By Mary Hausbeck... Downy mildew has been verified on field cucumbers in Ontario and Ohio this week. Michigan will be next, and it is likely that downy mildew has already infected cucumbers in our state but hasn’t yet been detected.

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By Dan Pavuk... The striped cucumber beetle, Acalymma vittata, and the spotted cucumber beetle (also known as the southern corn rootworm), Diabrotica undecimpunctata howardi. They are a significant insect pest of cucurbits in the North Central Region and generally in the United States and southern Canada east of the Rocky Mountains.

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By Mary Hausbeck... There has been a bit of a stir following the report of downy mildew on cucumbers growing in greenhouses in Ontario, Canada. The concern comes from the fact that the seeds (or sporangia) of the downy mildew are readily carried on air currents so it is certain that the downy mildew is being released into the outdoor growing environment each time a greenhouse vent is opened.

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Mary Hausbeck...The wet, foggy and humid weather that occurred over the weekend and extended through the early part of this week will cause downy mildew to increase rapidly and spread. This year’s weather is much more favorable for downy mildew than what we experienced last year. That means that if you were able to control downy mildew on cucumber last year by spraying every 10 days you should not assume that the same approach will work this year.

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Mary Hausbeck...On July 2, a technician from my lab detected downy mildew on cucumbers growing in Monroe County. This field was selected for scouting because it is where the spore trap is running (see spore counts at end of this article). The infection is very light in this field and no fungicides had been applied. Based on the leaf samples, the infection is relatively recent.

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Mary K. Hausbeck...As of this morning, July 9, downy mildew has been found in Allegan County on pickling cucumbers. This is in addition to the earlier confirmation from Monroe County (see map). All cucumber growers must apply downy mildew fungicides immediately! See the tables below for spray recommendations.

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Mary Hausbeck...Downy mildew has been confirmed in a small commercial slicing cucumber field in the Aylmer area which is located south of London in Ontario, Canada. Approximately 10 percent of the plants were infected by the downy mildew with 1-2 leaves showing disease. If last year is any indication, then Michigan growers can expect to see downy mildew symptoms appear in their fields within the next couple of weeks.

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Amanda Gevens, Brian Cortright, and Mary Hausbeck...Powdery mildew is perhaps one of the easiest diseases to identify because of the whitish, talcum-like, powdery growth that develops on leaf surfaces, petioles, and stems.  Infected leaves usually wither and die. Premature loss of foliage often reduces the size or number of fruit and the length of the harvest period. In addition, powdery mildew infection predisposes plants to other diseases such as gummy stem blight. Powdery mildew occurs each year, although the time of disease appearance is unpredictable. 

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Mary Hausbeck...Phytophthora capsici can survive in the soil for up to ten years, and has the ability to destroy entire crops within days. The pathogen affects the root, stem, and fruit of eggplants, tomatoes, peppers, snap beans, squash, melons, pumpkins and cucumber. Fumigants, combined with good management practices can reduce the likelihood of infection occurring in the field.

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Mary Hausbeck...Many Michigan vegetable crops such as squash, cucumber, eggplant, pepper, beans, watermelon, melon and tomato are suscepti­ble to Phytophthora capsici (view images). This pathogen causes disease on plant crowns, roots and fruit. Phytophthora can move in surface wa­ter, which is often relied upon for irrigation in Michigan. Research conducted by Michi­gan State University from 2002 to 2005 iden­tified Phytophthora in a river, ponds and ditches in several Michigan counties.

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Mary Hausbeck...Since last week’s Vegetable CAT Alert, downy mildew has been confirmed on cucumber at three new sites, Saginaw County on July 20, Bay County on July 21, and on a 4 site in Monroe County on July 24 (see map).

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Paul Marks and Jennie Stanger...Late on June 25, Paul Marks and Jennie Stanger visited a home gardener who felt his cucumbers were showing the same symptoms as last year when an unprecedented outbreak of downy mildew swept across the county in midsummer, killing nearly all home garden cucumber plants and many farm field plantings within several days. Unfortunately, he was correct and this may be the first confirmed outbreak in Michigan for 2007. It is not always fun to be first, and we will not identify the gardener even though he deserves credit for recognizing the symptoms and alerting MSU Extension so we can inform others.

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Mary Hausbeck...There are no confirmed reports of downy mildew in Michigan. The hot and dry air of the last couple of weeks is not favorable for development of downy mildew. Since there is a report of downy mildew in nearby Ontario greenhouses, cucumber growers in southeast Michigan are advised to begin downy mildew sprays immediately (Table 1).

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Mary Hausbeck...Downy mildew has been confirmed on greenhouse cucumbers in Essex County in Canada. These are not plug plants for field production but are “hothouse” cucumbers. Essex County is Canada’s southernmost county located on a peninsula of land that juts out into the region of the Midwestern United States. At this time, no field outbreaks have been reported in Canada or Michigan. The greenhouse outbreak in Canada is troubling news for Michigan pickle and cucumber growers.

