From Meg McGrath, Long Island Horticultural Research & Extension Center, mtm3@cornell.edu:
There is now increased risk of this disease for cucumber and cantaloupe crops in western NY with symptoms being found in Elgin County, Ontario on 7/14. Another potential source of the pathogen for WNY is downy mildew in Wayne County, Ohio, which was reported on 7/13. The forecast for 7/18 was issued before the occurrence in Canada was reported, therefore the forecast does not include this potential source. Crops in WNY receiving rain on Monday may have also received CDM spores. The active ingredient in Curzate has some kickback activity (at most about 2 days) and thus is a fungicide to consider for crops that did not have a fungicide applied within 7 days before a high-risk forecast. Curzate needs to be applied as soon as possible to obtain kickback activity and should be followed about 5 days later with an application of any downy mildew fungicide because Curzate has limited residual activity.
Today the first occurrence of downy mildew on Long Island in 2022 was found. Early symptoms were seen at low incidence and severity in a cucumber crop on the North Fork being examined weekly through the Cornell Cooperative Extension of Suffolk County IPM Program.
As expected, downy mildew has now been reported on cantaloupe in the northeast: Delaware and Massachusetts on 7/19. The pathogen clade that infects cucumber also infects cantaloupe, but not squash and pumpkins.
Conditions have been favorable for downy mildew to continue developing in affected crops. While rain plays an important role in moving CDM spores from air currents on to crops, once this disease is developing in a crop, additional infections occur when humidity is high (> 85% RH) during nighttime, especially combined with dew.
For more information about CDM and its management see disease factsheets at the Cornell Vegetables website and previous News postings:
- Cucurbit downy mildew now in southeast New York and Connecticut July 11, 2022
- Cucurbit Downy Mildew already in New Jersey June 14, 2022