Plant Diseases

If by examining the above list of pests you have not discovered an obvious cause for your plant problem, perhaps you need to consider the possibility of disease. Although there are numerous diseases that can attack your plants, home gardeners are likely to only experience a few of the more common ones. Click on any of the following to determine if this disease is your problem.

Botrytis blight
• Common to tulips, it's caused by a fungus.
• Light to dark colored spots appear on part or all leaves and flowers.
• In cool, moist weather a fuzzy brown or grayish mold forms; leaves and stems distort, and often rot off at the base.
• Bulbs have dark, circular, sunken lesions; and dark brown pinhead sized pellets form on the bulb husks.

Crown rots
• Most severe in overcrowded plantings, above 70 degrees F and moist conditions.
• Leaves irises grown from rhizomes die, leaf tips form downward.
• The leaf bases and possibly the rhizomes are dry brown, and rotted.
• Leaves and stems at soil level are rotted, and bulbs are soft and crumbly.

Leaf spots
• Several disease and environmental factors contribute to spotting and blotching of leaves. The most common are the fungal and bacterial left spots.
• Fungal leaf spots are 1/4 inch yellow, red, tan, gray, brown, or black circular spots on leaves.
• Bacterial leaf spots are usually tiny, angular dark colored and may be accompanied by rotting and oozing.

Powdery and downy mildews
• Flour like patches on the surface of leaves, buds, young stems and fruits.
• They thrive in both humid and dry weather.
• The spores are spread by the wind to healthy plants.
• They cause leaf yellowing, dwarfing, stunting and deformation.
• Common on roses, zinnias, phlox, lilacs, cucurbits, apples and grapes in shaded, crowded areas.