UC IPM: UC Management Guidelines for Powdery Mildew on Small Grains

UC Pest Management Guidelines

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 2/07)

In this Guideline:

Symptoms
Comments on the disease
Management

SYMPTOMS

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)

When choosing a pesticide, consider information relating to the general properties of the fungicide and environmental impact.

PROPICONAZOLE

(Tilt)

4 fl oz

see comments

MODE OF ACTION: A DMI (Group 3)¹ triazole fungicide.

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 R.E.I. exceeds the P.H.I.; the longer of these two intervals is the minimum time that must elapse before harvest may take place.
¹	Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions. Fungicides with a different Group number are suitable to alternate in a resistance management program. For more information, see http://www.frac.info/.

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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