Use integrated management strategies with Phytophthora on peppers

Recent heavy rainfalls have increased the risk of Phytophthora on peppers.

July 29, 2011 - Author: Mary K. Hausbeck, Michigan State University Extension, Department of Plant Pathology

Historically, Michigan producers grow 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 is favored by rain and warm temperatures and spreads readily via water. It has also been found in irrigation ponds and surface water sources.

Infection by Phytophthora in pepper may occur days before any visible symptoms of disease appear. Initially, the pathogen may enter the roots or crowns with symptoms first appearing as water-soaked lesions that rapidly progress to cause stem girdling, plant wilting, and death (Photos 1 and 2). When infected, the fruits and leaves may also have water-soaked lesions (Photo 3), and occasionally a white, “powdered sugar” layer of spores appear (Photo 4).

Phytophthora in a banana pepper field
Photo 1. Phytophthora in a banana pepper field.

Foliar blight, fruit rot, and stem lesion
Photo 2. Foliar blight, fruit rot, and stem lesion symptoms.

Lesion on banana pepper
Photo 3. Water-soaked Phytophthora lesion on a banana pepper.

Spores on bell pepper
Photo 4. “Powdered sugar” Phytophthora spores on a bell pepper fruit.

Recognizing Phytophthora on Pepper
  • Plant wilting and death
  • Water-soaked or brown lesions on the stems and leaves
  • “Powdered sugar” layer of spores on fruits

Integrated management strategies are required to control Phytophthora in peppers. Fields should be scouted regularly for disease symptoms. Cultivar selection plays an important role in disease management and several bell peppers are available that provide tolerance or resistance, including ‘Aristotle,’ ‘Declaration,’ ‘Intruder,’ ‘Paladin,’ and ‘Revolution.’ Some have been associated with the fruit blemish “silvering” (Photo 5). The cultivar Paladin has demonstrated the highest level of resistance to a virulent strain of Phytophthora from Michigan. Currently, no commercially available hot or specialty pepper cultivars are resistant to Phytophthora. MSU research demonstrated that Phytophthora isolates may vary in virulence among pepper cultivars. This has great implications for growers because cultivars with demonstrated resistance in certain regions may not be resistant in their field.

Silvering fruit blemish
Photo 5. Silvering fruit blemish on the skin of a bell pepper.

Management Strategies
  • Avoid using surface water for irrigation
  • Plant into well-drained, tiled fields
  • Plant resistant/tolerant cultivars Include rotational crops
  • Use black plastic mulch in combination with raised beds and drip irrigation
  • Scout fields regularly for Phytophthora
  • 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

Peppers should not be planted in rotation with other susceptible crops like cucumber, melon, squash, pumpkin, zucchini, tomato, eggplant, or snap beans. In fresh market production, raised beds covered in black plastic mulch used in combination with drip irrigation can be used to reduce disease incidence. Overhead irrigation should be used sparingly and avoided if possible during fruiting.

Foliar applications of fungicides directed at the base of the pepper plant have offered only limited protection from crown rot. Apply foliar sprays using ample water volumes to achieve good coverage. Be sure to apply the fungicide before and after a period of rainfall expected to exceed 0.5 inches.

Some populations of Phytophthora have become resistant to the fungicide mefenoxam (Ridomil Gold and Ultra Flourish) in Michigan. Alternate products to reduce the risk of the Phytophthora pathogen developing resistance to a particular fungicide.

MSU research clearly demonstrates that even frequent applications of foliar fungicides to a susceptible cultivar may not adequately protect against crown and root rot. Susceptible ‘Red Knight’ and resistant ‘Paladin’ were inoculated with a particularly “hot” strain of Phytophthora. Fungicides were applied at seven-day intervals and included Acrobat, Forum, Kocide 2000, Presidio, Prophyt, Reason, Revus, and Tanos. ‘Paladin’ had significantly less plant death and higher yields than ‘Red Knight.’ The fungicide treatments Revus and Presidio significantly reduced plant death compared to the untreated control. Greenhouse research compared drench and foliar applications of the same fungicides to the same cultivars. Drenches had a significantly reduced plant death than foliar applications. More work is required to evaluate the application methods in the field and for compatibility with irrigation equipment.

Fumigants Telone C35, Sectagon-K54, Sectagon 42, and Vapam HL are registered for use on pepper to control Phytophthora. Consult thePhytophthora and Fumigation bulletin for further information.

Preferred Fungicides for PEPPER
Product A.I. Comment
Acrobat 50WP, Forum 4.18SC dimethomorph
Presidio 4SC fluopicolide use in a fungicide tank mix
Revus 2.08SC mandipropamid include surfactant
Ridomil Gold SL, Ultra Flourish mefenoxam resistance concerns
Ridomil Gold Copper mefenoxam/ copper hydroxide resistance concerns

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.

Go to Mary Hausbeck’s Phytophthora Research page for more information on Phytophthora, or see Hasubeck’s Great Lakes Expo proceeding on pepper.

Dr. Hausbeck's work is funded in part by MSU's AgBioResearch.

Tags: msu extension, peppers, vegetables

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