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Mary Hausbeck...Several viruses infect and damage squash, cucumbers and pumpkins in Michigan. Among these are cucumber mosaic virus (CMV), zucchini yellows mosaic virus (ZYMV) and watermelon mosaic virus 2 (WMV2). This year, CMV and WMV2 have been confirmed. Each of these viruses may infect squash, cucumber, zucchini and pumpkin alone or in combination. Infected plants may be stunted and/or distorted.

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Mary Hausbeck...With the return to more moderate temperatures, the downy mildew has picked up across the state. Homeowners are reporting death of cucumbers and cantaloupes in their gardens. (view map) Commercial growers report that a 5-day spray schedule is needed on cucumbers to keep the disease under control. Cantaloupes appear to be doing well with a 5-day fungicide program depending on location within the state.

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Mary Hausbeck...As downy mildew moves across the state (see map), cucumber growers can be certain that their crop will become infected if it isn’t protected. With a few more weeks until the end of the growing season, it is unlikely that unprotected cucumbers will escape this disease.

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Mary Hausbeck...Fungicides will be needed for the duration of the growing season to protect cucurbit crops from downy mildew. This disease is extremely destructive and can kill an unprotected crop within 7 to 10 days. Since downy mildew is spreading across Michigan, no one should assume that their crop will not become infected.

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Mary Hausbeck and Amanda Gevens...All cucumbers in the state are now at a VERY HIGH RISK for downy mildew. Spray programs for cucumbers must be tight and not exceed a five-day application interval. The recommended fungicide program remains unchanged:

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Mary Hausbeck...Reports of downy mildew continue to increase both within southeast Michigan and nearby states. In Michigan, the outbreak thus far is still limited to southeast Michigan. Currently, there are two farms in Monroe with a third farm near the Lenawee/Monroe County border confirmed late last week. Only cucumber fields have been confirmed with the disease thus far. The recommended fungicide programs are working.

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Mary Hausbeck...It is astounding how many new reports of downy mildew have been made from important cucumber growing regions in the last three days. Several fields in Ohio are now showing symptoms although the fungicide program is keeping the disease in check. Ontario is not faring as well. They are experiencing an outbreak that is not being controlled. It seems they do not have the same effective fungicide tools that United States growers have. Further, Delaware has now reported the first occurrence of downy mildew in that state. To my knowledge, cucumber is the only crop that has been reported with downy mildew.

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Beth Bishop...There is an error in Bulletin E-312, 2006 Insect, Disease and Nematode Control for Commercial Vegetables. The insecticide, Actara® (Syngenta ), is not registered for use on vine crops (cucumbers, squash, pumpkins, melons) as is reported in the bulletin. Please make this correction to your copy.

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Mary Hausbeck...In Michigan, downy mildew on cucumbers remains limited to Monroe County. On June 29, a downy mildew outbreak on cucumbers was reported in southern Ontario. Information is being gathered to learn more about this latest report. Recent weather conditions have not been favorable for downy mildew spread in the north and west portions of Michigan. Many cucumber and cantaloupe growers have continued to keep a protective spray on their fields. Conditions in southeast Michigan will require that growers maintain a tight fungicide program.

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Bernard Zandstra...Cucumber growers anticipate another year of downy mildew infestation in their crops. There have been questions about mixing postemergence herbicides and fungicides for control of broadleaf weeds and diseases in a single pass across the field.

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Mary Hausbeck...Downy mildew was confirmed on June 9 on slicing cucumbers in Monroe County. Currently, there are two 8- to 10-acre fields with advanced disease. These two fields were planted in late April by direct seeding and plugs grown in an on-site greenhouse. At this time, there is no visible disease on nearby cantaloupe plantings. Other cucumbers in the Southeast area are only recently emerged and are not diseased.

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Beth Bishop...Large numbers of adult striped cucumber beetles have been reported feeding on young vine crops. The mild winter plus the recent heat and moisture have resulted in a high population of overwintered beetles. Cucumber beetles can severely damage or kill young plants. They also transmit bacterial wilt disease through their feeding. Cucumbers, melons, processing pumpkins, butternut squash and hubbard squash are susceptible to bacterial wilt.

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Mathieu Ngouajio and Guangyao Wang...Records as early as 1927 show Michigan as the leader in United States pickling cucumber production. In 2005, Michigan pickle production was valued at over $35 million. Michigan’s dominance in the pickle industry is the result of many factors, including use of high quality seed, good agronomic practices, and mechanical harvesting. Once over mechanical harvesting is without a doubt the single most important factor that improved pickling cucumber production in Michigan.

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