348 the sufficiency ranges for nutrients in the soil and possibly fertilizer recommendations. These recom- mendations depend on the laboratory procedures, plant, soil type, soil pH, soil electrical conductivity, nutrient ratios, cation exchange capacity, and organic matter content. It is important to use the same laboratory, sampling techniques, and testing procedures to properly observe changes over time. Table 1. Average concentration for Taxus baccata and sufficiency range for Taxus × media ‘Hicksii’ for dry weight tissue nutrients in 5 to 7.5 cm summer collected terminal cuttings (Mills and Jones 1996). Taxus baccata Phosphorus Potassium Calcium Magnesium Sulfur Manganese Boron Copper Zinc Molybdenum 1.98 0.21 1.21 0.60 0.16 0.14 36 490 17 4 114 0.30 Taxus × media ‘Hicksii’ Dry weight concentration of macronutrients (%) Nitrogen 2.0–4.0 0.17–0.40 1.00–2.00 0.60–1.25 0.20–0.30 0.15–0.17 Dry weight concentration of micronutrients (ppm) Iron 75–250 100–650 20–65 10–30 25–300 0.12–0.50 ADDITIONAL THREATS In addition to soil, water, and disease management, some insects can damage Taxus. Major insect pests include Otiorhynchus wistariae (black vine weevil), Otiorhynchus ovatus (strawberry root weevil), Cecidophyopsis psilaspis (Taxus bug mite), and Pen- tamerismus taxi (false spider mite) (Hibben and Cahilly 1996; Fraedrich 1999). Otiorhynchus wistariae is the most common and attacks Taxus by leav- ing semicircular holes or notches along the edges of the needles. The grub-like larvae may feed on roots, which could also cause needle chlorosis and dieback (Kaiser and Ward 2013). The other three pests tend to cause needle stippling (Hibben and Cahilly 1996). Many times, insect populations are at tolerable levels, but levels can occasionally reach a threshold where pest management is necessary. Taxus in the landscape are oſten situated near walkways and roads. De-icing salts applied to these areas to manage snow and ice can injure roots and foliage. Roots can be damaged by the high salt content that remains in soil near treated areas. Foliar symp- toms may not be apparent until plant growth begins in the spring when needles will rapidly turn brown, ©2014 International Society of Arboriculture Taylor: Preventing Death and Taxus which typically occurs on areas of the plant nearest to the salt applications (Kaiser and Ward 2013). SUMMARY AND RECOMMENDATIONS In review, the largest threat to Taxus in the landscape is saturated soils and Phytophthora root rot. Choos- ing the proper location and soil upon planting will lead to healthier, longer-lived plants. In situations where established plants are growing in areas prone to saturation, strategies should be implemented to reduce the degree and longevity of the saturated soils. This can be accomplished by grading the soil or installing swales to reduce the flow of water to the area of concern; redirecting downspouts; incorpo- rating organic matter into the soil, which will help flocculate and aggregate soil particles to improve drainage; installing French drains to move water away from the area at a faster rate; and reducing the potential of compaction from foot and vehicle traffic. Excessive mulching should also be avoided, since this will reduce the rate that soil dries, and coarse mulch should be preferred compared to shredded products that can compact and hold water (Smiley et al. 1999). Although wet conditions should be avoided with Taxus, plants can also suffer from periods of drought. Irrigation should be used during dry periods, particularly with newly installed plants. If saturated soil is a problem, the likelihood of infection by Phytophthora is much greater. Precautions should be taken to avoid the potential for infection. Phytophthora can be spread by soil cultivation equipment, irrigation water, or by using infected plant material (Gallo et al. 2007). Phytophthora cinnamomi, in particular, can readily be spread by irrigating with creek and pond water collected as runoff from infected areas (Mebalds et al. 1996). Even if there have not been host plants in the area, P. cinnamomi has appreciable competi- tive saprophytic ability and oospores can persist for long periods in fallow soil (Zentmyer and Mircetich 1966; Smiley et al. 1999). Additionally, disturbing soil during construction projects can damage roots and make plants more susceptible to disease. If plants in the landscape are thought to be infected with Phytophthora, testing should be done through the local plant disease diagnostic clinic. Each may have their own procedure for collecting samples and testing. ImmunoStrip® test kits are also available to
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