It’s the onset of a cold season, which usually starts from late June to October. Most farmers consider this season as the period to wind down their routine pest management practices. This is because the population levels of most insect pests decrease remarkably. Examples of such pests include aphids, whiteflies, thrips, spider mites, mealy bugs, fruit flies, leafminers, tomato leaf miner, cutworms, bollworms, stem and grain borers, fall armyworm and cabbage worm. A greater number of these insect pests have reduced activity in the cold season. Generally, insects are cold blooded and thus their body temperature is largely influenced by their surrounding environment. Cold temperatures usually decrease their rates of metabolism. As a result, they are less active and consume very little food. Their rates of growth and development as well as reproductive capacity are also slowed down. This explains why levels of pest’s infestation and damage on most crops are minimal during the cold season. Sometimes, there are instances of rainfall, which wash away insect pests that attach to the leaves. These are mostly the plant-sucking pests such as aphids, whiteflies, mealy bugs and spider mites. Therefore, you are not likely to see large numbers of these insect pests during the cold weather.
Contrary to the common belief that all pests die in the cold season, most insect pests have the ability to survive cold temperatures. Adults usually hide on the underside of leaves and lay eggs. Frequent periods of sunlight speed up the rates of growth and development, and also prompt these pests to emerge and thrive. Leaf-eating caterpillars and cutworms are particularly very active in the cold season. In addition, non-insect pests such as slugs, snails, beetles, millipedes and termites continue to cause significant damage to crops. Slugs and snails are especially very aggressive and feed on leaves of young vegetables. For all the farmers practising greenhouse farming, crop protection measures should be applied as usual. This is because the temperatures in the greenhouses are warmer and favourable for pests’ growth and development.
Farmers should also be on a high alert as cold and humid weather conditions favour the growth of plant pathogens such as fungi and fungus-like organisms. These pathogens cause crop diseases such as downy mildew and botrytis gray mold. Young seedlings of most crops become susceptible to damping-off diseases. Potatoes and tomatoes are also heavily affected by early and late blight.
Crop protection measures in cold season:
- Although pests’ challenges are minimal, farmers should inspect their crops regularly to avoid rapid buildup of populations and serious infestations. Special attention is required on the underside of leaves. Early infestations can be treated using homemade extracts such as neem, garlic and soap sprays. Commercial Bt (Bacillus thuringiensis) products are also effective against leaf-eating caterpillars. Pest management of early infestations prevents further spread and possible economic losses.
- Crop damages by slugs and snails can be reduced by good field sanitation practices. This involves the removal or burying of crop residues, which are used as hiding and egg-laying sites.
- Fungal diseases can be prevented by ensuring proper aeration of the crops. This can be achieved by decongesting the overcrowded crops. Removal of crop debris also limits the spread and proliferation of these diseases. In cases of attack, farmers are advised to use copper-based fungicides, which are commercially available in Kenyan agrovets. Examples include Sulcop 50 DF (Osho Chemical Industries Ltd), Isacop 50WP (Twiga Chemicals Ltd) and Demildex 50WP (Bio-Medica laboratories Ltd). Garlic extracts can also be used against downy mildew.
- Farmers should also ensure that their greenhouses are well ventilated to minimize the risks of diseases.
In conclusion, regular scouting of crops should be the custom for all farmers during this cold season. This will enable them detect the early symptoms of pests’ attack or diseases, apply prompt control measures and prevent severe crop damage.
Grace Kinyanjui is a crop protection expert pursuing a PHD in
Applied Entomology, Department of Biological Sciences, University
of Embu, Kenya. Gracekinyanjui11@gmail.com