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UC Pest Management Guidelines


Powdery mildew lesions on upper (above) and lower leaf surfaces.

Small Grains

Powdery Mildew

Pathogens: Each type of small grain is attacked by a specific form of the fungus Blumeria graminis (Erysiphe graminis): Erysiphe graminis f. sp. tritici infects wheat; Erysiphe graminis f. sp. hordei infects barley and weeds in the genus Hordeum; Erysiphe graminis f. sp. avenae infects oats and wild oats

(Reviewed 2/07, updated 2/09)

In this Guideline:


SYMPTOMS AND SIGNS

The disease first appears on lower leaves: white, cottony patches of fungal growth on the upper leaf surface that are opposite chlorotic spots on the underside of the leaf. The patches of white growth turn a dull gray-brown as fruiting structures, called cleistothecia, develop. Plants are often low in vigor.

COMMENTS ON THE DISEASE

The fungus overwinters in tiny, dark, spore-forming structures called cleistothecia that release airborne spores (ascospores) in spring. It also can overwinter as mycelium on volunteer wheat, barley, or oat plants and produce spores (conidia) that can cause initial infections; conidia from resulting lesions are windblown for secondary disease cycles at 10-day intervals. Disease development is optimal at 59° to 72°F (15° to 22°C) and is retarded above 77°F (25°C). Disease is favored by dense stands, high nitrogen fertilization, high relative humidity, and cool temperatures.

MANAGEMENT

Resistant cultivars of barley and wheat are available (see BARLEY and WHEAT CULTIVAR TABLES). Crop rotation, elimination of crop residue, and control of volunteer grains and weed hosts reduce inoculum survival from one season to the next.

Although normally not economical, foliar fungicides can be used to control disease outbreaks and provide partial disease control. Applications should be made between tillering and heading with the objective being to protect the flag leaf. Depending on weather conditions from tillering to early dough stage, one or more applications may be needed.

Common name Amount/Acre** R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
The following materials are listed in order of usefulness in an IPM Program, taking into account efficacy. Also consider the general properties of the fungicide as well as information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
A. PROPICONAZOLE
  (Tilt) 4 fl oz 24 see comments
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
  COMMENTS: For use on wheat, barley, triticale, oats, and rye. Best when applied to emerging flag leaf. Only 1 application/season. Do not graze or feed livestock treated forage or cut the green crop for hay or silage. Preharvest interval for oats is 40 days and 0 days for wheat, barley, triticale, and rye.
 
** See label for dilution rates.
+ 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.
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. In California, make no more than one application of fungicides with mode of action Group numbers 1, 4, 9, 11, or 17 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: Small Grains
UC ANR Publication 3466
Diseases
R. M. Davis, Plant Pathology, UC Davis
L. F. Jackson, Agronomy, UC Davis

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