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Goldie Slicing Tomato - Organic
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Preventing Late Blight
Late blight is here to stay. Particularly challenging for those who prefer the flavor of open-field-grown tomatoes is the seeming arbitrariness of the outbreaks. While many growers this past season in Maine were caught unprepared by an early onset of LB, others in parts of Massachusetts and Vermont were spared both early and late. Although cool temperatures, moist conditions, still air and lack of sunshine favor sporulation, spores can occur and advance in any condition of high humidity even in the absence of significant precipitation. LB might spread quickly…or not; wind-borne spores can travel hundreds of miles on storm fronts, but also can be baked into submission by the hot sun. Be prepared and employ as many preventive techniques as you are willing and able. Once LB lesions develop on your plants you need to take immediate action to halt the disease in hopes of salvaging a crop. Our recommendations:
- Where possible, use resistant varieties. Unfortunately, we have yet to find a resistant main crop variety that meets our high standards for flavor. Our search continues.
- Try to find tolerant cultivars—use anecdotal evidence and experiment.
- Grow your own tomato plants or buy locally grown seedlings. Know your farmer!
- Do not use saved potatoes as seed stock. Purchase only new certified disease-free seed potatoes. Click here for more potato-related info.
- Plant in areas with full sun and few wind blocks. Avoid shade and moist environments. Facilitate air movement. Maintain high soil fertility.
- Stay on top of the weather. Access state IPM reports, online forecasting models or smart phone apps. See vegetablemdonline.ppath.cornell.edu/ for excellent photos and info. University of Maine Cooperative Exension: Potato IPM bi-weekly tells where LB infections have been confirmed in Maine or the eastern United States, umaine.edu/potatoes, 1-888-USE-UMCE. Or use the forecast model uspest.org/risk/tom_pot_map to assess potential for spore germination and lesion formation in your area.
- If you choose to spray, have a plan and materials on hand in June, so you can make quick and timely application(s) when conditions indicate.
- OGS offers a full roster of preventive and post-ap products.
- Most market growers and many home gardeners now grow at least a portion of their tomatoes under cover. Homemade high tunnels, caterpillars, commercial hoophouses and greenhouses can greatly reduce vulnerability though still require vigilance.
- LB on tomatoes is not seed-borne. However, other tomato diseases can be seed-borne so be careful. Using fermentation to extract seed reduces risk.
- Late blight does not survive on dead tissue. In frozen northern areas infected plants may be composted. However, other tomato diseases can survive on dead tissue to infect your next crop so it is probably best not to compost any diseased tomato plants.
- It is unnecessary to place infected plants in trash bags. Instead, if the plants are beyond saving, pull them up and sun-cook or freeze them on the soil surface.
For all tomatoes, days to maturity are from date of transplanting.
9,000 seeds per oz, 0.1 gram pkt ~30 seeds, 0.2 gram pkt ~60 seeds, 0.5 gram pkt ~150 seeds.
Culture: Tender, cannot tolerate frost. Usually started indoors Feb–April. Avoid using fresh manure as it causes lush foliage with few ripe fruits. Instead use generous amounts of well-rotted cow or horse manure or compost to boost plant vigor, and crushed eggshells at the bottom of each hole for calcium. Heavy phosphorus needs. Respond well to foliar sprays.
Determinate (Det) bush varieties may be staked, should not be pruned.
Indeterminate (Ind) climbing varieties are customarily staked and pruned.
Tomato experts Carolyn Male and Kokopelli’s Dominique Guillet both oppose pruning, arguing more abundant foliage provides more photosynthesis.
Good seed retains viability so we often commission two-year productions. Organically and sustainably grown seed was rinsed with a sodium hypochlorite solution to reduce risk of seed-borne disease. This treatment poses no health risks.
Minimum germination soil temperature 50°, optimal range 60–85°.
- ASC: Alternaria Stem Canker
- EB: Early Blight
- F: Fusarium
- GLS: Grey Leaf Spot
- LB: Late Blight
- N: Nematodes
- SEPT: Septoria Leaf Spot
- TMV: Tobacco Mosaic Virus
- V: Verticillium
Diseases: Bacterial Canker, Spec and Spot
Cultural controls: Disinfect greenhouse materials & cages, farming tools & gloves, avoid overhead irrigation, don’t work crop when wet, rotate crops, use compost.
Cultural controls: Rotation, mulching, minimize plant wetness, staking, use compost.
Disease: Early Blight
Cultural controls: Rotation, avoid stressing plants, staking, keep leaf wetness to a minimum, mulching, indeterminate varieties are more resistant/tolerant, disinfect stakes & cages.
Material: Bacillus amyloliquefaciens (Monterey Complete Disease Control Biofungicide/Bactericide) or Streptomyces lydicus (Actinovate).
Disease: Late Blight
Cultural controls: Destroy cull potatoes & potato volunteers, avoid overhead irrigation.
Material: copper products.
Disease: Septoria Leaf Spot
Cultural controls: Space plants for good air circulation.
Materials: copper products.