216 Mmbaga and Oliver: Effect of Biopesticides on Foliar Diseases and Japanese Beetle Figure 3. Mean feeding damage and standard error (mean ± standard error of mean) from adult Japanese beetle in field trials for crapemyrtle (Lagerstroemia indica L.) during 2002 on (A) 11 July, (B) 28 July, and (C) 8 Au- gust. Despite these variations, Surround was consistently similar to Sevin in controlling feeding damage from adult Japanese beetles (Figure 3). DISCUSSION Alternative products for pest management, which are envi- ronmentally friendly and safer for workers, would be a valu- able addition to nursery production systems and landscape industry. In this study, we evaluated a number of biopesti- cides that are U.S. Environmental Protection Agency- registered as pesticides and other nonregistered products that are commercially available and have previously shown po- tential to control foliar diseases and pests. Among the prod- ucts evaluated, the neem-based product (Triact 70) was ef- fective in reducing foliar diseases on roses in agreement with reports by Horst et al. (1992) and Locke (1992, 1993). Other neem-based material (Neem Gold) was not as effective (Tables 1 and 2). Weekly applications of conventional fun- gicides such as strobilurines, triazoles, and benzimidazoles ©2007 International Society of Arboriculture are typically used to manage powdery mildew, whereas bi- monthly applications are used on black spot (Horst 1995). In our study, all products evaluated, including household soaps (Ajax and Equate), bicarbonate salt (Armicarb), neem seed oil extract (Triact 70 and Neem Gold), and kaolin clay (Surround) were more effective than the nontreated control and as effective as the conventional fungicides in reducing powdery mildew and black spot in roses (Tables 1 and 2). Only Surround was consistently effective in control- ling bacterial leaf spot on oakleaf hydrangea, and it was the best product for controlling powdery mildew in crapemyrtle (Table 3). Surround, UltraFine Sunspray oil (Whitmire Mi- cro-Gen Research Laboratories, Inc., St. Louis, MO), Armi- carb, and M-Pede (Mycogen Corp., San Diego, CA) are registered biopesticides for ornamental plants. Household soaps are not registered for use as biopesticides, but they are considered safe enough for household use and have repeat- edly shown potential for controlling foliar diseases (Mmbaga and Sauvé 2004; Sholberg and Boulé 2006). The slight leaf burn problem associated with soap use on hot sunny days may be eliminated by concentration adjustments. Recently, a lower soap concentration at 0.5% to 1.0% was shown to be as effective as a conventional fungicide program in controlling powdery mildew fungi in apple, cherry, and grape (Sholberg and Boulé 2006). These results support previous reports that biopesticides may be incorporated in disease management and reduce the dependence on conventional fungicides (Mmbaga and Sauvé 2004). Household soaps were not effective in reducing Japanese beetle feeding damage. Although the insecticidal soap M- Pede showed some potential in reducing adult Japanese beetle feeding damage in oakleaf hydrangea and crapemyrtle, its effect was not consistent (Figures 2 and 3). M-Pede has been reported to be toxic to beetles like coccinellid lady birds (Smith and Krischik 2000) and may have some toxicity to Japanese beetle. Neem-based products have been reported to have insect-repelling properties (Ladd et al. 1978; Held et al. 2001; Showler et al. 2004). However, Triact and Neem Gold were inconsistent and not effective in our studies. Surround was the only product that showed potential in controlling Japanese beetle feeding damage, and it was as effective as the conventional insecticide Sevin. Overall, Sur- round was the most effective compound for both pathogen and insect control. A disadvantage in using Surround is the white residue film that forms on plant foliage, which reduces the aesthetic appearance of landscape plants. The white film was tempo- rary and eventually washed off with overhead irrigation or rainfall. The sale of field nursery plants is mostly in spring when plants are dormant and have no leaves; therefore, no white Surround film would interfere with plant aesthetics. Thus, Surround would be a good alternative product in con- trolling adult Japanese beetle feeding in nurseries. In addition
May 2007
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