Department of Botany and Plant Pathology
Lilly Hall of Life Sciences
BP-18
Plant Disease Control

Recommendations for Cucumber, Muskmelon, and Watermelon Disease Control
Richard X. Latin, Extension Plant Pathologist

Cucumbers, muskmelons, and watermelons are threatened each year by a variety of infectious diseases. Proper control of these diseases involves modification of cultural practices, application of pesticides, and use of resistant cultivars. This publication describes recommended control measures for common diseases of these crops and is intended for use by commercial vegetable growers in Indiana.

Alternaria leaf blight (muskmelon): Apply protective fungicides (Table 1) beginning when vines touch within rows or at first sign of the disease. Rotation with other crops will significantly decrease the threat of Alternaria problems.

Angular leaf spot (cucumber and muskmelon): Apply copper bacteriacides (Table 1) at the first sign of disease. Alternate or tank mix with fungicides to maintain protection from other diseases. Several cucumber cultivars have resistance to angular leaf spot.

Anthracnose (cucumber, muskmelon, watermelon): Apply fungicides (Table 1) at the first sign of disease or when vines touch within rows. Fungicides which protect against Alternaria and gummy stem blight infection also will protect against anthracnose. Many cucumber cultivars are resistant to anthracnose. Rotation with non-cucurbit crops will decrease incidence of anthracnose.

Bacterial wilt (cucumber and muskmelon): Control of this disease depends on control of striped and spotted cucumber beetles. A systemic insecticide (Furadan) should be incorporated into soil before transplanting. Non-systemic insecticides such as Sevin, Pydrin, or Methoxychlor should be applied to seedlings before transplanting and then continued on a
regular basis after the systemic insecticide loses effectiveness (4-5 weeks). Control must be maintained throughout the season.

Damping off or Pythium (cucumber, muskmelon, watermelon): For damping off protection in greenhouses or coldframes, apply Ridomil 2E at 2 fl. oz./1350 sq. ft. before seedlings emerge. Irrigate lightly after application. A second application may be necessary for seedlings held for more than 4 weeks. Postemergence application at rates greater than 2 fl. oz./1350 sq. ft. may injure seedlings. For protection in field-seeded crops, apply Ridomil 2E at 2-4 pt./acre as a preplant broadcast spray in 50 gal. of water before or at time of seeding. Calibrate equipment accordingly for band applications over the row.

Seeds should be treated with captan or thiram (about 1/2 tsp./lb. seed) before planting. Most seed companies deliver pre-treated seed. Check the seed package to determine the kind of seed treatment used. If no treatment was applied, then treat seed with one of the fungicides mentioned above.

Downy mildew (cucumber, muskmelon, watermelon): Apply Ridomil MZ-58, a systemic fungicide, at the first sign of disease. Most fungicides that protect against Alternaria and gummy stem blight also provide some downy

Purdue University Cooperative Extension Service • West Lafayette, Indiana