Southeast Michigan vegetable regional report – June 25, 2014
Precipitation and high humidity are conducive for plant disease development; scout your crops and detect potential problems early.
In the past week, rainfall recorded in Southeast Michigan averaged 2.4 inches. The Michigan State University Petersburg Enviro-weather station recorded only 2.5 inches of rain, while the Romeo Enviro-weather station recorded 1.45 inches. Air temperatures in the Southeast have ranged from 56 to 84 degrees Fahrenheit, and most days were cloudy with 10 to 19 hours of humidity.
Based on the average of the Southeast Michigan Enviro-weather stations, we currently have reached 826 growing degree days base 50 F (GDD50) with a maximum of 879 GDD at the Petersburg Enviro-weather station, which is behind by 100 GDD when compared with the five-year average.
Precipitation events have resulted in low areas on fields flooded. Harvest of cruciferous crops and vine crops—cucumber, yellow squash and zucchini—continues.
Pumpkin vines are staring to bear flowers. Watermelon plants are bearing 3- to 5-inch fruit. The rain and the long periods of relative humidity have resulted in cucumber and yellow squash fruit close to the base of the plants being prone to soft rot pathogens, such as Choanephora. Beware that the rainy and humid weather we experienced can be conducive for the development of P. capsici in fields with history of this pathogen.
No cucurbit downy mildew has been detected at this time in cucumbers. However, the epidemic continues in the southern states. Continue to scout for cucurbit downy mildew symptoms, and submit any suspicious symptoms to MSU Diagnostic Services or your local MSU Extension educator as early detection is critical.
Squash vine borer adults are active. Five and three adults were captured in the Monroe County and Washtenaw County traps respectively. Winter squash varieties are most susceptible to squash vine borer damage. Direct insecticide application at the base of the plant to protect the tissue as larvae hatch, especially in fields where this pest has been problematic in the past. Striped and spotted cucumber beetle populations have increased. If you use BT products, BT aisaiwi has shown to be more effective than BT Kurstaki, according to Cornell University‘s “Resource Guide for Organic Insect and Disease Management.”
Early planted sweet corn ears are developing while later planted fields have not reached the R1 growth stage, or mid-silk. Moderate risk for corn earn worm was forecasted for June 24, but the forecast changed to low risk on June 25. No European corn borers have been caught at the Monroe County trap at this time.
Tomato plants are bearing 1-to 2-inch fruit and potato tuber development continues. Scout for late blight symptoms in potato and tomatoes. Late blight was reported in New York state potatoes last week. The Michigan late blight risk-monitoring website forecasted moderate risk of disease development, with total DSVs of 28 for the Petersburg Enviro-weather station. To get a fungicide spray recommendation based on your field emergence date, visit lateblight.org
Peppers continue to develop, and 15 to 30 percent are bearing flowers. Some fields have low incidence of symptoms that look like bacterial spot. Confirmation is ongoing; always remember to get an accurate disease diagnosis (see a checklist for submitting samples to MSU Diagnostic Services) since one is required to implement effective management. Control strategies differ by pathogen, as fungicides are often specific to a particular type of pathogen.
To manage bacterial diseases in the field, consider the following:
- Irrigation management. Be conservative; when irrigation is needed, aim for a balance that provides adequate soil moisture while minimizing irrigation events and duration.
- Avoid working fields when plants are wet; this minimizes bacterial spread from diseased to healthy tissue.
- Work fields with diagnosed diseases last to avoid moving the pathogen from problematic fields to clean fields.
- Sprays. Different copper formulations are labeled. It is important to tank mix or alternate with other products, such as Actigard, Tanos or Serenade; always read the labels. These products are labeled, but they are not considered as efficacious as copper products to manage bacterial diseases. However, including other modes of action is a tool to prevent and manage resistance to copper. For more information, visit the 2014 Midwest Vegetable Production Guide for Commercial Growers (page 118).
For next year, consider:
- Reducing the risk of introducing pathogens into fields by using certified seed, seed treatment options and disease-free transplants.
- Scouting transplants in the greenhouse, practicing sanitation when needed and rogue diseased plants.
- Using pathogen-free irrigation water and avoiding over-watering. See the Michigan State University Extension article, “How does irrigation influence the presence and severity of diseases?”
- Selecting crop varieties with resistance to bacterial disease when available.