How to Manage Pests

UC Pest Management Guidelines

Peppers

Powdery Mildew

Pathogen: Leveillula taurica (imperfect stage = Oidiopsis taurica)

(Reviewed 12/09, updated 5/10)

In this Guideline:


SYMPTOMS AND SIGNS

Powdery mildew primarily affects leaves on pepper plants. Although the disease commonly occurs on older leaves just before or at fruit set, it can develop at any stage of crop development. Symptoms include patchy, white, powdery growth that enlarges and coalesces to cover the entire lower leaf surface. At times the powdery growth is present on the upper leaf surface as well. Leaves with mildew growing on the undersurface may show a patchy yellowish or brownish discoloration on the upper surface. The edges of infected leaves may roll upwards exposing the white, powdery fungal growth. Diseased leaves drop from the plants and leave the fruit exposed to the sun, which may result in sunburning.

COMMENTS ON THE DISEASE

Powdery mildew can be severe during the warmest part of summer and can cause heavy yield losses. The pathogen has a very wide host range and inoculum from one host plant species can cross-infect other host plants. In California, powdery mildew inoculum can come from crops such as onion, cotton, tomato, all varieties of peppers, and weeds such as annual sowthistle and groundcherry.

This powdery mildew pathogen differs from powdery mildew pathogens in other genera in that it primarily occurs inside the leaf rather than on the leaf surface. Cleistothecia (sexual spores) of the Leveillula perfect stage rarely occur in California, but asexual spores (conidia) are produced and disseminated by wind. In general, high humidity favors germination of conidia. Infection of plants can occur over a wide temperature range (64° to 91°F or 18° to 33°C) under both high and low humidity. Under favorable conditions, secondary infections occur every 7 to 10 days, and disease can spread rapidly. Temperatures over 95°F that commonly occur in the interior valleys of the state can temporarily suppress development.

MANAGEMENT

Regular monitoring to detect powdery mildew, especially during warm weather, is important to time fungicide applications early enough to prevent damage. Powdery mildew is managed primarily with fungicides.

Cultural Control

The fungi that cause powdery mildew can survive between crop seasons on other crops and on weed species. The degree of survival depends on environmental conditions. Because of the wide host range of the fungus, it is difficult to control the amount of inoculum that overwinters in California. Thus, simple sanitation methods in and around pepper fields may not provide a sufficient reduction in the primary inoculum to provide disease control.

Most pepper cultivars used in California do not possess acceptable levels of resistance to powdery mildew. Currently, there are no breeding programs aimed at developing resistant cultivars to pepper powdery mildew.

Organically Acceptable Methods

Sprays of sulfur and potassium bicarbonate are acceptable for use on organically grown peppers.

Treatment Decisions

Fungicides can provide satisfactory control and prevent economic loss if applied during the early stages of the infection. Effective control requires spraying with high pressure and high volume of water for optimum penetration of the crop canopy by the fungicide. Good coverage is necessary for satisfactory control; ground applications give better coverage than air.

Common name Amount per acre R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
When choosing a pesticide, consider information relating to environmental quality. Not all registered pesticides are listed. Always read the label of the product being used.
 
A. SULFUR DF# 5 lb 24 0
  MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M2)
  COMMENTS: Provides only partial control even when applied early. To prevent injury to the crop, do not apply within 2 weeks of an oil application.
 
B. AZOXYSTROBIN
  (Quadris) 6–15.4 fl oz 4 0
  MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
 
C. PYRACLOSTROBIN
  (Cabrio EG) 8–12 oz 12 0
  MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
  COMMENTS: Do not apply more than 6 applications per season.
 
D. MYCLOBUTANIL
  (Rally 40W) 4 oz 24 0
  MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
  COMMENTS: Do not apply more than 4 applications per year. Do not apply more than 1.25 lb/acre. Use allowed under a Supplemental Label.
 
E. QUINOXYFEN
  (Quintec) 4–6 fl oz 12 3
  MODE-OF-ACTION GROUP NAME (NUMBER1): Quinoline (13)
  COMMENTS: Use allowed under a Supplemental Label. Alternate after each use with a fungicide that has a different mode of action.
 
F. TRIFLOXYSTROBIN
  (Flint) 1.5–2 oz 12 3
  MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
 
G. POTASSIUM BICARBONATE#
  (Kaligreen) 2.5–3 lb 4 1
  MODE OF ACTION: An inorganic salt.
  COMMENTS: While this product has been tested for other crops, research is lacking for its use in peppers and observations indicate it provides only partial control. Thorough coverage and frequent applications are necessary.
 
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
# Acceptable for use on organically grown produce.
1 Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions (for more information, see www.frac.info). Fungicides with a different group number are suitable to alternate in a resistance management program. For fungicides with mode-of-action Group numbers 1, 4, 9, 11, or 17, make no more than one application before rotating to a fungicide with a different mode-of-action Group number; for fungicides with other Group numbers, make no more than two consecutive applications before rotating to fungicide with a different mode-of-action Group number.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Peppers
UC ANR Publication 3460

Diseases

S. T. Koike, UC Cooperative Extension, Monterey County
R. M. Davis, Plant Pathology, UC Davis
K. V. Subbarao, USDA Research Station, Salinas
Acknowledgment for contributions to Diseases:
B. W. Falk, Plant Pathology, UC Davis

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