Septoria leaf spot is caused by the fungus Septoria helianthi. Little is known about the survival and dissemination, but the disease cycle is thought to begin when spores (conidia) are deposited onto leaves by wind and/or splashing water. The fungus directly penetrates host tissues, and develops fruiting structures (pycnidia) that produce more conidia. The disease develops most rapidly during moderate to warm weather with abundant rainfall, especially after flowering. The fungus can be seedborne, and is thought to survive between sunflower crops in and on infected crop debris.
Septoria leaf spot symptoms initially appear as water-soaked spots with a greasy-green appearance on the lower leaves of plants. Lesions can be circular to angular in shape, but often are gray with a dark margin. Some lesions may have a narrow yellow boarder that gradually fuses with surrounding healthy tissue. Tiny, black specks (pycnidia of the fungus) become apparent in mature lesions. Septoria leaf spot rarely causes economic losses in the High Plains because conditions favorable for disease seldom occur in the High Plains, but the disease can be damaging under heavy sprinkler irrigation.
No biological control strategies have been developed for Septoria leaf spot
Plant high quality seed free from the Septoria leaf spot pathogen. Practice a three-year or longer crop rotation, especially when sunflowers are grown with overhead irrigation. Sanitation of crop debris and volunteers may reduce pathogen survival, but experimental data is lacking.
Fungicides are rarely economical or required for Septoria leaf spot.
Product List for Septoria Leaf Spot:
Pesticide |
Product per Acre |
Application Frequency
|
Remarks |
|
Neem |
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Trilogy |
2 pt |
7-14 days |
Maximum of 2 gallons; 0 day PHI |
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Pyraclostrobin |
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Headline |
6-12 fl oz |
7-14 days |
Maxiumum of 24 fl oz/Acre; rotate with other fungicide chemistry; 21 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: Sunflower, Disease, Septoria Leaf Spot
Date: 04/10/2007