Seasonal Infectivity of Aster Leafhoppers in Carrot

Problem Defined: Each year, Wisconsin growers produce carrots on an average of 4200 acres grossing over $6 million dollars in revenues (USDA-NASS, 2007 annual bulletin). Unfortunately, carrot fields are threatened annually by the occurrence of aster yellows phytoplasma (AYp), which is obligately transmitted by the aster leafhopper (Macrosteles quadrilineatus Forbes). Current control practices strictly utilize insecticide sprays that target the aster leafhopper. Spray timing is guided by an aster yellows index that is based on the proportion of infective leafhoppers present in a field at a given point in time. Crop scouting and molecular diagnostic tools have decreased the inherent lag between finding inoculative leafhoppers and prescribed sprays. However, yield losses of 5-20% resulting from AYp are still commonplace (1). A more comprehensive and sustainable, multi-tactic control strategy is warranted to lower inoculum pressure in the areas surrounding susceptible crops. The management of off-crop habitats in ways that minimize the persistence and decrease the accumulation of AYp inoculum in the local environment has the potential to contribute to the sustainability of carrot production primarily through reductions in pesticide.