West central Michigan vegetables regional report – July 31, 2013

Cucurbit downy mildew is on the move, area cucumber and melon growers need to apply effective products promptly on a regular schedule.

In asparagus, application of fungicide sprays continues to be the main focus of asparagus management at present time.

Celery crop scouts report that aster leafhopper numbers remained relatively low in the celery growing region as of this Tuesday (July 30), although numbers were higher in a location in Hudsonville, Mich., last week. Aphid numbers have increased again in some areas and require control. Variegated cutworm adults have again been captured this week in traps placed out by a local crop scout.

In cucurbits, it is absolutely essential that cucumber, pickle and melon growers promptly apply effective fungicides on a regular schedule to prevent losses to cucurbit downy mildew, which can cause widespread damage in as little as 10 to 14 days. Cucurbit downy mildew was detected in Newaygo County in a sample taken on July 24, which is an early detection for a location this far north. In addition, the current weather pattern, which is forecast to bring light rains and cool weather followed by cool, clear weather, is ideal for a ramp up in downy mildew spread.

Presidio (a.i. fluopicolide) can be alternated with Ranman (a.i. cyazofamid) on a five-day schedule for cucumbers in areas where disease is not present, or a seven-day schedule in areas where it is not yet present; for melons, a seven-day schedule is recommended. Both products should be mixed with Bravo (a.i. chlorothalonil). Previcur flex (a.i. propamocarb hydrochloride) is another useful product that could be rotated in after an application of Ranman or Presidio; it also needs to be mixed with Bravo.

Importantly, some products that work well for other diseases or in other crops are not effective, or only partially effective, for downy mildew control in cucumbers and melons. For example, Tanos (a.i. famoxadone + cymoxanil) may be adequate to protect pumpkins and squash, which are less susceptible to downy mildew, but is not adequate for protection of cucumbers and melons. Cucurbit downy mildew is also resistant to Ridomil-Gold-based products and strobilurins; one example of a product that is effective for other pathogens, but not downy mildew, is Revus (a.i. mandipropamid). This product can be used for protection against Phytophthora capsici, but is not effective against cucurbit downy mildew. Michigan State University Extension recommendations are based on efficacy trials that were presented at last year’s Great Lakes Fruit and Vegetable Expo.

Zucchini and summer squash harvest is continuing in Oceana County. Cucumber harvest has also been underway in Newaygo County. Powdery mildew has also been detected in multiple locations in west Michigan, and symptoms of virus are increasing in areas to our south.

Onions had approximately 10 leaves in early plantings in Grant, Hudsonville and Hamilton yesterday (July 30), while younger plantings had as few as six leaves. Tops of early plantings in Hudsonville, Mich., were beginning to fall. 3+ provided effective early season control in many locations, with some growers skipping two weeks of sprays. However, numbers are now increasing in some locations. As we are relatively late in the season, MSU’s Zsofia Szendrei recommends using Radiant (a.i. spinetoram) if numbers are close to or above two thrips per leaf in your field. Radiant is effective at suppressing thrips late in the season once populations increase, and timely back-to-back sprays in fields over threshold could provide control for the first two weeks of August. After this time, another product could be used (e.g., Agri-Mek, a.i. abamectin, or Lannate, a.i. methomyl) to finish the spray season.

Importantly, symptoms associated with bacterial disease in onions have been observed in multiple locations in west Michigan. In the picture below, the center leaf of the plant on the left is dying; this symptom is strongly correlated with the occurrence of bacterial center rot, which has reached high incidence in at least one location this year. This same plant also has one outer leaf that’s dying. The plant on the right does not have a dead center leaf, but, like the plant on the left, does have an outer leaf that has a dead area with water-soaked margins. One of the bacteria associated with this symptom may enter the bulb to cause storage rot, however, less is known about how frequently the bacteria that cause leaf blight also cause bulb rot.

Bacterial rot
Symptoms of bacterial infection of onions.

Sunscald symptoms of peppers have been detected in southeast Michigan. This disorder occurs when pepper plant canopies do not adequately protect the fruit from the sun, resulting in large, brown areas of burnt tissue and potentially leading to fruit rot. This may have occurred in our area during the hot weather we had in previous weeks. Fields where canopies were poor due to other reasons would have been especially susceptible. Blossom end rot from hot weather in previous weeks may also be evident in peppers and tomatoes.

In potatoes and tomatoes, late blight continues to be of concern as the forecast suggests weather will be conducive to spread for two to four of the next five days. Symptoms have been appearing in tomatoes that are not consistent with any known disease and are under investigation.

Some snap bean plantings have been harvested in the past one to two weeks in Oceana and Mason counties.

In sweet corn, over the period of July 18-25 I captured four corn earworm moths in one trap in Hart Township, Oceana County; zero European corn borer adults in three traps in Hart Township; and three western bean cutworm adults in one trap in Hart Township and six in a second trap in Weare Township, Oceana County. Captures of corn earworm have slightly increased in Monroe and Lenawee counties, and may pick up in west Michigan as well. Densities of western bean cutworm eggs in central Michigan, to our east, have remained relatively low to date.

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