Pesticide Risk Reduction Strategies Initiative Interim Report

Transcription

1 Pesticide Risk Reduction Strategies Initiative Interim Report Pesticide Risk Reduction in Soybeans by Comparing Conventional, Organic and IWM systems and Soybean Cultivar Traits Dr. Andrew M. Hammermeister Dr. Darren E. Robinson Organic Agriculture Centre of Canada University of Guelph Nova Scotia Agricultural College Ridgetown Campus P.O. Box Main Street East Truro, NS B2N 5E3 Ridgetown, Ontario, N0P 2C0 Phone: (902) Phone: (519) Fax: (902) Fax : (519) ahammermeister@nsac.ca drobinso@ridgetownc.uoguelph.ca Executive Summary: Farmers hesitate to transition to reduced herbicide practices, including organic, due to challenges in weed management. The weed management priorities for soybean are: weed resistance in zero-till systems and the need for a systems approach to weed management. We compared 3 weed management strategies for soybean in on-farm demonstration trials: i) conventional zero-till (herbicides as normal), ii) integrated weed management (IWM) band-spraying (herbicides in crop row, mechanical between rows), and iii) organic (mechanical control). Analysis included effectiveness of weed control (weed species density and biomass), and yield comparisons. We will also make a cost analysis comparison, economic return, pesticide risk reduction analysis, and analyze energy use efficiency. Risk reduction analysis will be carried out using the EIQ pesticide risk measures, using provincial weed control guide recommendations to create a baseline. The study will be replicated in 5 fields and repeated over 2 seasons. One field day was held at two locations in Ontario in 2006 to

2 demonstrate the trials and to survey visiting farmers as to their perceived likelihood of adopting the IWM or organic practices. Objectives: To evaluate the efficacy of three weed management strategies for soybean in on-farm demonstration trials: i) conventional zero-till, ii) integrated weed management (IWM), and iii) organic; provide a cost benefit analyses and a measure of risk reduction from pesticides for these strategies; disseminate results of the study; and survey the likelihood of grower adoption of reduced risk weed management approaches recommended by this study. Materials & Methods: On-farm field studies were conducted at Palmyra (Litwin Farm), Blenheim (Gladstone Farm), two locations west of Chatham (Kerr Farm #1 and #2), and Fairview (Kerr Farm #3) in Ontario in Soybean ( 92M70 ) was directseeded into the stubble of a previous field corn crops at a rate of 175,000 seeds ha -1 on May 28 (Blenheim), May 29 (Palmyra), and June 5 (Chatham and Fairview). Plots were 3 m wide by 40 m long at Palmyra with row spacing of 50 cm, and 4.5 m wide by 40 m long at the other four locations in 75 cm rows. Each plot therefore had 7 soybean rows. The experiments were arranged in a completely randomized design with four replications, with three different weed management systems (conventional, integrated weed management (IWM), and organic). The conventional treatment

3 consisted of two applications of glyphosate (900 g a.e. ha -1 each) made to soybeans at the 1 st and 4 th trifoliate leaf stage. The IWM treatment consisted of an in-crop banded application of glyphosate (made at the 1 st trifoliate) plus interrow cultivation at the 4-5 th trifoliate stage of the soybeans. The organic treatment consisted of interrow cultivation and hand-weeding at the 1 st and 3 rd trifoliate leaf stages. Glyphosate was applied with a CO 2 -pressurized field sprayer, calibrated to deliver 200 L ha -1 with XR8002VS (Teejet XR8002VS Tip, Spraying Systems Co., Wheaton, IL 60188) flat-fan nozzles at 207 kpa pressure. Visual weed control was rated on a scale of 0 to 100% at 28 and 56 days after treatment (DAT). A rating of 0% was defined as no weed control and 100% was defined as complete weed control. Weed biomass was collected from three 1-m 2 quadrats per plot at 28 DAT, separated into broadleaf and grass weed species, and placed in a dryer at 60oC until they reached a constant weight, and weighed dry. The innermost three rows of each plot were harvested by hand from November 20 th to December 2 nd, and yields were adjusted to 13% moisture. Data at each location were subjected to analysis of variance (ANOVA) using the PROC GLM procedure of SAS (SAS 1999). Variances of weed control at 28 and 56 DAT, broadleaf and grass weed biomass, and yield were partitioned into the fixed effects of treatment and replicate. Error assumptions of the variance analyses (random, homogeneous, normal distribution of error) were confirmed using residual plots and the Shapiro-Wilk normality test. To meet the assumptions of the variance analysis, visual weed control at 28 and 56 DAT was subjected to an arcsine transformation and broadleaf and grass biomass data

