Phytophthora Foliar Blight and Fruit Rot of Pumpkins

M. Babadoost

Phytophthora foliar blight and fruit rot, caused by Phytophthora capsici, is one of the most serious threats to pumpkin production in Illinois. P. capsici was first described in1922 as the causal agent of blight of chili pepper in New Mexico. The pathogen was subsequently reported on more than 45 crops. Some of the major hosts of this pathogen are cucurbits (cucumbers, melons, pumpkins, squashes, watermelons, zucchinis), eggplants, peppers, and tomatoes. P. capsici can infect the host plant at any growth stage. It causes damping-off, leaf spot, foliar blight, and fruit rot. Under conducive environmental conditions, the yield losses could reach 100%. In the past four years, yield losses up to 100% caused by P. capsici occurred in commercial fileds of cucumber, eggplant, melon, pepper, pumpkin, watermelon, squash, and zucchinis, in Illinois.

P. capsici produces sporangia, zoospores, and oospores. Oospres have thick walls and are resilient. P. capsici survives as oospores and as mycelium in infested plant residue in the fields. Sporangia formed during the growing season release zoospores which are dispersed by irrigation or surface water. The pathogen spreads by soil, water, farm implement, animals, and wind. Wet condition is conducive for development of foliar blight and fruit rot.

No single control method is available for effectively controlling the diseases caused by P. capsici. A combination of measures should be practiced to reduce the damage caused by the pathogen on the crops. The most effective approach in controlling Phytophthora diseases on vegetables is to prevent the disease from becoming established. The following measures can help to manage Phytophthora diseases in cucurbit fields. 1. Select field with no history of Phytophthora. 2. Select field that had no cucurbits, eggplants, peppers, or tomatoes planted for at least 3 years. 3. Select field that are well isolated from infested fields. 4. Select well-drained field. 5. Clean farm equipment of soil between fields. 6. Avoid excessive irrigation. 7. Do not work in wet fields. 8. Do not leave cull fruit in the field. 9. Scout field for symptoms routinely, especially after major rain storms and particularly in low areas. 10. When symptoms are localized in a small area of the field, disk the area. 11. Discard infected fruits. 12. Do not place fruit on infested soil. 13. Plant resistant or tolerant varieties, if available. 14. Apply effective fungicides, when recommended. Seed-treatment with Apron XL LS and Allegiance FL is effective in preventing seedling death. Spray application of Acrobat 50WP plus a copper compound are effective against foliar blight and fruit rot of cucurbits, caused by P. capsici.