Late blight came in with a vengeance last summer. It caused severe tomato and potato losses, hitting home gardeners and organic farmers and larger commercial growers.

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Mary Hausbeck and Brian Cortright...Fusarium and Phytophthora effects on asparagus production Fusarium species and Phytophthora species can attack and kill asparagus crowns in both nursery and commercial fields. Both of these pathogens can be introduced early in the crown’s life as small infections on either the crown or roots. Over a period of growing seasons and under the right weather conditions, heavy rainfall or drought, these early infections can spread to healthy parts of the crown and start the process of crown death.

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Willie Kirk...After visiting several smaller acreage tomato growers in western Mecosta County last week, it became clear that the 2009 epidemic of late blight was extraordinary. All fields visited had late blight. The symptoms ranged from about 5 percent of the foliage and 1 percent of the fruits to 100 percent of the foliage and fruits infected. Clearly, this epidemic was beyond the experience of any of these growers who were largely stunned and certainly one of the worst I had ever experienced.

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^{By Mary Hausbeck... In the past week, downy mildew has been found on cucumbers in four new counties, Montcalm, Huron, Oceana and Newago.}

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By Jen Foster and Mary Hausbeck... The roots, crowns, stems, leaves and fruits of peppers can all be infected by Phytophthora capsici. This pathogen is favored by rain and warm temperatures and spreads readily via water.

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Martin Chilvers, Janette Jacobs, Ray Hammerschmidt and Jan Byrne... Now that flowering has begun and canopies are beginning to close, soybeans will be at risk to white mold. White mold is caused by the fungus Sclerotinia sclerotiorum. The fungus overwinters in crop debris or soil as sclerotia with an appearance similar to mouse droppings.

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By Mary Hausbeck... Downy mildew on cucumbers has been found in several counties across the state this week. In general, the number of plants infected has been low, but given the continued cool, wet weather, it will not take long for the disease to spread and cause rapid blighting and plant death.

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By Mary Hausbeck... Weather conditions this spring and summer have been very favorable for onion downy mildew and several fields both on the west and east sides of the state are now infected.

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By Willie Kirk... Potato late blight was reported and has been confirmed in St. Joseph County in three fields near Sturgis, Michigan. With the thunderstorms and heavy rains that have swept across the state in recent days, it is important to be extra vigilant when scouting fields for late blight.

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Mary Hausbeck...Downy mildew has been confirmed in three Michigan counties over the last 48 hours. They include Monroe, Saginaw and Tuscola. The Monroe sample came from a homeowner’s garden while the other samples are from commercial growers. All of the samples are from cucumbers. The spore counts across the state continue to indicate that the cucumber growing areas are being exposed to airborne downy mildew sporangia. As recommended earlier, all cucumber growers in the state should be spraying for downy mildew.

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By Mary Hausbeck... Michigan pickle and cucurbit growers have battled downy mildew, incited by the water mold, Pseudoperonospora cubensis, for four consecutive years. Downy mildew causes symptoms on the leaves of vine crops (such as cucumber, squash, and melon) similar to a mosaic or angular leaf spot.

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By Mary Hausbeck... Spore trapping in Michigan began last week and a high number of downy mildew sporangia have been picked up in Monroe County (http://plantpathology.msu.edu/labs/hausbeck/Research/2009DMSporetraptotals.pdf).

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Bernard Zandstra...The Michigan Department of Agriculture has approved a Section 24c label (SLN) for use of GoalTender postemergence on broccoli, cabbage and cauliflower. The label currently is in effect and EPA has 90 days to withdraw the label. Assuming the label is approved, it will be in effect for five years.

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Mary Hausbeck...Based on the disease outbreaks that we are seeing, I could swear that it is the middle of August. The wet weather early on in the growing season coupled with some warm nights has set us up for trouble on several fronts. I fully anticipate that this season will be tough on growers who are trying to rein in spots, blights, mildews and rots.

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 Mary Hausbeck...Several diseases limit asparagus production. Phytophthora spear and root rot is favored by excessive rainfall and poor soil drainage. The disease results in soft, water-soaked lesions and shriveling on shoots and roots, curving of spears, and loss of root mass and vigor. The rains received in many regions of the state during the last week are comparable to those of 2004. In the spring of 2004, after excessive rainfall during spear harvest, a spear and root rot was observed in several asparagus fields in Oceana, Ingham and Van Buren counties.

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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 and H. Rogers...Phytophthora capsici attacks both bell and hot peppers in Michigan (view images). This devastating dis­ease can wipe out entire pepper fields, caus­ing enormous losses in yield and profit. Be­cause of the destructive nature of Phy­tophthora, researchers at Michigan State Uni­versity are dedicated to the knowledge and management of this disease.

