INTRAVASCULAR INJECTION WITH PROPICONAZOLE IN LIVE OAK FOR OAK WILT CONTROL

The fungicide propiconazole was evaluated for oak wilt control in live oak by in vitro growth inhibition of Ceratocystis fagacearum, greenhouse inoculation trials on treated trees, and intravascular injection of field-grown trees. The EC50 values for four pathogen isolates were consistently less than 20 mug a.i./ml and as low as 2 mug a.i./ml. Container-grown live oaks infused with two fungicide formulations and artificially inoculated with C.fagacearum exhibited significantly less disease severity and fewer numbers of diseased trees than untreated controls. In field testing with natura[ infection, injected live oak plots and subplots consistently had lower levels of crown loss than untreated plots for 9-36 mo following treatment. Average levels of crown loss in seven treated plots containing 57 trees ranged from none to 41%, whereas crown loss in five untreated plots containing 43 trees ranged from 61 to 100%. Differences in disease progress between treated and untreated plots were apparent within 12 mo after injection. Tree injections at the presymptomatic, preventive stage resulted in better disease control than injections of trees with incipient symptoms.