The cranberry girdler, Chrysoteuchia topiaria, was first identified as a pest in British Columbia in 1981. Pheromone traps have been used to confirm presence of adults at nurseries throughout the province. A related species, Tehama bonifatella, (previously called Crambus nevadellus), has recently been found girdling container seedlings. These two species are small, snouted moths (family Pyralidae) and are a common pest of grasses. Because the larvae produce a characteristic webbing at the feeding site, they are known as sod webworms.
Cranberry girdler larvae attack bareroot 2+0 Douglas-fir and true firs and 2+0 container Douglas-fir and spruce during their 2nd year. To date, susceptible bareroot species have been attacked at facilities across British Columbia, but container stock has only been affected at Interior nurseries.
Larvae (Figure 67) feed on the bark and chew into the wood of the stem, leaving a ragged appearance. They generally attack the stem area 2.5 cm above and below the soil line (Figure 68) with some feeding damage to the upper roots. Major damage causes seedlings to become chlorotic unless girdling takes place late in the season, but often damage is not noticed until seedlings are lifted. By this time, larvae have formed cocoons in the soil which are hard to locate and difficult to control. Damage occurs in patches due to the solitary feeding habit of the larvae. They feed on approximately five seedlings at one location, then travel about 50 cm before feeding again.
Tehama bonifatella larvae have attacked 2-year-old container spruce seedlings at several nurseries in the Okanagan. Damage appears as a uniform ring 1-2 cm wide just at the soil line, resembling adult root weevil girdling. It differs by the presence of fine silk webbing at the surface of the container cavity and of larvae near the damaged seedling. Most damage occurs during August, but fresh girdling may be noticed as late as October. Damage occurs in small patches of 1-7 seedlings throughout the container nursery.
The adult moths are small and delicate, 1-2 cm long, with a protruding snout. The forewings of the cranberry girdler moth (Figure 70) are pale straw-colored, with touches of brown, silver, and black; the hind wings are silvery gray. Tehama bonifatella moths (Figure 71) have beige forewings with mottled brown markings and straw-colored hind wings. They are present from mid-June into July and lay up to 500 eggs each. Larvae hatch and live in the upper soil surface where they feed from late August to mid-November. Larvae are particularly attracted to sawdust placed on bareroot seedbeds to reduce frost heaving. Larvae are about 1.5 cm long, with a tan head capsule and dirty-white body covered with long and short hairs, black at the base and finely pointed.
The use of pheromone traps to monitor moth populations, combined with a foliar spray program, has proven successful in the control of cranberry girdler moths. Traps are placed 30 m apart in bareroot nurseries and open compounds, and one per greenhouse from early June to mid-August. Peak moth flight occurs from mid-June to mid-July. When an average of three moths are caught per pheromone trap in 1 week, larvae-caused damage will be significant in the fall. If this number is reached in any week, a single insecticidal spray is recommended. This spray works partly as a repellant to moths and, through contact activity, kills moths that alight on foliage to lay eggs. Cultural practices such as the removal or frequent mowing of grasses surrounding the nursery can help reduce endemic populations.
Tunnock, S. 1982. Cranberry girdler moth damage to Douglas-fir seedlings in Coeur d'Alene Nursery Idaho Panhandle National Forests. U.S. Dep. Agric. For. Serv. North. Reg. Rep. 82-28.
|
Principal, locally grown hosts |
Host age and season when damage appears |
|
Nursery type and location |
|
|
|
|---|---|---|---|---|---|---|
|
Bareroot |
Container |
|||||
|
Age |
Season |
Coastal |
Interior |
Coastal |
Interior |
|
|
True firs, Douglas-fir, and spruces |
2+0 |
Late summer to fall |
Yes |
? |
Yes |
Yes |
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Figure 67. Cranberry girdler larvae and damage. Note ragged appearance of girdled bark.
Figure 68. Cranberry girdler damage on container-grown Douglas-fir.
Figure 69. Life history of cranberry firdler (one generation per year).
Figure 70. Adult cranberry girdler.
Figure 71. Tehama bonifatella, larva and adult.