Tobacco, Flowering (Nicotiana)
Plant Health Problems
Diseases caused by Fungi:
Transplant rot, Pythium or Rhizoctonia.Week-old transplants fail to grow or suddenly collapse. Rotting of the stem just below the soil line appears as a wet decomposing slime or as a withered string of tissue. When stems are partially hollow, insect injury has preceded the rot. The causal fungi, Pythium and Rhizoctonia, may first attack the plant in transplant production.
Toughening plants before transplanting reduces the chances of direct infection after transplanting.
Black root rot, Thielavopsis basicola.Root troubles in general are indicated by stunted plants, irregular growth, and a ragged appearance to the field. Black root rot, caused by the fungus Thielavopsis, causes roots to have blackened areas along them with many stubby black ends. The symptoms are most severe when the soil pH is over 5.5 but they may occur in soils as low as 4.9.
Thus, lowering the pH of soil usually reduces the disease but does not always do so. Rotation away from tobacco for 2 or 3 years is the most effective control. Cold wet soils are prone to black root rot. Planting late when temperatures are warmer may help.
Blue mold, Peronospora tabacina.This is a leaf spot disease. Areas of the leaf from one-half to one inch in diameter begin to pale, turn a watery gray and then brown. Blue or gray mold under the leaf produces large numbers of spores which can become airborne and infect new plants. When dry, the dead tissues may fall out and leave holes in the leaf.
Affected plants should be removed and destroyed.
Leaf spot or fleck, Alternaria spp.
Very small necrotic spots appear in an irregular pattern on the upper surface of the leaf. In severe cases large dead areas may occur. Leaves become affected from the bottom of the plant upwards as they approach maturity, or become over-mature. Lesions which increase in size with circular target-like zonation are caused by the fungus Alternaria. Lesions which do not so increase may be caused by ozone damage resulting from air pollution. New areas of the leaf become mildly affected in rather sudden spurts. This generally occurs after hot-weather rains. The spots in these affected areas may gradually enlarge with time but do not spread to unaffected areas.
Sore shin, Rhizoctonia solani.This disease is a form of transplant rot occurring on older plants. Stalks develop a cankered area near the soil line or may be completely girdled just below the soil by a blackish collar. Mechanical injuries to the stalk help start the disease.
Avoid damage to stems or roots during transplanting.
Diseases caused by Viruses:
Mosaic virus (calico), Tobacco mosaic virus.Young leaves are usually distorted and show various degrees of pale-yellow and intense dark-green mottling. Older leaves develop both white and brown dead areas that resemble rust. The newest growth on the plant usually shows the most severe symptoms of distortion and stunting. The virus is extremely persistent and can be carried in chewing and smoking tobacco, on hands, implements, and clothing, and in the soil on plant debris. The disease spreads readily from infected plants to healthy ones when handled during cultural operations.
Control measures are based on sanitation to avoid successive handling of infected material and healthy plants. Avoidance of smoking or chewing tobacco when handling plants has proven helpful in reducing infection. Elimination of infected plants is also indicated, with suitable care to avoid contact with healthy plants. Washing the hands thoroughly with strong soap after handling infected plants eliminates the chance of further spread by handling.
The potato aphid and the green peach aphid commonly infest flowering tobacco plants. See Aphid fact sheet. Among the products registered for use in Connecticut, imidacloprid applied as a systemic for root uptake will provide season-long control.
Colorado potato beetle, Leptinotarsa decemlineata.
Adults and larvae of the Colorado potato beetle occasionally feed on flowering tobacco. Among the products registered for use in Connecticut, imidacloprid applied as a systemic to be taken up by the roots will provide season-long control. Other effective products include Beauveria bassiana and Bacillus thuringiensis var san diego products, which work well in combination. See Colorado potato beetle fact sheet .
