FAQ: What causes the leaves to get spots and drop off my bell peppers?

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."

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.

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.