Plant Health Problems
There are a number of conditions which are common to many types of houseplants, regardless of their habit or origin. The most common problems are listed as follows:
Diseases caused by Fungi:
Anthracnose, Colletotrichum, Glomerella.
Symptoms develop on leaves, petioles, and stems and appear as light tan to brown spots. As the spots enlarge and age, they frequently develop a target-like appearance, often with a concentric ring-type pattern.
Control strategies include careful attention to watering since the fungi can be easily spread with splashing water. Additionally, watering early in the day helps to minimize the chance for long periods of leaf wetness which favor disease. Other methods that maximize air circulation by plant spacing to avoid crowding and well-balanced fertilization and good cultural care help to minimize problems. Picking and removing symptomatic leaves also helps in control since it reduces the amount of the fungus available to spread to healthy leaves. Although fungicides are rarely necessary, 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 potassium bicarbonate and thiophanate-methyl. Consult the label for dosage rates, safety precautions, and indoor use.
Root and crown rot, Rhizoctonia spp. and Pythium spp.
The above-ground symptoms of crown and root rots are nonspecific 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 achieved by using a sterile potting mix and clean pots. It is also helpful to avoid overwatering, especially in the crown area of the plant. It is important to never let the plant sit in standing water. Highly symptomatic plants can be rogued and removed since recovery is unlikely.
Botrytis blight or Gray mold, Botrytis cinerea.
Both leaves and flowers can be infected. Infected flowers develop tan, papery patches and are often covered with gray, fuzzy masses. Senescing flowers are particularly susceptible. Tan to brown spots with a target-like appearance can also develop on the leaves. These patches are often associated with flowers which have dropped onto the leaf surface.
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 potassium bicarbonate and thiophanate-methyl. Consult the label for dosage rates, safety precautions, and indoor use.
Powdery mildew, Oidium spp.
White powdery spots or patches develop on the leaves. Symptoms often first appear on the upper surfaces of the leaves. White powdery patches can also develop on emerging blossoms.
Disease can be minimized 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. 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 potassium bicarbonate, neem oil, insecticidal soap, thiophanate-methyl, and sulfur. Consult the label for dosage rates, safety precautions, and indoor use.
Diseases caused by Physiological/Environmental Factors:
Soluble salt injury, excessive fertilization and accumulation of high levels of soluble salts in potting medium.
Although houseplants vary in their sensitivity to soluble salts, many can develop problems associated with the injury that it causes. Root injury caused by excessive levels of fertilizer in the potting mix results in a general decline or collapse of the plant. Symptoms are similar to those caused by root rot so soil analyses for soluble salt levels are often necessary for correct diagnosis. An indication of high soluble salts is the presence of white, crystalline deposits on the rim or outer surface of the pot or on the surface of the potting mix.
Soluble salts can sometimes be leached from the potting mix by running a stream of water through the pot for approximately 20 minutes. However, when salt levels are excessive, the plant can be repotted into fresh, sterile potting mix and a clean pot. It is also important to avoid excessive use of fertilizer, especially during periods of slow growth.
Plant collapse, overwatering.
One of the most common causes of decline and death for all types of houseplants is root rot associated with overwatering and water-saturated potting mixes. Affected plants show a slow decline or collapse, often with nonspecific symptoms similar to those associated with fungal root rot. When examined, roots appear discolored (brown to black) and mushy.
This problem can be avoided by careful attention to watering practices. It is also important to avoid letting plants sit in standing water for any length of time.
Tip necrosis, physiological.
Tips and margins of leaves develop dead or necrotic areas. This condition can be associated with a number of factors including low relative humidity, root damage due to excessive fertilization, and uneven watering.
This problem can be avoided by careful attention to cultural practices. In some cases, affected portions of leaves can be trimmed with clean, sharp scissors to improve the appearance of the plant.
Raised, scab-like swellings appear on the underside of leaves. These first appear as water-soaked blisters and may turn rusty-brown with age. This condition is often associated with inadequate light levels as well as overwatering, especially during periods of cloudy, cool weather.
This problem can be minimized by careful attention to moisture levels in the potting mix, especially during cloudy weather.
Bud drop, physiological.
Buds discolor and drop before opening. The cause is physiological, due to some adverse environmental factor related to humidity. Moving from one location to another, too much heat or dry air, or waterlogging or dryness at the roots may contribute to this trouble.
This problem can be minimized by maintaining constant levels of high humidity and uniform moisture levels in the potting mix. It is also helpful to maintain temperatures around 70 F and to avoid high temperatures, especially at night.
These are soft bodied, pear-shaped insects, from 1/12" to 1/4" (2-6 mm) long, whose identifying characteristic is the presence of cornicles, that look like tailpipes, on the top rear of the body. Antennae vary from being shorter than or longer than the body in length. Winged forms may be produced when food is getting scarce or when the aphid needs to get to an alternate host to overwinter. They have piercing-sucking mouthparts and excrete honeydew, which supports black sooty mold. The green peach aphid and other aphids often infest plants in the home and greenhouse. They may be controlled by spraying with insecticidal soap or ultrafine horticultural oil, which are among the compounds registered for use against this pest in Connecticut. Repeat applications may be necessary. Some aphids specialize on root feeding. Plants affected by root aphids may show loss of vigor. Imidacloprid, applied as a systemic to be taken up by the roots, will provide long-lasting control of root and foliage-infesting aphids. Consult the labels for dosage rates and safety precautions.
