During the past month, Downy Mildew has spread to many areas of the northeast United States. New discoveries were reported in Long Island (cucumber and pumpkin) and four counties in CT (pumpkin, cucumber, summer squash). Other areas in this region are also likely infected. Regions with existing DM epidemics have also experienced increased disease presence. Northampton and Dinwiddie counties in southeast VA reported disease on cucumber and pumpkin, respectively. As of September 6, the number of Michigan counties with Downy Mildew stood at 28 (all new finds on cucumber) and that number has likely increased since then. In late August the Forecast Center received a report of DM in northeast SC in Williamsburg County. There are definite signs of revitalization of DM in the Southeast in the last 10 days. Infections on cucumbers were reported in southern SC (Pee Dee region and Colleton County) and Colquitt County, GA.
Downy Mildew continues to spread across the northern U.S. and southern Canada. The majority of counties in central and southern MI (20 in all) now have confirmed DM. The new counties are St. Joseph, Midland, Gratiot, Ottawa, Ingham, Van Buren, Cass, Macomb, Kent, Montcalm, and Wayne. Southern Ontario is being hit hard with significant losses. We have our first-ever report of downy mildew from Quebec, which arrived in early August. This outbreak occurred on cucumber, as have nearly all others, though some downy mildew has also been observed on cantaloupe in 4 counties in eastern Michigan (Tuscola and Macomb most recently on August 11 and 9, respectively). A broad expanse of cucumber between Rochester and Buffalo in western NY (centered around Genesee County) is being affected by downy mildew. The disease report that arrived today indicates that DM has been quite destructive and growers have been battling the disease for much of the growing season. To the south, several fields of cucumber in Henderson County, NC were reported to have DM around August 6. Cucumber plots at the Research Station in New Hanover County, NC (southeast portion of the state) also have downy mildew. Downy mildew was confirmed and reported in fields of pumpkin and winter squash in Hunterdon County, NJ on August 9, indicating epidemic spread in that region.
A number of new disease reports have come in to the Forecast Center since our last update. There are now 9 counties in southern and central MI reporting downy mildew, including Monroe (report on cantaloupe July 27), Lenawee (cucumber on July 19, cantaloupe July 27), Tuscola (cucumber July 24, winter squash July 27), Bay and Arenac (cucumber July 24), Allegan and Saginaw (July 25, cucumber), Lapeer (cucumber July 27), and Kalamazoo (cucumber July 28). Estimation of first symptoms is mid to late July for these outbreaks. Disease incidence varies and most outbreaks are considered serious. In northern Ohio, serious outbreaks of downy mildew on cucumber were reported July 27 in Ottawa and Sandusky counties. Multiple hand-harvest pickle fields are showing high incidence of disease which continues to spread. We have the first reports of DM from New Jersey (July 26) and New York (July 22). The NJ outbreak is occurring on pumpkin in Cumberland County in the southern sections of the state. The NY outbreak is in Erie County (far west, adjacent to Lake Erie) on cucumbers. Both the NJ and NY outbreaks were estimated to have first shown symptoms during late July.
We have several new disease reports this week ... one from Greene County in NC; another from Blissfield, MI close to the first reported source from Monroe County; our first report from Maryland at a research farm near Salisbury in Wicomico County; and a very large and serious infection on a 130 acre field in Kosciusko County in northern IN. All of these outbreaks are on cucumber. The IN source is being added to the forecasts. All the other locations are served by existing forecasts and will be included in the analysis and evaluations.
July 8: DM report from another field in Monroe County, MI. Lesions found on two leaves in a 35 acre field. July 10: Elgin County, southern Ontario. Three different fields of cucumber totaling about 30 acres are showing infection levels of about 10% to 20%. July 11: First report from DE in Kent County. 1% of an approximately 150 acre planting of cucumbers is showing symptoms. Disease severity is around 5%. July 12: Two reports of DM on cucumbers from northern OH in Huron and Seneca counties. A 15 acre field has about 20% incidence in Huron County; there is about 1% incidence in a 26 acre field in Seneca County. July 13: DM reported in a 2 acre research plot at Virginia Tech's Eastern Shore AREC near Painter, in Accomack County, VA. Incidence is running around 5% and severity is low.
