Bacterial Spot, caused by xanthomonas campestri. This pathogen is found just about everywhere peppers are grown. Hot, wet summers encourage the disease. Unfortunately, even pepper seed can carry the disease so it is almost impossible to avoid. But it can be prevented.
HOW TO HANDLE:
Start by planting resistant varieties. Good seed catalogs list the disease resistance of the types they carry, so start by doing a little homework can go a long way before you buy seeds or plants. Keystone Resistant Giant, California Wonder, and especially Boynton Belle have shown excellent disease resistance for us.
The official treatment is spraying with copper-based fungicide. The unofficial treatment is to use a fungicide containing chlorothalonil, the same product used for Early Blight on tomatoes. Although bacterial spot on peppers isn't listed on the label as a use for this chemical, it works and has been used for this purpose for years by gardeners "in the know."
Thursday, June 30, 2011
FAQ: What is eating the leaves of my snap beans?
"Something is eating the leaves of my snap beans and chewing holes in the beans. What is responsible for this?"
A likely culprit is the aptly named Mexican Bean Beetle. These beetles eat the underside of the leaf, leaving an intact surface which dies and gives the leaves a distinctive lacy appearance. Both the adults (which are orangey-brown with black spots) and the cream colored larvae do the damage.
Japanese beetles can attack beans, as well. They chew holes all the way through the leaf, ultimately leaving only the vein structure behind. Control is the same for Mexican Bean Beetles and Japanese Beetles.
WHAT TO DO:
Growing fast maturing varieties sown in spring and fall may help you evade the pest, as they are most active in summer.
A likely culprit is the aptly named Mexican Bean Beetle. These beetles eat the underside of the leaf, leaving an intact surface which dies and gives the leaves a distinctive lacy appearance. Both the adults (which are orangey-brown with black spots) and the cream colored larvae do the damage.
Japanese beetles can attack beans, as well. They chew holes all the way through the leaf, ultimately leaving only the vein structure behind. Control is the same for Mexican Bean Beetles and Japanese Beetles.
WHAT TO DO:
Growing fast maturing varieties sown in spring and fall may help you evade the pest, as they are most active in summer.
FAQ: Why are my tomato plants starting to lose leaves from the bottom up?
"Every year the same thing happens to my tomatoes. At first they grow great but then in early summer they start losing leaves from the bottom up. Eventually the whole plant is trashed and tomato production stops. What is happening and how can I stop it?"
Two words: Early Blight. It's the lucky (and rare!) gardener who doesn't see this problem. The cause is a fungus and control involves several elements.
HOW TO CONTROL:
Garden Cleanup: Be sure to remove as much diseased plant material as possible. At the end of the season, clean up well and don't compost debris. Just throw away all debris.
Crop Rotation: If possible, grow tomatoes on a different site every year, not using the same site for at least three years. However, unless you have a huge garden, this can be pretty difficult.
Staking & Caging: Keeping the tomato plants off the ground helps tremendously, as often the spores linger in the soil.
Mulching: One of the most common sources of Early Blight infection comes from soil splashing on the lower leaves of the plants, either from rain or irrigation. Mulch prevents this. Wheat straw, newspaper, biodegradable plastic, or flattened cardboard boxes work great. Plus, your plants get the advantage of a more evenly moist root zone, which increases yields and reduces fruit cracking.
Timely Fungicide Spraying: Get a fungicide containing chlorothalonil or mancozeb, and spray at recommended rates a couple days after setting your plants out. Then spray every 10 days or so. Spray after rain, too. Keeping up with this spray program will protect your plants all summer and into the fall.
Two words: Early Blight. It's the lucky (and rare!) gardener who doesn't see this problem. The cause is a fungus and control involves several elements.
HOW TO CONTROL:
Garden Cleanup: Be sure to remove as much diseased plant material as possible. At the end of the season, clean up well and don't compost debris. Just throw away all debris.
Crop Rotation: If possible, grow tomatoes on a different site every year, not using the same site for at least three years. However, unless you have a huge garden, this can be pretty difficult.
Staking & Caging: Keeping the tomato plants off the ground helps tremendously, as often the spores linger in the soil.
Mulching: One of the most common sources of Early Blight infection comes from soil splashing on the lower leaves of the plants, either from rain or irrigation. Mulch prevents this. Wheat straw, newspaper, biodegradable plastic, or flattened cardboard boxes work great. Plus, your plants get the advantage of a more evenly moist root zone, which increases yields and reduces fruit cracking.
Timely Fungicide Spraying: Get a fungicide containing chlorothalonil or mancozeb, and spray at recommended rates a couple days after setting your plants out. Then spray every 10 days or so. Spray after rain, too. Keeping up with this spray program will protect your plants all summer and into the fall.
FAQ: Why are random branches dying on my rhododendron?
"Random branches keep dying on my rhododendron. I cut them off, but then sometime later another branch wilts and dies. Why does it occur?"
