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How to Manage Pests

UC Pest Management Guidelines

| More pests | More crops | About guidelines |

Irregular yellow-brown spots caused by downy mildew, Peronospora parasitica.

Cole Crops

Downy Mildew

Pathogen: Peronospora parasitica

(Reviewed 6/07, updated 11/08)

In this Guideline:

SYMPTOMS

Infections begin as irregular yellow patches on leaves; these chlorotic lesions later turn tan to light brown. If conditions are favorable, white fluffy growth of the fungus develops on the undersides of leaves. If disease development is extensive, leaves may take on a blighted effect as a result of numerous infection sites. Systemic infections can cause internal black streaks and patches to form in stems and floret branches of broccoli and cauliflower. Early symptoms on transplants may resemble bacterial leafspot symptoms. Severely diseased seedlings may be stunted or die.

COMMENTS ON THE DISEASE

Peronospora parasitica requires cool, moist weather for infection and disease development to take place. The pathogen survives between crops on weed hosts or as resilient oospores in crop residue. Spores are airborne. This disease is most serious on young seedlings; if cotyledons and the first true leaves are severely infected, the young plant may die.

MANAGEMENT

A few broccoli varieties are available that are resistant to downy mildew. Fungicide treatment of susceptible varieties is needed when the disease occurs on transplants or early in crop development in the field; repeated applications may be required, depending on weather. Treatment during early flowering is required on seed crops.

Organically Acceptable Methods
Resistant varieties and some copper sprays are suitable for organically grown crops.

Common name Amount/Acre R.E.I.+ P.H.I.+
(trade name)   (hours) (days)
The following materials are listed in order of usefulness in an IPM Program. Also, consider information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
A. CHLOROTHALONIL
  (various products) Label rates 12 7
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M5)
  COMMENTS: Use at 7- to 10-day intervals, if necessary.
 
B. MEFENOXAM/CHLOROTHALONIL
  (Ridomil Gold/Bravo) 76.5 1.5 lb 48 7
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M5) and phenylamide (4)
  COMMENTS: Use at 14-day intervals, if necessary.
 
C. FOSETYL-ALUMINUM
  (Aliette) Label rates 12 3
  MODE OF ACTION GROUP NAME (NUMBER1): Phosphonate (33)
  COMMENTS: Use on a 7- to 21-day intervals as necessary. Do not tank mix with copper compounds.
 
D. COPPER# Label rates see label 0
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M1)
  COMMENTS: Not all copper compounds are approved for use in organic production; be sure to check individual products.
 
+ 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 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 http://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: Cole Crops
UC ANR Publication 3442
Diseases
S. T. Koike, UC Cooperative Extension, Monterey County
K. V. Subbarao, Plant Pathology,UC Davis, Salinas

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Statewide IPM Program, Agriculture and Natural Resources, University of California
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