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Each Roundup Ultra application was broadcast at the rate of 1 quart per acre. Application of each spray solution was made using a backpack sprayer in order to eliminate the damage that might be done by spray vehicle wheel tracks. Spray solution volume was 20 gallons per acre. The herbicide carrier was water. The study was designed around the assumption that the crop variety had no effect on the final results of the work. Therefore, a Roundup Ready soybean variety was planted for all treatments in order to eliminate the risk of killing the soybeans planted in the non-Roundup treatment (treatment number 5). The study was designed as a randomized complete block with six replications, using Gylling's Agriculture Research Manager. Analysis of 2001 data was also achieved with ARM. Analysis of three year data was by SAS Statistical Analysis Program. This year the plots were planted on May 23. Prairie Brand 3550RR was the variety planted. Planting was done with a 6' wide, Tye no-till drill. Seeding rate was 224,000 seeds per acre. Row spacing was 10" wide. The standard, non RR soybean treatment (T5) was made on May 16, seven days prior to planting. Giant foxtail and common waterhemp were 1-4" tall and the pressure was rated at light to heavy, depending upon the plot treated. Two treatments (T1 & 4) required planting-time burndown treatments that were made on May 23 to light to moderate infestations of 1-6" common waterhemp & giant foxtail, and to moderate to heavy infestations of 10-12" little barley. The 2 week after planting, delayed burndown treatment (T3) was made on June 11 to moderate to heavy infestations of 1-8" tall giant ragweed, common waterhemp and giant foxtail. The 4 week after planting application (T2) required in treatment 2 was made on June 26 to light to moderate infestations of 10-14" tall giant ragweed, common waterhemp and giant foxtail. Harvesting was accomplished on October 3 using a Massey Ferguson 35 plot combine. The center 6' of each plot was harvested and weighed. Subjective weed control ratings were taken July 3 and September 10 (end-of-season rating). The end-of-season for 2001 are reported in this report. Results of 2001 test & 3 year summary: Weed control ratings taken on September 10 provided the end-of-season, overall weed control ratings as follows:
Relative to weed control, each year of the test and the mean of the three year data is in table 2 below. In 2001, treatment 5 provided considerably less end-of-season weed control than it did the previous two years. The reason for this is primarily due to the poor initial control of giant foxtail provided by the pre-emergence treatment.
The 2001 plots were harvested on October 3. The 1999-2001 plot data can be found in Table 3.
The economic calculations for the three years of data are shown in Table 4.
Discussion: There was no statistical difference in soybean yields between treatments 2 through 5 in 1999 or 2000. Treatment #1, the pre-emergence burndown treatment alone suffered from a serious and uncontrolled second flush of weeds in both years. The standard treatment failed in 2001 and it yielded significantly less than all other treatments. The lack of initial giant foxtail control, and its competitive effect on yield, is most likely the reason for this.. The highest yielding treatments, in all three years, were the treatments that required two Roundup applications (T3&4). When end-of-season weed control is considered, this data suggest that there is considerable flexibility in the application timing of the Roundup burndown that will be followed by a mid to late post treatment of Roundup. The single application of Roundup, made at four weeks after planting (T2) performed remarkably well. The three-year mean yield was significantly less than the most recommended treatment of starting clean and then applying a Roundup treatment to 6-8" tall weeds, but it did provide good yields and end-of-season weed control. From a statistical standpoint, when cost of production was considered, it was as profitable as the most recommended treatment. The standard treatment (T5 - Prowl + Canopy + 2,4-D burndown) provided poorer profitability than all other treatments. The reason for this was most likely due to the inadequate giant foxtail obtained by the initial burndown treatment in 2001. From a profitability standpoint, and when statistics were applied, all of the treatments using a post application of Roundup (T2-4) provided net returns that were the same. Even though the 4 WAP, delayed burndown treatment (T2) yielded less than the two more timely burndown treatments, followed by post Roundup, the difference in herbicide and application costs made up for the loss of soybean yield. It is evident from this work that the single, soil applied pre-emergence herbicide, weed control program requires an earlier planting date than we were able to use in 2000 and 2001. While the Canopy + 2,4-D provides good burndown control of broadleaf weeds, it provides poor control of giant foxtail that is 2-4" tall. It also lacks the ability to control winter annual grasses like we had in 2000. Earlier planting would help overcome the lack of giant foxtail control obtained from the burndown treatment but it would not overcome the problem with winter annual grass control. The results obtained in 2000 and 2001 would indicate that if grassy are present at planting time, Roundup should be substituted for 2,4-D in the initial pre-emergence application. A summary of the three year data showed that the most weed-free, end-of-season treatment was the two week after planting, delayed burndown treatment, followed by another treatment of Roundup three weeks later (T3). However, this treatment yielded significantly less than the most recommended treatment (T4) in 2001. The three year mean showed no significant yield differences. In 1999, the soybean performance in the very delayed, 4 week after planting treatment of Roundup (T2) did not suffer yield reduction from the early weed competition that was present in the plots. This treatment did not perform as well in 2000 or 2001. Some of the very large, early emerging weeds in this treatment were not controlled with the late Roundup application in 2000. In 2001, the extended competitive effect of the uncontrolled weeds early in the growing season was likely the reason for poorer soybean performance. Outreach: The study was explained in this year's Hundley-Whaley Field Day report. Over 850 copies of the report was distributed to people attending the field day. The data from this study will be shared with northwest Missouri producers at three winter meetings. The data will also be shared with north Missouri producers through newsletters and newspaper articles this winter.
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