In India, wheat crops are typically thought to have less bug and pest difficulties. However, since the "green revolution" and the introduction of the rice-wheat farming system in the Indo-Gangetic plains, insects that were previously thought of as minor pests of wheat, such as aphids, pink borer, and armyworm, have been observed to cause considerable harm to the crop.
More than 11 different aphid species have been identified as attacking wheat crops in India, although only four are known to be the most common: Rhopalosiphum maidis (Fitch), R. padi (L.), Sitobion avenae (Fab.), and S. miscanthi (Takahashi). The most commercially significant aphid species of the Northwestern Plains is R. maidis, which is also known as the corn leaf aphid (CLA).
The aphids attack wheat crops starting at the seedling stage, but because of their small size and green color, they are difficult to discern on the crops, especially during the vegetative stage. By draining the sap from the plants, the insect can reduce output directly by 3–11%, or indirectly by 20–80% by spreading viral and fungi infections. Additionally, the importance of storing wheat has grown as the Government of India stores 40–45 million tonnes of wheat through government programs.
Numerous insect species are connected to grains and grain products under storage circumstances, but 14 species are well adapted to living in grains and are in charge of the majority of the damage.
About 175 species of insects and mites are considered minor pests, and their numbers can become harmful to grains and grain products. In one season, almost all insect pests that attack grains in storage may multiply impressively quickly, destroying 10-15% of the grains and contaminating the remaining grains with unpleasant flavours and odours. The chemicals that result from this process are extremely harmful to human health since they can lead to acute dysentery and chronic conditions like liver cirrhosis and cancer.
A variety of management choices namely., cultural, physical, mechanical, biological and chemical methods have been tried for management of insect-pests in field as well as storage conditions.
1. Aphids (Sitobion avenae, Rhopalosiphum padi and various other species)
Distribution: All wheat growing areas, especially in North West Plain Zone (NWPZ) and Peninsular India.
Development: The aphids come in a variety of phases, including wingless (apterous), winged (alates), sexual, and asexual varieties. Through asexual reproduction, when females give birth to nymphs instead of eggs, the spread happens quickly. Up until crop maturity, infestation typically takes place during the second fortnight of January.
Management: They can do significant harm when feeding in large numbers, although under typical circumstances, losses are minimal. If the number of aphids per tiller during the vegetative phase and the reproductive phase exceeds 10 and 5, respectively, chemical insecticides are advised to control this pest in wheat. However, this pest must be watched carefully. Spraying single spray of 20 g Actara/Taiyo 25 WG (thiamethoxam) in 80- 100 litres of water per acre using knap sack sprayer or in 30 litres of water per acre with power sprayer will provide effective defense against this pest. The number of this pest is often kept in check by natural enemies found in the field.
Punjab Agriculture University also suggested their neem extract by boiling 4.0 kg terminal parts of the shoots of neem trees including leaves, green branches and fruits in 10 litres of water for 30 minutes. Then, filter this material through muslin cloth and use the filtrate for spraying at the recommended dose
2. Brown Wheat Mite (Petrobia lateens)
Distribution: In most of the wheat growing areas, under rainfed conditions, especially in the states of Rajasthan, Haryana and Madhya Pradesh. Sometimes, under irrigated condition the pest can be seen in humid and warm weather conditions.
Development: Brown wheat causes harm by sucking mouthparts of mite infestation. Mites can leave leaves with a silvery flecking when they are abundant. The size of individual mites prevents easy observation with the naked eye. Shaking the infected leaves on a white piece of paper will reveal them.
Management: Most of the time, mites do not limit wheat yield, thus no control procedures are necessary. However, it's crucial to keep an eye out for this pest so that it doesn't influence the next cropping order.
3. Army Worm (Mythimna separate)
Distribution: Mostly in the warmer climates of central India and to some extent in northern plains.
Development: The larvae are found in the cracks of soil and hide during the day but feed during night or early morning. In wet and humid weather, they may feed during day time also. They survive during summer on the subsequent crops like rice and also continue to exist in rice stubbles before wheat crop comes in the field. Recently, this pest is catching attention in the northern India under Rice-Wheat rotation and where rice stubbles / straw remains in the fields.
Management: As per PAU (Punjab Agricultural University) suggestion spraying 80–100 litres of water per acre with a hand-operated knapsack sprayer or 30 litres of water with a motorized sprayer when using 40 ml Coragen 18.5 SC (chlorantraniliprole*) or 400 ml Ekalux (quinalphos). Spraying should be done in the evening when armyworm larvae are more active for the pesticide to work more effectively. These pesticides are also effective against aphids. Alternately, before initial watering, spread an acre with 20 kg of damp sand mixed with 7 kg of Mortel/Regent 0.3 G (fipronil) or 1 litre of Dursban 20 EC (chlorpyriphos).
4. Legume Pod-borer Helicoverpa armigera (= Heliothis armigera)
Distribution and Importance: This is a polyphagous insect that attacks various legumes as a pod border. It is seen damaging wheat ear heads at grain development stage when major hosts are not available. However, the damage is below economic threshold level. It is found mostly in northern and central parts of India. Wheat can serve as a bridge host for carry over of this polyphagous pest.
Management: Spray 800 ml Ekalux 25 EC (quinalphos) in 100 litres of water per acre with hand operated knap sack sprayer.
5. Termites (Odontotermis obesus, Microtermis obesi)
Distribution: Mainly in the northern and central India, but also in some pockets of peninsular India.
Early Symptoms of Damage: Termites attack the crop at various growth stages,
from seedlings to maturity. The severely damaged plants can be easily uprooted and look wilted and dried. In case roots are partially damaged, the plants show yellowing.
Management: For effective management, chemicals like endosulfan, chlorpyriphos and carbosulfan can be used both for seed treatment and for broadcast of treated soil in standing crop.
As per the management suggested by PAU (Punjab Agriculture University) treating the seed by diluting 40 g Cruiser 70 WS (thiamethoxam) or 160 ml Dursban/Ruban/Durmet 20 EC (chlorpyriphos) or 80 ml Neonix 20 FS (imidacloprid+hexaconazole) in one litre of water and spray the same on 40 kg seed spread as a thin layer on the pucca ground or tarpaulin or polythene. Seed treatment with Neonix also control smuts of wheat. Seed treated with insecticide is less attacked by birds.
Generally, termites cause more damage in sandy soil and irrigating the affected fields result in some control of termite damage. In case of severe infestation, broadcast 7 kg Mortel 0.3 G (fipronil) or 1.2 litre Dursban 20 EC (chlorpyriphos) per acre mixed with 20 kg of moist sand before first irrigation.
