Look for Phytophthora disease on summer squash and zucchini now

Recent rains favor the spread this disease, so act now to protect your crop.

In 2010, Michigan producers grew over 75,000 acres of vegetables that are susceptible to Phytophthora capsici, including cucumber, zucchini, summer and winter squash, watermelon, cantaloupe, pumpkin, pepper, eggplant, tomato, and succulent bean. The pathogen may overwinter in the soil and persist for many years (more than 10 years). Phytophthora capsici is favored by rain and warm temperatures and spreads readily via water. It has also been found in irrigation ponds and surface water sources.

Summer squash and zucchini are very susceptible to Phytophthora, and symptoms are usually visible on both the plant and fruit. Most often, the first noticeable sign of Phytophthora is water-soaking of the crown and roots that are black or brown in color. The plant appears wilted and the roots water-soaked. Symptoms on the fruit include dark, water-soaked lesions and a white, “powdered sugar” layer of spores.

It is possible to harvest infected fruit that looks healthy, but this fruit may deteriorate in transit or on grocers’ shelves. This can happen because symptoms can take several days to appear on fruits once infection has occurred. A sure way to avoid a disease outbreak is to take preventive measures before a problem occurs. Do not plant crops susceptible to Phytophthora in a field with a history of the disease.

The best method for preventing disease is to scout fields early and often, especially during periods of wet and warm temperatures. If Phytophthora is spotted in the field, remove the diseased plants and the healthy-looking plants that border the diseased area. Never dump diseased fruits back into a production field. Remember to clean all equipment. Summer squash and zucchini are very susceptible to Phytophthora, and symptoms are usually visible on both the plant and fruit. Most often, the first noticeable sign of Phytophthora is water-soaking of the crown and roots that are black or brown in color. The plant appears wilted and the roots appear water-logged. Symptoms on the fruit include dark, water-soaked lesions and a white, “powdered sugar” layer of spores.

A sure way to avoid a disease outbreak is to take preventive measures before a problem occurs. Do not plant crops susceptible to Phytophthora in a field with a history of the disease. The best method for preventing disease is to scout fields early and often, especially during periods of wet and warm temperatures. If Phytophthora is seen in the field, remove the diseased plants and the healthy-looking plants that border the diseased area. Never dump diseased fruits back into a production field. Remember to clean all equipment that has been in the infested field before moving to another field.

Summer squash and zucchini should be planted into raised beds at least six inches in height whenever possible. It is extremely important to only plant in well-drained fields since Phytophthora is spread via water and drip irrigation is recommended.

Fungicides can help manage Phytophthora, and may need to be applied frequently when weather is wet and conducive to disease. Rotating fungicide chemistries is vital to avoid the development of resistance. There are several different chemicals registered for use on summer squash and zucchini. Some populations of Phytophthora have demonstrated resistance to mefenoxam (Ridomil Gold, Ultra Flourish) and thus, those products are no longer effective in some areas of Michigan.

Fumigants Telone C35, Sectagon-K54, Sectagon 42, and Vapam HL are all registered for use on squash to control Phytophthora. Please consult the fumigation bulletin for further information.

Remember that the pesticide label is the legal document on pesticide use. Read the label and follow all instructions closely. The use of a pesticide in a manner not consistent with the label can lead to the injury of crops, humans, animals, and the environment, and can also lead to civil or criminal fines and/or condemnation of the crop. Pesticides are good management tools for the control of pests on crops, but only when they are used in a safe, effective and prudent manner according to the label.

Summer squash
Water-soaking and white spores on summer squash.

Zucchini
Water-soaking and white spores on zucchini.

Summer squash water-soaked
Water-soaking of steams and immature fruit of summer squash.  

Summer squash wilted.
Wilting of infected summer squash.

Stand loss
Loss of plant stand due to Phytophthora infection.

Recognizing Phytophthora on Summer Squash and Zucchini

  • Wilted or dead plants
  • Water-soaked lesions on fruits, stems, and leaves
  • White, “powdered sugar” layer of spores on fruit

Management Strategies

  • Avoid using surface water for irrigation
  • Plant into well-drained, tiled fields
  • Include rotational crops
  • Use raised beds and drip irrigation
  • Irrigate sparingly
  • Powerwash equipment after it has been in infested fields
  • Remove any diseased plants and adjacent healthy plants
  • Apply fungicides preventively and at short intervals when needed
  • Do not dump diseased culls in production fields

Product

A.I.

Comment

Preferred Fungicides for SUMMER SQUASH and ZUCCHINI

Acrobat 50WP, Forum 4.18SC

dimethomorph

Gavel 75DF

mancozeb/zoxamide

Presidio 4SC

fluopicolide

tank mix with another fungicide

Revus 2.08SC

mandipropamid

include surfactant

Ridomil Gold MZ

mefenoxam/mancozeb

resistance concerns

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