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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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Mary Hausbeck...Downy mildew was confirmed on cucumber in a third Michigan county, Lenawee, on July 17 (see map). Fungicide recommendations continue to be as follows:

• Fungicides should be applied to cucumbers every FIVE to SEVEN days.
• Fungicides should be applied to pumpkins, melons, cantaloupes, squash, zucchini and gourds every SEVEN to TEN days.

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Dr. Mary Hausbeck...Downy mildew was confirmed on cucumber in Gratiot County on July 9.  Fungicide recommendations are summarized here:

Fungicides should be applied to cucumbers every FIVE (5) to SEVEN (7) days.

Fungicides should be applied to pumpkins, melons, cantaloupes, squash, zucchini and gourds every SEVEN (7) to TEN (10) days.

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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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Phill Wharton & Willie Kirk...Seven new high resolution potato diseases extension bulletins are now available for purchase at http://www.emdc.msue.msu.edu/ for $1.50 each. The new group of publications includes the recent potato late blight bulletin and bulletins on early blight, pink rot, Fusarium dry rot, Rhizoctonia diseases, potato common scab, white mold and seed piece management. For more information, call 517-353-6740. You can also download these bulletins from this web page http://www.potatodiseases.org/extensionpubs.html as PDF files from our late blight website.

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Beth Bishop...Stewart’s wilt symptoms have been found in a sweet corn field in southwest Michigan. Stewart’s wilt is a bacterial disease that is harbored inside of and spread by the corn flea beetle (view photos). Michigan winters are hard on corn flea beetles, and the overwintering survival of the beetle (and the disease) depends on how severe the winter. We predicted higher than normal Stewart’s wilt infestation this year based on both winter temperatures and a high prevalence of Stewart’s wilt symptoms in field corn last fall (see Vegetable CAT Alert article from April 18, 2007).

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Mary Hausbeck...Damping-off (caused by Pythium spp., Phytophthora spp. and Rhizoctonia sp.) affects all vegetable seedlings and is also common among flowering bedding plants. Damping-off results in collapse of the plant at the soil surface. To prevent damping-off, avoid over watering because some fungi that cause damping-off prefer wet conditions.

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Mary Hausbeck...The updated table of daily spore counts in Michigan can be found here. Monroe County is the only site currently being monitored. Please see the updated county map of confirmed downy mildew reports.

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Catarina Saude and Mary Hausbeck...As growers of processing carrots prepare for harvest, problems on the roots may become evident. Last year, a survey was conducted to determine which diseases Michigan carrot growers may face. Pictures and descriptions of the problems found in Michigan fields are included with this article.

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Mary Hausbeck...Downy mildew continues to be a struggle for growers of pickling cucumbers. This crop is particularly sensitive to this disease. Now that the disease is widespread within the state, stretching the interval between fungicide sprays beyond five days will not work for extra-sensitive crops such as pickling cucumbers or slicing cucumbers. (view pdf1 and pdf2)

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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...Phytophthora is a problem this year for pepper and cucurbit growers. The heavy rains experienced in some areas of the state are certain to cause a rapid increase in disease in fields that were showing early symptoms.

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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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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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Mary Hausbeck...The threat of downy mildew continues to drive the spray recommendations. Last Friday, the North Carolina State University Cucurbit Downy Mildew Forecast issued the following prediction for southeast Michigan:

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Amanda Gevens and Mary Hausbeck...Downy mildew causes symptoms on leaves that include angular yellow lesions and brown, dead leaf areas (Figure 1). The tell-tale symptom of downy mildew is the dark, purplish/gray fuzz on the underside of the leaf, giving a somewhat “dirty” or “velvety” appearance (Figure 1). This fuzz, which is the accumulation of spores, may be most evident in the morning. Leaves of all ages can become infected, including cotyledons.

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Mary Hausbeck...It has been a relatively quiet week with no new cases of downy mildew found. The two cucumber fields with downy mildew have not been destroyed and will likely be in production for the next four weeks. We are working to determine the threat that these fields pose to the cucumber and cantaloupe producers in the state. The diseased fields have been under an intensive fungicide program to keep the downy mildew limited.

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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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Mary Hausbeck...Purple spot on asparagus spears, caused by the fungus Stemphylium vesicarium, is present in many fields this year. During epidemic years spotting can occur on 60 to 90 percent of the spears and may result in rejection of the crop, especially for fresh-market sales. Spots also occur on the asparagus ferns, affecting the main stem, secondary branches and needles (cladophylls). Severe infection of the fern can result in premature defoliation of the plant. Increase in the severity of purple spot disease is associated with extended periods of rainfall, fog or dew.

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Mary Hausbeck...The recent overcast and humid conditions are very favorable for Botrytis development on vegetable transplants being held in the greenhouse. Do not wait for this gray mold to develop. It is better to be proactive with cultural and fungicide applications to prevent this disease from becoming established.

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Mary Hausbeck...Disease prevention and prompt diagnosis are key components in vegetable seedling production because there are relatively few fungicides registered for controlling diseases on these crops (see Table 1).

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