Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu
Late blight on tomato is now confirmed in Maryland (Baltimore County). We do not yet know what strain or genotype it is. Until additional information is available, growers should assume that both tomatoes and potatoes are at risk. The pathogen is very aggressive and can complete its life cycle and sporulate in as little as 7 days. Tomato growers should scout their crop aggressively and modify their spray program. Conventional growers should add translaminar fungicides, which can move into and through leaves are more effective than a protectant only program. The following are some fungicides that have performed well on tomato in our region. Growers should apply them with a protectant and rotate among them based on rotation of products that are in a different FRAC grouping.
- Curzate–3.2 to 5.0 oz 60DF/A
- Forum–6.0 fl oz 4.18SC/A
- Presidio–3.0 to 4.0 fl oz 4SC/A
- Previcur Flex–1.5 pt 6F/A
- Ranman–2.10 to 2.75 fl oz 400SC/A
- Reason–5.5 to 8.2 fl oz 500SC/A
- Revus Top–5.5 to 7.0 fl oz 4.16SC/A
- Tanos–8.0 oz 50WG/A
The best option for organic growers is an OMRI approved copper product. While research results indicate that copper is the best available option in organic production, remember that it is a protectant. That means it must be present on tissue to work. Keep protecting plants with repeated applications as new tissue forms.
Different products are available on potato. Please refer to Maryland, Extension Bulletin 236 (in Delaware, Extension Bulletin 137) for additional information.
Because this disease can spread rapidly by air, advise home gardeners with infected plants to use fungicides – or to kill their plants and bag them or place them under a tarp. This will avoid allowing the spores to spread to neighboring farms.