Perhaps 14 or 15 species of moths, the larvae of which are called cutworms, feed on flowering tobacco. All belong to the family Noctuidae, and all are somber-colored moths. In most cases, the larvae feed at night and remain just below the soil surface during the day. Most of these cutworms reach a length of 1 to 2". They are smooth, naked caterpillars, dull gray, greenish or brownish in color, indistinctly marked with spots and longitudinal stripes. Some have one generation each year and others have two or more, but most of those that are troublesome in the field are probably of the single generation type that hibernate as partly grown larvae. Most of these commonly feed on grasses and weeds, but will feed upon a variety of plants when cultivation or other causes destroy their regular food supply. A few species are able to travel across large plowed fields to find food.
See Cutworm fact sheet.
Garden springtail, Bourletiella hortensis.
Minute, dark purple, yellow-spotted insects eat small holes in the leaves of seedlings. These insects have no wings but are equipped with forked, tail-like appendages by means of which they project themselves into the air. They are usually found only on small plants near the surface of the soil. Control is not usually necessary.
Potato flea beetle.
This small, black, active beetle feeds chiefly on the undersides of the leaves and may damage the foliage. Injury is usually most severe to newly set plants early in the season. See the Flea beetle fact sheet.
Stalk borer, Papaipema nebris.
The eggs of this caterpillar are laid in the fall by the moths on surrounding grasses and weeds. After hatching in the spring the borers feed on these plants and later may migrate into adjacent plants where they cause injury. The caterpillars are very active. Their restless habit of frequently changing from one plant stem to another increases the damage. Keeping the borders of the garden well-mowed and controlling weeds may help deny these insects their breeding grounds.
Tobacco hornworm, Manduca quinquemaculata.
The larvae of this insect and that of the tomato hornworm often feed upon the leaves of flowering tobacco. When fully grown, this larva is about 4" long, green with oblique whitish bands along each side and a horn on the tail end of the body. The adults of both moths have mottled gray-brown forewings and a wingspread between 4 and 5". Although these caterpillars become large and consume a substantial quantity of leaf material, they are rarely abundant enough to require more than handpicking in gardens. Their abundant natural enemies usually regulate the population. Among the compounds registered for control of this pest in Connecticut are Bacillus thuringiensis var. kurstaki, spinosad, or rotenone, which must be used when larvae are still small. Handpicking is more effective in gardens when the larvae are larger and more obvious. Consult the label for dosage rates, safety precautions, and preharvest intervals.
The greenhouse whitefy, Trialeurodes vaporariorum, the sweetpotato whitefly, Bemisia tabaci, and silverleaf whitefly, Bemisia argentifolii, commonly infest flowering tobacco under glass, as well as many other kinds of plants, and are often carried into gardens where they may persist. The life cycles of these species are similar. The tiny, white moth-like adult has a mealy appearance due to the small particles of wax that it secretes. It lays groups of eggs on the undersides of leaves. The eggs hatch into small oval crawlers, which then settle down and become scale-like nymphs that suck sap from stationary locations on the leaves. These then spend about 4 days in an immobile pupal stage before becoming adults. About 5 weeks are required to complete the life cycle in the greenhouse.
Yellow sticky traps are an effective way to monitor populations of whiteflies, and may even be attractive enough to reduce minor infestations.
Biological controls can be effective against whiteflies, especially in a greenhouse environment. The predatory ladybeetle Delphastus pusillus, specializes in whiteflies and feeds on all three whitefly species. The parasitoid, Encarsia formosa, can control the greenhouse whitefly in the greenhouse, but not the other species. Another parasitoid, Eretmocerus californicus, attacks all three species and can assist in controlling minor infestations in the greenhouse. Insecticidal soap or ultrafine horticultural oil, sprayed on the undersides of leaves, can be used against whiteflies in the greenhouse or the field. Azadiractin (neem) and fenoxycarb are registered for control of this pest in Connecticut; to be most effective these materials have to be directed to the undersides of the leaves. Repeat applications of sprays will probably be needed because insecticides do not affect some stages in the life cycle. Chemical control using conventional insecticides is difficult because of widespread insecticide resistance. Consult the label for dosage rates and safety precautions.