West central Michigan vegetable regional report – July 8, 2015

Counties traditionally not affected by cucurbit downy mildew will likely be challenged by this disease in 2015.

Asparagus rust uredospore (left) and purple spot (right) lesions high up on untreated fern. Conditions have likely been favorable for continued disease development.

Asparagus rust uredospore (left) and purple spot (right) lesions high up on untreated fern. Conditions have likely been favorable for continued disease development.

Crops

Asparagus fields were being colonized by Japanese beetles this week. Asparagus rust uredospore and purple spot lesions were present high up on the fern in untreated research plots that were unharvested this year. Most fields have expanded cladophylls now. This is the time to begin your regular fungicide program if you haven’t already.

Bean planting is expected to start following pea harvest this week in Oceana County. Be on the lookout for bacterial blight in your snap beans.

Carrot fields were already showing signs of leaf blight in west Michigan as of last Thursday, July 2. Aster leafhopper numbers were too low in area fields to obtain a sample for infectivity this week.

Celery fields have been colonized by scattered aphid colonies according to scouts, and caterpillar pests have been detected. Cabbage looper larvae may be present as well as variegated cutworms. So far this week there has been insufficient numbers of aster leafhoppers to obtain and test a sample for aster yellows infectivity.

Cucurbit downy mildew was confirmed in Allegan County this week. Arrival and spread of this disease were rapid and is roughly two weeks ahead of schedule this year. Michigan State University Extension plant pathologist Mary Hausbeck expects this disease to spread to west Michigan counties much earlier than normal and become a problem even in counties that traditionally do not see this disease until later or not at all. Hausbeck’s trials suggest that pickle and melon growers should be applying downy mildew fungicides on a seven-day schedule in counties where the disease has not been detected, and tighten this interval to four days once it arrives. Hausbeck gives an example spray program for downy mildew control. Please send photos via email to .(JavaScript must be enabled to view this email address) showing both the tops and bottoms of leaves if you suspect your cucumbers or melons have this disease. A factsheet for home gardeners provides a good general description of this disease.

Striped cucumber beetle adults continue to be active. Squash bugs were reported by Ottawa County consultants. Cucumber beetles and squash bugs can be scouted for at the same time. Check five plants at five locations. Early flowering is one critical period for squash bug control. During this time, look for egg masses. A threshold during early flowering is one egg mass per plant. Pheromones traps for squash vine borers should be placed out now; be on the lookout for squash vine borer eggs.

Squash vine borer and bug
Squash vine borer eggs (A; left) are laid singly or in very small groups on stems at the base of plants. Squash bug eggs (B; right) are laid in clusters on the underside of pumpkin and winter squash leaves, often where two veins meet.

Onion thrips numbers have not reached threshold in some western and southwestern onion growing areas, though numbers have increased above threshold in the Newaygo County area in some fields. Other growers report they have either not had to apply insecticides to date or have made their first Movento application. If you are able to skip your early applications and find yourself in a warm, dry period where numbers are increasing quickly, skip Movento and move to Radiant – if numbers are very high – or another product such as Agri-Mek or Lannate – if numbers are moderate. Note, a threshold of one thrips per leaf can be used for all products but Radiant, while a threshold of three per leaf can be used for Radiant. Weather has continued to be very conducive for disease development.

Pepper fields were colonized by aphids in some west Michigan locations this week. To scout, check five plants at five locations per field. On each plant, check two upper leaves and two lower leaves. Record the number of aphids per leaf and average across them. Prior to fruit set, insecticide application may be worthwhile if numbers remain between five and 10 aphids per leaf for two weeks in a row. After fruit set, make an application whenever numbers average above five per leaf. Note, Beleaf and Fulfill are aphid-specific products that should be soft on beneficials. Fulfill works by paralyzing aphid mouthparts so they cannot feed. This means aphids will still be visible, but starving, for up to a week after application. Movento is also labelled for aphid control in peppers. Good success has been obtained with aphid control in celery, though MSU trials have not been conducted in peppers. When used with a penetrating surfactant, this systemic product has been able to clean up and provide two to three weeks of aphid control in celery.

Potato and tomato growers should be aware that conditions have continued to be very conducive for late blight. Colorado potato beetles of all life stages are now visible and potato leafhoppers are also present. The MSU late blight forecaster predicts weather will create a high risk of late blight development for three to four out of the next five days, tomorrow through next Monday. Potato blackleg has been detected in southern Michigan.

Sweet corn growers should consider placing corn earworm traps out near sweet corn between green silk emergence and brown silks. Insectforecast.com predicts low to no risk of corn earworm migration through the weekend. Western bean cutworm traps should also be placed out now. Western bean cutworm females find corn where tassels are just about to emerge highly attractive. A universal moth trap, available at suppliers such as Great Lakes IPM, can be used in combination with a pheromone lure and pest kill strip to monitor emergence of western bean cutworms. Once moths are detected, include this pest on your list when scouting 20 plants at five locations for other pests.

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