Efficacy of fluazinam in suppression of Monosporascus cannonballus, the causal agent of sudden wilt of melons

Sudden wilt (vine decline) of melon, caused by Monosporascus cannonballus, is a worldwide problem in arid and semi-arid regions. Soil disinfestation b y fumigation with methyl bromide before planting is a common treatment for disease management but, because methyl bromide is expected to be banned fro m use within the next 10 years, alternative measures for disease suppressio n are needed. The efficacy of 29 fungicides against M. cannonballus was eva luated in vitro. Among the fungicides tested, fluazinam and kresoxim methyl were the most effective and both totally inhibited the growth of M. cannon ballus in culture at concentrations of 10 mu g a.i /ml. Because fluazinam a lso was effective in inhibition of Pythium aphnidermatum, which also may be involved in sudden wilt syndrome, and kresoxim methyl was not, fluazinam w as chosen for further tests. The effective dose of fluazinam for M. cannonb allus that reduced mycelial growth by 50% was 0.09 mu g a.i./ml. Fluazinam efficacy was evaluated in three field experiments conducted in the spring a nd in the late summer cropping seasons. In two of the experiments, applicat ions of fluazinam resulted in approximately 87% wilt reduction, whereas in the third experiment it was only 32%. The mobility of fluazinam in soil was determined in samples taken from the field. Fungicide mobility in soil was relatively limited; most of the compound was adsorbed to soil particles, r esulting in a zone of high concentration that decreased with depth and dist ance from the application site. Nevertheless, rates measured even at a dept h of 25 cm were sufficient to control M. cannonballus. This study shows tha t fluazinam may be used as one component in an integrated approach for supp ression of sudden wilt of melons.