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Protecting tomatoes from late blight

Tomato    Zone 7B

The recent very wet weather seems to be helping late blight emerge early this year and I have plenty of tomato plants that I need to try and protect. I don't use fungicides, my plants are well spaced. Does anybody know of anything organic I can use to protect my tomatoes?


Posted by: cara smith (1 point) cara smith
Posted: July 13, 2013




Answers

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Lots of light, good air circulation, no extra nitrogen, and no overhead watering are the best cultural practices to help avoid late blight on tomatoes.

You should find out which copper products are registered in your state for late blight. Copper is acceptable for use on commercial organic farms, but it's not considered very effective, and works only as a preventive measure. You have to apply it on every leaf surface (including the undersides) for it to work at all. It won't help if disease has already hit your plants, and it washes off with every rain.

Plant breeders have developed several late-blight resistant varieties of tomatoes in recent years. I grow Defiant, Mountain Magic, and (this year) Plum Regal--resistant varieties, but I haven't had an outbreak in my garden in the four years I've been growing them. I had Juliet, another somewhat-resistant variety, the year we got struck hard. Juliet didn't resist that outbreak. It got infected as early as the other varieties. We lost all 75 plants before harvesting a single fruit.


Posted by: Peg Boyles (3 points) Peg Boyles
Posted: July 14, 2013




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If weather is favorable, late blight is really tough to manage on susceptible varieties. Advice in the earlier post is great...also you can try biologicial control products (preventive only) such as Actinovate (Streptomyces lydicus) or Serenade MAX (Bacillus subtilis) but I think copper products will be a bit more reliable.


Posted by: Joan Allen (4 points) Joan Allen
Posted: July 15, 2013




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Late Blight in Tomatoes is caused by a fungal like organism, called an Oomycete. The scientific name is Phytophthora infestans. This organism is essentially aquatic as produces infective stages called zoospores that swim. Knowing that it is aquatic is vital. If you are not using pesticides or fungacides you have work really hard on reducing water on the leaves. Thin them out very well. Cut off (and place in a plastic bag to be destroyed) the lower leaves. Apply water to the base of the plant if needed and not spraying with a can or hose.

Use the copper as recommended by Peg. But remove lots of the leaves near the base. The plant will photosynthesize enough without them. Sunshine is not limiting this time of year.

About copper. From here http://www.extension.org/pages/18351/...

"Copper fungicides can be highly effective if applied prophylactically (before infection) and with complete coverage of all plant foliar surfaces, including the undersides of leaves where the pathogen typically sporulates. In the European BlightMOP project, across many trials in countries across the EU, foliar potato late blight was controlled on average by 27% with an average yield increase of 20% (Speiser et al., 2006). In a single season field trial at Oregon State University in 2007, four applications of 1.9 lbs elemental copper as cupric oxide suppressed foliar disease development by 88% (Stone, 2007)."

You might also want to consult this sheet about copper as a synthetic.
http://www.extension.org/pages/18360/...


Posted by: David Hughes (54 points) David Hughes
Posted: July 15, 2013




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