PESTS OF WHEAT
MAJOR PESTS
1. Wheat Aphid
2. Climbing Cutworm / Armyworm
3. Ghujhia Weevil
4. Gram Pod Borer
5. Termites
6. Molya Nematode / Cyst Nematode
7. Wheat-Gall Nematode
MINOR PESTS
8. Aphid
9. Hopper
10. Jassids
11. Wheat Bug
12. Wheat Thrips
13. Cut Worms
14. Pink Borer
15. Shootfly
16. Whorl Maggot
17. Flea Beetle
1. Wheat Aphid: Macrosiphum miscanthi (Aphididae: Hemiptera)
Distribution and status: Widely distributed in wheat growing areas.
Host range: Wheat, barley, oats, Cynodon dactylon Damage symptoms: Like other aphids, the nymphs and adults suck the sap from plants, particularly from their ears. They appear on young leaves or ears in large numbers during the cold and cloudy weather. The damage is particularly severe in years of cold and cloudy weather. A heavily manured, well-irrigated and succulent crop will harbour the pest for a longer period and suffer greater damage. Bionomics: The insects are green, inert, louse like. The nymphs and the females look alike, except that the latter are larger. It breeds at a fast rate during cold weather and reaches the height of its population in February-March when the ears are ripening. The females give birth to young ones) and are capable of reproducing without mating. During the active breeding season, there are no males and the rate of reproduction is very high. When the wheat crop is ripe and the summer is approaching, the winged forms of both males and females are produced and they migrate to other plants like doob grass (Cynodon dactylon). It is not known how the pest passes the summer and the monsoon season. In October-November, the aphids again appear on wheat. If available, barley is preferred to wheat. The losses due to aphids have been reported upto 36 per cent. ETL: 5 aphids/ear head Management: Spray 375 ml of dimethoate 30 EC or oxydemeton methyl 25 EC or monocrotophos 36SL in 500 L of water per ha. Since the aphids appear first on the borders of the crop, spray only the infected strip to check further spread.
2. Armyworm: Mythimna separata (Noctuidae: Lepidoptera)
Distribution and status: Cosmopolitan. Sporadic and has gained prominence as a pest of wheat only recently, particularly after the introduction of Mexican varieties in India
Host range: Wheat, sugarcane maize, jowar, bajra, baru grass (Sorghum halepense) and other graminaceous crops. Damage symptoms: The freshly emerged larvae spin threads from which they suspend themselves in the air and then with the help of air currents reach from one plant to another. In the early stages, they feed on tender leaves in the central whorl and later feed on older leaves and skeletonize them totally. The grown-up caterpillars throw out faecal pellets, which are quite prominent. In the case of a severe attack, whole leaves, including the mid-rib, are consumed and the field looks as if grazed by cattle. The larvae feed voraciously and migrate from one field to another. The pest may also eat away ears, including the awns and immature grains. Bionomics: Pale brown adults live for 1·9 days and lay eggs singly in rows or in clusters on dry or fresh plants or on the soil. Freshly laid eggs are round, light green, turn pale yellow and finally black. Egg period 4-11 days in summer 19 days in winter. Freshly emerged larvae are very active, dull white and later turn green. In spring, the larval stage is completed in 13-14 days, but in the winter it is prolonged to 88-100 days. In the pre-pupal stage, the insect spins a cocoon. The pre-pupal stage lasts 1-11 days during January to May. Pupation usually takes place in the soil at a depth of 0.5-5 cm, but it may also occur under dry leaves among the stubble or fresh tillers. Generally, the larvae before pupation seem to select sites near the water-channels. The pupal period is 9-13 days in May and 36-48 days in winter.
Management: The pest can be suppressed by collecting and destroying the caterpillars. (ii)Spray 500 ml of dichlorvos 85 SL or 3 kg of carbaryl 50 WP or 1.0 L of quinalphos 25 EC in 500 L of water per ha.
3. Wheat-gall Nematode: Anguina tritici (Tylenchidae: Tylenchida)
Distribution and status: Cosmoplitan. It causes ear-cockle or mamni disease. The nematode is also the carrier of the bacterial yellow slime ear-rot (tundu disease) caused by Corynebacterium tritici
Host range: Rye, spelt and emer. Oats and barley are immune. Damage symptoms: If the black rounded mamni galls are soaked in water overnight, the coat softens and a large number of larvae are set free.Affected plants are more or less stunted and their leaves are wrinkled, rolled or twisted. A variable number of grains in an infested ear may produce galls. The diseased ears are shorter and thicker than the healthy ones and the glumes are spread farther apart Bionomics: Under natural conditions, the dry galls either fall to the ground from the ripe ears or they are harvested and find their way to the stores along with the healthy produce. The galls though dry remain viable for long periods. Single gall contains 800 to 30,000 larvae which revive and become active when the gall is moistened. When wheat is sown, the galls become soft on imbibing moisture and the larvae are set free into the soil. From there, they reach the host plants, if available within a distance of one third of a metre. They rise up the plant and find a site for feeding as free parasites on the young leaves and the growing-points. Later on, as the plants approach the earing stage, they penetrate into the primordia of the flower-buds and form the galls instead of normal seed. In the developing galls, the larvae mature into males and females, as the case may be. A single gall at this stage may contain 40 females and an equal number of males. They mate within the gall and the gravid females lay a large number of eggs. The young larvae on emerging from the eggs develop up to the second stage and then become dormant. They remain in that state in the dry galls till the next sowing season. There is only one generation in a year. Management: The wheat gall nematode can be controlled by separating the galls from the wheat seed by floating them on water in a tub. The galls, being lighter, float on the surface and may be skimmed off. The seed should then be dried before sowing. (ii)The pest can also be suppressed by sowing clean seed in uninfested soil. Only one year's fallowing is sufficient to eradicate this nematode from the fields. |
