HPIPM:Septoria Leaf Spot
From Bugwoodwiki
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Author: Howard F. Schwartz and David H. Gent
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Contents |
Identification and Life Cycle
Septoria leaf spot is caused by the fungus Septoria lycopersici. Septoria leaf spot is a very common and destructive disease of tomato wherever it is grown, but is most severe during extended wet, humid periods. The disease cycle begins when fungal spores (conidia) are deposited onto and directly penetrate leaves through natural openings. Disease symptoms can develop within 6 days of infection when moisture is abundant and temperatures are cool to moderate (68 to 77ºF). Extended periods of leaf wetness, high humidity, and warm temperatures favor rapid disease development and spread of the pathogen. The pathogen can be disseminated in and on equipment, plant stakes, contaminated seed, insects, and workers. Fungal spores are readily spread by splashing rain and irrigation water. S. lycopersici survives between tomato crops in infected crop debris, on solanaceous weeds such as horsenettle, and contaminated seed.
Plant Response and Damage
Septoria leaf spot symptoms usually appear on lower leaves after the first fruit sets, but they may also appear on stems, petioles, the calyx, and rarely fruit. Lesions are about 0.1 inch in diameter, but lesion may approach 5 mm under disease favorable conditions. Lesions have dark brown margins and tan to gray centers; leaf lesion centers are often dotted with black fungal fruiting bodies (pycnidia). Stem, petiole, and calyx lesions are generally smaller than leaf lesions and may or may not contain pycnidia. A small yellow halo is apparent around leaf lesions. The disease progresses from the oldest to youngest tissues and, if disease is severe, can cause leaves to turn slightly yellow, brown, and then wither. Septoria leaf spot can be a very damaging disease when temperatures are moderate and rainfall is abundant. Severe infections can damage foliage so much that fruit fails to mature or become sunscalded.
Management Approaches
Biological Control
No biological control strategies have been developed for Septoria leaf spot.
Cultural Control
Plant high quality seed free from the Septoria leaf spot pathogen. Practice a 2-year or longer crop rotation between tomato crops. Eliminate weeds in and around tomato fields and rotation crops that can serve as alternate hosts for the Septoria leaf spot pathogen. Deeply bury crop debris soon after harvest to reduce pathogen overwintering and survival. Promote rapid leaf drying by avoiding dense plantings, staking plants, and orientating rows parallel to the prevailing wind direction. Avoid overhead irrigation if possible, and time irrigations to end before dusk and avoid prolonged periods of leaf wetness. Reduce the contact between foliage and soil. Do not work in tomato fields when foliage is wet to reduce plant-to-plant spread of the fungus.
Chemical Control
Regular fungicide applications may be necessary to control Septoria leaf spot when weather conditions are favorable for disease, but chemical controls are most effective when combined with as many cultural control strategies as possible.
Product List for Septoria Leaf Spot:
| Pesticide | Product per acre | Application Frequency (days) | Remarks |
|---|---|---|---|
| Captan | |||
| Captan 4F | 4 pt | 5-7 days | 4 day REI |
| Captan 50 | 2 lb | 5-7 days | 4 day REI |
| Chlorothalonil | |||
| Bravo 720, Ensign | 1.5-3 pt | 7-14 days | Do not graze or feed debris to livestock; 7 day PHI |
| Bravo Ultrex | 1.7-2.2 lb | 7-10 days | Maximum of 18.3 pounds per season; 0 day PHI |
| Bravo Weather Stik | 1.5-3.0 pt | 7-10 days | Maximum of 20 pints per season; 0 day PHI |
| Echo 720 | 1.5 -3.0 pt | 7-10 days | Maximum of 2.5 gallons per season; 0 day PHI |
| Echo 90DF | 1.7-2.5 lb | 7-14days | Maximum of 16.67 pounds per season; 0 day PHI |
| Echo Zn | 3-4 pt | 7-10 days | Maximum of 3.6 gallons per season; 0 day PHI |
| Ridomil/Bravo | 2-3lbs | 14 days | Maximum of three applications; 14 day PHI |
| Copper Fungicides | |||
| Champ Dry Prill | 1.33 lb | 5-7 days | |
| Champ Formula 2 | 1.33 pt | 5-7 days | |
| Copper-Count-N | 4-6 pt | 7 days | |
| Cuprofix Disperss | 2.5-6 lb | 7-10 days | |
| Kocide 101 | 1.5-3 lbs | 5-7 days | |
| Kocide DF | 1.5-3 lbs | 5-7 days | |
| Kocide 4.5LF | 1-2 pts | 5-7 days | |
| Kocide 3000 | 0.75-1.75 lb | 5-10 days | |
| Nordox | 1.5-2.0 lb | 7-10 days | |
| Tri Basic Copper | 2-4 pt | 7-10 days | 1 day PHI |
| EBDC, Copper EBDC, and EBDC/Zoxamide | |||
| Cuprofix Disperss MZ | 1.75-4.75 lb | 3-10 days | Maximum of 21 pounds per season; 5 day PHI |
| Dithane DF | 2-3 lb | 7-10 days | Maximum of 8.5 pounds per season; 5 day PHI; use a non-ionic surfactant to improve performance |
| Gavel 75DF | 1.5-2.0 lb | 7-10 days | Maximum of 4 (west of Rockies) to 8 (east of Rockies) applications or 16 pounds per season; 5 day PHI; include a nonionic surfactant to improve performance |
| Maneb 75 DF | 1.5-2.0 lb | 7-10 days | Maximum of 8.0 pounds per season; 5 day PHI |
| Manex 80W | 1.5-2.0 lb | 7-10 days | Maximum of 7.5 pounds per season; 5 day PHI |
| Manex | 1.2-2.4 qt | 7-10 days | Maximum of 16.8 quarts per season; 5 day PHI |
| ManKocide | 2.5-5.0 lb | 3-10 days | Maximum of 42.7 pounds per season; 5 day PHI |
| Manzate | 0.75-1.0 lb | 3-7 days | Maximum of 8.5 lbs per season; 5 day PHI |
| Penncozeb 80W | 1.5-2.0 lb | 7-10 days | Maximum of 7.5 pounds per season; 5 day PHI. |
| Penncozeb 75DF | 1.5-2.0 lb | 7-10 days | Maximum of 8.0 pounds per season; 5 day PHI. |
| Famoxadone + Cymoxanil | |||
| Tanos | 8.0 oz | 5-7 days | alternate/tank-mix with other fungicides; 3 day PHI |
| Fenamidone | |||
| Reason 500SC | 5.5-8.2 fl oz | 5-10 days | Maximum of 24.6 fl oz; 14 day PHI |
| Penthiopyrad | |||
| Fontelis | 10-24 fl oz | 7-14 days | Rotate with other chemistry; Maximum of 72 fl oz/season; 0 day PHI |
| Strobilurin and Strobilurin Mixtures | |||
| Cabrio | 8-12 oz | 7-14 days | Maximum of 6 applications or 96 oz per season; Do not make more than 2 applications before alternating with a fungicide with a different mode of action; 0 day PHI |
| Flint | 2-3 oz | 7-10 days | Maximum of 4 applications or 16 ounces per season; Rotate with fungicides with a different mode of action such as Maneb or copper-containing products; 3 day PHI |
| Quadris | 5-6.2 oz | 5-14 days | Maximum of 5 applications or 1.15 quarts per season; Alternate Quadris with fungicides with different modes of action; 0 day PHI |
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.
