Snap beans are grown in New York State for processing uses and fresh markets. New York is ranked second in the nation in fresh market snap bean production, with a value of $48.1 million harvested from 4168 ha. New York’s processing snap beans were valued at $15 million from 8053 ha. Pod blemishes reduce the market value of snap beans and when incidence and severity are high, blemishes will result in rejection of the crop by markets and processing plants. Outbreaks of pod blemishes occurred in 2000, 2006, and 2007. Snap bean producers were unable to predict when the disease would occur and potential severity levels. Documented yield losses varied from 8 to 20 percent, and the threat of rejection of entire fields loomed high. Growers requested identification of the pathogen and a set of integrated pest management (IPM) strategies for control of the disease. Research in the Dillard laboratory resulted in identification of two fungal pathogens responsible for causing the disease referred to in the industry as “spotty beans.” In addition, fungicides were identified that provided control of one or both pathogens, and commonly used snap bean varieties were tested for tolerance to the disease. The information collected in these studies provided growers with the tools needed to initiate research-based management of the disease.

Snap beans are a high value profitable vegetable crop grown in New York, Pennsylvania, and Maryland for processing uses and fresh markets. Pod blemishes reduce the market value of snap beans and when incidence and severity are high, can result in rejection of the crop by markets and processing plants. In 2000, severe outbreaks of snap bean pod blemishes occurred in New York and Maryland. The causal agent was identified as Plectosporium tabacinum. Symptoms were associated with heavy rainfall or thunderstorms near the time of harvest. In 2006 and 2007, blemishes were again observed on processing snap bean pods that resulted in losses of 8 percent to 20 percent in some fields in New York and Pennsylvania. Processors were unable to remove the spots prior to packaging the finished product. The unsightly pods were deemed unmarketable and were discarded, resulting in significant losses at the farm gate. Symptoms on the pods consisted of small dark flecks on the pod surface and in the pod suture. The flecks sometimes coalesced to produce long dark streaks on the pods. The symptoms in 2006 & 2007 were similar to but not consistent with those caused by Plectosporium tabacinum. The additional causal agent of spotty beans was eventually identified as Alternaria alternata.

In 2000, 2006, and 2007, fungal isolates were collected from snap bean pods with spots. Isolates were tested for pathogenicity and later identified as Plectosporium tabacinum and Alternaria alternata. Due to the complexity of the fungal genus Alternaria, DNA fingerprinting techniques were used to positively identify the Alternaria isolates to species alternata. In 2007, disease severity on farms was lower due to drought conditions in much of the snap bean growing regions of New York State. In mist chamber tests, the A. alternata and P. tabacinum isolates collected in 2006 produced mild to severe symptoms on bean pods of several widely used varieties (Titan, Hystyle, Summit, Caprice, Gold Mine, Bronco, Diplomat, and Secretariat). In fungicide trials conducted in mist chambers (not in the field), Headline, Bravo, Quadris, and Champion provided at least 43 percent control of bean pod infection caused by A. alternata or P. tabacinum. Endura, Switch, and Rovral provided A. alternata control. Topsin M provided control of P. tabacinum. From this research project, we now know which fungicides have potential to control the disease in the field (depending on which species of pathogen is present), and we also know that all of the commonly used varieties of snap beans are susceptible. Growers and processors are aware of these studies from presentations at commodity meetings and conferences.

This applied research is still in progress, thus the full impact has not been realized. It is clear that the most commonly used varieties of snap bean are susceptible to both pathogens and that newly released varieties will need to be characterized for their susceptibility to this disease. Fungicides with potential for disease control have been identified, but field application rates and timing have not been determined. The additional measures needed to control the disease are likely to reduce profitability of snap bean production, especially in the processing sector. Thus, additional research on the economics of proposed control measures is also needed. The research goal for 2008 is to determine an integrated approach to disease control, which would simultaneously manage all fungal diseases on snap beans (white mold, gray mold, spotty beans).