 |
ProCrop |
Diamondback Moth (Plutella xylostella)
The migrating diamondback moth usually arrived in late May or early June in the north central part of North Dakota. It’s life cycle takes about 32 days to complete from egg to adult. There are several generations during a single growing season, so all different life stages (eggs, larvae, pupae, adults) can be found in the field at the same time. The adult is small about 1/2 inch long, drab brown in color and at rest the forewings of the male moth form three diamonds - hence the name diamondback. Females lay up to 160 eggs during the night. Egg hatch in five to six days into pale yellowish-green caterpillars with a forked posterior end. The newly emergence larvae burrow into the leaf and mine the leaf for several days to a week. Then, the larvae exit the leaf and feed externally for another 7 to 14 days. When disturbed, the larvae thrash backwards violently and often drop from the plant on a strand of silk. The larvae pupate for 5 to 15 days in a white net-like cocoon attached to the leaves, stems or seeds.
Larvae feed on the leaves, buds, flowers, seed pods, the green outer layer of the stems, and occasionally, the developing seeds. The amount of damage will depend on the crop stage and the larvae densities and size. Extensive feeding on the flowers will delay plant maturity, cause the crop to develop unevenly, and significantly reduce seed yield. As leaves wilt and drop in late July to early August, the larvae will feed on the stem, pods, and developing seeds. Damaged seeds will not fill completely and may shatter. Severely damaged pods appear whitish in contrast to the normal yellowing and browning of ripening pods.
Pest Management
Sex pheromone traps are useful tools for detecting the flights of the adult diamondback moth. The recommended trap design is the sticky wing trap suspended near the crop at the field’s edge. Traps provide an early indication of a possible infestation. There is usually 2-3 flights in North Dakota. The second flight is the most important flight because it is usually present when the crop is susceptible to damage, blooming to early podding. The third flight is usually too late to damage most crops except for the very late planted fields.
If high numbers of adults (>100 moths per trap week) are being captured in the traps during bloom to early pod development, monitor fields for diamondback larvae by beating or dislodging the larvae from plants. Again, check several locations per field. The action threshold for canola at the pod stage is about 20 per square foot (two to three larvae per plant). No threshold has been established for the early flowering stage, however, insecticide applications are likely required at larval densities of 10-15 larvae per square foot (one to two larvae per plant). Early monitoring of adults and larvae, and judicious use of insecticides only when fields are above thresholds are the best pest management practices for preventing losses from diamondback moth on canola. A number of natural factors can also negatively affect diamondback moth populations. For example, the heavy rainfalls in June drowned many larvae of the first generation during 1998. Humid conditions associated with rainfall can also favored the development of fatal fungal diseases like Entomophthorales. In addition, there are several parasitic wasps and predators (flies, lacewings, pirate bugs, spiders and birds) that prey on the larvae of diamondback moth.
For more information see the Insect Control guide at http://www.ext.nodak.edu/extpubs/plantsci/pests/e1143w1.htm
Back to Insects - Canola
Menu
Back to Canola Menu
Back to Main ProCrop Index
