–by Dr. Jeff Whitworth and Dr. Holly Schwarting
Dectes (soybean) stem borer damage is becoming more and more apparent as soybean harvest is delayed throughout north central Kansas. The dectes stem borer was first detected infesting soybeans in Kansas in about 1985 in south central parts of the state. Annually, the adults emerge from soybean stubble, where they overwinter as larvae, around the 4th of July. They mate and deposit eggs around soybean leaf petioles. The small larvae bore into the plants and feed, making their way into the main stem.
Dectes stem borer larvae are cannibalistic, so as these larvae come into contact with others only one survives to tunnel down the main stem to the base where they girdle around the interior of the stem, typically just prior to harvest. This girdling activity often goes unnoticed. However, the stems are weakened and wind will blow girdled plants over. Fields with significant infestations will have serious lodging, as we are seeing now in parts of NC KS. Harvesting these lodged plants is very difficult at best, and if harvest is delayed further, the grain lying on the ground may be lost to rodents, disease, etc. Infested fields should be harvested as soon as possible, hopefully before any additional lodging occurs! There is no preventative or rescue treatment available for dectes stem borers in soybeans.
For more information on the biology of the dectes stem borer, please visit Dectes Stem Borer, MF2581: https://www.bookstore.ksre.ksu.edu/pubs/MF2581.pdf
by–Dr. Raymond Cloyd
This is the time of year we start getting inquiries regarding the parsleyworm or black swallowtail (Papilio polyxenes) caterpillars. The caterpillars primarily feed on the leaves of dill, fennel, and parsley although they will sometimes feed on plants such as Queen Anne’s lace, celery, and similar plants in the carrot family (Apiaceae or Umbelliferae). Young caterpillars are mottled black and white, which results in them resembling bird droppings. Mature caterpillars possess bands of green, yellow, white, and black. Furthermore, there are six yellow spots within each black band. Full-grown caterpillars can be up to 2.0 inches in length.
Figure 1: Parsleyworm — October 2015
Parsleyworm overwinters as a pupa or chrysalis attached to the bark of trees, sides of buildings, or other protected habitats. Adults typically emerge in May and June, and mated females deposit eggs on plants in the Apiaceae or Umbelliferae family; laying several eggs per location. After eggs hatch, caterpillars feed for 3 to 4 weeks during which time they undergo a series of color changes as they mature. Full-grown caterpillars eventually move off plants to find a place to pupate. The caterpillars form gray pupae, which blend in with the surrounding background. After about two weeks, adults emerge from the pupa or chrysalis.
Figure 2: Parsleyworm Caterpillar
Adults are large black swallowtail butterflies with a wingspan of 2.0 to 3.5 inches. They are shiny black in color, occasionally with iridescent blue; and yellow bands or spots along the edge of the forewings and hindwings. The adults feed on the nectar of many different flower types. Females and males mate, and then females lay eggs that will result in the occurrence of the second generation sometime in August. There are usually two generations per year.