Primer on plant problems, how to treat them! Part TWO
-BACTERIAL BLIGHT
Symptoms: Small, water-soaked spots appear on vegetable leaves. The spots eventually get bigger and turn brown. The leaves either turn tallow and die slowly, or turn brown and rapidly fall off. In cool weather yellow halos may border the infected spots. Sometimes lone, reddish lesions show up on the stems as well.
Cause: Xanthomonas and pseudomonas bacteria.
Remedy: Like so many of the diseases we've talked about so far, this one also thrives (and spreads) in wet conditions, so minimize overhead watering and never work in a wet garden patch. Buy certified disease-free seed and use blight resistant varieties when available. Rotating crops also helps, and by rotating I mean keeping the same crops out of the soil where they grew previously for at least two years. Be sure and clean up plant debris at the end of the season. Unfortunately, there are no chemical controls for bacterial blight.
-CLUBROOT
Symptoms: Abnormal enlargement and distortion of roots of plants in the crucifer family. Cabbage and Brussels sprouts are most susceptible, followed by broccoli, cauliflower, etc. Lowest leaves may turn yellow and drop off. Yield is usually greatly reduced, but in very favorable soil conditions the symptoms may not even be noticed until the plants are pulled up and the roots examined after harvest.
Cause: Soil borne Plasmodiophora brassicae fungus.
Remedy: Keep soil beds well drained by adding lots of organic matter since clubroot thrives in soils that are cool, wet, and heavy. I always make sure that the soil pH is above 7.2 for these crops as well, since a high pH has been shown to inhibit clubroot. Long crop rotations (up to seven years) works well, though it is often not practical nor possible.
-BLACKSPOT
Symptoms: Rose leaves develop circular black spots up to a half-inch in diameter. Leaves turn yellow and drop off. The flowers themselves are usually not affected.
Cause: Diplocarpon rosae fungus.
Remedy: Blackspot is usually not a fatal disease, but affected plants often try to grow replacement foliage late in the season and that new growth may suffer cold damage when frost hits. The best way to minimize blackspot is to plant resistant varieties and avoid overhead watering because the disease thrives on wet foliage. Cut the bushes back hard in the spring to remove any canes that may have blackspot fungus on them and to improve air circulation. Remove old mulches and apply a thick new mulch around each bush after you give the roses their first feeding this will serve as a barrier between any blackspot fungus on the ground and the newly developing rose leaves. I've had excellent results with controlling and curing blackspot (seemingly overnight) with the "Fermented Salmon" liquid foliar spray. No one seems to be able to explain to me how or why it works so well in controlling this disease, but have my own theory as to why that I'm currently experimenting with (results to be published later!). Otherwise, there are many reliable, commercially available rose sprays that contain various fungicide ingredients if you don't mind using these products in your garden. The key is vigilant spraying throughout the growing season.
-GRAY MOLD
Symptoms: Fruit, vegetables and flowers are all affected. Leaves, flowers and fruit (green or ripe) especially near the soil in the densest area of the leaf canopy turn light brown and develop a gray fuzzy covering. Gray mold will often sprout on soft ripe fruits like strawberries and raspberries after they have been picked.
Cause: Botrytis cinerea fungus.
Remedy: Sanitation is more important than anything in reducing the chances of gray mold from developing. As you walk around the flower garden, the vegetable patch, the fruit trees, pick and destroy all fading flowers and blighted foliage, remove and destroy and diseased leaves, blossoms or fallen fruits. It is also important to space your plants far enough apart so that sunshine and air can penetrate the entire plant. Harvest fruits in advance of rainy, humid and cool conditions whenever possible. Use mulches like pine needles in strawberry beds to keep the fruit off the ground. Fungicides like Captan or chlorothalonil work well to eliminate gray mold.
There are many more possible plant disease that can affect your garden such as Fusarium and Verticillium wilt, early and late blights, scab, leaf curl, brown rot, apple scab, fire blight, cucumber mosaic and so on. A good deal of plant diseases can be avoided by simply using good cultural practices, that is, avoiding over-head watering, providing plenty of air circulation between plants (that means dividing perennials on a regular basis!), maintaining a good healthy soil structure with lots of organic matter, regular weeding and keeping a spotless sanitary garden by quickly removing any spent or diseased plant tissue.
