Late Blight
Identification
Late blight takes the appearance of irregular gray patches on affected plants' leaves. These lesions are visible from either side of the leaf. Eventually, the spots may look white on the underside of the leaf. Other possible signs of late blight include brown areas on plant stems and rapid leaf loss.
Damage prevention
Late blight spreads rapidly under warm, moist conditions. Staking tomato plants and avoiding overhead watering can be helpful in prevention.
Physical control
Remove and destroy infected plants immediately. Do not compost infected plants.
Chemical control
It is highly recommended to try physical prevention/control methods before resorting to chemical control. If you choose to use a fungicide, select a product that is labelled for late blight and rotate products where possible to minimize resistance. Not all fungicide products work on all types of fungal diseases. Check local regulations (or your local Extension Office where applicable) to identify products that can be used in home gardens in your area. Follow label instructions carefully for safe and effective fungicide application and to ensure that edible crops are safe to harvest. Test fungicide on a few plants before widespread application. Spray fungicides in the late evening and try to avoid spraying during blooming to minimize negative impacts on pollinators- some fungicides are directly lethal to pollinators, and others can have indirect negative impacts. Fungicides may not help if the plant is already severely diseased; it works best when used early (or preventatively in cases where you know you have a particular disease susceptibility). Severely diseased plants may need to be removed and disposed off site.
Plants Affected
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