Cause A fungus, Stagonosporopsis caricae (syns. Stagonosporopsis citrulli, Stagonosporopsis cucurbitacearum, Didymella bryoniae, Phoma cucurbitacearum), which overwinters in associaton with infected crop debris for at least two years. This fungus can also be seedborne. Numerous other cucurbits are affected, including cantaloupe, watermelon, cucumber, and pumpkin. A small wound on the fruit, such as a fingernail scratch, is sufficient to allow an entry for the fungus and subsequent disease development. This disease can affect all parts of the plant. Pseudothecia develop on crop debris and produce ascospores which can move on wind currents to susceptible cucurbits. After initial infection, this fungus will produce conidia in pycnidia in the centers of lesions and these asexual spores are disseminated by splashing water such as rainfall or overhead irrigation. The disease is promoted by warm, humid conditions with 68°F to 75°F being optimum temperature range. The fungus will not grow below 50°F.
Symptoms On leaves, brown to black circular spots generally associated with the leaf margins progress toward the center of the leaf. Stem infections can girdle the plant. On fruit, the fungus causes circular water-soaked spots which expand and may take on a black, leathery appearance. Regardless of where the lesion occurs, a gummy exudate is usually in the center of diseased spots. The spot becomes covered with white mycelium and tiny black fungal fruiting structures (pycnidia and pseudothecia) when under a higher relative humidity.
Cultural control
- Use pathogen-free seed.
- Rotating out of cucurbits at least 2 years is the best control.
- Avoid injuring fruit during harvest.
- Store only perfectly healthy fruit.
- After harvest, cure squash 2 weeks at 75°F to 85°F.
- Store squash slightly below 50°F if possible.
- Avoid overhead irrigation when possible.
Chemical control
- Carboxamide (Group 7) formulations are registered for use. Do not make more than two (2) sequential applications before alternating to a labeled fungicide with a different mode of action.
- Endura at 6.5 oz/A on 7- to 14-day intervals. Preharvest interval is 0 days. 12-hr reentry.
- Fontelis at 12 to 16 fl oz/A on 7- to 14-day intervals. Preharvest interval is 1 day. 12-hr reentry.
- Chlorothalonil formulations (Group M5) are labeled.
- Bonide Fung-onil is available for home gardens. H
- Bravo Ultrex at 1.8 to 2.7 lb/A. May apply through sprinklers. 12-hr reentry.
- Echo 720 at 2 to 3 pints/A on 7-day intervals. Preharvest interval is 0 days. 12-hr reentry.
- Copper products (Group M1) are not recommended as stand-alone materials.
- Badge SC at 0.5 to 2.5 pints/A on 5- to 7-day intervals. Preharvest interval is 0 days. 24-hr reentry for greenhouse use; 48-hr reentry for all other applications.
- Bonide Liquid Copper is available for home gardens. H
- Cuprofix Ultra 40 Disperss at 1.25 to 2 lb/A on 5- to 7-day intervals. 48-hr reentry.
- Kocide 2000 at 1 to 2.25 lb/A or Kocide 3000 at 0.5 to 1.25 lb/A on 5- to 7-day intervals. 48-hr reentry. O
- Previsto at 0.75 to 2 quarts/A on 5- to 7-day intervals. 48-hr reentry. O
- Demethylation-inhibiting (DMI) fungicides (Group 3) are registered for use. Alternate or tank-mix with a non-Group 3 fungicide for resistance management.
- Proline at 5.7 fl oz/A on 5- to 10-day intervals. Preharvest interval is 7 days. 12-hr reentry.
- Rhyme at 5 to 7 fl oz/A on 7- to 14-day intervals. Preharvest interval is 0 days. 12-hr reentry.
- Topguard at 10 to 14 fl oz/A on 7-day intervals. Preharvest interval is 0 days. 12-hr reentry.
- Omega 500F (Group 29) at 12 to 24 fl oz/A on a 7- to 10-day interval. Applications should be directed to provide coverage of the lower stem area. Preharvest interval is 7 days. 12-hr reentry.
- OSO 5% SC (Group 19) at 6.5 to 13 fl oz/A on 7- to 14-day intervals. Can be applied the day of harvest. 4-hr reentry. O
- Regalia (Group P5) at 1 to 4 quarts/A plus another fungicide on 7- to 10-day intervals. Does not benefit from the addition of an adjuvant. Preharvest interval is 0 days. 4-hr reentry. O
- Strobilurin fungicides (Group 11) are labeled for use. 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.
- Cabrio EG at 12 to 16 oz/A on 7- to 14-day intervals. Preharvest interval is 0 days. 12-hr reentry.
- Evito 480 SC at 3.0 to 5.7 fl oz/A. Preharvest interval is 1 day. 12-hr reentry.
- Quadris Flowable at 11 to 15.5 fl oz/A on 10- to 14-day intervals. Do not apply within 1 day of harvest. 4-hr reentry.
- Topsin M 70 WP (Group 1) at 0.5 lb/A on 7- to 14-day intervals. May be applied through sprinkler irrigation lines according to label directions. 12-hr reentry.
Note: Premixes of fungicides are available and offer ease for fungicide resistance management. 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; for other fungicide groups apply no more than two (2) sequential applications alternating with another fungicide with a different mode of action.
- Aprovia Top (Group 7 + 3) at 10.5 to 13.5 fl oz/A on 7 to 14-day intervals. May be applied the day of harvest. 12-hr reentry.
- Dexter Max (Group M3 + 11) at 2.1 to 3.2 lb/A on 7- to 10-day intervals. 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. Preharvest interval is 7 days. 24-hr reentry.
- Inspire Super (Group 3 + 9) at 16 to 20 fl oz/A on 7- to 10-day intervals. Preharvest interval is 7 days. 12-hr reentry.
- ManKocide (Group M1 + M3) at 2 to 3 lb/A on 7- to 10- day intervals. Under moderate to severe disease pressure use the higher rate on 5- to 7-day intervals. Do not apply within 5 days of harvest. 48-hr reentry.
- Merivon Xemium (Group 11 + 7) at 5.5 fl oz/A on 7- to 14-day intervals. Preharvest interval is 0 days. 12-hr reentry.
- Miravis Prime (Group 7 + 12) at 9.2 to 11.4 fl oz/A on 7- to 14- day intervals. 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.
- Pristine (Group 7 + 11) at 12.5 to 18.5 oz/A on 7- to 14-day intervals. Preharvest interval is 0 days. 12-hr reentry.
- Quadris Opti (Group 11 + M5) at 3.2 pints/A or Quadris Top (Group 11 + 3) at 10 to 14 fl oz/A. Preharvest interval is 1 day. 12-hr reentry.
- Switch 62.5WG (Group 9 + 12) at 11 to 14 oz/A on 7- to 10-day intervals. Do not apply within 1 day of harvest. 12-hr reentry.
Biological control
- Double Nickel LC at 1 to 6 quarts/A on 3- to 10-day intervals. Can be applied the day of harvest. 4-hr reentry. O
- LifeGard WG at 1 to 4.5 oz/A on 7- to 14-day intervals for activating plant resistance. Refer to label for appropriate rate per application volume. Preharvest interval is 0 days. 4-hr reentry. O