Symptoms: Small, water-soaked spots appear on vegetable leaves. The spots eventually get bigger and turn brown. The leaves either turn tallow and die slowly, or turn brown and rapidly fall off. In cool weather yellow halos may border the infected spots. Sometimes lone, reddish lesions show up on the stems as well.
Cause: Xanthomonas and pseudomonas bacteria.
Remedy: Like so many of the diseases we've talked about so far, this one also thrives (and spreads) in wet conditions, so minimize overhead watering and never work in a wet garden patch. Buy certified disease-free seed and use blight resistant varieties when available. Rotating crops also helps, and by rotating I mean keeping the same crops out of the soil where they grew previously for at least two years. Be sure and clean up plant debris at the end of the season. Unfortunately, there are no chemical controls for bacterial blight.
-CLUBROOT
Symptoms: Abnormal enlargement and distortion of roots of plants in the crucifer family. Cabbage and Brussels sprouts are most susceptible, followed by broccoli, cauliflower, etc. Lowest leaves may turn yellow and drop off. Yield is usually greatly reduced, but in very favorable soil conditions the symptoms may not even be noticed until the plants are pulled up and the roots examined after harvest.
Cause: Soil borne Plasmodiophora brassicae fungus.
Remedy: Keep soil beds well drained by adding lots of organic matter since clubroot thrives in soils that are cool, wet, and heavy. I always make sure that the soil pH is above 7.2 for these crops as well, since a high pH has been shown to inhibit clubroot. Long crop rotations (up to seven years) works well, though it is often not practical nor possible.
-BLACKSPOT
Symptoms: Rose leaves develop circular black spots up to a half-inch in diameter. Leaves turn yellow and drop off. The flowers themselves are usually not affected.
Cause: Diplocarpon rosae fungus.
Remedy: Blackspot is usually not a fatal disease, but affected plants often try to grow replacement foliage late in the season and that new growth may suffer cold damage when frost hits. The best way to minimize blackspot is to plant resistant varieties and avoid overhead watering because the disease thrives on wet foliage. Cut the bushes back hard in the spring to remove any canes that may have blackspot fungus on them and to improve air circulation. Remove old mulches and apply a thick new mulch around each bush after you give the roses their first feeding this will serve as a barrier between any blackspot fungus on the ground and the newly developing rose leaves. I've had excellent results with controlling and curing blackspot (seemingly overnight) with the "Fermented Salmon" liquid foliar spray. No one seems to be able to explain to me how or why it works so well in controlling this disease, but have my own theory as to why that I'm currently experimenting with (results to be published later!). Otherwise, there are many reliable, commercially available rose sprays that contain various fungicide ingredients if you don't mind using these products in your garden. The key is vigilant spraying throughout the growing season.
-GRAY MOLD
Symptoms: Fruit, vegetables and flowers are all affected. Leaves, flowers and fruit (green or ripe) especially near the soil in the densest area of the leaf canopy turn light brown and develop a gray fuzzy covering. Gray mold will often sprout on soft ripe fruits like strawberries and raspberries after they have been picked.
Cause: Botrytis cinerea fungus.
Remedy: Sanitation is more important than anything in reducing the chances of gray mold from developing. As you walk around the flower garden, the vegetable patch, the fruit trees, pick and destroy all fading flowers and blighted foliage, remove and destroy and diseased leaves, blossoms or fallen fruits. It is also important to space your plants far enough apart so that sunshine and air can penetrate the entire plant. Harvest fruits in advance of rainy, humid and cool conditions whenever possible. Use mulches like pine needles in strawberry beds to keep the fruit off the ground. Fungicides like Captan or chlorothalonil work well to eliminate gray mold.
There are many more possible plant disease that can affect your garden such as Fusarium and Verticillium wilt, early and late blights, scab, leaf curl, brown rot, apple scab, fire blight, cucumber mosaic and so on. A good deal of plant diseases can be avoided by simply using good cultural practices, that is, avoiding over-head watering, providing plenty of air circulation between plants (that means dividing perennials on a regular basis!), maintaining a good healthy soil structure with lots of organic matter, regular weeding and keeping a spotless sanitary garden by quickly removing any spent or diseased plant tissue.
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Friday, August 11, 2006
