Description of the Pest
When at rest, the adult diamondback male moth's wings meet over its back to show three yellow diamonds. The female moths are about 0.4 inch long and lay minute eggs singly or in groups of two or three on the undersides of leaves. Each female lays an average of 75 eggs. First instar larvae mine leaves, then are external leaf feeders for the remaining three instars. Mature larvae are about 0.4 inch long, are pale green and wriggle actively when disturbed. An openly woven silk cocoon holds the pupa in place under leaves. Development from egg to adult is 29, 16, and 12 days at temperatures of 68°, 77°, and 87°F, with the greatest survival at 77°F.
Diamondback moth larvae chew small circular holes in leaves from the undersides, giving the leaves a shot-hole appearance. Very high populations can defoliate plants. Affected flowers include sweet alyssum, stock, candytuft, wallflower, and other plants in the cruciferous family.
A number of parasites, both tachinid flies and parasitic wasps, attack Lepidoptera larvae and reduce their population growth rate. However, most of these larvae continue feeding through to the last instar, so parasitized larvae will still damage crops. Viruses also do not usually kill the larvae until later instars. The parasitic stingless wasps Cotesia plutellae, Diadegma insulare, and Microplitis plutellae are commercially available for control of diamondback moth. Applying insecticides other than Bacillus thuringiensis (Bt) products are likely to exclude parasites because the residues are lethal to these beneficial insects. For more information, see BIOLOGICAL CONTROL.
Because these pests feed on a large variety of plant species, keep production areas free of weeds (e.g., mustards) that serve as hosts to diamondback moths. Exclusion of winged adults can be accomplished by covering openings to greenhouses with screens. Screens are especially important when lights are used at night in greenhouses to control flowering because lights attract adult moths. Individual seedling flats may also be covered with screens to exclude adults and larvae. Row covers can be a practical measure to exclude moths in field production as long as the mesh prevents entry of adults and the row cover is held above the plant surface to eliminate oviposition through the fabric. Also, intermittent overhead irrigation can disrupt oviposition by diamondback moth.
Monitoring and Treatment Decisions
If Bt sprays are planned, use pheromone traps to determine adult flight activity and mating. Once adults are caught in traps, it is very likely that larvae are present and Bt should be applied as soon as possible because it is most effective against young larvae. Use regular visual inspections of plants to detect larvae and their damage. Diamondback moth is resistant to many insecticides. For guidelines on when to treat, see ESTABLISHING ACTION THRESHOLDS.
Selected Materials Registered for Use on Greenhouse or Nursery Ornamentals
Read and follow the instructions on the label before using any pesticide. Before using a pesticide for the first time or on a new crop or cultivar, treat a few plants and check for phytotoxicity. Also consider pesticide resistance management and environmental impact.
|Manufacturer||REI1||Mode of action2||Comments|
(PT Pyrethrum TR)
|Whitmire MicroGen||12||3/—||An aerosol.|
|insect growth regulator||A.||azadirachtin
|OHP||4||un||Must contact insect. Repeat applications as necessary. Label permits low-volume application.|
|Chemtura||12||15||May damage poinsettias if used over labeled rate.|
|Valent||4||11||Most effective against early instar larvae; pheromone trapping recommended for timing applications.|
(Orthene T, T&O Spray)
|Valent||24||1B||A number of chrysanthemum varieties have exhibited phytotoxic reactions. In greenhouse only labeled for greenhouse use on anthurium, cacti, carnation, rose, orchids, some foliage plants, young poinsettia, and some varieties of chrysanthemum. Can stunt new growth in roses.|
(PT 1300 Orthene TR)
|Whitmire MicroGen||24||1B||An aerosol only for greenhouse use.|
|Whitmire MicroGen||12||3||Check label. A fogger for greenhouse use only.|
|FMC||12||3||Label permits low-volume application.|
|OHP||12||3||Label permits low-volume application.|
(Tame 2.4EC Spray)
|Valent||24||3||Label permits low-volume application.|
|Wellmark||12||3||Label permits low-volume application. Also labeled as a cutting dip at 5 fl oz/100 gal.|
|FMC||12||3||Direct application to blooms may cause browning of petals. Marginal leaf burn may occur on salvia, diffenbachia, and pteris fern. Label permits low-volume application. Do not apply more than 2 lb a.i./acre/year.|
|4||5||Do not apply more than 10 times in a 12-month period. Compatible with most beneficials, but highly toxic to bees and hymenopteran parasites. Direct contact can cause significant mortality to Phytoseiulus persimilis.|
|1||Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing.|
|2||Rotate chemicals with a different mode-of-action Group number, and do not use products with the same mode-of-action Group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a Group number of 1B; chemicals with a 1B Group number should be alternated with chemicals that have a Group number other than 1B. Mode of action Group numbers are assigned by IRAC (Insecticide Resistance Action Committee).|
|3||PBO = piperonyl butoxide|
|*||Restricted use material. Permit required for purchase or use.|
|#||Acceptable for use on organically grown ornamentals.|