Plant Health Problems

Diseases caused by Fungi:

Wilt, Fusarium, Verticillium.
Vascular wilts are troublesome diseases of carnations. Infected plants first develop a dull green color and eventually wilt and turn straw-color. Symptoms often appear on one section of the plant. Plants may be attacked at any stage; young plants can suddenly dry up or older plants might develop a pale green color accompanied by wilting of lower leaves. This is frequently followed by a general wilting and death of the entire plant. Plants may wilt in the middle of the day and seem to recover at night. Some plants may show no signs of infection until they come into flower, when they suddenly collapse. When the stem is cut, a brown discoloration or streaking may appear in the vascular tissues.

Control of these diseases is difficult since the pathogens are commonly found in soil. One of the key strategies for control of vascular wilts is prevention. Therefore, it is important to avoid planting aster in infested soil. It is also helpful to maximize plant vigor by good cultural care and watering. Careful handling of plants will avoid root injury which enables the fungus to enter the plant. Since repeated use of the same area greatly increases the amount of disease, rotation is essential. When available, it is also helpful to use resistant varieties. Chemical controls are not effective for these fungi.

Root and crown rots, Rhizoctonia solani, Pythium.
The above-ground symptoms of root and crown 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.

Leaf spots, Septoria, Alternaria.
Pale tan to brown spots with purple borders appear on leaves. These can vary in color, size, and number.

Efforts to maximize plant vigor by fertilizing and watering are helpful. However, watering should be done early in the day to give the foliage a chance to dry before nighttime. It is also helpful to pick and remove symptomatic leaves as soon as they develop. 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 chlorothalonil and thiophanate-methyl. Consult the label for dosage rates and safety precautions.

Rust, Uromyces.
Chocolate-brown pustules develop on leaves and stems. When these rupture, the leaves often dry out and turn brown. Infected plants can be stunted and leaves can curl.

This disease 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.

Botrytis flower rot, Botrytis cinerea.
Flowers turn a papery brown and become covered with gray, fuzzy masses. Senescing flowers are particularly susceptible. Tan to brown streaks can also develop on the leaves. These patches are often associated with flowers which have dropped onto the leaf surface. This disease is particularly troublesome during periods of extended cloudy, humid, wet weather.

Good sanitation practices including grooming the plants and removing spent or senescing flowers can minimize the potential for infection. These affected tissues should be carefully removed and discarded when they are dry. It is also important to avoid wetting the flowers when watering and crowding plants. Adequate spacing between the plants can promote good air circulation. Control can also be achieved with the use of fungicide sprays applied as soon as symptoms are visible. Among the compounds registered for use in Connecticut are chlorothalonil, copper sulphate pentahydrate, and thiophanate-methyl. Consult the label for dosage rates and safety precautions.

Diseases caused by Bacteria:

Bacterial wilt, Pseudomonas.
Primary symptoms of infection include wilting of plants or shoots as well as splitting of the stems and frayed yellow streaks in the vascular system. Tissue just under the epidermis is sticky and cutting across the stem shows discoloration and a bacterial ooze. The disease appears to spread rapidly at high temperatures.

Control involves using clean cuttings, roguing and removing symptomatic plants, and avoiding overhead irrigation and splashing water. Infected plants should not be composted. Sanitation is also very important since this disease is highly contagious. All equipment should be disinfested between use with 10% household bleach, 70% alcohol, or one of the commercially available compounds.

Insect Problems:

Aphids, Myzus persicae and Aphis helichrysi.
The green peach aphid and the leaf curl plum aphid, Aphis helichrysi, infest the young leaves and buds, suck the sap, and are often troublesome in greenhouses. When needed, insecticidal soap, ultra-fine horticultural oil or malathion, which are among the compounds registered for control of this pest in Connecticut, will be effective against aphids. Imidacloprid can be applied as a soil drench to provide long-lasting systemic control. Consult the labels for dosage rates and safety precautions.

Twospotted spider mite, Tetranychus urticae.
This pest infests the undersides of the leaves, which become light yellow in color, and the plants have a generally unhealthy appearance. Sometimes the mites form webs, which more or less enclose the upper as well the lower leaf surface. Among the compounds registered for control of this pest in Connecticut are insecticidal soap and ultrafine horticultural oil. Spraying with insecticidal soap will give sufficient control if applied at least twice at 7-10 day intervals. The predatory mite, Neoseiulus fallacis, is most commonly found feeding where there are mite infestations. A single application of ultrafine horticultural oil (1% dilution) can be effective if predatory mites are present. Special care should be taken with soap or oil to obtain thorough spray coverage, because they only work on contact. Consult the labels for dosage rates and safety precautions. Abamectin is an effective restricted use product. Avoid applying carbaryl or pyrethroids, which tend to be much more toxic to the predators than to the pest spider mites.

Variegated cutworm, Peridroma saucia.
Larvae of the variegated cutworm frequently infest greenhouses in the fall and are responsible for considerable injury. They climb the stems and eat holes into carnation buds, and feed on many other plants. The moth has a wingspan of between 1.5 to 2", with brownish gray forewings. The caterpillar is light brown mottled with darker brown. Normally there are two annual generations outside, but there may be more in the greenhouse.

Among the compounds registered for control of this pest in Connecticut are Bacillus thuringiensis, spinosad, and carbaryl. Control measures in a flower bed could be Bacillus thuringiensis var. kurstaki applied as a spray when small caterpillars are present or a carbaryl spray if large caterpillars are present in damaging numbers. Consult the labels for dosage rates and safety precautions.