Powdery mildew of wheat is caused by the obligately parasitic fungus Erysiphe graminis f. sp. tritici. The strains that attack wheat do not attack other hosts. The pathogen is found in humid and semi-arid environments throughout the world, and survives between wheat crops on volunteer wheat as cleistothecia on crop debris and as conidial spores in warm climates.
Disease symptoms of powdery mildew on wheat are similar to powdery mildews on other plants, and include white cotton-like mycelium on leaves that later turn a dull gray-brown. Disease symptoms can appear anytime after seedling emergence, and are usually most severe on the upper surfaces of lower leaves. The opposite side of the leaf normally appears chlorotic. Fungal fruiting bodies (cleistothecia) are visible on infected plants as distinct brown to black dots within mildew colonies. The pathogen reduces wheat photosynthetic area and vigor, utilizes host nutrients, and increases water transpiration. Heavily infected plants can be killed. Yield losses from powdery mildew can approach 40% under disease favorable conditions, and are most severe when infection occurs when disease develops before or during flowering.
No biological control strategies have been developed for powdery mildew.
Resistant varieties provide a practical disease control strategy, but resistance can quickly breakdown if a new race of the fungus develops. Provide adequate but not excessive fertilizer to the crop. Crop rotation and sanitation of wheat residue and volunteers can reduce pathogen survival, but airborne conidia and disease favorable environmental conditions can result in severe disease.
Fungicides effectively control powdery mildew, but may be cost prohibitive in some production systems. Certain seed treatments control seedling infections.
Product List for Powdery Mildew:
Pesticide |
Rate per Acre (or 100 lbs) |
Application Frequency |
Remarks |
|
Difenoconazole |
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|
Dividend Extreme |
1-4 fl oz |
-- |
Seed treatment; 55 day PHI |
|
Dividend |
0.5-1 fl oz |
-- |
Seed treatment; 55 day PHI |
|
Tebuconazole: various formulations and mixtures available |
|||
|
Raxil-Thiram |
3.5-4.6 fl oz |
-- |
Seed treatment |
|
Raxil MD |
5-6.5 fl oz |
-- |
Seed treatment |
|
Raxil MD-W |
5 fl oz |
-- |
Seed treatment |
|
Raxil MD Extra |
5 fl oz |
-- |
Seed treatment |
|
Raxil Xt |
0.16-0.20 oz |
-- |
Seed treatment |
|
Propiconazole |
|||
|
PropiMax EC |
4 fl oz |
1 spray at Feeks 8 |
40 day PHI |
|
Tilt 3.6E |
2-4 fl oz |
1 spray at Feeks 8 |
40 day PHI |
|
Strobilurin and Strobilurin/Propiconazole |
|||
|
Headline |
6-9 fl oz |
10-14 days, begin at Feeks 10.3-10.5 |
Maximum of 2 applications; 14 day PHI |
|
Quadris |
6.2-15.3 fl oz |
10-14 days, begin at Feeks 10.3-10.5 |
Maximum of 2 applications; 45 day PHI |
|
Stratego |
10 fl oz |
10-14 days, begin at Feeks 8 |
Maximum of 2 applications; 35 day PHI |
|
Triadimenol |
|||
|
Baytan 30 |
0.75-1.5 fl oz |
-- |
Seed treatment |
|
The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality. |
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Categories: Small Grains, Disease, Powdery Mildew
Date: 3/9/2005