Efficacy of Three Macroinfused Fungicides to Control Laurel Wilt on Avocado in Martin and Brevard Counties

Abstract

Laurel wilt, a lethal disease of trees in the Lauraceae, is caused by Raffaelea lauricola (Raf) which has several ambrosia beetle vectors. Three rates each of macroinfused thiabendazole (Arbotect® 20-S), propiconazole (PropiconazolePro®), and tebuconazole (Teb #1—proprietary formula, Rainbow Treecare) were tested for efficacy against the disease on avocado trees in Martin and Brevard Counties. Seven trees were not treated with fungicide, and five to six were infused with Arbotect® (1.0, 2.0 or 3.0 oz. of product per inch trunk dia.), or PropiconazolePro® or tebuconazole (0.7, 1.0, and 1.4 oz. per inch trunk dia.) on 12–13 July 2011. On 13–14 October 2011, all trees were inoculated with the pathogen, and 60, 239, and 558 days after inoculation (dai) laurel wilt development was rated. Laurel wilt developed to a greater extent on trees treated with either tebuconazole or Arbotect®, 60 dai, than those treated with PropiconazolePro® (no symptoms developed at any rate of this fungicide). However, by 239 dai a large proportion of the treated trees had developed laurel wilt symptoms, regardless of the fungicide that was used (mean incidences of 83%, 89%, and 94% for, respectively, PropiconazolePro®, Teb#1, and Arbotect®). By 239 and 558 dai, disease severities and the recovery of the pathogen were lower in trees treated with PropiconazolePro® or tebuconazole, compared to Arbotect®. Although lower disease severities developed in the former trees, disease variability among trees within treatments suggests that other factors (e.g., cultivar and rootstock) may have influenced the results. Current recommendations for managing this disease are discussed.