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Bruce Burdick
1109 S. Birch St.
Albany, MO 64402
660-726-5610
Email: BurdickB@missouri.edu

Hundley-Whaley Center phone
660-726-3698

Objective: The objective of this study was to try to determine the optimum time to apply Roundup to both wide rowed and drilled soybeans. Optimization in this study would be measured by soybean seed yield. The Roundup treatments would also be compared to common standards used in northwest Missouri.

Methods and Materials: The study was conducted at the Hundley- Whaley Research Farm at Albany, Missouri. It was designed as a split block study with 22 treatments. There were 11 herbicide treatments for each of two row widths. Row widths were 36" and 10". Plot size was 12' wide by 30' long.

Asgrow 3701 soybeans were planted into a conventionally tilled seedbed on June 2. Wide rowed beans were planted with a 7300 John Deere vacuum planter at the rate of 180,000 seeds/acre. The 10" rows were planted with a Tye no-till drill at the rate of 226,000 seeds/acre.

Herbicide treatments are in the table below. DAP represent "days after planting". All Roundup ultra treatments were at the rate of 1 quart/acre and each included ammonium sulfate (AMS) at the rate of 17 pounds/100 gallons of spray solution. All rates our in product amounts per acre, except additives. They are generally expressed in percent volume/volume.

Pre-emergence     Post-emergence    Post-emergence
Treatment/Acre        Timing        Treatment
-----------------------------------------------------------------
none used             21DAP         Roundup Ultra, 1 qt
none used             28DAP         Roundup Ultra, 1 qt
none used             35DAP         Roundup Ultra, 1 qt
none used             39DAP         Roundup Ultra, 1 qt
Prowl 3.3 EC, 2.9 pt  28DAP         Pursuit 2 EC, 4 oz +
                                    Status 2 EC, 12 oz + UAN, 1%
                                    and Sunnit II, 1% vol/vol
Authority Broadleaf,  28DAP         Roundup Ultra, 12 oz
6.8 oz
none used             21DAP         Galaxy, 2 pt +
                                    Poast Plus, 2.25 pt +
                                    Crop Oil Concentrate, 2 pt
none used             21 and 39DAP  Roundup Ultra, 1 qt followed
                                    by Roundup Ultra, 1 qt
none used             28DAP         Pursuit 2EC, 4 oz +
                                    Status 2EC, 12 oz + UAN, 1%
                                    and Sunnit II, 1% vol/vol
none used             21DAP         Pursuit 2EC, 4 oz +
                                    Cobra 2EC, 4 oz + UAN, 1%
                                    and Sunnit II, 1% vol/vol

The weeds present at time of the post application, and their size is in the table below. These were not the only weeds in the plot area. Just the major ones or the ones that were providing a moderate to high pressure. There was also a light infestation of ivyleaf morningglory and waterhemp.

Applica
-tion    Date      -------------   Weeds and Size   --------------
Time     Applied   Grass       Sunflower   Cocklebur   Velvetleaf
------------------------------------------------------------------
21DAP    June 23   4-6" tall   4-6" tall   4-6" tall   1-3" tall
         June 30   6-8" tall   12-18" tall 10-16" tall 4-8" tall
         July 7    8-12" tall  12-20" tall 12-15" tall 12-16" tall
         July 11   16-20" tall 24-30" tall 20-28" tall 20-28" tall
         July 11   1-2" tall   1-3" tall   2-4" tall   1/2-1" tall
         following
         June 23
         Roundup
------------------------------------------------------------------
*Grasses - approximately 50% giant foxtail and 50% large crabgrass

All herbicide applications were made with a Farmall C tractor equipped with a front mounted 12" wide boom. Nozzles were wide angle flat fan delivering 0.2 gallons of spray solution per minute. Nozzle spacings were 18" on the boom and boom height was adjusted to be 12" above the tallest plants in the plots. Spray pressure was 28 p.s.i. and the propellent was compressed air.

The weather at the Hundley-Whaley farm started off wet. Soils did not dry up until mid-May. It turned off dry after memorial day. The fist significant rain following planting and pre-emerge herbicide applications was on June 15 (0.74"), nearly two weeks after planting. The summer could be charicterized as being dry but mild. We only received 1.37" of rain in June and 1.83" of rain in July. Temperatures were in the 70 to 95 degree F for most of that period. We did experience two days of 100 degree temperatures (July 25 & 26). It turned off wet again in the fall (after mid-October) and this delayed harvest.

Weed control ratings were taken at various times during the year but only the last rating will be reported here.

Harvest was done on November 18 with a Massey Harris Super 35 combine converted to harvest small plots.

Results and Discussion: Dry weather, along with shallow seed placement in the drilled soybeans, resulted in poor stand of drilled soybeans. The wide rowed beans did emerge early and uniformily. The data in this report will only cover the wide rowed soybeans.

Figure 1 shows the weed control provided by the six Roundup Ultra treatments in wide rowed soybeans. The best overall weed control was provided by the split Roundup application. The next best treatments was the pre-emergence application of Authority Broadleaf followed by the reduced rate of Roundup. There was no statistical difference in weed control between these two treatments. The lack of weed control provided by the 21DAP Roundup application was due to a new flush of weeds following the initial application. We would have expected different and better results in the drilled soybeans if we had had a good stand. The 28 and 35 DAP Roundup applications provided good weed control but the 39DAP application failed to provided a high level of grass and velvetleaf control. This 39DAP application did control nearly all of the giant foxtail but did not control the large crabgrass in the plots.

Figure 1

Figure 2 shows the late weed control ratings of the two best Roundup treatments, compared to four standard treatments. The best overall weed control from the standard treatments was provided by the pre Prowl followed by the 28DAP Pursuit + Status treatment. The 28DAP Pursuit + Status treatment failed to control the grass species in the plots. That there was a very significant difference in the grass control provided by these two treatments was surprising, given the lack of rainfall following the pre-emergence Prowl application. The 21DAP Galaxy + Poast Plus treatment failed to control wild sunflower in this study and the sunflower pressure was heavy.

Figure 2

Figure 3 graphically illustrates the yield of soybeans for the Roundup treatments. From a statistical standpoint, there was no difference in yield from the split Roundup treatment, the Authority Broadleaf followed by a reduced rate of Roundup, the 21DAP Roundup treatment and the 28DAP Roundup treatment. The 35 and 39 DAP treatments yielded significantly less than the other Roundup treatments.

Figure 3

None of the standard treatments yielded as well as the four top yielding Roundup treatments. The Galaxy + Poast Plus, Pursuit + Cobra and Pursuit + Status treatments each yielded between 20 and 25 bushels per acre. The best yielding standard treatment was the pre-emergence Prowl followed by the 21 DAP Pursuit + Status treat- ment. It yielded 36 bu/acre which was statistically the same soybean yield as provided by the 21 and 28 DAP Roundup alone treatments. This treatment did yield significanly less than the split Roundup treatment and the Authority Broadleaf followed by a reduced rate of Roundup. Figure 4 shows a graph of selected Roundup treatments compared to the standards.

Figure 4