Bean Bollworm

Disease

Bean Bollworm

Helicoverpa armigera

insect

In a Nutshell

    Young larvae feed within flower buds, flowers and podsFeeding damages on leaves and stems can cause defoliationBlack holes and larvae hanging out of pods can be observedPods may shrivel or contain half-eaten seeds

Hosts: %1$s

· Bean

Symptoms

Eggs are yellow-white to brown, about 0.5 mm in diameter and are laid in clusters around floral structures and young leaves. Young larvae can feed on all parts of the plant but they prefer to feed on the flowers and pods of beans. In large pods, the larvae also attack the seeds, resulting in shriveled or half-eaten seeds. Damaged flowers abort and do not set pods at all. Black holes, larval frass, and sometimes larvae hanging out of the pods while feeding are visible on the pods. If no flowers or pods are available, larvae may also feed on leaves and shoots. Severe infestations cause defoliation and considerable yield losses.

Trigger

Adults are about 1.5 cm long and have a wingspan of nearly 4.0 cm. Their gray brownish body has a hairy thorax and light-brown forewings with a light brown band lined with blackish spots on the margins. Hindwings are white with yellowish margins and have a broad black edge with a paler patch. Females lay yellowish white eggs on plants which are flowering or are about to flower. Larvae have variable aspects but they usually have little black spots scattered over the body and dark heads. Lines and bands also develop on their bodies as they grow older. The duration of the different life stages is tightly linked to environmental conditions, mostly temperature and the availability of food.

Biological Control

Try to keep up a population of beneficial insects attacking helicoverpa like Trichogramma wasps, Microplitis, Heteropelma, Netelia sp. and predatory bugs like big-eyed bug, glossy shield bug and spined predatory shield bug. Some ant species and spiders also attack the larvae of Helicoverpa. Bio-insecticides based on spinosad, nucleopolyhedrovirus, Metarhizium anisopliae, Beauveria bassiana and Bacillus Thuringiensis can also be used. Botanical products, such as neem extracts, chili or garlic may be applied as foliar sprays to control the pest.

Chemical Control

Consider an integrated approach together with preventive measures and biological treatments. Monitor population levels to ascertain the necessity of a chemical approach. The insect has developed a certain degree of resistance to insecticides based on pyrethroid.

Preventive Measures

    Chose a tolerant varietyKeep a minimum distance between your plants at sowingTry to grow large and vital plants with a good fertilization schemeTry to keep up a population of beneficial insectsAvoid to over-irrigate the fields as this would favor the pestMonitor your plants frequently and check the presence of the larvae regularlyIntercrop with non-host species to stop the progression of the pestPlow after harvest to expose the larvae to predators




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