By Cynthia M. Ocamb and Hannah Rivedal
Cause The common storage diseases of squash are Alternaria fruit rot (Alternaria cucumerina), black rot (Didymella bryoniae), Fusarium rot (many Fusarium spp. including F. solani f. sp. cucurbitae, the cause of crown and foot rot), scab (Cladosporium cucumerinum), and bacterial soft rot (Erwinia carotovora subsp. carotovora = Pectobacterium carotovorum subsp. carotovorum). These diseases can be in the field in the growing season or during postharvest handling and storage. Skin wounds after bruising are especially prone to decay. Clean wounds in squash often heal without decay. Bruises do not, especially if the skin breaks. Fusarium equiseti also penetrates cut stem ends and F. culmorum causes rot of the blossom end.
Chilling injury, whether from frost in the field or from improper storage or transit conditions after harvest, also can result in rots. All cucurbits have tropical ancestors and are physiologically disrupted at low temperatures. The freezing point of winter squashes average 29.3°F with maximum-minimum extremes of 29.5°F and 28.9°F. The longer the exposure and the lower the temperature, the greater the damage.
Symptoms Alternaria fruit rot-fruit decay is dry and tough on the surface but moist and spongy inside the squash.
Black rot-circular, water-soaked spots develop on the fruit surface. Lesions can have a drop of gummy exudate in the center. Later, under humid conditions, the spot becomes covered with white mycelium and the tiny black fungal fruiting structures (pycnidia and perithecia). Infected flesh is brown, soft, dry, and odorless.
Fusarium rot-there are a wide range of symptoms, from small pits, corky dry rot, or a colored, spongy rot ranging from grayish, whitish to pinkish, purplish, or reddish coloration that can occur in storage, often starting at the stem end, except for F. culmorum which is associated with rot of the blossom end.
Scab-lesions are dark and sunken, forming a cavity. A dark green, velvety layer can occur in the cavities.
Bacterial soft rot-flesh disintegrates into a soft mass. If the skin ruptures further, it releases infective juices and a foul odor.
Chilling injury-early symptoms include numerous water-soaked or sunken spots. Tissue has an increased tendency to fungal or bacterial decay. Symptoms may not develop until fruit is returned to higher temperature.
Cultural control Control lies in integrated disease control in the field and very careful handling, good curing, and right storage environment.
- Rotate out of squash and other cucurbits for 4 years.
- Avoid fields with a history of severe disease and avoid moving soil with pathogen propagules from infested fields to other fields.
- Use laboratory-tested pathogen-free seed, which will help prevent introduction of pathogen into new fields.
- Select fields with good water drainage and avoid over-irrigation.
- Dry-land or water-limited production has shown a reduction in overall storage rot in squash.
- Avoid the injury of fruit during harvest, packing, and transport.
- Before frosts, take all marketable mature and immature squash from the field.
- Do not cure winter squash in the field. Move promptly from field to curing room.
- Remove stems completely to prevent stem-end infections.
- Handle squash with care to avoid wounds and bruises during harvest, packing, and transport.
- Remove and destroy all infected or damaged fruit before storage.
- Dry squash thoroughly for 2 weeks with circulating air at 80°F to 85°F. However, temperatures higher than 65°F may increase pink rot.
- Store squash at 50°F to 55°F and at 70°F to 75% relative humidity. Do not store winter squash long below 50°F. Hard-shelled squash such as Hubbard can be stored up to 6 months if properly handled and cured.
Chemical control Preventative sprays are recommended for preventing fruit rot pathogens from causing disease on foliage, which can then aid in reducing some fruit rot problems when integrated with the cultural controls above.
- Bravo Ultrex (Group M5) at 1.8 to 2.7 lb/A. May be applied through sprinklers. 12-hr reentry.
- Copper products are not recommended as stand-alone materials.
- Cueva at 0.5 to 2 gal/100 gal water on 7- to 10-day intervals. May be applied on the day of harvest. 4-hr reentry. O
- 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
- Liqui-Cop at 2 to 3 teaspoons/gal water. H
- Endura (Group 7) at 6.5 oz/A on 7- to 14-day intervals; alternating with another appropriate fungicide. To limit the potential for development of resistance, do not make more than four (4) applications of Endura per season. The preharvest interval is 0 day. 12-hr reentry.
- JMS Stylet Oil at 3 to 6 quarts/100 gal water. Effectiveness is unknown in the Pacific Northwest when used alone. Do not spray if temperature is below 50°F or above 90°F, when plants are wet, or under heat or moisture stress. 4-hr reentry. O
- 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.
- Orius 3.6F (Group 3) at 4 to 6 fl oz/A on 10- to 14-day intervals. Do not apply within 7 days of harvest. 12-hr reentry.
- 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. Preharvest interval is 0 days. 12-hr reentry.
- Pristine at 12.5 to 18.5 oz/A. Preharvest interval is 0 days. 12-hr reentry.
- Quadris Flowable at 11 to 15.5 fl oz/A. Do not apply within 1 day of harvest. 4-hr reentry.
- Quadris Opti at 3.2 pints/A or Quadris Top at 12 to 14 fl oz/A. Preharvest interval is 1 day. 12-hr reentry.
- Reason 500 SC at 5.5 fl oz/A. Do not apply within 14 days of harvest. 12-hr reentry.
- Trilogy at 0.5% to 1%. Not labeled for use in Oregon. Do not use above 90°F or when plants are under heat or moisture stress. Do not use when foliage is wet as good coverage is essential. Poor control as a stand-alone product. 4-hr reentry. O
References Babadoost, M., and Zitter, T.A. 2009. Fruit rots of pumpkin: A serious threat to the pumpkin industry. Plant Disease 93:772-782.
Rivedal, H.M., Stone, A.G., and Johnson, K.B. 2018. First report of Fusarium culmorum causing fruit rot of winter squash (Cucurbita maxima) in Oregon. Plant Disease 102:2659.
Snowdon, A.L. 1992. Color Atlas of Post-Harvest Diseases and Disorders of Fruits and Vegetables, vol. 2. Boca Raton, FL: CRC Press.