M.J. Wheeler, E.L. Ayes and W.E. Mitchem

1. Evaluation of Chateau Tank Mixes in Apple Wheeler*, M.J. 1 , Ayers, E.L. 2 , Mitchem, W.E. 3 1. County Extension Agent, University of Georgia Cooperative Extension, Gilmer County, Ellijay, GA 30540 2. County Extension Coordinator, University of Georgia Cooperative Extension, Fannin County, Blue Ridge, GA 30513 3. Extension Associate, North Carolina State University, Fletcher, NC 28732 ABSTRACT Weed control in apple orchards allows the limited allocation of water and nutrients to best serve the trees. A burndown study was developed to evaluate the effectiveness of different combinations of tank mixes using Chateau on three year old Arkansas Black apple, Malus domestica, var. Arkansas Black , on MM106 rootstock. In March 2007, a three ounce per acre rate of Chateau was applied to prepare the site for an early summer application of Chateau, and to encourage emergence of summer weeds. Treatments were then applied in late May. The treatments consisted of tank mixes of glyphosate at 1 qt/a, Rely at 4 qt/a + ammonium sulfate (8 lb/100 gal) + non-ionic surfactant (0.25% v/v), Rely at 4 qt/a + ammonium sulfate + crop oil concentrate (1% v/v) + Aim at 0.8 fl oz/a, Aim at 1.6 fl oz/a + Poast 1.25 pt/a + ammonium sulfate + crop oil concentrate, and Gramoxone Inteon at 4 pt/a + non-ionic surfactant. Visual estimates of control were noted nine and 28 days after application. Weed density counts were taken at the same time. Significant differences (p≤0.05) were found between the nontreated control and the treatments when evaluating percent bare ground at nine days and 28 days after treatment. There were significant differences in the total weed counts (# of weeds/ft 2 ) at nine days (p≤0.05) and 28 days after treatment (p≤0.10; actual p=0.0554). Both Rely treatments provided better control than comparable glyphosate standard, but the costs of these treatments were approximately twice that of glyphosate. INTRODUCTION Chateau is a relatively new preemergence herbicide registered for use in bearing apple orchards last year. Chateau contains flumioxazin, which when tank mixed with glyphosate the spray is prone to inversion under certain environmental conditions, moving the herbicide into the tree canopy damaging fruit. Glyphosate is the preferred postemergence herbicide for growers due to its effectiveness, but after tree leaf out it should not be tank mix with flumioxazin. A trial was conducted at the Mountain Research and Education Center in Blairsville, GA to evaluate other non-selective postemergence herbicide options for tank mixing with flumioxazin. MATERIALS AND METHODS Three year old Arkansas Black apple, Malus domestica, var. Arkansas Black , on MM106 root stock was used to establish the treatments. A five foot herbicide, 2.5 feet per side, by 20 feet strip was applied for every treatment (Table 1). The treatment application rate on a per acre basis was 27 gallons/acre. Treatment design was a randomized complete block with four replications. Table 1. Treatment Descriptions RESULTS Significant treatment differences for percent bare ground, p ≤0.05, were seen nine and 28 days after treatment (Table 2). White clover, Trifolium repens , was a significant weed species throughout the study period. A weed response across treatments was seen nine and 28 days after treatment, p≤0.05 (Table 3). In addition, significant treatment differences were observed when total weed density was measured. Total weed count, number of weeds per square foot, nine days after treatment had significant differences at p≤0.05. Total weed count 28 days after treatment had significant treatment differences at p≤0.10 (Table 4). Table 2. Treatment Differences for Percent Bare Ground, p ≤0.05 Table 3. Treatment Differences for White Clover Weed Count, p ≤0.05 Table 4. Treatment Differences for Total Weed Count DISCUSSION Bare ground treatment differences are attributed to the amount of white clover at the study site. The herbicide treatments able to control white clover did a better job at keeping the weed from re-establishing itself in the plots. This trend can also be seen by evaluating total weeds per square foot. The treatments that initially performed well, also continued to keep weeds from re-establishing in the plots. When the costs of the different treatments were included in with the analysis of the results, a clearer picture was made about these findings. Even though treatments 2 and 3 were the best performing tank mixes, they are both approximately twice the cost of treatment 1. Treatment 5 was the next best tank mix and was only 22% more than the cost of treatment 1. For most producers, using treatment 5 as a post-emergent herbicide application will provide the best weed control for the money. ACKNOWLEDGEMENTS Many thanks go to Joe Garner, Research Station Superintendent and Herman Garrett, Senior Agricultural Specialist of the Mountain Research and Education Center. Non Treated Control Treatment 2 Treatment 5 Study Site Non Treated Control 6 pt/ac % v/v oz/ac 4 0.25 8 Gramoxone Inteon Nonionic Surfactant 80:20 Chateau 5 fl oz/ac pt/a lb/100 gal % v/v oz/ac 1.6 1.25 8 1 8 Aim Poast Ammonium Sulfate Crop Oil Concentrate Chateau 4 qt/ac lb/100 gal % v/v oz/ac fl oz/ac 4 8 1 8 0.8 Rely Ammonium Sulfate Crop Oil Concentrate Chateau Aim 3 qt/a lb/100 gal % v/v oz/ac 4 8 0.25 8 Rely Ammonium Sulfate Nonionic Surfactant 80:20 Chateau 2 qt/ac oz/ac 1 8 Glyphosate Chateau 1 Rate Unit Rate Treatment Name Treatment Number 7.5 d 41.3 c 6 70.0 b 96.8 a 5 40.0 c 90.0 a 4 88.8 a 98.5 a 3 85.0 a 98.5 a 2 30.0 c 65.0 b 1 Bare Ground 28 DAA, % Bare Ground 9 DAA, % Treatment Number 8.3 abc 1.38 b 5 12.4 ab 2.88 ab 4 2.4 c 0.25 b 3 4.8 bc 1.13 b 2 13.0 a 4.75 a 1 Total Weed Count 28 DAA, #/ft 2 (p ≤0.10) Total Weed Count 9 DAA, #/ft 2 (p ≤0.05) Treatment Number 4.83 b 0.38 b 5 16.50 a 1.50 ab 4 1.50 b 0.38 b 3 0.63 b 0.00 b 2 6.25 b 2.75 a 1 White Clover Weed Count 28 DAA, #/ft 2 White Clover Weed Count 9 DAA, #/ft 2 Treatment Number