Post by johno on Aug 30, 2009 11:45:42 GMT -5
Patrick has said it already: spores are microscopic. Nothing short of total enclosure in a sterile environment using the sterile method is going to prevent spores from potentially getting to the plants. Using row covers to keep out spores is like using a sieve to keep out water. They are airborne, and it's just luck that some plants are in their path and some aren't. That being said, there are ways to minimize the chances.
Here are some links about the disease that hopefully will help us find a way...
www.gardensalive.com/article.asp?ai=942&bhcd2=1251646614
"A single spore can travel many miles."
vegdis.cas.psu.edu/03Diseases/D107.html
Last paragraph notes vertical and horizontal resistance.
cru.cahe.wsu.edu/CEPublications/eb0958/eb0958.html
"Clear polyvinyl shelters can be constructed to offer protection from rain, but should also be designed to allow air circulation from the sides. These shelters are most practical for tomato production, and with some modification can extend the growing and harvesting season and also protect plants from frost damage in the spring and fall. Close sides to adequately protect from frost. If favorable weather for late blight has occurred, closely monitor plants and remove any suspicious foliage or shoots."
www.agronomy-journal.org/index.php?option=article&access=standard&Itemid=129&url=/articles/agro/pdf/2008/04/a8063.pdf
"Our results showed that Cupressus benthamii and Vetiveria zizanioides extracts were the most effective preparations, leading to 23% and 35% inhibition of sporangial germination, respectively, and to 86% and 77% disease reduction. A clear relationship between disease latency and disease severity was established."
www.thedailygreen.com/green-homes/blogs/organic-gardening/late-blight-organic-tomatoes-460809
"The Fungicide we're using is Serenade, available at well stocked garden centers or online at suppliers like Peaceful Valley Farm Supply. It's approved for organic gardening and is a fairly effective prophylactic as long as it's applied frequently. Late blight can't be cured, and if it's well established it can't be stopped. But if it hasn't yet taken hold it can be held at bay by Bacillus subtilis, the "good" bacteria that is Serenade's active ingredient."
So, it looks like Michael has something. Ventilated plastic tents won't keep the spores out, but they can minimize the chances of exposure - as could low tunnels with ventilated ends. Properly constructed, the ventilation could help keep the plants dry, reducing the chances of infection over dew-covered plants. Keeping plants dry is the first line of defense.
Some sources say there are resistant varieties. Vertical resistance means there is a gene present that creates resistance to a single strain, horizontal resistance means there are several genes acting together against multiple strains. This means we can breed resistance into varieties we are fond of.
There is research into biological extracts that reduce the occurrence and severity of late blight. So there is hope on the horizon for effective organic sprays. Also there is some control using Serenade as a preventative.
Here are some links about the disease that hopefully will help us find a way...
www.gardensalive.com/article.asp?ai=942&bhcd2=1251646614
"A single spore can travel many miles."
vegdis.cas.psu.edu/03Diseases/D107.html
Last paragraph notes vertical and horizontal resistance.
cru.cahe.wsu.edu/CEPublications/eb0958/eb0958.html
"Clear polyvinyl shelters can be constructed to offer protection from rain, but should also be designed to allow air circulation from the sides. These shelters are most practical for tomato production, and with some modification can extend the growing and harvesting season and also protect plants from frost damage in the spring and fall. Close sides to adequately protect from frost. If favorable weather for late blight has occurred, closely monitor plants and remove any suspicious foliage or shoots."
www.agronomy-journal.org/index.php?option=article&access=standard&Itemid=129&url=/articles/agro/pdf/2008/04/a8063.pdf
"Our results showed that Cupressus benthamii and Vetiveria zizanioides extracts were the most effective preparations, leading to 23% and 35% inhibition of sporangial germination, respectively, and to 86% and 77% disease reduction. A clear relationship between disease latency and disease severity was established."
www.thedailygreen.com/green-homes/blogs/organic-gardening/late-blight-organic-tomatoes-460809
"The Fungicide we're using is Serenade, available at well stocked garden centers or online at suppliers like Peaceful Valley Farm Supply. It's approved for organic gardening and is a fairly effective prophylactic as long as it's applied frequently. Late blight can't be cured, and if it's well established it can't be stopped. But if it hasn't yet taken hold it can be held at bay by Bacillus subtilis, the "good" bacteria that is Serenade's active ingredient."
So, it looks like Michael has something. Ventilated plastic tents won't keep the spores out, but they can minimize the chances of exposure - as could low tunnels with ventilated ends. Properly constructed, the ventilation could help keep the plants dry, reducing the chances of infection over dew-covered plants. Keeping plants dry is the first line of defense.
Some sources say there are resistant varieties. Vertical resistance means there is a gene present that creates resistance to a single strain, horizontal resistance means there are several genes acting together against multiple strains. This means we can breed resistance into varieties we are fond of.
There is research into biological extracts that reduce the occurrence and severity of late blight. So there is hope on the horizon for effective organic sprays. Also there is some control using Serenade as a preventative.