4 were square root transformed (Bartlett 1947). Treatment means were separated using orthogonal contrasts. Means of weed control and biomass were compared on the transformed scale and were converted back to the original scale for presentation of results. The Type I error was set at 0.05 for all statistical comparisons. Results and Discussion: Weed control, weed biomass and soybean yield at the Palmyra location (Litwin Farm) are presented in Table 1. Weed control in the conventional treatment was greater than the IWM treatment. Despite the significant difference in visual weed control, weeds in the IWM treatment produced little biomass, and soybean yield was unaffected by weed competition. The soybean crop in this trial produced a canopy that covered the rows early in the season, which may have reduced weed growth by attenuating light (Légère and Schreiber 1989). Weed control was significantly less and grass weed biomass was significantly greater in the organic treatment than in the conventional IWM treatments, and there was a corresponding reduction in crop yield. Weed control, weed biomass and soybean yield at the Blenheim location (Gladstone Farm) are presented in Table 2. Weed control, grass biomass and soybean yield in the conventional, IWM and organic treatments were not different from one another, despite the increase in biomass of broadleaf weeds. It is hypothesized that the lack of yield reduction in the organic treatment occurred because early season weed control was good, and that broadleaf weeds did not

5 begin to interfere with the crop between the 1 st and 3 rd trifoliate, the critical period of interference in soybean (Van Acker et al. 1993). The effect of treatment on weed control, weed biomass and soybean yield at the first Chatham location (Kerr Farm #1) is shown in Table 3. As a result of very high grass pressure, weed control at 28 DAT was poorer and grass weed biomass was greater in the conventional treatment than in the IWM treatment. However, the grass weeds were killed by the second glyphosate application, so weed control at 56 DAT was similar in the conventional and IWM treatments. Though there was not a significant yield difference between these treatments, the IWM tended to yield higher than the conventional treatment. Weed control at 28 DAT was lower, and broadleaf weed biomass was greater in the organic treatment than in the other treatments, which corresponded to a yield reduction. Broadleaf weeds have a greater impact on soybean yield loss than grass weeds (Weaver 2001), which may explain why yield in the organic treatment was reduced more than in the conventional treatment. Weed control, weed biomass and soybean yield at the second Chatham location (Kerr Farm #2) is presented in Table 4. Weed control at 28 DAT was lower and grass biomass pressure was higher in both the conventional and organic treatments than in the IWM treatment. Despite these differences, the conventional and IWM treatments had similar soybean yields. Broadleaf weed biomass was higher and soybean yield was correspondingly lower in the organic treatment than in the IWM treatment. Again, it is hypothesized that interference from broadleaf weeds in the organic treatment reduced soybean yield.

6 The effect of treatment on weed control, weed biomass and soybean yield at the final location (Fairview) is shown in Table 5. Weed control at 28 DAT was very poor in the organic treatment compared with that in the conventional and IWM treatments, and corresponded to much higher broadleaf weed biomass in the organic treatment. Despite this difference in weed control, soybean yield was not impacted by weed control treatment, suggesting that weed interference did not influence soybean yield. References Cited: Bartlett, M.S The use of transformations. Biometrics 3: Légère A., M.M. Schreiber Competition and canopy architecture as affected by soybean (Glycine max) row width and density of redroot pigweed (Amaranthus retroflexus). Weed Sci. 37: [SAS] Statistical Analysis Systems The SAS System for Windows, Release 8.0. Cary, NC: Statistical Analysis Systems Institute. 3884p. Van Acker, R. C., C. J. Swanton, and S. F. Weise The critical period of weed control in soybean [Glycine max (L.) Merr.]. Weed Sci. 41: Weaver S. E Impact of lamb's-quarters, common ragweed and green foxtail on yield of corn and soybeans in Ontario. Can. J. Plant Sci. 81: