Tobacco

Pests of Field Crops in Southern Africa

TOBACCO

(Nicotiana tabacum, Solanaceae)

Text Box: See aphids in potato section. The main species of importance on tobacco is Myzus persicae, the “green peach aphid”, which is 1.25 to 2.5 mm in length, pale green to yellowish-green, with long green cornicles and antennae about two-thirds as long as the body. It is of particular importance in tobacco as a vector of rosette virus, which it may transmit to the plants both in the seedbeds and the lands. Aphid infestations often start in the seedbeds and these should therefore be kept pest-free and planted away from kitchen gardens or potato crops which are alternative hosts. Peak infestations occur in November to December and the infestation is spread by the winged forms. The strictly enforced planting and destruction dates for tobacco in Zimbabwe are based on the flight times of this aphid, and are a successful control measure to limit damage by the virus. Other species of aphids, such as “potato aphid” (Macrosiphum euphorbiae), are also recorded on tobacco. Numerous systemic insecticides, both in spray and granular form, are registered for control of aphids on tobacco. TOP

Text Box: See African Bollworm in general section. In the spring Helicoverpa armigera moths lay eggs on the buds and young leaves of tobacco plants in the fields, and the resultant caterpillars may cause considerable damage to the plants by chewing holes in the leaves or causing distortions by damaging the growing points. These may be controlled by routine spray or “cupping” applications of insecticide applied to the tops of the plants. Newer approaches involve scouting or monitoring for the presence of the pest and applying insecticides by necessity rather than the older regime of routine sprays. TOP

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General Sucking Pests

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Text Box: See general section. Cutworms may be a pest in both seedbeds and the land. In the land, control measures are generally by cupped applications applied to the base of the plants, sprays directed to the base of the plants or by general spray applications over the tops of the ridged beds. The most commonly used insecticides are synthetic pyrethroids. TOP

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Þ Tobacco Slug

Tobacco Leafminer

Text Box: Stinkbugs can be a significant though sporadic pest of tobacco. Damage takes the form of wilting or collapse of young leaves where the pest has injected its toxic saliva, and tends to be more concentrated at the borders of fields. Symptoms of damage are usually noticed rather than the pest itself, and appear a couple of days after the damage has been inflicted. Although “tobacco whitefly” (Bemisia tabaci) is widespread and common it is seldom a pest of tobacco, which is fortunate, since whitefly are capable of transmitting viruses to tobacco. Thrips (not really a sucking pest) are likewise seldom a problem in tobacco although both Thrips tabaci and Frankliniella spp. are recorded. It appears that the stickiness produced by the hairs of tobacco plants is very detrimental to these pests. In recent years, a species of spider mite, Tetranychus evansii, has on occasion been reported on tobacco, and seems to cause quality problems in the cured product. TOP

Text Box: See Tuber Moth (Phthorimaea operculella) in potato section. In the past this pest caused severe damage in tobacco in certain seasons. These days, routine sprays applied for other pests usually prevent the pest from becoming established. Leaf-mining usually begins on the lower leaves, and damage is most serious during the first few weeks after transplanting, especially when growth is slowed by hot, dry weather. The infestation can move up the plant, and sometimes larvae mine in the stems, weakening them and causing distorted or stunted growth. Not all insecticides used on potato for the same pest are suitable for use on tobacco, and only those that are approved for use should be applied. A very similar pest known as the Tobacco Stem Borer, Scrobipalpa heliopa, greatly resembles the leafminer in the larval and moth stages, but damages the plant by mining from the leaf down the petiole into the stem, and forming a gall in which it completes its development. Attack is usually on young plants where the swollen stems are quite noticeable. Pupation takes place within the galls, and the life cycle takes some two months, the moths emerging from small holes in the galls. Brinjals are an alternate host for this pest. TOP

General Sucking Pests

Text Box: This pest (Meloidogyne javanica) is not dealt with here, but is undoubtedly one of the most serious pests of tobacco. The pest is kept within reasonable levels of control by the rigid application of strict rotations with non-hosts (both other crops and grass leys), by the use of soil fumigants and nematicides, and lately by the increasing use of resistant or tolerant tobacco varieties. TOP

Root Knot Nematode

Text Box: Whitegrubs are often a problem in sandy soils, which is where the majority of tobacco is grown. Tobacco is also attacked by both “lesser” and “greater” false wireworms. The former has been described in detail already. The latter are the larval stages of the much larger surface beetles commonly called “tok-tokkies” (from their habit of beating the ground with the tip of their abdomens to attract mates), most commonly species of the genus Psammodes. These beetles emerge after the first rains of the season and lay their eggs in the soil. The resulting larvae, although still straw-coloured, cylindrical and tough skinned, reach a much bigger size (up to 30 mm in length) than lesser false wireworms and take much longer to reach maturity (up to three years). They are very tough creatures, and a situation has even been encountered where they caused serious damage to a subterranean drip irrigation system by biting holes into the submerged plastic tubing. Routine transplanting hole treatments with products such as chlorpyrifos added to the planting water mostly keep these soil pests under reasonable control. Ploughing and land preparation between seasons will also help to control those species that live for longer than a year, by disrupting the life cycle. TOP

Root Knot Nematode

Text Box: See general section. Termites of the genus Macrotermes, and Ancistrotermes latinotus, can do significant damage to tobacco. The period after transplanting into the field will place plants under considerable stress, and plants in this state are susceptible to termites. The routine transplanting hole treatments (see following pest) will usually give sufficient control. TOP

Tobacco Leafminer

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Text Box: Amongst the many pests which are found on tobacco, but which are only occasionally of significance, are the elegant grasshopper (see general section), other grasshoppers such as the edible grasshopper (Ruspolia differens), laceworm (see Cotton Leafworm), Lesser Armyworm (see pea section), semi-loopers (see soyabean section) and chafer beetles (see general section). These seldom require specific control measures, but are usually kept under control by treatments applied for more regular pests. TOP

Cutworm, found around the plant base.

Green stinkbug.

False wireworm (above). Whitegrub (below).

Semi-looper caterpillar.

Beetle of greater false wireworm (Psammodes sp).

Tobacco leaf miner. (Photo: David James, Univ. Georgia. Bugwood.org)

Tobacco budworm.

Myzus persicae adults and nymphs on tobacco. (Photo: W Cranshaw, Colorado State Univ. Bugwood.org)