Gail A. Bresnahan, Alan. G. Dexter and Leonard W. Cook
Research Assistant, Extension Sugarbeet Specialist North Dakota
State University and University of Minnesota, Fargo and Chemist II,
Biochemistry Dept. North Dakota State University, Fargo
Pursuit is registered for the control of broadleaf weeds and grasses in soybean, dry edible bean, peanut, alfalfa and IMI corn hybrids. Pursuit is effective applied preplant incorporated, preemergence or postemergence. Pursuit will provide season long weed control through residual activity with a single soil or foliar application in the early growth stages of the crop. Sequential application 0.03 + 0.03 lb/A has resulted in improved control of both broadleaved and grass weeds as compared to a single full-rate application. Effective times of application of Pursuit varies by species and location (York et al, 1995). Pursuit residual soil activity has proved to be a valuable tool for weed control in tolerant crops. Due to long soil persistence, Pursuit also can have a negative effect on crops that are planted in years following application of this herbicide. Crops that are especially susceptible to Pursuit damage include sugarbeet, turnip, oilseed rape, canola and grain sorghum with sugarbeet being the most susceptible (Onofri, 1996). Corn has intermediate tolerance to Pursuit and must hydroxylate the herbicide rapidly to limit the amount of compound that reaches the meristematic regions of the plant (Mallipudi et al, 1994).
Imidazolinone herbicides inhibit acetohydroxy acid synthase, the first enzyme essential to the biosynthesis of a number of amino acids (Cole et al, 1989). Imazethapyr penetrates rapidly into the plant and is translocated throughout the plant system. Plant tolerance to this herbicide has been linked to individual species ability to metabolize the herbicide rapidly or, in some species, the absorption rate at different growth stages (Shaner and Mallipudi, 1991). Biodegradability has been linked to bioavailability which is affected by soil characteristics and environmental conditions following applications that may favor or inhibit microbial growth (Cantwell et al, 1989).
The focus of this research was to determine the influence of soybean density when Pursuit was applied, on the level of soil residue. To determine the influence of Pursuit residual in the soil on yield of wheat, susceptible corn and IR corn seeded in the next growing season after application.
FIELD
`McCall` soybean was seeded at 60 lb/A at a location near Prosper, ND, on May 18, 1993 in 18 cm and in 76 cm rows. One set of plots was not seeded. Pursuit at 0.06 lb/A and 0.19 lb/A was applied on July 9 and July 20, 1993 to soybean with three and six trifoliolate leaves and to base soil. Soil samples were taken at the time of application and frozen until analysis. Soil samples were again taken the following year following application. Air temperature was 21 and 28C and 6 inch soil temperature was 17 and 21C respectively. Soil moisture was good. Precipitation at Fargo for the 1993 growing season was 17 cm and for the 1994 growing season precipitation was 17 cm. Plant residue was determined at the 3 and 6 trifoliate growth stage using the line transect method (Sheldon et al, 1990). `Pioneer 3751`, and `Pioneer 3751IR` (imidazolinone resistant) corn was planted in six 56-cm wide rows and `Marshall` wheat was planted in 2 m strips with 18-cm row spacing across the plots on May 19, 1994. Wheat in 12 ft samples per plot was harvested using a combine on August 21, 1994. Corn ears were hand harvested September 25, 1994, from two rows out of the plot center.
Section 22, located 8 miles north of North Dakota State University, was seeded with `McCall' soybean on May 18, 1993. This experiment was canceled due to wet weather. Soybean was planted in 1994 employing the same procedures used in the Prosper experiment. Pursuit at 0.06 lb/A and 0.19 lb/A was applied on June 28 and July 24, 1994. to soybean with three and six trifoliate leaves. Soil samples were taken at the time of application and frozen until analysis. Soil samples were again taken the following year. Air temperature was 29 and 23C and 6 inch soil temperature was 22 and 20C respectively. Soil moisture was high. Precipitation was 19 cm for the 1994 growing season and 15 cm for the 1995 growing season. Corn and wheat were planted on May 16, 1995 using the same planting techniques as at the Prosper location. Due to flooding of the plots in 1995 the plots were not harvested.
Soil was extracted with 0.5M sodium hydroxide and then filtered and partitioned into methylene chloride. The methylene chloride was evaporated and further cleanup was achieved by passing an alkaline solution of the compound through a C-18 solid-phase extraction column. The effluent from the C-18 column was acidified and the compound extracted form the acid solution using a cationic exchange SPE column. After eluting the compound from the SPE column using a phosphate buffer, pH 6.5, the compound was partitioned into methylene chloride and concentrated for measurement by high performance liquid chromatography. A reverse phase C-8 column was used during this determination.
Pursuit soil residual, analyzed by HPLC, was greater in plots treated with 0.19 lb/A compared to 0.06 lb/A at both the Prosper and Section 22 locations (Table 1).
