West central Michigan vegetable regional report – June 24, 2015

Weather has been favorable for earlier than normal disease development, so keep an eye out for symptoms and initiate controls promptly.

Asparagus rust uredospore lesions have a “blistered” appearance (right lesions in photo). This stage can rapidly reproduce in the right conditions. They’re preceded by aeciospore lesions (left lesion in photo), an earlier, slower reproducing stage.

Asparagus rust uredospore lesions have a “blistered” appearance (right lesions in photo). This stage can rapidly reproduce in the right conditions. They’re preceded by aeciospore lesions (left lesion in photo), an earlier, slower reproducing stage.

Crops

Asparagus rust uredospores were present in one unsprayed field I visited in west Michigan last week. This is the stage that can create epidemics of rust during favorable weather conditions. An application of Tebuconazole can be made along with chlorothalonil to target rust.

Carrot fields visited this week all were hosting aster leafhoppers. However, infectivity continues to be low, with zero percent of leafhoppers infected with the aster yellow’s phytoplasma in an Oceana County sample taken last week.

Celery fields in one southwest Michigan location had low numbers of aster leafhoppers last week. Infectivity from samples analyzed last week ranged from 0-2.7 percent. At 2.7 percent infectivity, the threshold for celery is 13 leafhoppers per 100 sweeps.

Cucurbit downy mildew was confirmed from Monroe County cucumbers Monday, June 22, roughly 10-14 days earlier than most years for a first detection. Michigan State University Extension specialist Mary Hausbeck wrote an excellent article detailing how to keep abreast of and manage this disease, “Cucumber downy mildew makes an early appearance in Michigan.” Please report any potential sightings of this disease to .(JavaScript must be enabled to view this email address).

Vine crop plantings continue to be challenged by striped cucumber beetles where conventional chemicals were not applied. To make control decisions, you can use thresholds based on counts of beetles per plant on 25 plants per field.

Take striped cucumber beetle counts on five plants at five locations per field, and average across your counts. Compare these numbers to the below rough thresholds to decide if making an application of a control is worthwhile. Grower experience and damage tolerance are important considerations when deciding if a threshold makes sense for your farm.

Striped cucumber beetle thresholds

Stage

Threshold

Cotyledon and one leaf

0.5 beetle per plant

Two- to four-leaf

1 beetle per plant

More than four leaves

3 beetles per plant

Fruit developing

20 percent of fruit with scars

Onion thrips were above threshold in one west Michigan location this week. Now is a good time to consult scouting data. If thrips numbers are over one per leaf, an application of Movento with the appropriate surfactant can be made.

Potato and tomato growers should be aware that conditions have been very conducive for late blight this year. Make destruction of volunteer potatoes a priority wherever this is practical. Late blight has been detected in North Carolina to date, but there are no confirmed reports from the Midwest. Keep abreast of its spread nationally at USAblight and keep updated on Michigan conditions at Michigan Late Blight Risk Monitoring.

Sweet corn growers should place corn earworm traps in plantings that are silking. Pheromone traps can be placed either inside or outside the field with the trap bottom at ear height. Importantly, place the trap in a location where prevailing winds will blow pheromone into the corn field being monitored. At this point in the season, the threshold for initiating control programs is detection of any moths.

Corn earworms have already been detected in Indiana, so monitoring will be important. Pheromone lures should be changed every two weeks and traps checked once or twice a week. One approach is to check traps weekly, but keep informed of potential weather fronts that could blow moths at Insect Forecast. If conditions are favorable, make a special trip to check your traps at that time regardless of when you last checked them. With only a weekly check, it is easy to miss a significant flight, which can literally happen overnight. 

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