Originally Published In The Deseret News -- Thursday, May 7, 1998
For those who noted last week's advice on planting raspberries, we now have the proverbial "rest of the story."
Unfortunately, raspberries, like most other garden plants, can be plagued by insects. Most problems do not show up until later in the season, but pests must be controlled now rather than waiting until damage is evident. Pests do not make it impossible to grow the delectable fruits, but they do make it more challenging.
Among the common aggravating pests in Utah are the borers. These include several different insects that get into and destroy raspberry canes.
Raspberry crown borer damage shows when canes wilt and become weak and spindly. The foliage turns prematurely red and dies, even on fruit-bearing canes. Infested crowns swell and the canes from those crowns can die. Infested canes break easily when pulled and the larvae may be found where they break. Injured plants have roots and crowns girdled and marked with swellings or galls. Piles of sawdust-like dust may be present.
The adult raspberry crown borer is a clearwing moth with a wingspan of 11/4 inches. Yellow bands across its black abdomen make this moth resemble a yellowjack et. Larvae are dull white with brown heads and are about 1/2 to 3/4 inches long by the end of the first summer. They reach a length of 1 1/4 inches when fully grown during the second summer.
The pest takes two years to complete its life cycle. Moths live for about a week. In September and October, hatching larvae invade canes below the soil line. In the spring they tunnel into the canes, girdle them and pass the second winter in the roots. They pupate inside the plant, then adults emerge.
Control raspberry cane borers by destroying infested canes and crowns. Diazinon may be used around the base of plants in early May to reduce larval numbers.
Other cane borer insects also attack raspberries.
The raspberry cane borer has a two-year life cycle. Adult beetles feed on the cane tips, chew two rings around canes and deposit an egg between the rings. Eggs hatch into larvae that feed inside the cane, boring down to the base by fall and into the crown by the next summer. Larvae feed at the crown level for the next full season.
Control this pest by pruning and destroying canes with wilted tips as soon as they are noticed. Foliage sprays of diazinon provide some control if applied to the base of the canes just before blossoms begin to open. Do not spray the upper plant or you will kill the bees.
Raspberry cane maggots cause wilted cane tips by tunneling inside the stem and girdling it. Canes wilt rapidly and darken in color, producing a symptom called "limberneck."
The adult is a small fly about 1/4-inch long. The larvae are legless maggots about 1/3-inch long. The pest overwinters as pupae in the soil and adult flies emerge in early spring and lay eggs on rapidly growing primocanes. Larvae tunnel inside and girdle the stem.
Cut off the infested part of canes a few inches below the girdle and destroy the prunings as soon as wilted tips are detected. Insecticides are not recommended.
Other insect pests include earwigs. These are easily recognized because they have two long pincers on the ends of their abdomens. They are difficult to control and can do considerable damage to the fruit. Hand picking or traps will sometimes help if there are not too many pests. Sprays are effective but cannot be used on bearing plants because they will kill pollinators. Scattering baits at the base of the plants will sometimes prevent major damage to the fruit.
Do not let these pests discourage you from growing raspberries. The juicy berries are a wonderful reward for keeping the pests at bay.
© 1998 Deseret News Publishing Co.