IDENTIFICATION OF FACTORS ASSOCIATED WITH ONION BACTERIAL DISEASES TO FACILITATE THE DEVELOPMENT OF AN INTEGRATED PEST MANAGEMENT PROGRAM

During the past 5 to 10 years, bacterial bulb decay, caused by a number of different bacterial pathogens, has assumed much greater importance in the Northeast region. In PA and NY, annual losses range from 5 to 40%. However, these losses are variable, between fields and within the same field; in many cases the full extent of disease losses is not evident until at or post-harvest. In part this is because bacterial bulb decay often affects only a single internal scale while outer scales remain firm, such infected bulbs are virtually impossible to detect. Such onion are shipped and consequently rejected, which often results in entire loads being dumped, despite only a small percentage of bulbs being infected. In order to develop an integrated pest management plan it is important to understand what factors are associated with increased bacterial disease. One key factor is identifying where the bacterial pathogens are coming from (transplants, weeds, soil, etc.) so that management efforts can be directed towards excluding or reducing the pathogen from the field. For example, if we learn that bacteria present on the surface of visibly healthy onion transplants are associated with disease losses observed later in the growing season then research could be directed towards determining the most effective way to obtain pathogen-free transplants. Another potential factor is onion thrips, the most common insect pest in onion fields in the Northeast region and worldwide. The damage caused during feeding creates a wound or opening for the bacteria to get into the plant. Additionally, observations from grower fields and preliminary on-farm research trials in PA and NY suggest that excessive nitrogen fertility is also correlated with greater losses from bacterial diseases. By gaining a better understanding of the factors contributing to bacterial diseases in commercial production fields we will be able to fine-tune current management recommendations to reduce the likelihood of severe losses from bacterial pathogens as well as facilitate additional research trials to develop more targeted research-based management plans. The ultimate goal of this project is to develop knowledge-based, sustainable and cost-effective management strategies for bacterial diseases of onion in the Northeast and in other relevant production regions. In the long-term, success of the project will be reflected in reduced economic losses from bacterial diseases and reduced reliance on copper-based fungicide inputs through the integration of cultural management practices that include the optimization of nitrogen inputs for maintaining yields, minimizing thrips-induced injury and protecting plantings against wind-induced injury.