Home Garden Disease Controls
The Pennsylvania State University
Cooperative Extension
Cucurbits: Cucumber, Muskmelon, Watermelon, Squash, and Pumpkin
How important are diseases on cucurbits?
Two diseases most frequently appear on cucurbits in Pennsylvania. These are bacterial wilt and powdery mildew. A few other diseases appear infrequently, but can be very severe at those times.
What diseases can affect cucurbits?
Listed below are seven groups of diseases that occur on various cucurbits. Symptoms are described briefly. Colored pictures of disease symptoms can be seen in the publication Identifying Diseases of Vegetables.
Bacterial Wilt
Plants wilt and die. Cucumber beetles transmit the disease. Presence of beetles and/or beetle chewing injury helps with diagnosis.
Control: Use hotcaps or other plant covers to keep beetles from chewing on young plants when they are most susceptible. Control cucumber beetles if the problem appears yearly.
Powdery Mildew
A white powdery growth develops on leaves and is heaviest on the lower leaf surface.
Control: When possible, grow varieties that are resistant to powdery mildew. Resistance is available for many cucumber varieties (see scab resistant varieties below) and some muskmelon varieties (All Star, Ambrosia, Athena, Cordele, Laguna, and Morning Dew). For susceptible muskmelons, squash and pumpkins, several fungicides are labeled for powdery mildew control, but application must start as soon as mildew first appears.
Viruses
Plants are stunted and new leaves are mottled and distorted.
Control: When possible, grow varieties that are resistant to specific viruses. Resistance is available for many cucumber varieties (see scab resistant varieties below) and some summer squash varieties (crookneck type includes Prelude II and Freedom III; straightneck type includes Liberator; and zucchini type includes Dividend, Jaguar, Revenue, and Tigress; the yellow fruited Multipik variety maintains the normal yellow color when infected but can be distorted).
Leaf Spots and Downy Mildew
Yellow to brown spots develop on leaves; crown leaves are affected first.
Control: Choose a sunny planting site. Avoid areas where vine crops were grown within 3 years. Where needed, several fungicides are labeled for use on cucurbit crops. Remove plants as soon as harvest is completed.
Scab
Dry dead spots, sometimes with wet or dried sap exudate, sometimes appear on cucumber fruit. On muskmelons, scab like spots on fruit may have a grayish-green mold within the scab area. On leaves, young leaves and young vine tissue appears to be most susceptible and is affected worst; when small affected leaves grow, the leaf tissue tears around the early leaf scab spots, thus producing a ragged leaf, with tears around some spots
Control: Follow controls suggested for leaf spots. For cucumbers, there are good scab resistant varieties including Raider, Speedway, Dasher II, Thunder, Turbo, Cyclone, and Marketmore 76; these varieties also are resistant to powdery mildew and cucumber mosaic virus (CMV).
Muskmelon Fusarium Wilt
An affected plant usually wilts; presence of a broad dark streak at the side of the stem near soil level, and absence of cucumber beetles, helps distinguish Fusarium wilt from bacterial wilt.
Control: Avoid areas where muskmelons were grown in recent years. Where possible, grow wilt resistant varieties such as Athena. Other varieties with resistance to only Race 2 include Eclipse, Market Star, Pulsar, Rising Star, Saticoy, and Superstar.
Fruit Rots on Pumpkin and Winter Squash
Dry rots and sometimes wet rots develop on the fruit surfaces.
Control: Choose a sunny planting site. Avoid areas where vine crops were grown within 3 years. Pumpkin varieties that appear to be least affected are Small Sugar, and Spooky followed by Jack-O-Lantern, Young's Beauty, Thomas Halloween, and Howden. Harvest fruit before vines are killed by frost. Keep pumpkins in a dry cool place before use. If necessary, fungicides used to control leaf spots may also help control fruit rots.
Note: Where trade names are used, no discrimination is intended
and no endorsement by the Cooperative Extension Service is implied.
Information provided is intended for consideration by the user, but is not
intended to be a recommendation. Production decisions should be based on
consideration of many types of information (scientific, experiential, economic,
legal, etc.) available to the user.
