West Central Michigan vegetable regional report - June 25, 2014
Disease development could start earlier than normal this year, so immediate attention to disease control programs is essential.
The most important news has been the extended periods of leaf wetness area vegetables have experienced due to wet and/or foggy weather, which has been accompanied by relatively warm overnight temperatures. These conditions could favor earlier than normal disease development. This year is not the year to debate application of preventive fungicides and bactericides. These products are best applied before disease spreads. Symptoms from initial disease spread this week may not be evident for 7 to 14 days. If and when these symptoms occur, you will have missed your main opportunity to prevent the problem. Michigan State University Extension recommends starting your programs as appropriate and continuing them throughout the stages where crops are vulnerable, either on a regular interval, or using weather-based disease models when appropriate.
In asparagus, wet and relatively warm weather over the past week could again promote development of asparagus rust and purple spot in fields where harvest has ceased. A note that bears repeating: One of the mainstays of our rust control program, Folicur (a.i. Tebuconazole), has often been used by growers after rust develops due to price and the fact that it has some curative activity, however, like most fungicides it is most effective when used preventively.
In celery, scouts report that aster leafhopper numbers were relatively low in the Decatur, Michigan area early this week. A local scout reports capturing variegated cutworm moths in Ottawa County again this week; the first egg mass was detected three weeks ago, so egg laying by females has likely been ongoing.
In cole crops, slug activity was evident at one Ottawa County location in cabbage this week. Conditions have been very favorable for slugs, which can cause problems as both slugs and their feces serve as contaminants. Slugs are mostly active at night. To find them, go out in the early morning and look between the leaves at the base of the plant. Materials for slug control include the poison baits Deadline, a.i. metaldehyde, and various formulations of iron phosphate. The latter includes some OMRI approved products.
In cucurbits, North Carolina is the farthest north that cucurbit downy mildew had been confirmed to date, with another report from a cucumber field on June 24.
In onions, as we approach the traditional season of thrips activity, remember that research shows that application of Movento, a.i. spirotetramat, can be avoided if thrips populations are below a threshold of one thrips per leaf. If thrips are present, but below this threshold, you can delay application until thrips populations increase. Remember to apply this product using a penetrating surfactant.
In potatoes and tomatoes, weather will be very conducive of late blight for two to four out of the next five days through Sunday, June 29, according to www.lateblight.org. Now is the time to start scouting your fields for late blight and rogue out any volunteer potatoes. Potato leafhoppers were present in the celery fields I swept in Ottawa County, and are active in other crops and parts of the state.
In sweet corn, there will be a low risk of corn earworm moth activity for the Midwest through this upcoming weekend, according to forecast models. Sweet corn planted on plastic was at row-tassel yesterday in Ottawa County. At tassel emergence, any European corn borer larvae feeding in the whorl will move down the plant before boring into stalks, making this a good time to apply controls if you detected this pest feeding in whorls in non-resistant corn varieties. After this pest bores into stalks, it is protected from chemical control. There are other sweet corn caterpillars that you may detect; learn about their biology and control in Purdue Extension’s Managing Insects in Commercially Grown Sweet Corn.