Leaf Spot Threatens Panhandle Peanuts
Evidence of the exceptionally wet weather in July and August is beginning to show up as the Florida Panhandle peanut harvest begins. The common foliar disease, leaf spot, caused by a fungus is making an area wide appearance.
“Many counties in the Florida panhandle received so much rain during the late summer period that spraying with a tractor was not feasible or was substantially delayed,” said Dr. Barry Tillman, peanut specialist at the UF/IFAS North Florida Research and Education Center in Marianna, Florida. “Growers were left with few options, none of which will ultimately help the bottom line,” Tillman said. Even the peanut cultivars with good leaf spot resistance under normal conditions are showing signs of injury by the unusually heavy leaf spot epidemic.
In many cases aircraft were the only possibility for spraying fungicides on the waterlogged fields. Timing of application and spray coverage were compromised by the long waiting lines for airborne delivery and the low water volume of fungicide sprays. This delay created the opportunity for leaf spot to get established and to eventually thrive. “Some growers are now facing the dilemma of immature peanuts with quickly deteriorating vine health induced by leaf spot defoliation,” said Tillman.
Using fungicides to salvage severely diseased peanuts may produce only marginally better yields and may not be economically feasible, especially with more rainfall in the forecast. In these cases, the harvest decision will depend on balancing pod maturity and vine health. The only potentially profitable choice is to track peanut maturity with a pod-blast sample and keep a close eye out for sign of leaf spot. Chief among the telltale symptoms are defoliation, stem lesions and peg strength. “With that information, a good decision can be made to set the digging date which will optimize maturity and minimizes losses from leaf spot” said Tillman.