Plant Protection: Insect Orders, Disease Diagnosis and Pesticide Dose Calculation
This section tests insect orders and mouthparts, disease symptoms with their causal organisms, IPM logic and pesticide dose calculations.
Insects
- Lepidoptera: moths and butterflies with chewing larvae such as bollworm, fruit borer and leaf folder.
- Hemiptera: piercing-sucking bugs such as aphid, jassid and whitefly, which are major virus vectors.
- Coleoptera: beetles and white grubs with chewing mouthparts. Thysanoptera: thrips with rasping-sucking mouthparts. Orthoptera: grasshoppers. Diptera: maggots.
- Complete metamorphosis (egg, larva, pupa, adult) in Lepidoptera, Coleoptera and Diptera; incomplete in Hemiptera and Orthoptera.
Diseases
- Fungal: wheat yellow rust (Puccinia striiformis), brown rust (Puccinia triticina) and loose smut; bajra downy mildew (Sclerospora graminicola) and ergot; mustard white rust (Albugo candida); groundnut tikka (Cercospora).
- Bacterial: citrus canker and bacterial blight of cotton.
- Viral: tomato leaf curl and yellow mosaic of pulses, both spread by whitefly; use resistant varieties plus vector control.
- Nematode: root-knot (Meloidogyne) controlled by rotation with non-hosts, neem cake and nematicide.
IPM and formulations
- Sequence: cultural, mechanical, biological (Trichoderma, Trichogramma, NPV), then need-based chemical spray at the economic threshold level.
- Formulations include EC, WP, SC, granule and dust. Rotate chemical groups to delay resistance and respect the pre-harvest interval.
Worked example
Recommended dose 2 ml per litre with a spray volume of 400 litres per hectare. Product needed = 2 multiplied by 400 = 800 ml per hectare. For a 0.25 ha plot, 200 ml is diluted in 100 litres of water. If the label is a 20% EC, active ingredient applied = 800 multiplied by 0.20 = 160 ml a.i. per hectare.
Traps
- Attributing rust to bacteria; rusts are fungal.
- Confusing dose per litre with dose per hectare.
- Spraying in peak afternoon heat or just before rain, which destroys the deposit.