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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
Email Richard.Cowles@po.state.ct.us
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INSECT PROBLEMS Fletcher scale, Parthenolecanium fletcheriThis small, brown, hemispherical soft scale overwinters as a fully-grown female or as eggs under the female's scale cover. Crawlers hatch in May or June, settle onto twigs or needles, begin feeding, and grow a scale cover. High scale populations lead to stunting of growth, stickiness from honeydew, and unsightly growth of sooty mold. Crawler activity can readily be monitored with double-sided adhesive tape encircling branches infested with adult scales. The incidence of Fletcher scale is directly influenced by weevil management activities. Several species of beneficial parasitoids (Kosztarab 1996) normally maintain this scale at low populations. Sprays of bendiocarb and bifenthrin, in particular, used for controlling black vine weevil adults exclude parasitoids and scale populations resurge. The insecticides used to kill scale crawlers and black vine weevil are mutually exclusive, so chlorpyrifos or diazinon (scale killing insecticides) may be tank-mixed with the weevil spray. Finding ways to eliminate the use of broad-spectrum insecticides against black vine weevil thus may also reduce the need to apply chlorpyrifos or diazinon to control Fletcher scale. Approximately 34% of yew acreage in Connecticut is infested with Fletcher scale. Controls Available Chemical ControlChlorpyrifos (Dursban Allpro 4E). This product is applied at the rate of 1 lb a.i. /100 gal. when crawlers are active. With 100 - 1000 gal/Ac., this translates to 2 - 10 lb per acre. Diazinon (Diazinon 4E or 50 W). This product is applied at the rate of 0.5 lb a.i. /100 gal. when crawlers are active. With 100 - 1000 gal/Ac., this translates to 0.5 - 5 lb per acre. Imidacloprid (Marathon 1G or 60 W). This product can be used at a rate of up to 0.4 lb/Ac of a.i. However, the current pricing of this product would entail a cost of $800 per acre, and growers have not adopted its use. Malathion (Malathion 8E). This product is used at a rate of 1 - 2.5 pt/100 gal, which translates to 1 - 25 lb/Ac of a.i. Oil (dormant oils, SunSpray Ultrafine Oil, Lesco Horticultural Oil). Oil on yew can be applied at a 3% concentration (v:v) as a dormant application, or a 1 - 2% concentration (v:v) during the growing season. As a non-residual contact insecticide, oil requires thorough coverage, so growers tend to apply higher volumes of spray than for other foliar applications (200 - 1,000 gal./Ac.). This translates to use rates of 2 - 12 gal/Ac of product. Other issues. Materials with good activity against black vine weevil adults tend to not control Fletcher scale, and vice versa. The elimination of foliar sprays of long residual, broad-spectrum insecticides, especially carbamates and pyrethroids is necessary to prevent disruption of the scales' natural enemies. Therefore, shifting from the current practices towards applying oil or imidacloprid should have immediate value in IPM. Mealybugs, Dysmicoccus wistariae and Pseudococcus affinis Plants infested with either species (taxus mealybug or obscure mealybug) end up with white cottony masses on leaf surfaces and in leaf axils. These insects damage plants by sucking sap, further resulting in honeydew, which supports the growth of sooty mold. Shipments containing infested plants may be rejected by plant inspectors and then must be destroyed. Approximately 16% of yew acreage grown in Connecticut is infested with mealybugs. This pest is normally controlled with insecticides directed for control of Fletcher scale, so no special sprays were applied to control mealybugs in 1999. Controls Available Chemical ControlChlorpyrifos (Dursban Allpro 4E). This product is applied at the rate of 1 lb a.i. /100 gal. when crawlers are active. Imidacloprid (Marathon 1G or 60W). This product can be used at a rate of up to 0.4 lb/Ac of a.i. However, the current pricing of this product would entail a cost of $800 per acre, and growers have not adopted its use. 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 thorough coverage, and so growers tend to apply higher volumes of spray than for other foliar applications. Other issues. Intensive spray practices to eliminate Fletcher scale also tend to control taxus mealybugs, thus making this pest of much less importance. The elimination of foliar sprays of long residual, broad-spectrum insecticides, especially carbamates and pyrethroids is necessary to prevent disruption of the mealybugs' natural enemies. Therefore, shifting from the current practices towards applying oil or imidacloprid should have immediate value in IPM. |
| Production Facts | Insect Problems: Black Vine Weevil | Insect Problems: Fletcher Scale & Mealybugs |
| Insect Problems: Mite Pests & White Grubs | Insecticide Products | Herbicide Products & References |
| BLACK VINE WEEVIL BIOLOGY AND MANAGEMENT ARTICLE |
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