2026 Cucurbit Downy Mildew Updates
Figure 1. Symptoms and signs of downy mildew on the upper and lower leaf surfaces of cucumber. Photo: Jennie Mazzone, Penn State
September 23, 2026 Update
Cucurbit downy mildew activity remains unchanged from the September 9 update, with both clades present on the same cucurbit crops in the same states previously reported, including Pennsylvania. This is the final cucurbit downy mildew update of the 2026 growing season.
September 9, 2026 Update
A new report of cucurbit downy mildew on butternut squash has been confirmed in Lancaster County, Pennsylvania. Along with the earlier report on cucumber, this indicates that both pathogen clades are present in the state, and all vine crops are at risk for downy mildew. Continue managing for downy mildew.
September 1, 2026 Update
Cucurbit downy mildew continues to spread throughout the region on cucumber, with new reports in New York and Ontario. These along with recent reports from Pennsylvania (cucumber), Ohio (watermelon and cucumber), and New Jersey (cucumber and squash), highlight the need for all cucurbit growers to be using fungicides with strong activity against downy mildew as part of their management program (see recommendations below).
August 26, 2026 Update
Cucurbit downy mildew was found in Pennsylvania on cucumber in a Lancaster county sentinel plot on August 24. This is the first report of the disease in Pennsylvania this season. Nearby in Ohio, a new downy mildew report was made on watermelon. A recent report on cucumber and butternut squash was made in southern New Jersey, although it does not yet appear on the cucurbit downy mildew ipmPIPE map. Together, these detections indicate that both cucurbit downy mildew clades are present in the region. All Pennsylvania cucurbit growers should be including products with strong activity against downy mildew in their disease management program at this time (see recommendations below).
August 18, 2026 Update
New reports of clade 2 cucurbit downy mildew have been confirmed in two Michigan counties on cucumber. Conditions continue to favor the movement of downy mildew spores into Pennsylvania. Continue using products with strong activity against downy mildew in your disease management program for cucumber and cantaloupe (see details in management below). Of the available options, Orondis Opti and Ranman have demonstrated the strongest activity against cucurbit downy mildew in Michigan State University research trials.
August 12, 2026 Update
A new report of cucurbit downy mildew has been confirmed in Ohio. The outbreak was reported on August 11 on cucumber in Fulton County. Additionally, the existing cucumber downy mildew outbreak in North Carolina has expanded, with new reports confirmed in Edgecombe and Wilson counties.
Current storm systems are expected to facilitate further spread of the pathogen across the region. Pennsylvania growers should include products with strong activity against downy mildew in their fungicide program, especially in cucumber and cantaloupe.
August 5, 2026 Update
Cucurbit downy mildew is now present in Indiana, Tennessee, North Carolina, Georgia, and Florida. The newest reports are from commercial cucumber in Indiana on July 23rd, and squash and cucumber plantings in Tennessee on July 20th. For Pennsylvania growers, this update serves as a reminder to intensify scouting, especially in cucumber and cantaloupe, and ensure fungicide programs include products with strong activity against downy mildew (see management recommendations below).
The good news is, these observations have occurred later in the growing season compared to recent years. Researchers believe the delay was driven by unusually dry conditions and high temperatures earlier in the season in the Southeast, where the disease typically originates, and across parts of the Midwest. Recent cooler temperatures, rainfall, and higher humidity are expected to favor disease development and movement northward.
July 29, 2026 Update
Cucurbit downy mildew was confirmed in North Carolina on July 20 from a commercial cucumber field in Lenoir County. Cucumbers are primarily infected by clade 2 of the downy mildew pathogen population, which infects cucumber and cantaloupe. Pennsylvania cucumber and cantaloupe growers should increase scouting efforts immediately and ensure fungicide programs include products with strong activity against downy mildew (see management recommendations below).
Recent weather conditions across the region, including frequent rainfall and storm activity, may favor disease development and long-distance pathogen movement. Downy mildew spores are readily dispersed by wind currents and can travel more than 600 miles within 48 hours, placing Pennsylvania cucurbit crops at risk.
Growers should monitor cucurbit plantings closely for symptoms and signs of downy mildew and contact their local Extension Educator immediately if the disease is suspected. The Penn State Plant Disease Clinic also accepts plant samples for diagnostic confirmation. Early detection and reporting are critical for tracking disease movement and providing timely management information to growers across the region.
July 14, 2026 Update
No new reports of cucurbit downy mildew have been documented since the June 30 update. The next update will be July 29.
