210 Mmbaga and Oliver: Effect of Biopesticides on Foliar Diseases and Japanese Beetle Arboriculture & Urban Forestry 2007. 33(3):210–219. Effect of Biopesticides on Foliar Diseases and Japanese Beetle (Popillia japonica) Adults in Roses (Rosa spp.), Oakleaf Hydrangea (Hydrangea quercifolia), and Crapemyrtle (Lagerstroemia indica) M.T. Mmbaga and J.B. Oliver Abstract. This study evaluated efficacy of biopesticides for reducing foliar diseases and feeding damage from Japanese beetle adults on hybrid T rose (Rosa spp.), oakleaf hydrangea (Hydrangea quercifolia), and crapemyrtle (Lagerstroemia indica). The materials tested included household soaps with Triclosan active ingredient (Equate and Ajax), kaolin clay (Surround), neem seed oil extract (Triact 70 and Neem Gold), potassium salt of fatty acids (M-Pede), horticultural oil (UltraFine Sunspray oil), and bicarbonate salt (Armicarb) applied to plants grown under greenhouse, shadehouse, and field conditions. Two fungicides, trifloxystrobin (Strobilurin) and triadimefon (Triazole), and the insecticide carbaryl were included for comparison. All materials tested were effective in controlling black spot (Marssonina rosae, anamorph Diplocarpon rosae) and powdery mildew (Sphaerotheca pannosa) of roses. Kaolin was effective in reducing disease severity of bacterial leaf spot (Xanthomonas campestris) on oakleaf hydrangea and powdery mildew of crapemyrtle. Based on data from repeated trials, the biopesticides were as effective as conventional fungicides in suppressing foliar diseases. Kaolin clay was as effective as carbaryl in controlling Japanese beetle adult feeding damage on oakleaf hydrangea, roses, and crapemyrtle, but other products were not effective. Results from this study indicate kaolin clay may be an alternative product to conventional pesticides in foliar diseases and insect pest management for roses, oakleaf hydrangea, and crapemyrtle. Key Words. Black spot; fungicides; insecticides; Japanese beetle; pest management; powdery mildew; Xanthomonas leaf spot. Nursery production of ornamental plants relies heavily on conventional pesticides to manage disease and insect pests (Sinclair et al. 1993; Windham 1994; Hagan and Mullen 1995; Garber and Hudson 1996; Daughtrey and Hagan 2001; Jones and Benson 2004). Powdery mildew fungi (Oidium spp. and Oidiopsis spp.) are widespread and problematic in the production of many ornamental plants, including Cornus florida, Quercus spp., Lagerstroemia spp., Photinia serru- lata, Lonicera spp., Malus spp., Platanus spp., Syringa spp., Magnolia liliflora, Euonymus spp., Hydrangea spp., Rosa spp., Spirea spp., Leucothoe spp., and Viburnum spp. (Sin- clair et al. 1993). In addition to reducing the aesthetic value of landscape plants, powdery mildew reduces leaf expansion, photosynthetic capability, and overall plant growth (Ellis et al. 1981). Powdery mildew caused by Sphaerotheca pannosa (Wallr. Ex Fr.) (anamorph Oidium spp.) is a serious disease in green- houses and field grown roses (Horst 1995). Roses are also affected by black spot [Marssonina rosae (Lib.) Lind, ana- ©2007 International Society of Arboriculture morph Diplocarpon rosae Wolf]. Black spot (Figure 1) is a devastating and widespread problem that often occurs in epi- demic proportions in landscape roses, but it is less of a prob- lem in greenhouses as a result of the use of drip irrigation and relative humidity control (Horst 1995). Black spot overwin- ters on infected buds or leaf debris, and once established on a susceptible host, it is a persistent problem causing severe defoliation (Horst 1995). The optimum temperature for black spot is 21°C (69.8°F) to a maximum of 33°C (91.4°F) (Horst 1995; Philley et al. 2001). Free moisture (i.e., 100% relative humidity) for at least 7 hr is required for spore germination and infection establishment. No infection occurs at relative humidity below 90%. Thus, good air circulation around plants reduces disease severity. Oakleaf hydrangea (Hydrangea quercifolia Bartr.) and crapemyrtle (Lagerstroemia spp.) generally have few disease problems. However, when grown under warm, humid to moderately wet conditions, oak leaf hydrangea are suscep- tible to a bacterial leaf spot (Xanthomonas campestris L.)
May 2007
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