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| Introduction Symptoms Disease Cycle Diagnosis/Sampling |
| INTRODUCTION Sweet corn decline syndrome emerged as a significant disease in the Willamette Valley of Oregon in the 1990’s. Root rot has been implicated as a major player in this disease complex (Figs. 1-3), but crown rot and nodal darkening may also contribute to this syndrome. Sweet corn decline reduces yield and ear quality of sweet corn. Because primary symptoms occur on the roots, disease may progress unnoticed until the end of the season when the above ground foliage begins to show secondary symptoms of leaf chlorosis (commonly called “firing”). As a consequence, ear size is reduced, tips fail to fill, and kernels dimple. Significant losses in yield have been reported, particularly for the historical industry standard variety, “Golden Jubilee” (Fig. 3). Oregon ranks 4th in the US for sweet corn production with the crop valued at $31 million in 2003. Sweet corn was grown on 32,000 acres predominately in the fertile Willamette Valley (89% for processing). Sweet corn is a valuable and integral crop to the Oregon vegetable industry. Local processors rely on a steady crop to round out their production schedule. The majority of the research reported here is on the root rot phase of the disease. Researchers at OSU have currently identified four soil-borne fungal or fungal-like pathogens causing root rot: Pythium arrhenomanes, Phoma terrestris, Drechslera sp., and Fusarium graminearum. These organisms are ubiquitous and infect roots throughout the growing season. Because of the diverse nature of these pathogens no chemical control has been identified and none of the currently-available cultivars are resistant. However, tolerant cultivars have been identified. Tolerant cultivars, while not resistant, maintain a commercially acceptable yield even when grown in fields of high root rot potential. Integrated strategies are typically required for the management of soil-borne diseases. Ongoing research is focusing on factors that influence this syndrome. Researchers from OSU including Alex Stone (Vegetable Crops Specialist), Jim Myers (Vegetable Breeder), Cynthia Ocamb (Extension Plant Pathologist), and Ed Peachey (Research Specialist) are exploring the manipulation of cultural practices such as irrigation and herbicide management, crop rotation, microbial seed treatments, and suppressive cover crops to manage this disease. The vegetable breeding program, in cooperation with regional processors, is working to identify germplasm and cultivars resistant or tolerant to this disease. |
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