Aphids are the sucking insect pest which are major attacking pest in vegetable crops. Since they can reproduce and multiply in very short period and can cause direct or indirect effect to the production of farmers, special attention for management of this pest is necessary. Their reproduction and multiplication rates are higher at high relative humidity, farmers should be aware about their damage in the production system, which we are going to describe it in this coming section.
Identifying damage symptoms:
Aphids have light green to green or yellow or yellow mixed or black color of body. They have very soft body and the back part of abdomen consists of two thin tail like structure. They may be both winged or wingless which prefer to remain in gregarious form (mass or group). Nymph aphids are alike to adult in their body color and shape but they are comparatively smaller than adults.
Major aphids found in Nepal are Green peach aphid (Myzus persicae), Cabbage aphid (Brevicoryne brassicae), mustard aphid (Lipaphis erysimi), Cowpea aphid (Aphis craccivora), Bean aphid (Aphis fabae), Cotton aphid (Aphis gossypii), Banana aphid (Pentalona nigronervosa) etc which have high occurrence.
Female aphid either reproduce sexually or parthenogenetically (asexually where male is not needed) which are fully developed within a week and start reproducing themselves. As they have short life span, their number reaches maximum within very short period. Their infestation problem is higher during winter season than summer season.
Aphids suck the juice or sap from leaves, young branches, flowers and fruits with their sucking mouth parts which cause disease infestation to the plants, stunting, yellowing leading to production loss. There will be no pod formation or even pods are formed there will be poorly grain filling and development. Aphid infested leafy vegetables are not suitable for consumption. Apart from this, different viral diseases (Mosaic, leaf rolling, spindle, veinal necrosis, etc.) are transmitted by aphids in the crop. Aphids excrete sugary excreta which is called honey dew where fungal growth occurs to cause fungal diseases and the portion is later turned into black leading to poor photosynthesis eventually causing more and more disease. Infested leaves consist of green raised spots in them. Cooler climate favors the faster development of aphids. Aphids generally cause indirect effect rather than direct effects.
Monitoring is very important aspect of Integrated pest management (IPM). If assessment of pest occurrence is carried out in the early stage, management practices can be carried out without causing hazard to environment or only in localized area or using low chemical amount. Survey surveillance is carried out to monitor the insect pest in the field. Monitoring is to be done before pest attack the crop considering the following points:
- When observing both sides of vegetable leaves if there is presence of aphids and climate is also favorable for their growth and development; then management practices should be followed.
- For monitoring the winged aphids, install 4 yellow sticky traps per ropani area at crop height and if aphids are sticked in that trap, management practices should be then carried out as mentioned below:
Integrated Management practices:
For the best management of aphids, monitoring and applying the management practices are necessary which will be wise decision.
- Apply balanced fertilizer in the crop. Using higher dose of nitrogenous fertilizer cause greater succulence in leaves which are easily attacked by aphids.
- Plant the healthy seedlings which are raised in nursery surrounded with net on all sides.
- Natural enemies like ladybird beetle, chrysoperlla and different predatory insects feed on aphids which are to be protected for environment friendly management practices to work out. Department of Entomology Khumaltar has already developed Chrysoperlla mass rearing techniques.
- Apply the ash powder in the morning period. Also apply red soil at the surface of plants is also found useful.
- Soap water or soap water + ash powder will be beneficial in controlling aphids. For the mixture, apply ash in water at the rate of 1:4 ratio keeping it for 12 hours and filtering with clothes and mixing 10 grams soap per liter filtrate.
- Neem seed kernel extract, tobacco extract solution, Mint leaves/stem extract, titepati leaves/stem extract, Bakaino seeds extract, soap + tobacco leaves extract etc. are mixed and added to water at proper amount and sprayed to control the aphid.
- Cow urine in the ratio of 1:4 with water is also applied. Bitter & Spices crops like Khirro, Neem, Titepati, Asuro, Sisnu, Pyaaj (Onion), Garlic (Lasun), Bakaino, Bojho, Banmara, Ketuki, Simal, Gandhe, Besar, Bhaimara, Pire jhar, Timur, Aduwa (ginger), Surti (tobacco) etc. are mixed with cow urine and fermented to form JHOLMOL and kept for 20-35 days in the closed tank. After that it is filtered and the filtrate is mixed with water in ratio of 1: 6 and sprayed in the crop for aphid control.
- Biopesticide like Verticillium lecani @ 1 ml or if powder @ 2 gram per liter is mixed in water and sprayed to control the aphids. It has no effect to environment.
- Spray Derrisom @ 2 ml/liter of water in the crop.
- Spraying of Malathion 50% @ 1-2 ml/liter of water or Dimethoate 30 EC @ 1 ml per liter of water is sprayed at 15 days interval.
- Spraying of Nitenpyram 10% @ 0.75 ml per liter of water will completely eradicate the aphids from the crop but it is mainly use in crop for seed production which has relatively lower effect in human health.
Important point to consider is that to prevent resistance development by insect pest, same pesticide/ insecticide should never be used in the same crop cycle. Alternatively use the pesticide to prevent resistance development. Hapazard use of insecticide can cause outbreak of secondary or minor pest. So, before applying pesticide consult with specialist for proper recommendation.