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Agronomy Day 2008

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Major Fruit Rots of Cucurbits in Illinois

Mohammad Babadoost
Department of Crop Sciences
Phone: 217-333-1523; E-mail: babadoos@illinois.edu

There are 18 different preharvest and postharvest fruit rots identified in cucurbits. Only three of them, including Phytophthora rot, Fusarium rot, and bacterial spot/rot, commonly occur in Illinois.

Phytophthora Fruit Rot. Phytophthora fruit rot, caused by Phytophthora capsici, is a serious disease in all cucurbits. Fruit infection can occur from the time of fruit set until harvest, during transit, and in storage. Severe foliar blight and fruit rot often occurs during moist condition. A combination of cultural practices and fungicide applications are Fusarium fruit rot of curcurbits needed to reduce the damage caused by P. capsici on seedlings, vines, and fruits. No cucurbit variety with measurable resistance is available. The most effective approach is preventing the pathogen form being moved into the field. The following practices can help to manage P. capsici in cucurbit fields. 1) Select fields with no history of the plant infection with P. capsici. 2) Avoid excessive irrigation. 3) Practice 3 years of crop rotation with non-host crops. 4) Do not irrigate plants from a pond contaminated with P. capsici. 5) Apply effective fungicides, when recommended. Seed treatment with mefenoxam (Apron XL LS) effectively protects seedlings until five weeks after sowing seed. Mandipropamid (Revus), Dimethomorph (Acrobat or Forum), famoxadone + cymoxanil (Tanos), cyazofamid (Ranman), and mefenoxam (Ridomil Gold compounds) have been found effective against P. capsici.

Fusarium Fruit Rot. Fusarium rot is one of the important preharvest and postharvest diseases of cucurbit fruits. Fruits of all cucurbits are susceptible to one or more species of Fusarium. Infected areas of fruit are covered with white mold consisted of mycelium and conidia of the pathogen. Many of the fruit-rotting Fusarium species are reported to be seed-borne. Fusarium species can also survive as thick-walled spores (chlamydospores) in soil. Chemical control of Fusarium species has been ineffective. Planting pathogen-free seed is essential. Field with a history of Fusarium fruit rot should be avoided. Crop rotation of three years or longer with non-host crops is recommended. Avoidance of wounding of fruits during harvest and handling provide some protection against postharvest decay.

Bacterial fruit rot of pumpkin Bacterial Fruit Spot. Bacterial spot, caused by the bacterium Xanthomonas campestris pv. cucurbitae, is a serious disease of cucumbers, gourds, pumpkins, and squashes. Initial lesions are small, slightly sunken, circular spots, about 1/ Phytophthora fruit rot of curcurbit 16 inch in diameter, with a beige center and a dark- brown halo. Later the lesions enlarge, reaching up to 1/2 inch in diameter. On mature fruit, saprophytic fungi often colonize the dead, tan tissue at the center of the lesion. The bacterium is a seed-borne pathogen. Also, the bacteria can survive in association with infested crop residue. The most effective method for control of the disease is planting pathogen-free seed. Rotation with noncucurbit crops is effective in managing the disease. Application of copper compounds during early formation and expansion of fruit may result in substantial fewer symptomatic pumpkins. Copper spray, however, is ineffective once an epidemic is underway.

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