Arboriculture & Urban Forestry 32(2): March 2006 63 species on 3 m (10 ft) centers in February 2000 at the Davey Big Tree Nursery, Jacksonville, Florida. The soil is a sandy loam. Plastic tree shelters were placed around the stem of each tree. Trees were fertilized annually with commercial fertilizer (N15-P5-K15) at 336 kg/ha (300 lb/ac) using a broadcast spreader. Plots were treated twice annually with the herbicide Roundup at label rate to control weeds in the rows. In April 2002, 50 trees of approximately the same size (height, stem diameter, and canopy spread) of each species were selected as test trees. Ten groups of five nearby trees were designated as test blocks (replicates) for each tree spe- cies. Individual trees in each of the ten blocks were randomly assigned one of five treatments. The design for each tree species was a randomized complete block with ten replicate blocks each with the following five treatments: 1. MycorTree Injectable was injected with water at label rate at 150 psi in1L(1qt) volumes, 20 cm (8 in) deep in soil, at eight locations uniformly placed in a 60 cm (24 in) radius area over the root zone of each treated tree. This treatment was applied once in April 2002. This inoculant contains spores of two ectomycorrhizal fungi (Pisolithus tinctorius and Scleroderma citrinum), spores of four species of VAM fungi (Entrophospora columbiana, Glomus etunicatum, G. clarum, and G. in- traradices), six species of spore-forming rhizobacteria (Bacillus licheniformis, B. megaterium, B. polymyxa, B. subtilis, B. thuringiensis, and Paenibacillus azoto- fixans), complex carbohydrates to support microbial growth, sea kelp, and humic acids. 2. Compete Plus and Yuccah were applied as an8L(2 gal) drench each month for 5 months at label rates over a 60 cm (24 in) radius area over the root zone. Compete Plus contains a cocktail blend of the aforementioned six species of spore-forming rhizobacteria, plus Streptomy- ces griseoviridis and Trichoderma harzianum, complex carbohydrates to support microbial growth, sea kelp, and humic acids. Yuccah is a wetting agent derived from natural saponin and increases the wettability of soil, which aids in the dispersal and soil penetration of the microbes and other ingredients in the inoculant. 3. A combination of treatments 1 and 2. 4. Subdue was applied as a soil drench at the label rate in a 60 cm (24 in) radius around each treatment tree at study installation to control fine root diseases associated with Phytophthora and Pythium species. 5. Nontreated control. One root ingrowth (RIC) core, a 7.5 cm (3 in) diameter × 20 cm (8 in) long perforated plastic core (Marx et al. 1997), was placed about 20 cm (8 in) from the stem of each test tree and 20 cm (8 in) deep in the soil. Each RIC was filled with root-free soil collected from around test trees. A total of 150 RICs were installed. All trees in treatment groups 1, 4, and 5 were drenched with 8 L (2 gal) of water over a 60 cm (24 in) radius of the root zone each month for 5 months to standardize the water applied in treatments 2 and 3. In August 2002, all trees were pruned to shape the canopy. Study Assessments Stem diameters were taken 10 cm (4 in) above the root flare on the north side of each test tree at study installation in April 2002 and in April 2003. In April 2003, RICs were removed by cutting roots from around the outside of each RIC. Soil and roots in each RIC were removed and roots were separated from the soil overa4mm mesh (0.16 in) screen. Roots were wrapped in moist paper towels, placed in a labeled Ziploc plastic bag, and stored in coolers with freezer tabs. One day later they were refrigerated. After 4 days, fine roots 2 mm diameter (0.08 in) or less were separated from roots of vari- ous weeds, washed, and weighted (fresh weight). The fine roots of both oak species were visually assessed (5× magni- fication) for ectomycorrhizae, and the elm roots were as- sessed for VAM development after standard root clearing and staining and microscope procedures (Kormanik and McGraw 1982). All data were statistically analyzed using standard analysis of variance, and significantly different (P 0.05) means were further separated using the Duncan multiple range test. RESULTS Survival of the test trees was not affected by treatment. All of the live oaks survived and 44 of the 50 test trees (88%) of laurel oak and Drake elm survived. Live Oak Measurements of root growth were confounded by weed roots in the RICs. Many ectomycorrhizal roots were lost dur- ing their physical separation from the weed roots. Fine root production was significantly greater for trees treated with the mycorrhizal fungi with and without the rhizobacteria plus Yuccah than the other treatments (Table 1). Many of the ectomycorrhizae were formed by P. tinctorius and S. citri- num. These specific ectomycorrhizae were identified based on their color, morphology, and mycelial strand features. These morphotypes were not observed on noninoculated trees. Although the percentage of fine roots colonized by the introduced fungi was low, significantly more were observed on the fine roots of trees in the mycorrhizal fungi treatment with and without the rhizobacteria and Yuccah. The inci- dence of naturally occurring ectomycorrhizae was very low. Compared to noninoculated trees, Subdue and the rhizobac- teria treatments had no effect on ectomycorrhizal develop- ment of live oak. The stem diameter of trees receiving the mycorrhizal fungi and rhizobacteria treatments was significantly greater than ©2006 International Society of Arboriculture
March 2006
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