Benomyl Root Treatment Controls Brown-Spot Disease on Longleaf Pine in the Southern United States

Abstract

Root systems of longleaf pine seedlings, Pinus palustris Mill., were wetted and then coated with various benomyl/kaolin (clay) mixtures (0 to 20 percent a.i. benomyl) prior to seedlings being outplanted on sites in Louisiana, Mississippi, Alabama, Georgia, and Florida. Survival, percent brown-spot needle blight infection (caused by Scirrhia acicola (Dearn.) Siggers), and growth were evaluated annually for 3 years following planting. Seedling survival generally decreased in a west to east gradient. Survival also decreased with increased benomyl levels at all sites. Interactions of survival and levels of benomyl with measured soil properties were investigated. For increased benomyl levels there was a negative correlation of survival with increased percentage of sand in the soil and a positive correlation of survival with increased levels of silt in the soil. Benomyl root treatments provided effective brown-spot disease control during the 3-year period, which in turn stimulated rapid height growth. A 5 percent a.i. benomyl/kaolin mixture is recommended for root treatment over the natural range of longleaf pine in the southern United States. Forest Sci. 32:506-511.