West central Michigan vegetables regional report – Aug. 7, 2013

With wet weather in our region, be on the lookout for continued spread of diseases.

Adult asparagus miner fly numbers have increased in the two Oceana County locations where populations are being monitored, indicating onset of the second generation of this pest.

Sporadic aphid outbreaks in celery have continued and require control. Aster leafhopper numbers have continued to be low. Scouts have not detected any egg masses of variegated cutworm to date and problematic celery leaf tier populations have not been found.

In cucurbits, Monday and Tuesday’s (Aug. 5-6) weather forecast suggested a high risk of cucurbit downy mildew spread, with spores predicted to move from the south in north and northeast directions. If you suspect this disease is present, please contact your local Michigan State University Extension educator. (I cover the west central area and can be contacted via email at .(JavaScript must be enabled to view this email address)). Detection of this disease will not just benefit you, but it will also help nearby growers take the actions they need to save their crop. Cucumber and melon crops are most susceptible to this disease.

The prevalence of symptoms of bacterial infection in onions is considerably higher this year than last year. In particular, symptoms of bacterial leaf blight and the associated bacterium have been detected from onion fields in Hamilton, Stockbridge, Grant Hudsonville, Marshall and Charlotte, Mich. While we have much to learn about the most widespread bacterial species that has been detected, experiences in Georgia suggest the species in question is of concern for development of storage rot.

Copper-based pesticides offer the main source of protection against bacterial disease in vegetables. However, we currently have much to learn about if and how they can be used to effectively limit bacterial rots in onions. MSU researchers have experience learning to protect against bacterial disease in other vegetables like tomatoes. In tomatoes, researchers found that bacteria were present long before symptoms developed. In this system, applying copper-based products early is key. Once symptoms have developed and become noticeable, bacterial populations are correspondingly high, which makes it difficult for a preventive product like copper to reduce further spread. In specific, bacterial cells are microscopic and reproduce in very short time periods (10s of minutes, not hours), which means that by the time symptoms are visible, bacterial populations are large and have undergone rapid, exponential growth. As a result, in the tomato system it has been found that copper-based products can be effective, but only when applied early and consistently as a preventive measure.

Bacerial rot of onion
An outer onion leaf with a brown lesion and water-soaked margins, which are associated with bacterial infection. Note the observations suggest that other pathogens can also be present on blighted leaves. However, the presence of greasy-looking or “water-soaked” tissue is typical of bacterial infections. Photo credit: Ben Werling, MSU Extension

Symptoms of blossom end-rot in peppers have continued to be detected in areas to our south due to hot, dry weather earlier in July. Anthracnose fruit rot of pepper has also been detected in southeast Michigan. This disease produces circular or angular, sunken lesions on both fruit and also stems and leaves.

Late blight has been confirmed in potatoes near Constantine, Mich., in St. Joseph County and symptoms have been observed in a Kalamazoo, Mich., location on tomatoes. Conditions will be conducive to spread in two to three out of the next five days in most areas. Tomato growers who are considering growing their crop into September can include an oomycete-specific fungicide into their rotation to provide increased protection during the late-summer/early fall conditions that favor this disease.

In sweet corn, over the period July 26-Aug. 2, I captured six corn earworm moths in one trap in Hart Township, Oceana County; zero European corn borer adults in three traps in Hart Township; and one western bean cutworm adult in one trap in Hart Township and zero in a second trap in Weare Township in Oceana County. Populations of corn earworm have continued to be low to our south in Indiana. Cool weather there may delay onset of the second generation of moths, which could mean there will be lower numbers of corn earworm flying to Michigan late this summer.

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