Cactus scale, Diaspis echinocacti.
This light gray circular scale infests certain species and varieties of cactus under cultivation. When needed, spray with malathion outdoors or insecticidal soap, which are among the compounds registered for control of this pest in Connecticut, two or three times at 10-day intervals. Consult the labels for dosage rates and safety precautions.
Fungus gnats, Bradysia spp.
Fungus gnats are dainty, mosquito-like flies that breed in moist organic matter. The larval stage grows to 1/2", is clear, slime covered, and has a small black head capsule. Larvae feed on fungi, root hairs, larger roots and underground stems. Plants especially susceptible to injury include cacti and poinsettias, in which larvae will feed internally in the plant above the soil level. Adults can be seen swarming near the soil if the population is large, and can become a major household or greenhouse nuisance. A soil drench of Bacillus thuringiensis var. israeliensis or dimilin, which are among the compounds registered for use against this pest in Connecticut, will control the larvae. The insect pathogenic nematode, Steinernema feltiae, is also effective against fungus gnats. Read and follow all label directions. Avoid using incompletely composted ingredients when formulating potting media.
Mealybugs, Phenacoccus citri, P. gossypii, P. longispinus.
Abutilon, dracaena, hoyas, arboricola, China doll, rubber plant and other plants in greenhouses and homes are commonly infested with mealybugs. White cottony masses appear on leaf surfaces, in leaf axils and sheaths. These insects damage plants by sucking plant sap. Sprays of insecticidal soap, ultrafine horticultural oil or resmethrin, which are among the compounds registered for control of this pest in Connecticut, are most effective against crawlers. Because of overlapping life stages in a home environment, multiple applications will be needed to control this pest. The spray needs to contact the insect so direct it downward into growing tips and leaf axils and upward to contact mealybugs under leaves. Root mealybugs specialize as root feeders, and the only above-ground sign of infestation is loss of vigor in infested plants. Foliar-feeding and root mealybugs can be controlled with imidacloprid, which is among the products registered for control of this insect in Connecticut, applied as a systemic to be taken up by the roots. Microencapsulated diazinon is an effective restricted use product. Read and follow all label directions for any insecticide used.
Mites such as the twospotted spider mite sometimes attack houseplants such as gardenia, English ivy and the rubber plant. Most mites are microscopic, have eight legs and spin webs. Most of them like hot, dry conditions and will multiply rapidly under these conditions. They feed on the undersides of leaves with their piercing-sucking mouthparts. Symptoms of mite feeding are a yellow stippling of leaves and, when the infestation is severe, webbing may encase the plant. At this point, it's very difficult to penetrate the webbing with miticides to obtain direct contact.
Control should begin with keeping the air in the home or greenhouse somewhat humid. Insecticidal soap and ultrafine horticultural oil, which are among the compounds registered for use against this pest in Connecticut, will control mites. Multiple applications may be needed. Hexythiazox or abamectin are effective restricted use products. Consult the labels for dosage rates and safety precautions.
Some scales that attack houseplants are the fern scale, hemispherical, and soft scale. Houseplants, such as some of the ornamental figs, grown in the tropics and sold in the north can have black scale. Some houseplants that are susceptible to scale are cactus, ferns, arboricola, schefflera and the woody figs. The Florida red scale, Chrysomphalus aonidum, is a circular, dark reddish-brown scale that stands out prominently from the leaf; the nipple is pointed; in fact, the profile of the scale is almost conical. This scale commonly infests rubber plants, palms, oleander, camellia, and citrus trees. Rubber plants are sometimes attacked by Morgan's scale which is very similar to Florida red scale.
The scales commonly found on houseplants are categorized as armored or soft. A hard shell that is made up of their shed skins covers the armored scales. It is not attached to the body, so the scale cover can be flipped over to observe the insect feeding underneath. These scales do not produce honeydew and can only readily be controlled during their crawler stage when they are exposed. Soft scales secrete honeydew, making the foliage beneath them sticky and black with the growth of sooty mold. They also can be controlled in the crawler or immature stage. Insecticidal soap and ultrafine horticultural oil, which are among the compounds registered for use against this pest in Connecticut, will control scale crawlers. Multiple applications will be needed because generations overlap in the home or greenhouse situation. Spray when crawlers are active, at about 10-day intervals. Imidacloprid, applied as a soil drench, will provide season-long systemic control of only the soft scale species. Consult the labels for dosage rates and safety precautions.
Whitefly, Trialeurodes sp.This whitefly commonly infests abutilon, hibiscus, fuchsia and other plants in greenhouses and homes. They feed on the underside of leaves and adults readily take flight when disturbed. They are visible to the naked eye. Their immature form is scale-like, losing its legs. See Fuchsia for a detailed description of the life cycle and control measures.