of the fungus varied among treatments, with no spores formed on the mancozeb + oxadixyl-treated medium, versus profuse sporulation on m edium treated with bitertanol or iprodione. Because of strong inhibition of C. thromboides and relatively low cost, mancozeb at concentrations of 10.0 , 2.0, 1.25, 0.5, 0.08, and 0.016% was further evaluated in vitro. The fung us growth cut-off point, midway between 1.25 and 2.0% mancozeb, was calcula ted, and a rate of 1.625% active ingredient per liter of water was used to treat greenhouses housing C. thromboides-infected Russian wheat aphid colon ies. In addition, sanitary measures were followed diligently, which include d fumigation of contaminated greenhouses with potassium permanganate + form aldehyde, construction of new rearing cages, and a change in the watering p rotocol. These curative and preventative measures were used successfully to decontaminate the Russian wheat aphid colonies.