June 30, 2026 Update
New reports of cucurbit downy mildew have been confirmed in four counties in Georgia. All reported cases involve cucumber, and three of the four counties have also reported infections on cantaloupe. These Georgia outbreaks began in early June. There is still no report of cucurbit downy mildew in Pennsylvania or neighboring states, but growers should continue scouting and be prepared to implement management.
June 24, 2026 Update
No new reports of cucurbit downy mildew have been documented since the June 17 update.
June 17, 2026 Update
There is still no report of cucurbit downy mildew in Pennsylvania or neighboring states. However, details on the cucurbit downy mildew outbreak in Florida are now available through the Cucurbit Downy Mildew IPM PIPE monitoring system. Downy mildew has been reported in three Florida counties on cucumber and watermelon, crops that are susceptible to both clades of the pathogen, with initial detections occurring as early as May 4, 2026.
Michigan State University continues to detect clade 2 spores through air samples, but no downy mildew disease has been reported on actual cucurbit plants in Michigan. Growers are encouraged to continue scouting fields.
June 10, 2026 Update
Cucurbit downy mildew has been reported in Florida, though the full extent of the outbreak remains unknown. Airborne spores have been detected in several Michigan counties; however, no confirmed infections have been observed on plants there or in nearby production regions. These detections serve as an early warning, indicating that disease could develop if favorable conditions occur. Growers are encouraged to regularly scout fields, especially cucumbers and cantaloupes, and be prepared to implement management strategies if needed.
June 3, 2026 Update
A recent article from Michigan State University reported cucurbit downy mildew outbreaks in Florida fields. This information was obtained through communication with vegetable pathologists at the University of Florida, but has not yet been posted to the Cucurbit Downy Mildew IPM PIPE monitoring website, so details on the extent of the outbreak and the specific cucurbit hosts affected are currently unknown.
Additionally, Michigan State University has detected cucurbit downy mildew spores from air samples collected from four Michigan counties between May 19 and May 26. The spores were identified as clade 2, which affects cucumber and cantaloupe. According to Michigan State, these spores “may have originated from local or regional cucumber production greenhouses or from early field plantings of cucumbers and melons grown in low or high tunnels.”
It is important to note that the detection of cucurbit downy mildew spores in air samples does not confirm the presence of the disease in the field. However, it serves as an early warning that disease development may occur within days to weeks, depending on environmental conditions. The pathogen favors cool, wet weather.
If downy mildew develops on cucurbits in Michigan or neighboring states, fungicide applications are recommended to protect susceptible crops.
At this time, growers are encouraged to regularly scout cucurbit plantings, particularly cucumbers and cantaloupes grown in low or high tunnels.
May 27, 2026 Update
There are no reports of cucurbit downy mildew in the United States at this time.
Cucurbit Downy Mildew
Cucurbit downy mildew is a fast‑moving, destructive vine crop disease that does not overwinter in Pennsylvania and arrives annually by wind‑spread spores from the south. Penn State Extension monitors the disease each year and reports its movement so that growers can protect their crops when it approaches. Updates for the 2026 season will be posted on this webpage as the disease is detected and moves into the region. Penn State's efforts are part of the Cucurbit Downy Mildew IPM PIPE monitoring system, which tracks confirmed reports across the United States to help predict disease movement and risk nationwide.
There are two types of the cucurbit downy mildew pathogen: clade 1, which primarily infects watermelon, pumpkin, and squash, and clade 2, which primarily infects cucumber and cantaloupe. Cucurbit downy mildew causes pale green, yellow, or light brown spots on the upper leaf surface and signs of gray-brown to purplish sporulation on the underside of the leaf (Figure 1). Growers who suspect cucurbit downy mildew should contact their nearby Penn State Extension Educator or submit a plant sample to the Penn State Plant Disease Clinic. See our Call for Cucurbit Downy Mildew article for additional information on the disease, reporting, and monitoring efforts.
Cucurbit Downy Mildew Management
Use tolerant or resistant cultivars when available and begin fungicide applications preventively when the strain affecting your crop is nearby. Applications made before infection are far more effective than those made after symptoms are observed in the field. Rotate materials with different modes of action (FRAC codes) and include a protectant fungicide (e.g. chlorothalonil or mancozeb) in each spray to reduce resistance pressure and manage other diseases like anthracnose and plectosporium blight. Recommended fungicides include Orondis Opti (FRAC 49 + M05), Ranman (FRAC 21), Elumin (FRAC 22), and Zampro (FRAC 40 + 45). Refer to the 2026-27 Mid-Atlantic Commercial Vegetable Production Recommendations for a complete list of crop-specific fungicide recommendations.
Please email Jennie Mazzone at jrd5407@psu.edu if you have any questions.
