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
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
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.
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.