Southeast Michigan vegetable regional report – July 30, 2014

Dry conditions predominated in southeast Michigan, cooler temperatures have slowed down crop development and delayed some planting of fall crops. It is time to implement a management strategy for carrot foliar blights.

Weather

In the last week, dry conditions predominated in the area, however, rain and scattered showers occurred on Sunday and Tuesday night respectively. An average of 7.3 humid hours and 0.42 inches of rain were recorded for the weather stations in the southeast region. The Petersburg Enviro-weather station recorded 0.83 inches of rain while Commerce Township station recorded 0.31 inches.

Air temperatures in the southeast have ranged from 43 to 71 degrees Fahrenheit, with partly cloudy days. Based on the average of the southeast weather stations, we currently have reached 1518 growing degree days base 50 F (GDD50), 2263 (GDD45) and 2605 (GDD42) placing the 2014 growing season behind by 216, 254 and 277 respectively, when compared with the 5-year average.

Table 1. Regional degree days (GDD) for the SE region. (http://enviroweather.msu.edu/)

Station

GDD42

GDD45

GDD50

Petersburg

2333

2009

1518

Commerce Township

2143

 1827

1348

Romeo

2275

1952

1462

Hudson

 2326

 2006

1518

Average of stations in this region

2269

1949

1461

Weather outlook

Temperatures are forecasted to range from 53 to 83 degrees over the next week, with chances of rain ranging from 25 to 53 percent for the following week (August 1-8).

Vegetable crops

Cool weather has benefited cole crop development and harvest, however, transplant of fall crops has been delayed for some growers due to the dry soil conditions.

Vine crops fruit development has slowed down. Harvest of melons (watermelon and muskmelons), spaghetti and acorn squash has started and continues for zucchini, yellow squash. Cucumber harvest continues at a slower pace as fruit development has slowed down due to cooler nights. There are no reports of cucurbit downy mildew in our area, and spore counts in the Monroe spore traps continue to be lower compared with the influx of spores counted in the Bay and Saginaw spore traps. The epidemic of this downy mildew continues in Michigan with a recent report in Tuscola County.

Pumpkin fruit development continues at a slower pace, while the incidence of powdery mildew continue to be low at this time, no major insect problems have been observed or reported in pumpkins.

Banana and bell pepper harvest will commence this week while jalapenos are not ready yet. Bacterial diseases continue to be problematic in peppers and tomato. The lack of significant and frequent rain events and cooler temperatures have slowed down the development of peppers and tomatoes and as well as the severity of bacterial diseases. The key to manage bacterial diseases in pepper was discussed by Dr. Mary Hausbeck in her article “Bacterial spot damages Michigan peppers.”

Fresh market tomato harvest continues in tunnels and is in full swing in the field. Processing tomato fields are in various degrees of maturity, with early-planted fields reaching 90-95 percent crop cover and 30 percent of the fruit ripe. Continue protecting your tomatoes from late bight (See Michigan State University specialist Dr. Hausbeck’s recommendations) as the cooler weather is conducive for the development of this disease.

The Petersburg station has accumulated 3 DSV for late blight of potatoes. Visit lateblight.org to get a recommendation based on your location and potato planting date. Potato leafhopper populations have reached threshold in small acreage potato fields, but remain below threshold in larger potato fields.

Sweet corn harvest continues. The risk of western bean cutworm is high in our region (http://www.insectforecast.com/). Six 6 western bean cutworm moths were caught in the last 7 days in the Monroe County trap. Low corn earworm migration risks were predicted for July 25 and 26 and one corn earnworm moth was caught in the last 7 days in one of the Monroe County traps in the last week, and low risk continues to be forecasted for the area. No European corn borer moths have been caught in the Monroe traps this week.

Symptoms of fungal foliar pathogen of carrots and red beets were observed in the last week. Foliar blights caused by Cercospora and Alternaria are common diseases of carrot. They are both fungal pathogens and can affect young and old foliage. Symptoms start as circular small lesions that expand and can coalesce, according to Mary Hausbeck, Cercospora can develop quickly and is often more difficult to control than Alternaria blight.

'' ''
Left, Alternaria. Right, Carrot foliar blight caused by Cercospora. Photo credits: M. Grabowski, University of Minnesota (left) and G. Holmes, California Polytechnic State University, Bugwood.org (right)

Considerations for managing carrot foliar blights

Be conservative when irrigation is needed. Aim for a balance that provides adequate soil moisture while minimizing irrigation events and duration. This will help decrease the number of humid hours conducive to the disease as well as minimize dispersal of the pathogen from disease to healthy tissue.

Avoid working fields when plants are wet, which minimizes pathogen spread from diseased to healthy tissue. Also, work fields with diagnosed diseases last to avoid moving the pathogen from problematic fields to clean fields.

Fungal blights can be managed with a fungicide program that alternates applications of chlorothalonil products (Bravo, Echo etc) and the strobilurins (FRAC group 11: Quadris, Cabrio, Pristine, or Flint). Strobilurin products are single site fungicides and should not be overused. Alternation with other FRAC codes is imperative to prevent resistance development.

For more information on labeled fungicides, consult the Michigan State University Extension publication E-312 “2014 Insect, Disease and Nematode Control for Commercial Vegetables, or visit the Midwest Vegetable Production Guide for Commercial Growers 2014 (page 180).

When available, the TOM-CAST disease forecasting system can be used to time sprays for both fungal blights (Cercospora and Alternaria).

Since carrot leaf blight pathogens can survive in infected plant debris, practice the following.

  • A two-to three-year rotation will contribute to the decline of the pathogen population.
  • Working the field by either disking or fall plowing can enhance decomposition of crop residues and therefore help mange the pathogen numbers in the field.

For next year, consider reducing the risk of introducing pathogens into fields by using certified, disease free seed and using seed treatment options (the latter is especially important for bacterial blight in carrots). Select crop varieties with resistance to fungal and bacterial blight of carrots when available. Consider using some of the varieties tested in Michigan by the Hausbeck lab.

For more information on commercial vegetable production, contact Lina Rodriguez Salamanca 517 264 5310 or at .(JavaScript must be enabled to view this email address).

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