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Crucifer Flea Beetles (Phyllotreta cruciferae)
The Crucifer flea beetle has a single generation a year. The adult beetles overwinter in the shelterbelts and leaf litter near last year’s canola fields. The adults start to emerge as the temperatures warm up to 68oF. Depending on the temperatures, populations will emerge at a slow pace with cool temperatures or at a fast pace with warm temperatures. The tiny, black colored flea beetles with a metallic bluish sheen move into the canola fields just as the seedlings are emerging. Adults feed on the cotyledons and first true leaves of seedlings causing pitting and coalescing of holes in the leaves. This is the most damaging stage and can lead to seedling death and significant stand loss. Eggs are laid in the soil and hatch in 12 days into larvae that feed on the roots of the canola plant. The larvae feed for 3-4 weeks, pupate for 1 week, and then emerge as the new generation of adult flea beetles in mid July to early August. These beetles feed on maturing crops by chewing on the epidermis of green pods, stems, and leaves for several weeks. Fortunately, populations of summer flea beetles are usually not high enough to cause serious damage like the stunted growth of the pods. However, if pod feeding is increasing and spreading throughout the field, control may be necessary to prevent small seeds and shattering during harvest. After feeding, the adult beetles move into shelterbelts and other overwintering sites. Large numbers of summer populations often indicate that flea beetle pressures may be high next spring.
Pest Management
Currently, the most effective control measure is the use of insecticides. The seedling stage is the critical period, and insecticides need to be applied as a seed treatment or at-planting versus foliar application to protect the crop from flea beetle damage. If growers used treated (e.g., gaucho) canola seed, the seedlings should be protected for at least part of the seedling stage. Gaucho usually provides approximately 3 weeks of protection or 2 weeks after canola emergence in the field. In contrast, lindane treated seed will protect for only 11 days after seeding or 5-6 days after emergence.
Remember that adult flea beetles are active and continually emerging for a 3-4 week period in the spring. As a results, field monitoring is critical for any untreated or partially protected fields, or fields with a history of high flea beetle populations. Growers should watch his seedling fields for flea beetle attack on a daily basis following germination. Check several locations in the field (e.g., edges and center). Hot, sunny weather increases feeding activity and movements; while cool, damp weather slows feeding and favors crop growth. In some instances, crucifer flea beetles can move quickly and infest large fields by flying; in other instances beetles invade slowly and creep moving from plant to plant in a field. Yellow sticky traps can be used as monitoring tools to indicate when and how many flea beetles are moving into fields.
If the seed treatment did NOT provide adequate protection or were not used, a foliar insecticidal application may be necessary. However, foliar applications are ONLY recommended when an ECONOMIC THRESHOLD is reached -- 25% OF THE PLANT’S SURFACE DAMAGED. When flea beetle populations are high, more than one application may be required due to the short residual of insecticides labeled for crucifer flea beetle control in ND, and the threat of re-infestation from surrounding areas. Foliar applications must be applied quickly for effective control. One of the problems growers’ face is being able to cover large numbers of acres quickly when feeding pressure is high. Registered products in ND for foliar applications include: capture (2.1-2.6 fl. oz/acre), ethyl-methyl parathion (0.5 lb/acre), and methyl parathion (0.5 lb/acre). All of these insecticides are highly toxic insecticides and EPA restricted use product.
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