Alternaria Leaf Spot
Small, round reddish brown spots with white to Gray centres form on the upper surface of the leaves and along the midrib. The lesions may encircle the stems and cause wilt. This disease is worse in warm, wet, or very humid weather. Avoid getting water on the foliage and provide plenty of air circulation. Remove infected plant parts (when plants are dry).
Bacterial Slow Wilt or Stunt
This causes wilting, twisting, curling, and stunting of the lower leaves followed by death of the lower leaves. Stunted plants have narrow, yellow green leaves. Remove and destroy infected plants.
Botrytis
This fungus causes a grey mould on flowers, leaves, stems, and buds. It thrives in cool wet weather conditions. Remove affected plant parts, avoid watering at night and getting water on the plant when watering, make sure plants have good air circulation.
Downy Mildew
This fungus causes whitish grey patches on the undersides and eventually both sides of the leaves. Avoid getting water on the foliage and provide plenty of air circulation. Remove infected plant parts (when plants are dry).
Powdery Mildew
This fungus disease occurs on the top of the leaves in humid weather conditions. The leaves appear to have a whitish or greyish surface and may curl. Avoid powdery mildew by providing good air circulation for the plants by good spacing and pruning.
Aphids
Greenish, red, black or peach coloured sucking insects can spread disease as they feed on the undersides of leaves. They leave a sticky residue on foliage that attracts ants. Introduce or attract natural predators into your garden such as lady beetles and wasps who feed on aphids. You can also wash them off with a strong spray or use an insecticidal soap.
Cabbage Looper
These worms are green with a white stripe on either side, about 1-1.5 inches long. Hand pick off of plants. Floating row covers can help prevent their laying eggs on the plants.
Cyclamen Mite
These mites damage plants by sucking juice from stems and leaves. They multiply rapidity in hot, dry weather. They can only be seen using a magnifying glass. Plants will look distorted and stunted and may not bloom. Flowers will be distorted, streaked, and blotched. Leaves can become cupped, curled, dwarfed, and thickened. Discard plants that are severely infested. Avoid working with infested plants. Keep plants watered in dry weather.
Spider Mites
These tiny spider-like pests are about the size of a grain of pepper. They may be red, black, brown or yellow. They suck on the plant juices removing chlorophyll and injecting toxins which cause white dots on the foliage. There is often webbing visible on the plant. They cause the foliage to turn yellow and become dry and stippled. They multiply quickly and thrive in dry conditions. Spider mites may be controlled with a forceful spray every other day. Try hot pepper wax or insecticidal soap.
Thrips
Thrips are tiny needle-thin insects that are black or straw coloured. They suck the juices of plants and attack flower petals, leaves and stems. The plant will have a stippling, discoloured flecking or silvering of the leaf surface. Thrips can spread many diseases from plant to plant. Many thrips may be repelled by sheets of aluminium foil spread between rows of plants. Remove weeds from the bed and remove debris from the bed after frost.