July 5: DM reported in a 1/4 acre field of cucumber in Wayne County, OH. 65% of the field is infected. July 6: First report from NC in Sampson County. DM discovered in cucumber plants in a research plot, plants were located on the borders of a 2-3 acre field. Field is set to be disked within 10 days. July 7: Norfolk-Haldimand County in southern Ontario. A 3.5 acre field of cucumber is showing 50% infection. This field is 1/2 mile from the earlier discovery in Brant County. July 7: Six counties in NC have reported DM within the past week, all on cucumber, and all 6 counties (Greene, Wilson, Hyde, Nash, Edgecombe, Sampson, and Hertford) are in eastern NC. Disease incidence and severity vary. Other infections are suspected.
June 29: Downy mildew reported on cucumber in Brant County, southern Ontario, Canada. First symptoms probably occurred mid-June. 20 acre field with about 5% infected. Later update on July 4 indicates 30% infection in the 20 acre field. Disease may have begun in part from infected transplants, which were set from a greenhouse near June 1.
June 8: DM reported in a 2 acre field of summer squash in Decatur County, GA. 100% incidence. Field later disked and crop destroyed. June 9-12: Well-established infection of DM on cucumber reported in Monroe County, MI. Two 8-10 acre fields. June 15: Brooks County, GA on cucumber, involving one 88 acre field (75% infected) and other fields of 48 and 27 acres. Disease present for about two weeks. Fields disked under and replanted shortly after discovery.
An update to our 16 May report: The downy mildew outbreak referred to as Lake County on the 16th is actually in fields that straddle the Orange and Lake County line. Disease was first seen on or shortly before May 9, when harvesting began. Previous conditions had been extremely dry, but two weeks of morning fogs combined with recent rain has provided favorable conditions for disease development.
Downy mildew has been reported to be of moderate incidence on cantaloupe in Manatee County. Downy mildew is also occurring on cucumber in Lake County, northeast of the Manatee location. The Lake County source has been reported to be moderately serious.
Downy mildew has been reported to be moderately serious on cucumber approximately 50 miles East of Monterey, Mexico. Recent weather was reported to have been favorable for disease development in this area. Approximately 50% of the 40 acre field is infected. The date of first occurrence was reported on May 1.
The NAPDFC has received an update from the current southern FL source locations. In the Palm Beach County, FL source location, downy mildew continues to be widely present on cucumber and squash. The incidence and severity is moderate to high in some locations especially on cucumbers. Some growers report the disease activity is the worst they have ever seen.
Immokalee, FL reports that downy mildew remains present on cucumbers, cantaloupe, and squash. The disease is also beginning to appear on watermelon in this area.
The NAPDFC has received an update on the downy mildew occurrences in southern FL. Downy mildew remains widely present on cucumber and squash in a number of locations around Palm Beach. Incidence and severity is moderate to high in some locations especially on cucumbers.
The Immokalee area indicated downy mildew is present on cucumbers, cantaloupe and squash on a number of farms.
Reports from Homestead indicate low incidence of downy mildew on cucumber in the area.
Downy mildew reports from locations near Palm Beach, Immokalee, and Homestead, FL have been received. The disease is widely present on cucumber and squash in Palm Beach County with moderate to high severity especially on cucumbers. Near Immokalee, downy mildew is present on cucumbers, cantaloupe, and squash. Reports suggest that the disease continues to be less aggressive than last season in this area. Dade County (Homestead), FL indicate low incidence of downy mildew on cucumber.
Hendry County (Immokalee), FL reported downy mildew on cucumber. The estimated date of first occurrence was February 20. The report suggests the crop is still young and the spread has been slower than last season.