Diamondback moth, Plutella xylostella (L.), is commonly known as the cabbage moth.
Diamondback moth larvae feed on all plants in the Brassicaceae family, mainly Cabbage, kales and Weeds in this family. They cause damage by chewing the vegetative parts of the Crop leading to skeletonization or stunted growth by feeding on the growing points.[vc_single_image image=”998″ img_size=”full” add_caption=”yes” alignment=”center” style=”vc_box_outline” border_color=”green”]Life Cycle
Diamondback moth takes about 32 days to develop from egg to adult, but this timing can vary from 21 to 51 days depending on the environment and available food sources. Diamondback moth can have up to four generations per year. Generations usually overlap, and all four life stages (egg, larva, pupa and adult) may be present in the field at the same time.
Early infestation combined with favorable environmental conditions can produce a larger population buildup and result in greater crop damage.
Adults
The adult moth is approximately 8 to 9 mm long with a wing span of 12 to 15 mm. At rest, the moth folds its wings over the abdomen in a tent-like manner. The folded wings flare upwards and outward at the tips. The wing tips are fringed with long hairs. Moths will flutter up out of the canopy when the canopy is disturbed.
The forewing margins have a series of yellow wavy markings. When the wings are folded while the moth is at rest, these markings come together to form three yellow diamonds, hence the name “diamondback.”
Adult females lay an average of 160 eggs during their life span of about 16 days. Egg-laying occurs at night. The greatest number of eggs are laid the first night after emergence, and egg-laying continues for about 10 days.[vc_single_image image=”1000″ img_size=”full” add_caption=”yes” alignment=”center” style=”vc_box_outline” border_color=”green”]Eggs
Eggs are oval, yellowish-white and tiny. They are glued to upper and lower leaf surfaces singly or in groups of two or three, usually along the veins or where the leaf surface is uneven. The eggs hatch in four to eight days.
Larvae
Immediately after hatching from the egg, first-instar larvae burrow into the leaf and begin mining the leaf tissue internally. The three subsequent larval instars feed on the surface of leaves, buds, flowers and pods. Each instar has a duration of approximately 4 days, but the larval stage can range from 10 to 21 days depending upon temperature and the availability of food.
The larvae are pale yellowish-green to green caterpillars covered with fine, scattered, erect hairs. The posterior end of the caterpillar is forked. At maturity, the larvae are cigar-shaped and about 12 mm long.
The diamondback moth larva is easily identified by its reaction to being disturbed. It will wriggle backward violently and may drop from the plant, suspended by a silken thread. After several seconds, the larva will climb back onto the leaf and continue feeding.
Pupa
Larvae pupate in delicate, white, open-mesh cocoons attached to the leaves, stems or seed pods of the host plant. Initially, the pupae are light green, but as they mature, they become brown as the adult moth becomes visible through the cocoon. The pupal stage lasts from 5 to 15 days, depending on environmental conditions.[vc_single_image image=”1001″ img_size=”full” add_caption=”yes” alignment=”center” style=”vc_box_outline” border_color=”green”]Host Plants and Damage
Host plants of diamondback moth include all plants in the Brassicacea family. This group includes canola, mustard and the vegetable cole crops such as broccoli, cabbage, cauliflower and kale.
Crop damage is caused by the larval stage. Diamondback moth larvae feed on any green tissue of canola and mustard plants but prefer leaves. The amount of damage varies greatly, depending on plant growth stage, larval density and larval size.
Control
- Environmental control
Cool, windy weather reduces adult activity, and females often die before they lay all their eggs. Heavy rainfall can drown small larvae and reduce numbers by more than half. Humid conditions within the crop following a rainfall can promote the spread of fatal fungal diseases throughout the diamondback moth population.
- Chemical control
Despite the abundance of potential biological control agents, the only effective way of controlling a diamondback moth outbreak once the population exceeds the economic threshold is to apply an insecticide
Insecticide selection will depend on cost, environmental conditions, days to harvest, availability of product and the presence of other pests
Always consult the product label for appropriate rates and application guidelines.
Insecticides should always be applied with enough water to ensure adequate coverage. Use high water volumes and label rates when the crop canopy is dense.
Chemical Recommendation
Spray ESCORT 10ml/20l + INTEGRA 3 ml/20l and repeat the spray after 7 days.
- Cultural control
Pre-seed weed control and tillage reduce the availability of cruciferous weeds and volunteer host plants, preventing the successful establishment of first generation larvae when moths arrive before emergence.
Best Management Practices
- Early season control of Brassicaceous weeds including volunteer crops helps to eliminate host plants for early arriving diamondback moth.
- Scout for early arriving diamondback moth and larvae damage on seedlings.
- Monitor crops at least twice per week, scouting for larvae.
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