Raspberry Horntail

Raspberry Horntail, Hartigia cressonii, is one of the most damaging pests of raspberries in Utah. The horntail exclusively attacks first-year growth. The upward tunneling of young larvae in the cambium and heavy feeding of larvae near the tips of canes can cause the cane tip to soften, wilt, and die back. The downward tunneling of older larvae in the center pith can cause structural damage to the canes. Damaged canes have reduced fruit yields

Raspberry is an important agricultural crop in Utah. Utah growing conditions are conducive to caneberry production, and there is a strong local market for the tasty fruits.

The eggs of the raspberry horntail are pearly white and oblong, with a curved point at one end. Mature larvae are white and cylindrical, with dark heads and a short spine on the tail end. They have three pairs of legs, no prolegs, and attain a length of up to 1 inch (2.5 cm). The adult wasps, which are seldom seen, vary from 0.5 to 0.75 inch (12–18 mm) in length. The females are marked with bright yellow and black; the males are mostly black.

Life Cycle: Beginning in April, female horntails insert their eggs just under the epidermis, about 2 inches below the tips of the canes, causing pronounced swelling inside new shoots. Eggs are pearly white and oblong, with a curved point at one end. The eggs hatch into very small larvae a few days after being laid. The young larvae spirally girdle the tips of the canes and cause wilting. The cane becomes weak in the area of the crook and often breaks at this point during pruning and training. The larvae later feed throughout the terminal portion of the cane, which often causes dieback. When mature, larvae burrow down the canes in the pith and spend the winter in silk-lined cells in the burrows. In spring they pupate and the adults emerge through a round hole cut in the sides of the canes. In some locations they may have two generations per year.

Damage: The raspberry horntail exclusively attacks first-year growth, or primocanes. Both summer- and fall-producing varieties of raspberries are attractive hosts. The upward tunneling of young larvae in the cambium and heavy feeding ofolder larvae near the tips of canes can cause the cane tip to soften, wilt and die back. Cane-tip wilting becomes evident in June and July. In larger diameter canes, less wilting symptoms have been observed. The cane tip may recover, but the cane is crooked and weakened.

The downward tunneling of older larvae in the center pith in late summer can cause structural damage to the canes. Damaged canes may die, break off, and have reduced fruit yields. Yield loss studies have not been conducted, but when canes die back or are pruned to remove horntail larvae, the number of fruit-producing buds is reduced.

Tips of young shoots damaged by horntails wilt during the spring. The tips of the cane may girdle and wilt. The cane may suffer dieback by the summer. Cutting open the affected portion of the cane may reveal the thick white worm or the tunnel containing brownish granular material.

Controls: Prune plants to remove developing stages before adult emergence(early May in Colorado). Prune plants to remove developing stages before adult emergence (early May in Colorado).

Healthy plants are less attractive to insect pests and better able to withstand environmental stresses. Good crop production practices include selection of suitable planting sites, selection of raspberry varieties adapted to a site, soil preparation before planting, maintaining optimal soil fertility, and prevention of nutrient deficiencies such as iron chlorosis, which is common to alkaline soils of Utah. Use of good production practices is important to reduce horntail infestation.

Prune and destroy infested canes when tip-wilting becomes apparent; this will remove larvae and reduce the population for the next season. Wilting of cane tips is apparent from June to August. Cut the canes about 6 inches below the tip to ensure that larvae are removed. Cane tips with a larva feeding in the pith often become soft. In small plantings, or if infestation levels are low, larvae can be killed by squeezing the soft cane near the tip with gloved fingers. Prune or mechanically destroy horntail larvae one to two times per week to ensure that larvae do not tunnel down the canes and escape removal.

Natural Enemies: Parasitic wasps attack horntail larvae during late June to mid August in northern united states. Parasitism of horntails occurs in the upper portion of canes where cane diameter is smaller and tissues are softer to facilitate egg-layingby parasitoid adults into canes.

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