Spot blotch is a foliar disease of wheat caused by the fungus Bipolaris sorokiniana (syn. Helminthosporium sativum). The pathogen is a common soil organism found in soils worldwide. The fungus also can cause root and foot rots, seedling blight, and infect seeds. Foliar symptoms generally appear in wet weather as plants near maturity. Temperatures of 68 to 77ºF and 100% relative humidity favor spot blotch. Spot blotch is generally most severe when plant roots are also infected by B. sorokiniana. The pathogen can survive on other grass hosts and weeds, in soil as conidia, in crop debris, and in seed.
Disease symptoms appears as distinct, elongate, brown to black lesions that rarely exceed 0.5 inches in diameter. Symptoms are most obvious after heading and are most frequent on older leaves. The dark lesions contrast sharply with green or straw-colored leaf tissues.
No biological control strategies have been developed for spot blotch.
Reducing root and foot infections by the spot blotch pathogen can reduce foliar spot blotch. Shallow seeding reduces seedling infection, but may not be practical for dryland production. Delay planting until soil temperatures are cool in mid- to late- autumn to reduce seedling exposure to warm soil temperatures that favor the pathogen. Provide adequate but not excessive nitrogen fertility. Rotate to non-hosts for at least two years to reduce inoculum. Wheat varieties vary widely in their resistance or tolerance to spot blotch and host resistance can provide a practical disease control strategy.
Product List for Spot Blotch:
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Pesticide |
Rate per Acre |
Application Frequency |
Remarks |
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Copper fungicides: not all formulations listed |
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Champ DP |
1.0-1.33 lb |
10 days, beginning early heading |
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Cuprofix Disperss |
2.0-2.5 lb |
10 days, beginning early heading |
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Kocide 101 |
1.5-2.0 lb |
10 days, beginning early heading |
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Nordox |
1.5-2.0 lb |
10 days, beginning early heading |
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Nu Cop 50 WP |
1.5-2.0 lb |
10 days, beginning early heading |
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Copper/EBDC |
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Cuprofix MZ Disperss |
2.5-4.75 lb |
10 days, beginning early heading |
Maximum of 15.7 pounds per season; 26 day PHI; grazing restrictions |
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ManKocide |
2.0-2.5 lb |
10 days, beginning early heading |
Maximum of 32 pounds per season; 26 day PHI; grazing restrictions |
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EBDC: not all formulations listed |
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Dithane DF |
2.1 lb |
7-10 days; beginning early heading |
Maximum of 3 applications; Performance improved by addition of non-ionic surfactant; 26 day PHI; grazing restrictions |
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Manzate 75DF |
2 lb |
7-10 days; beginning early heading |
Maximum of 3 applications; 26 day PHI; grazing restrictions |
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Penncozeb 75DF |
1.0-2.0 lb |
7-10 days; beginning early heading |
Maximum of 3 applications; 26 day PHI; grazing restrictions |
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Propiconazole |
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PropiMax EC |
4 fl oz |
1 spray at Feeks 8 |
40 day PHI |
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Tilt 3.6E |
2-4 fl oz |
1 spray at Feeks 8 |
40 day PHI |
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Strobilurin and Strobilurin/Propiconazole |
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Headline |
6-9 fl oz |
10-14 days, begin at Feeks 10.3-10.5 |
Maximum of 2 applications; 14 day PHI |
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Quadris |
6.2-15.3 fl oz |
10-14 days, begin at Feeks 10.3-10.5 |
Maximum of 2 applications; 45 day PHI |
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Stratego |
10 fl oz |
10-14 days, begin at Feeks 8 |
Maximum of 2 applications; 35 day PHI |
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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, Spot Blotch
Date: 3/9/2005