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Raspberry Horntail Research Update

unknown parasite found in currant cane
Raspberry horntail parasitoid larva
A variety of species of parasitoids were found inside the raspberry canes, but have not yet been identified.  The top images shows a pupa of a parasitiod wasp, and the bottom image shows a larva.

Raspberry horntail, Hartigia cressonii, is one of the most damaging pests of raspberries in Utah. The horntail exclusively attacks first-year growth (primocanes). 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. For more information and images, see the Utah Pests Fall 2009 issue.

Research at the USU research farm in Kaysville in 2009 and 2010, in summer- and fall-bearing raspberries, showed that cane wilting was first detected in late June to early July (Fig. 1). Young larvae tunneling upward in canes were present earlier, but visible symptoms were not evident until this time. Horntail densities peaked in early July in both years, and then declined by mid August.

raspberry horntail graph
Fig. 1.  Raspberry horntail abundance in summer- and fall-bearing raspberries in 2009 and 2010, Kaysville, UT.

Several species of parasitic wasps were found attacking horntail larvae within canes. Parasitism rates peaked at 33-100% in late July in both years, and were slightly higher in 2009 than 2010 (Table 1). Parasitism of horntail larvae infesting summer-bearing raspberry canes was higher than for fall-bearing raspberries in both years.

Table 1.  Parasitism rates of raspberry horntail larvae in 2009 and 2010, Kaysville, UT.
  % Parasitism of larvae
  Summer varieties Fall varieties
Date 2009 2010 2009 2010
June 24 0 - 9.1 -
July 1 - 0 - 25.6
July 8 35.1 25.8 41.7 20.0
July 15 32.1 21.7 25.5 44.1
July 22 - 73.1 - 47.1
July 29 98.4 59.1 10.0 33.3
August 5 61.5 80.0 25.0 0
August 13 70.0 - 40.0 -

There was a wide range in susceptibility of raspberry varieties to horntail, and variability among the two years (Table 2). For 17 summer-bearing varieties evaluated, Royalty, Cascade Dawn, Cascade Delight, and Moutere were the least susceptible in the two years of study, while Canby, Willamette, Reveille, and Saanich were the most susceptible. For 10 fall-bearing varieties, Polana, Caroline and Summit had the fewest horntail and Jaclyn, Himbo Top, and Anne had the most, especially in 2010.

Table 2.  Susceptibility of 17 summer- and 10 fall-bearing raspberry varieties to raspberry horntail in 2009 and 2010, Kaysville, UT.
Summer Variety Mean # Larvae 2009 Mean # Larvae 2010    Fall Variety
Mean # Larvae 2009 Mean # Larvae 2010
Royalty 2.8 0.3 Polana 3.0 1.8
Cascade Dawn 1.5 2.0 Caroline 4.8 2.0
Cascade Delight 1.8 2.8 Summit 5.5 3.3
Moutere 3.0 2.0 Heratige 8.3 1.5
Coho 4.8 1.8 Ruby 5.3 4.5
Cowichan 4.3 2.3 Joan J 3.3 7.3
WDNV2 6.3 1.0 Polka 7.5 3.3
Georgia 4.5 4.8 Jaclyn 4.3 6.8
Chemainus 5.5 3.8 Himbo Top 3.0 8.3
Tulameen 5.8 3.8 Anne 5.5 11.3
Titan 5.3 5.3  
Cascade Bounty 6.0 6.8
Lauren 10.8 2.0
Canby 8.5 5.8
Willamette 12.0 4.3
Reveille 10.3 6.5
Saanich 7.0 12.3

The primary control tactic for horntail has been to prune cane tips when tip-wilting is evident, which removes fruit-producing buds. For fall- or ever-bearing varieties, pruning canes at ground level in the spring will remove larvae that have overwintered in the previous year’s canes, and help reduce populations. Using an insecticide against adults in the late spring may reduce egg-laying and cane infestation. In 2010, several commercial raspberry fields were treated with insecticides in early June when adult horntail wasps were first observed, and resulting control levels were moderate to good. Research is ongoing to better define the adult emergence period and improve predictive timing for control.

-Diane Alston, Entomologist