Helminthosporium leaf spot is caused by several fungi in the genus Bipolaris. Little is known about the disease cycle, inoculum sources, or how the pathogen overwinters. The pathogens are favored by cool to moderate temperatures (60 to 70°F) during wet or humid weather. The pathogen is likely spread by splashing rain, irrigation water, and wind. The fungus may survive between millet crops in and on infected crop residue as spores and fungal mycelial masses and perhaps on alternate hosts.
Helminthosporium leaf spot symptoms develop during and after heading, and can be varied. Lesions may be in the form of small brown flecks, linear streaks, or oval or irregularly-shaped spots. The number and size of lesions may increase, coalesce, and form long streaks. Lesions are initially dark brown but become tan or gray-brown with a faint dark brown border. During wet weather, lesions develop a dense gray-brown appearance. Black conidial and mycelial growth may be apparent on individual grains in the head. The disease generally is of minor concern in the High Plains region.
No biological control strategies have been developed for Helminthosporium leaf spot.
Cultural controls are not required in most years in the High Plains because symptoms tend to develop late in the season. Crop rotation, incorporation of crop debris, and planting of less susceptible varieties will reduce Helminthosporium leaf spot.
Chemical controls are seldom necessary for Helminthosporium leaf spot.
Product List for Helminthosporium Leaf Spot:
Common/Trade Name |
Rate per 100 lb seed |
Application Frequency (days) |
Remarks |
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Captan—various formulations available |
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Captan 75 |
6-9 oz |
Seed treatment |
Broad spectrum, but weak against Pythium |
|
Fludioxonil |
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|
Maxim 4FS |
0.034-0.068 fl oz |
Seed treatment |
Suppression of Fusarium and Rhizoctonia spp. |
|
Metalaxyl/Mefenoxam |
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Apron XL LS |
0.32-0.64 fl oz |
Seed treatment |
Suppression of Pythium and Phytophthora spp. |
|
Allegiance-FL |
0.75-1.5 fl oz |
Seed treatment |
Suppression of Pythium and Phytophthora spp. |
|
Ridomil Gold EC |
0.25-1 pts |
Broadcast application |
Suppression of Pythium and Phytophthora spp. |
|
Thiram |
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42-S Thiram |
8 fl oz |
Seed treatment |
Broad spectrum |
|
Thiram 50WP |
8 oz |
Seed treatment |
Broad spectrum |
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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: Millet, Disease, Helminthosporium Leaf Spot
Date: 03/22/2005