HPLC was also used to analyze the amount of herbicide residue in the soil as influenced by soybean density and stage of plant growth at application. Pursuit soil residues in 1993 at Prosper and 1994 at Section 22 were not influenced by soybean density or stage of plant growth at application (Table 2). Soil samples were taken again from Prosper in June 1994 and Section 22 in June 1995, negligible Pursuit residue was determined.
Percent soybean plant residue on the soil surface in 1993 at Prosper and 1994 at Section 22 was greater with solid seeded soybean than with row seeded. Plant residue was also less at the 3rd trifoliate than the 6th trifoliate stage of plant growth (Table 3).
Total wheat grain yield in 1994 at Prosper was not affected by density of soybean plants or rate of Pursuit applied in 1993. Wheat yield was not taken from Section 22 in 1995 due to Plot flooding conditions (Table 4).
The total corn grain yield in 1994 at Prosper was not affected by density of the soybean at application or the rate of Pursuit applied in 1993 (Table 5). Corn at Section 22, was not harvested in 1995 due to plot flooding.
Pursuit susceptible corn and Pursuit resistant corn(IR) was planted at Prosper and Section 22. The yield of the IR and susceptible corn was similar in all treatments at Prosper. Yield was not determined at Section 22 (Table 6).
Redroot pigweed control in both Prosper and Section 22 taken in August one year after Pursuit was applied was greater from Pursuit at 0.19 lb/A than from 0.06 lb/A in both locations. Seeding method and date of application had little effect on control.
Pursuit soil residue was not affected by soybean density at application in 1993 at Prosper or in 1994 at Section 22. As would be expected, the herbicide soil residue was greater at both locations when soil was treated with 0.19 lb/A rather than 0.06 lb/A. Although, with the higher rate of herbicide, Section 22 had less residue than at Prosper. This may be due to the wetter conditions experienced at Section 22 in 1994 compared to Prosper in 1993. Previous research by Goetz et al, 1990 suggests that amount of rainfall during the summer months after application affects the persistence of Pursuit.
Soil moisture was adequate for active microbial degradation through most of the 1993 growing season at Prosper and more than adequate in 1994 at Section 22 where water stood on the plots for part of the growing season. At Prosper, remaining Pursuit residues in 1994 were insufficient to cause yield losses in corn or wheat. No yields were taken from the Section 22 experiment in 1995 because the plots were flooded after crop emergence and water stood on some of the plots long enough to cause yield loss.
In the early growth stages, `Pioneer 3751' showed less vigorous growth when compared with `Pioneer 3751 IR'. However, when yields were analyzed, both Pursuit resistant and Pursuit susceptible corn yielded similar amounts.
Finally redroot pigweed control was greater with 0.19 lb/A than 0.06 lb/A Pursuit.
We thank Dr. James R. Fleeker and John L. Luecke for their technical assistance with this project.
1. Cantwell, J.R., Lieble, R.A. and Slife, F.W. 1989. Biodegradation Characteristics of Imazaquin and Imazethapyr. Weed Sci. Vol. 37:815-819.
2. Cole, T.A., Wehtjie, G.R., Wilcut, J. W. and Hicks, V.T. 1989. Behavior of Imazethapyr in Soybeans (Glycine max), Peanuts (Arachis hypogaea), and Selected Weeds. Weed Sci., Vol. 37: 639-644.
3. Goetz, A.J., Lavy, T.L. and GBur,Jr.,E.E. 1990. Degradation and Field Persistence of Imazethapyr. Weed Sci. Vol. 38:421-428.
4. Mallipudi, M.N., Lee,A., Fiola, R., daCunha, A.R. and Safarpour, M. 1994. Metabolism of Imazethapyr (AC 263499) Herbicide in Corn. J.Agric. Food Chem. 42, 1213-1218.
5. Onofri,A. 1996. Biological activity, Field persistence and safe recropping intervals for imazethapyr and rimsulfuron on a silty-clay soil. Weed Research, Vol. 36, 73-83.
6. Shaner, D.L. and Mallipudi, M.N. 1991 mechanisms of Selectivity of the Imidazolinone Herbicides. D.L. Shaner and S.L. O'Connor, eds. CRC Press, Inc., 2000 Coporate Blvd, N. W. Boca Raton, Florida 33431.
7. Sheldon, D.P., Dickey, E.C., Jasa, P.J., Kanable, R., and Smydra, S.R., 1990. Using the line-transect method to estimate residue cover. U of Nebraska-Lincoln Extension Service, Neb Guide G 90-981, June 1990.
8. York, A.C., Wilcut, J.W., Swann, C.W., Jordan D.L. and Walls, Jr., R.F. 1995. Efficacy of Imazethapyr in Peanut (Arachis hypogaea) as affected by Time of Application. Weed Sci. 43:107-116.
1996 Sugarbeet Research and Extension Reports. Volume 27, pages 72-82.