This disease is commonly called Rhododendron Dieback. It's caused by a fungus (Botryosphaeria), and the symptoms are just as you describe: a branch wilts and dies on an otherwise healthy-looking plant. The bad news is that there's no sure cure for this disease, but keeping your plants healthy and unstressed will aid in control. Don't let them suffer from drought, cut off any diseased parts (sterilize your pruners with a 10% bleach solution to ensure you don't spread the disease), and make sure the plants are well mulched and in well drained soil. Planting a resistant variety helps. Boursalt, Cunningham's White, English Roseum, and Chionoides have shown resistance to this problem.
This disease is commonly called Rhododendron Dieback. It's caused by a fungus (Botryosphaeria), and the symptoms are just as you describe: a branch wilts and dies on an otherwise healthy-looking plant. The bad news is that there's no sure cure for this disease, but keeping your plants healthy and unstressed will aid in control. Don't let them suffer from drought, cut off any diseased parts (sterilize your pruners with a 10% bleach solution to ensure you don't spread the disease), and make sure the plants are well mulched and in well drained soil. Planting a resistant variety helps. Boursalt, Cunningham's White, English Roseum, and Chionoides have shown resistance to this problem.
FAQ: Why are my azaleas' leaves turning yellowish?
Sounds like chlorosis, a disease not caused by any bug or fungus. This is an iron deficiency in our plant, the plant version of human anemia. The most common cause of iron chlorosis in azaleas is a soil that's too alkaline. Even if you've been using iron-rich fertilizer, the iron is unavailable to the plant if the soil pH is too high. This problem shows up most commonly with relatively new plantings, by the way. Big established azaleas that have survived the first few years can actually influence soil conditions favorably for themselves.
Overly wet soil can also be a cause of chlorosis in azaleas, which have shallow root systems that rot easily in heavy clay soils with inadequate drainage. Middle Tennessee has a wide variety of soils, but clay soils that are relatively alkaline are quite common, thanks to the limestone bedrock not far below us.
WHAT TO DO:
Azalea chlorosis is cured by lowering the pH of the soil using sulfur and improving drainage by adding organic material to open up tight clay soil.
Get your soil pH tested by your county Extension Agent first, so you can figure out how much sulfur to add to lower your pH to the appropriate level.
Don't use aluminum sulfate to lower soil pH for azaleas and rhododendrons as it's easy to put on toxic amounts.
Overly wet soil can also be a cause of chlorosis in azaleas, which have shallow root systems that rot easily in heavy clay soils with inadequate drainage. Middle Tennessee has a wide variety of soils, but clay soils that are relatively alkaline are quite common, thanks to the limestone bedrock not far below us.
WHAT TO DO:
Azalea chlorosis is cured by lowering the pH of the soil using sulfur and improving drainage by adding organic material to open up tight clay soil.
Get your soil pH tested by your county Extension Agent first, so you can figure out how much sulfur to add to lower your pH to the appropriate level.
Don't use aluminum sulfate to lower soil pH for azaleas and rhododendrons as it's easy to put on toxic amounts.
FAQ: My azaleas' leaves are pale. What's wrong?
That's the handiwork of the Azalea Lace Bug. If you look on the underside of a leaf, you may see the adult of the culprit species, a 1/8" long insect with transparent wings marked with a lacy pattern in a grayish brown. The suck sap from the leaf, causing light stipple marks, and a heavy infestation will pretty much suck the color out of the leaves. If you don't see an adult, you're sure to see lots of diagnostic black dots which are either cast of skins of the larvae or excrement deposits. Evergreen azaleas are their main target, although they will attack deciduous types, too. Azaleas planted in sunny sites are victimized much more than those in shade.
HOW TO CONTROL:
Control consists of using repeated foliar sprays containing acephate, horticultural oil, a pyrethoid like bifenthrin or cyfluthrin, imidacloprid, or disulfoton. (Don't get scared by all that jargon!) The last two have a systemic action, which means they're absorbed by the leaves into the plant's system to give longer protection. Pesticide containers always list the active poison on the front label, so look there for any of these chemicals alone or in combination.
Spraying should begin in early spring when the overwintered eggs start hatching (around the first week of April is a good rule of thumb for Middle Tennessee), followed by another application about 10 days later, and then once a month or so to catch any interlopers that come in on the breeze.
HOW TO CONTROL:
Control consists of using repeated foliar sprays containing acephate, horticultural oil, a pyrethoid like bifenthrin or cyfluthrin, imidacloprid, or disulfoton. (Don't get scared by all that jargon!) The last two have a systemic action, which means they're absorbed by the leaves into the plant's system to give longer protection. Pesticide containers always list the active poison on the front label, so look there for any of these chemicals alone or in combination.
Spraying should begin in early spring when the overwintered eggs start hatching (around the first week of April is a good rule of thumb for Middle Tennessee), followed by another application about 10 days later, and then once a month or so to catch any interlopers that come in on the breeze.
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