Compatibility of Beauveria bassiana with fungicides in vitro and on zucchini plants infested with Trialeurodes vaporariorum

The effect of fungicides on the entomopathogenic fungus Beauveria bassiana strain ATCC 74040 (Naturalis®) was evaluated in vitro and in vivo. The formulated fungicides Cantus® (boscalid), Frupica (mepanipyrim), Galben (benalaxyl), Melody® Compact (iprovalicarb + Cu oxychloride), Oracle™ (fenamidone + Cu), Prosper® 300 CS (spiroxamine), Signum® (boscalid + pyraclostrobin), Switch® (cyprodinil + fludioxonil) and Talendo® (proquinazid) were tested on fungal colony growth from 10 field dose (10FD) to 10−4 FD. Each product mixed with Naturalis at FD was also tested against Trialeurodes vaporariorum on zucchini plants. Fungal colony growth was not affected by Cantus, Galben, Melody Compact, Oracle and Talendo at FD, while Frupica and Prosper 300 CS reduced colony growth by 9.7% and 6.9%, respectively. All these products did not inhibit the activity of B. bassiana on whiteflies at FD. On the contrary, Signum and Switch significantly inhibited colony growth at all doses and reduced the entomopathogenic activity on whiteflies when applied in mixture with B. bassiana. The toxic effect of both fungicides on B. bassiana persisted for 10 days after treatments, with a 91.2% reduction in nymph mortality in comparison to control for Signum and 87.4% for Switch. The mode of action of their active ingredients, boscalid, pyraclostrobin, cyprodinil and fludioxonil, individually and in mixture (boscalid + pyraclostrobin and cyprodinil + fludioxonil), was studied on fungal colony growth, spore germination, germ tube elongation and spore survival from 10FD to 10−2 FD. All these parameters were reduced by the four active ingredients at all doses, pyraclostrobin and fludioxonil completely inhibited spore germination, fludioxonil alone and in mixture with cyprodinil also inhibited completely spore survival.