West central Michigan vegetable regional report – June 5, 2013

Pest and disease activity are picking up throughout west central Michigan.

Asparagus. This past week, asparagus rust aeciospores were observed in one Oceana County location at the base of stems on developing asparagus fern. Purple spot lesions are also common in young asparagus fields, and may co-occur with rust aeciospores. At this time of year, both diseases create elliptical lesions. However, rust aeciospores are orange throughout and raised or blistered above the plant surface, while purple spot lesions have a dark center and are sunken.

The product Folicur can be used post-harvest in 1- to 2-year-old fields and has some curative activity against aeciospores. As we approach the fern season, Michigan State University Extension says to remember that Folicur, and all other fungicides, are most effective when used preventively when conditions for disease appear. Folicur (a.i. Tebuconaloe) does have preventive and some curative activity.

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Purple spot lesions and rust aeciospores can co-occur on developing asparagus fern. Rust aeciospores are orange throughout and blistered, while purple spot lesions are dark and not raised. Photo credit: Ben Werling, MSU Extension

Celery. Aster leafhopper captures in Ottawa and Allegan county celery fields were still in single digits this week; numbers are still low with a slight increase in numbers observed in one field yesterday (June 4). Growing degree day models suggest that variegated cutworm adults have not emerged yet. Scouts have begun placing out traps for this pest.

Cole crops. Diamondback moth and imported cabbage worm activity were reported from southeast Michigan this week; activity has likely already begun or will begin soon in west central Michigan. Cabbage maggot damage has also been detected in southeast Michigan and could be occurring in the west central area. If you detect wilted seedlings, you can dig them up and look for maggots to determine if they could be the cause.

Cucurbits. Winter squash planting has continued this week in both Ottawa and Oceana counties. MSU plant pathologist Mary Hausbeck said it is important to remember that Phytophthora capsici, a major pathogen of cucurbits, is not present in field soil unless it has been brought there from another source (i.e., a previously infested field). If you have fields where this pathogen has established already, you can limit its spread to uninfested fields by working problem-fields after your “clean” fields. This can be difficult, especially when a third party is doing custom work. One possibility is to hand the individuals doing your custom work a map of your fields with numbers indicating a potential order to work fields in. Online mapping websites contain aerial photos and could be used to create such a map.

Power-washing equipment with soapy water will also remove soil that could contain inoculum, limiting spread between fields via equipment. It is far less costly to prevent this disease than to manage it once it is established.

Striped cucumber beetles continue to be active in the state. Remember that FarMore FI-400 treated seed contains the insecticide thiamethoxam, a systemic neonicotinoid. If you planted FarMore FI-400 treated seed, an additional drench with the neonicotinoids Admire (a.i. imidacloprid) or Platinum (a.i. thiomethoxam) is unnecessary for early striped cucumber beetle control.

Onions. The section 18 label for Movento is available. This product has proven very effective in trials for providing thrips control the first few weeks of their activity window. It is only effective, however, if applied in combination with a penetrating, non-ionic surfactant that allows the compound to penetrate the plant tissue and become systemic. It can be co-applied with the fungicides Dithane F45 Rainshield, Rovral 4F, Scala SC and Quadris F; a penetrating surfactant must still be used if you tank-mix Movento with this product.

Sweet corn. True armyworm damage has been detected in some areas of Indiana and Kentucky; keep an eye out for this pest that feeds on corn foliage. Black cutworm adults have also been captured in central Michigan. Corn earworm activity has also been detected in Indiana and could begin here soon. Placing out corn earworm traps in or near silking sweet corn fields will allow you to detect them early when control is still possible. If you place them adjacent to a field, make sure they are on the upwind side so that prevailing winds blow the pheromone over the field to attract moths.

For corn silking prior to mid-July, research from Purdue University suggests that any non-zero trap catch of corn earworm merits treatment for fresh market corn when it is silking. After mid-July, a trap catch of 10 moths per night can be used as a threshold. The two keys to economic and effective control are:

  1. Don’t apply insecticides when corn is not vulnerable, i.e., when it is not silking.
  2. When it is silking, monitoring and prompt insecticide application are essential.

Insecticide residues must be present on the silks when corn earworm larvae hatch; if insecticide is not present prior to egg hatch, they are more likely to survive and move into the tips of the ears where they will be protected from insecticide by the ear leaves.

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