Brambles - Production Management and Marketing

Bulletin 782-99

Chapter 4 Insects and Mites

The intent of this chapter is to assist bramble growers in the diagnosis of frequent arthropod problems. Some of the injury inflicted is slow to develop, and growers often do not recognize symptoms. It is important for the growers to frequently walk fields to examine for pests. Growers should be familiar with symptoms of all of the primary pests mentioned here. Often, pests build up in a bramble patch over a period of several years until production is severely curtailed. One of the most underestimated of the bramble pests is the raspberry crown borer.

Our aim in this publication is to give you some hints as to cultural control but not to cover chemical control. The number of applications of chemicals can be reduced through pest management, i.e., being familiar with the pest and being able to recognize potential problems.

Root and Crown Pests

Raspberry Crown Borer, Pennisetia marginata (Harris)

The raspberry crown borer is the most insidious pest of bramble crops in North America. The movement of this clearwing moth into a field is so gradual that it goes practically unnoticed. Even after a field is heavily infested and with little vigor, it is difficult to pinpoint the culprit due to the cryptic nature of the larval state.

Symptoms
Above-ground symptoms are visible only to the trained eye. Loss of vigor and spindly canes can be confused with disease symptoms; however, when individual canes are withered, wilted, and bent over with dying or dead foliage, commonly with half-grown fruit still attached, suspicion of raspberry crown borer is justified. The final proof is to put on leather gloves and give such canes a tug. Infested canes will break away easily, revealing borer damage. At times, a larva will be found in the portion of the cane that broke off.

The injury to the crown is conspicuous only if the plant is dug up and the crown examined. Telltale signs are the girdled roots and crowns, and cavities burrowed into the exterior of crowns. Often, to find a larva or pupa in an infested crown, it is necessary to cut it open. This is a difficult task even with long-handled loppers or a strong pair of pruners.

Life History
Unlike most other bramble pests, the raspberry crown borer lays eggs individually on the underside of the leaflets in late summer (Figure 23). The larva begins its two-year life cycle by forming a blister-like hibernaculum just below soil level at the base of a stem. In the spring, the larva bores extensive galleries and, by the middle of the second summer, the crown may be extensively damaged. At midsummer, pupation begins and by late August the clearwing moths, strongly resembling yellowjacket wasps, begin to emerge. After mating, a female lays about 140 eggs, and a new cycle begins.

Figure 23: Eggs of raseberry crown borer are laid individually on the underside of a leaf.

Description
The larval stage does all of the damage. Young larvae are small and white with a light-brown head. By the second winter, larvae are 12 to 19 mm (1/2 to 3/4 inch) in length. They become mature, 25 to 31 mm (1- to 1-1/4-inches) long (Figure 22) by the following July, and pupate. The pupae are about 19 mm (3/4-inch) long and reddish-brown in color. They pupate inside the base of the plant.

Figure 22: Mature larva of raspberry crown borer extracted from crown of raspberry or blackberry.

The adult (Figure 21) is a clearwing moth in the same family (Sesiidae) as the peachtree borer, lesser peachtree borer, and lilac borer. It has a black body with four yellow transversal stripes. Its appearance is quite similar to a yellowjacket wasp.

Figure 21: Adult female of the raspberry crown borer. Note yellow jacket like apperence.