Plant Health Problems

Diseases caused by Fungi:

Rusts, Coleosporium, Puccinia.
Symptoms of rust infection are first visible as chlorotic lesions on the upper leaf surface. Diagnostic symptoms then develop on the underside of the leaf and appear as pustules which break open to reveal the orange-rusty powdery spores for which these diseases get their name. Depending upon the particular rust fungus, alternate hosts may be involved including several types of pine. Rusts can result in some defoliation, especially when plants are crowded.

These diseases can be minimized by cleaning up plant refuse in the fall and by adequate spacing of the plants to promote good air circulation. Although not usually necessary, applications of fungicides can be made when new growth emerges in the spring. Among the compounds registered for use in Connecticut are mancozeb, maneb, and triadimefon. Consult the label for dosage rates and safety precautions.

Powdery mildew, Erysiphe.
White powdery spots or patches develop on leaves and occasionally on stems. Symptoms often first appear on the upper surfaces of the leaves and are usually most pronounced during hot, humid weather. Heavily infected leaves turn brown and shrivel.

Disease can be minimized by avoiding overcrowded spacing of plants and by carefully picking off affected leaves as soon as symptoms are evident. Symptomatic leaves can be placed into a plastic bag in order to avoid spreading the spores of the fungus to other plants. Use of fungicides is usually not necessary. However, applications can be made as soon as symptoms are visible. Among the compounds registered for use in Connecticut are horticultural oil, sulfur, potassium bicarbonate, and thiophanate-methyl. Consult the label for dosage rates and safety precautions.

Root rots, Rhizoctonia solani, Fusarium sp.
The above-ground symptoms of root rots are non-specific and include a general wilting, decline, and collapse of the foliage and the entire plant. This general droopiness or flaccid appearance is often accompanied by browning and rotting of the roots and the crown. Yellowing and death of the outer leaves follows, until finally the entire plant is dead.

Control can be difficult once plants are infected so prevention is important. It is helpful to avoid overwatering, especially in heavy soils, and to avoid watering directly into the crown area of the plant. Highly symptomatic plants can be rogued and removed since recovery is unlikely.

Insect Problems

Foxglove aphid, Aulacorthum solani.
This green aphid injures bellflower by sucking plant sap. They may be managed by spraying with insecticidal soap or ultrafine horticultural oil, which are among the compounds registered for control of this pest in Connecticut. Consult the labels for dosage rates and safety precautions.

Garden slugs, Limax maximus.
Greenhouses, as well as moist, shaded outdoor gardens, are sometimes infested by garden slugs. These slugs are molluscs with no shell. They feed mostly at night, eating notches along the margins and holes in the interior of tender leaves, leaving a slimy, iridescent trail wherever they crawl. During the day, they hide under rubbish.

Slugs can be controlled by lightly cultivating the ground in the spring to destroy dormant slugs and their eggs. A band of diatomaceous earth put around newly set plants will control slugs by rupturing their epidermis. Placing a small board in the flowerbed for the slugs to hide under during the day makes it easy to destroy many at one time. A bowl of beer, sunk into the ground, with a roof to protect from sun and keep large animals out, will act as a bait and the slugs will drown. If necessary, chemicals such as metaldehyde, which is among the compounds registered for use against this pest in Connecticut, will control slugs. Consult the label for dosage rates and safety precautions.

Onion thrips, Thrips tabaci.
Thrips are very small insects with narrow, fringed wings that are lacking in the nymphs. In feeding, a thrips leaves a whitish chain-like mark on the surface. They may be managed by spraying spinosad, which is among the compounds registered for control of this pest in Connecticut. Consult the label for dosage rates and safety precautions.