Cause The fungus, Cladosporium cucumerinum, which overwinters in cucurbit debris in soil, in greenhouse cracks and corners, and on seed. It can infect and severely injure fruit at all growth stages, particularly when young. Spores can travel long distances in moist air and can also be disseminated by insects, clothing, and tools. They penetrate the host less than 9 hours after germination; infection is visible in 3 days, and spores may be produced in 4 days.
Symptoms At first, a slightly water-soaked, paler-green area appears on foliage generally near or on veins. Spots usually are numerous. Gradually, they turn gray to white and become angular often with yellow margins. Fine veinlets in the spots may remain brown or tan and are distinct against the white background. Dead tissue cracks, breaking away until the whole leaf looks ragged.
Fruit exudes a sticky substance in drops, much as if from an insect puncture. Spots gradually turn gray, become slightly sunken, and enlarge to about 0.12 inch in diameter. The spot grows darker, and the tissue collapses further into the squash, forming a pronounced cavity lined with a dark green velvety layer of fungal spores.
Cultural control
- Rotate out of cucurbits 2 to 3 years.
- Plow under plant debris right after harvest.
- Thoroughly clean and disinfect greenhouses between crops.
Chemical control
- Aprovia Top (Group 7 + 3) at 10.5 to 13.5 fl oz/A on 7- to 14-day intervals. Do not make more than two (2) sequential applications before alternating to a labeled fungicide with a different mode of action. May be applied the day of harvest. 12-hr reentry.
- Bravo Ultrex (Group M5) at 1.8 to 2.7 lb/A. May be applied through sprinklers. 12-hr reentry.
- Dexter Max (Group M3 + 11) at 2.1 to 3.2 lb/A on 7- to 10-day intervals. Do not make more than one (1) application of a Group 11 fungicide before alternating to a labeled fungicide with a different mode of action. Preharvest interval is 5 days. 24-hr reentry.
- Dexter Xcel (Group M3 + 11 +3) at 72 fl oz/A on 7- to 10-day intervals. Do not make more than one (1) application of a Group 11 fungicide before alternating to a labeled fungicide with a different mode of action. Preharvest interval is 7 days. 24-hr reentry.
- Liqui-Cop (Group M1) at 2 to 3 teaspoons/gal water. H
- Miravis Prime (Group 7 + 12) at 9.2 to 11.4 fl oz/A on 7- to 14- day intervals. Do not apply more than two (2) sequential applications. Preharvest interval is 1 day. 12-hr reentry.
- Orondis Opti (Group M5 + 49) at 1.75 to 2.5 pints/A on 7- to 14-day intervals. Do not apply more than two (2) sequential applications. May be applied the day of harvest. 12-hr reentry.
- OSO 5% SC (Group 19) at 3.75 to 13 fl oz/A on 7- to 14-day intervals. Can be applied the day of harvest. 4-hr reentry. O