Originally posted in VegNet Newsletter, June 17,2018
Phytophthora blight was diagnosed last week in pepper plants from Huron County, Ohio. This is several weeks earlier than we normally see Phytophthora blight in northern Ohio, but heavy rains and periods of high temperatures likely contributed to an early appearance of the disease. Growers should scout both peppers and cucurbits for typical symptoms of Phytophthora blight Phytophthora is a water mold that thrives under conditions of high moisture and high temperature. It produces motile spores (zoospores) that are attracted to plants, then form a structure that allows them to infect, and aggressively attack any type of plant tissue. Zoospores can be splashed onto leaves, stems and fruits during rain events and overhead irrigation. Phytophthora blight is often seen first in low spots or other poorly drained areas of production fields, but the disease also occurs on well-drained, even sandy soils if the environmental conditions are right. An integrated, preventative program to manage Phytophthora blight is more effective than in-season rescue treatments with fungicides. During the growing season, fungicide application is the main option for management of Phytophthora blight (see below). In small plantings prompt removal of diseased plants is also recommended.
Effective management of Phytophthora blight in peppers requires an integrated approach:
Crop rotation. Phytophthoraproduces structures called oospores that can survive for a number of years in the soil. Plan to rotate out of peppers, cucurbits or green beans for 4-5 years if Phytophthora blight has been a problem.
Resistant varieties. A few pepper varieties are resistant to the root rot phase of the disease. In general, these varieties are susceptible to the crown rot phase, which affects foliage and fruits. Varieties with moderate to good resistance to Phytophthora blight are: Paladin, Aristotle, Declaration, Intruder, Vanguard (bell); Hechicero (jalapeño); and Sequioa (ancho).
Well-drained soil. Avoiding standing water is critical to limiting the movement of Phytophthora from plant to plant.
Avoid surface water for irrigation. We have found Phytophthora in irrigation ditches and ponds as early as late June in vegetable production-intensive areas in Ohio. Using surface water for irrigation is risky, especially if Phytophthora is present in fields near surface water sources.
Plant on raised beds. Prepared properly, raised beds will help prevent standing water near pepper plants. If possible beds should be domed, and there should be no depressions in the soil surrounding the plants.
Sanitation. Phytophthora can be moved from an infested field to a clean one on soil clinging to boots, equipment, etc. Power washing to remove soil is a good first step, followed by rinsing with a sanitizer. Do not build cull piles containing discarded peppers or cucurbits – plant material needs to be disposed of, preferably by burying, far from fields and surface waters.
Fungicides. There are a number of fungicides labeled for use on peppers to manage Phytophthora blight (see table below). The newest product, Orondis, has very good efficacy against this disease. It is available as a pre-mix with either Revus (Orondis Ultra), Ridomil (Orondis Gold) or Bravo (Orondis Opti). There are many restrictions on the use of Orondis – including the number of applications (no more than 1/3 of total applications for Phytophthora blight) and when it can be applied (to the soil or to the foliage but not both). Orondis Ultra and Orondis Gold can be applied in transplant water or through the drip, although Orondis does not move much in soil and emitters need to be right next to the plant. If the pepper variety is susceptible to Phytophthora blight, it may be a good idea to apply Orondis Gold or Orondis Ultra at planting, and follow up later with a program containing at least two of the fungicides with activity against Phytophthora (see table). If the pepper variety is resistant to Phytophthora, any of the three Orondis products can be used in a foliar fungicide program that includes other effective fungicides. The Bravo component of Orondis Opti will not help with Phytophthora blight, but will control anthracnose. Orondis Gold is considerably more expensive than Orondis Ultra and Orondis Opti, and resistance in Phytophthora to the Ridomil component of Orondis Gold has been found in numerous locations.
For in-season control where an at-plant application of one of the Orondis products has not been made, foliar applications can be very effective if undertaken preventatively. Results of our research in 2016/2017 on squash indicated that Orondis Ultra could be alternated with Presidio, Ranman or Tanos + Kocide with equivalent results (see chart Squash Phytoph Orondis foliar 1 slide-2eauh2g).