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CUES: Center for Urban Ecology and Sustainability

Yews in Connecticut
Richard S. Cowles
Conn. Agric. Expt. Station, Valley Lab.
P. O. Box 248
Windsor, CT 06095
Phone (860)683-4983
Fax (860)683-4987


Mite Pests, Oligonychus ununguis
The spruce spider mite is a sporadic pest in yew nurseries, and mostly can be found in damaging numbers during the spring and fall. These mites build up to high enough populations to form webbing entirely enclosing shoots on the shrubs. If populations are left unchecked, sufficient chlorophyll can be removed from needles to make the plants unsalable. Like the sucking insects, spider mite problems mostly occur where broad-spectrum insecticides have been applied to control black vine weevil, thereby eliminating the mite predators. In 1999, 0.4% of the acres of yew required treatment for controlling spider mites.


Available Chemical Control
Abamectin, (Avid 0.15 EC). Avid is used at a rate of 4 fl oz per 100 gal. This translates to a use of approximately 8 fl oz per acre. This product is exceptionally useful for integrated management of spider mites because at this low use rate it selectively kills pest mites.

Dicofol (Kelthane 35 W or 50 W). Kelthane is used at a rate of 0.25 - 0.5 lb a.i. per 100 gal.

Oil (SunSpray Ultrafine Oil, Lesco Horticultural Oil). Oil on yew can be applied at a 1 - 2% concentration (v:v). This translates to use rates of 2 - 20 gal/Ac of product. As a non-residual contact insecticide, oil requires absolutely thorough coverage, and so growers tend to apply higher volumes of spray than for other foliar applications. Horticultural oil is highly selective, inexpensive, and effective, so it has extraordinary value for controlling spider mites.

White grubs, including the European chafer, Japanese beetle, and oriental garden beetle, Rhizotrogus majalis, Popillia japonica, and Exomala orientalis, respectively
These three species share the following aspects of their biology: adults emerge in May and June, mate, and lay eggs in the soil. Eggs require moisture to hatch. Larvae have three larval stages and usually overwinter as last instars. Their presence in a root ball can cause the rejection of plant shipments, especially to states having none or a few Japanese beetles. Damage occurs in the root system, resulting in fewer fibrous roots, consequently making harvest (and the formation of a root ball) difficult. The presence of Japanese beetles usually indicates that there has been poor control of grassy weeds, as the females orient to grasses when laying eggs (Smitley 1994). Oriental beetles are a special problem in drought years if the grower irrigates fields, because these females are attracted to moist, high organic content soil to lay eggs. Of these three species, only Japanese beetles feed to any extent as adults before laying eggs. White grubs are present in varying numbers in all yew fields.


Available Chemical Control
Imidacloprid (Marathon 1G or 60 W). This product can be used at a rate of up to 0.4 lb/Ac of a.i., and is unexcelled for virtually eliminating white grub populations (RSC, in press). However, the current pricing of this product would entail a cost of $800 per acre, and growers have not adopted its use.

Post-harvest control practices. A post-harvest Dursban 4E root ball disinfestation dip procedure is registered but is not used by growers. The reasons for not using this procedure are 1) hazards to workers, 2) requirement for specialized dipping tanks, 3) potential for phytotoxicity, and 4) high cost (chemicals, labor, and equipment).

Other chemicals. Various insecticides applied as foliar sprays for controlling black vine weevil may also have limited benefit in controlling the adult stage of white grubs. However, these beetles may not feed in the nursery, so their exposure to insecticides may be limited to their contact with treated soil immediately prior to laying their eggs in the soil. There may be potential for controlling Japanese beetle adults by spraying highly attractive food hosts adjacent to the field, such as grape foliage.

Production Facts Insect Problems: Black Vine Weevil Insect Problems: Fletcher Scale & Mealybugs
Insect Problems: Mite Pests & White Grubs Insecticide Products Herbicide Products & References

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Last modified on March 06, 2013