By: Dr. Gretchen Pettis, BioSafe Systems Entomologist
While my husband has assured me it’s too early yet for pumpkin spice lattes or fall decorations, it’s definitely not too early for nursery and greenhouse managers to think about chrysanthemum production. Hardy garden mum production is going on now for late summer and fall sales. While generally a relatively trouble-free crop, one group of key insect pests of chrysanthemum can do a significant amount of damage to flowers, foliage, and stems in a relatively short amount of time – caterpillars! Multiple species of these larvae of moths and butterflies can cause issues for mum production in the field and greenhouse.
The various caterpillar larvae attacking mums can feed on all above ground portions of mum plants. Newly hatched larvae initially cause only small holes or skeletonizing damage to select leaves. As the caterpillars grow over a 2-4 week period they begin consuming larger holes in leaves or devour entire leaves and stems. Some species will even bore into or girdle stems causing wilting and death of large portions of the plant.
The most common two species found on mums in the greenhouse and field are the corn earworm and beet armyworm. But, other species such as cabbage loopers, saltmarsh caterpillars, European corn borer, European pepper moth, and omnivorous leaf roller are all known to cause damage. Depending on the species, damage may be localized in one area of the crop or widely dispersed. As caterpillars get larger, they will often migrate to new plants in search of food.
Feeding damage from caterpillars is certainly unsightly, but the tissue wounding their chewing create can allow entry for plant disease organisms as well, so it is wise to manage caterpillars in your hardy garden mum crop. Prevention of caterpillar infestations should always be your first pest management step. Keep moths and butterflies from flying into greenhouses via doors or vents whenever possible and, for outdoor grown plants, exclusion from moth or butterfly egg laying with netting. If caterpillars do happen to infest your crop, choose a biorational option such as BT NOW. This Bacillus thuringiensis subspecies kurstaki (Btk) based bioinsecticide provides highly effective, caterpillar specific activity and preserves beneficial species that provide additional pest management benefits. BT NOW can be applied up to the day of harvest and has only a 4-hour re-entry interval and can be applied when pollinators such as honeybees are foraging.
As with any insecticide, early detection and treatment is important. BT NOW works best on young, actively feeding caterpillar larvae. Once larvae feed on BT NOW they cease feeding within hours and die within days, providing rapid protection of your crop. Good coverage of foliage will ensure that larvae quickly consume a sufficient dose. Many of the species of caterpillars that feed on mums are most active at night. Evening applications of BT NOW will take advantage of this pest behavior and protect the UV sensitive Btk spores to give you a longer period of residual activity. Treatments should ideally be done when you are not expecting rain or overhead irrigation events within 6-8 hours.
Make sure your fall mum production season is all treat and no tricks from beastly caterpillars with BT NOW.