West central Michigan vegetable regional report - July 23, 2014

This year is posing significant disease control challenges; continue to keep on top of fungicide programs.

Cercospora symptoms on carrot foliage. Cercospora lesions are initially circular. Photo credit: Norm Myers

Cercospora symptoms on carrot foliage. Cercospora lesions are initially circular. Photo credit: Norm Myers


To date, asparagus purple spot is more prevalent than asparagus rust. Note that the fungicide chlorothalonil is the foundation of purple spot control programs and can be applied using the TomCast disease model. Quadris (active ingredient azoxystrobin) is also labelled for purple spot control and is a potential alternative; however, it does not provide the additional protection against rust that chlorothalonil can.


Aster yellows symptoms were visible in two locations this week. When walking your field, look for reddish foliage, then pull up the carrot to see if it has hairy roots, both of these are symptoms of aster yellows disease. Cercospora has also been found in at least one location in west Michigan. Protectant fungicides can be applied using the TomCast disease model.


Early blight, caused by the fungus Cercospora, was confirmed as present in a southwest Michigan location earlier this year. This disease is more aggressive than Septoria, so make sure to stay on top of preventive programs for Cercospora. Note, for general weed control in celery, some growers have found a preemergence application of Chateau (active ingredient flumioazin) to be useful. This product has a different mode of action than Caparol (active ingredient prometryn) and is listed as providing “excellent” control of pigweeds, spurge, nightshades, mustards, wild radish and common lambsquarter, and listed as providing good control of other problem weeds such as purslane. A supplemental label expiring in June 2017 is available for use in celery.


Michigan State University traps have showed sustained captures of cucurbit downy mildew spores in Saginaw and Bay counties. There has not been a second confirmed report since the initial detection in Gratiot County, however, disease developed rapidly at this location, suggesting conditions were conducive to production of further inoculum. This continues to be a year when a preventive cucurbit downy mildew program could be beneficial for susceptible crops such as pickles and cucumbers. Products for use in such a program can be viewed at “Spray Recommendations for Downy Mildew.”

Powdery mildew has started to develop in southeast Michigan. Keep an eye out for this disease in varieties that are not tolerant, and consider including an effective powdery mildew product such as Torino (active ingredient cyflufenamid) or Quintec (active ingredient qunoxyfen) into your program if disease starts to develop.

Striped cucumber beetle activity and squash bug egglaying were evident at one Newaygo County location this week. Squash vine borer larvae were present in a homeowner sample in Muskegon County and could be present in some commercial plantings. If you have had this pest in the past, you are more likely to have it in the same location again, so keep an eye out for it. Insecticides for squash vine borer need to be applied before the eggs hatch and larvae enter the stem, where they are protected, and sprays need to reach the crown of the plant where eggs are laid.


Onion downy mildew has been detected in Michigan, as has purple blotch and anthracnose. This disease may have developed earlier than is typical this year because of early, wet conditions. Fungicides for use on this group of pathogens – the oomycetes – are different than those typically used in standard spray programs. In other crops, fungicides including Revus (active ingredient mandipropamid), Forum active ingredient dimethomorph) and Zampro active ingredient ametoctradin/dimethomorph) have proven effective against this group of pathogens, the oomycetes. Michigan State University Extension recommends considering incorporating one of these products into your spray program along with products for other foliar diseases. For thrips control, Agri-Mek (active ingredient abamectin) is one option for use in the middle of the thrips season. A threshold of 1 thrip per leaf can be used to make control decisions. Remember to always use a penetrating surfactant with products such as Agri-Mek.


Aphids have been present in area vegetable fields recently, including peppers. Beneficial insects, including parasitoid wasps, green lacewings and ladybird beetles, were also observable at one location I visited. In some crops and locations, application of broad spectrum insecticides can, counterintuitively, lead to increases in aphid problems by killing beneficial insects. Consider incorporating an insecticide friendly to beneficial insects into your aphid control program, such as Beleaf (active ingredient flonicamid) or Fulfill (active ingredient pymetrozine). These products will be more effective if applied before populations reach economic levels.

Potatoes and tomatoes

Late blight has been detected at additional locations within Montcalm County, the isolate appears aggressive. According to MSU’s Willie Kirk, disease severity values have continued to accumulate in recent weeks, so spread is likely.

If you detect late blight in potatoes, please contact your nearest MSU Extension vegetable educator as prompt sampling will help determine what fungicides might best control the strain.

Sweet corn

According to forecast models, there is a low risk of continued corn earworm migration this week. Two corn earworm moths were captured over the past seven days in an Ottawa County location. Low captures of western bean cutworm were made in Montcalm County over the past week, while higher captures were made in southeast Michigan. If you are already treating for corn earworm, then you should be providing protection against western bean cutworm, as similar products will control both pests.

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