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The study was designed as a split-block with six replications. One block was used for the May planted soybeans, and the second block was used for the June planted soybeans. Plot size was 10' wide by 30' long. Weed control was planned around all of the soybeans being resistant to glyphosate (RR beans). However, the addition of the two Fontanelle varieties, which were not RR, caused us to change to a different weed control program. All plots received a pre-emergence application of Lasso + FirstRate at full labeled rates for weed control. The second block was weed free at the June 13 planting date, however, we applied another application of Lasso + First Rate at 1/3 of the full labeled rate in order to get extended weed control. The soybean seed was counted at the rate of 150,000 seeds per acre and planted with a John Deere 30" wide row planter equipped with cone planting units. Variety maturity was noted and the soybeans were harvested with an MF 35 plot combine as soon as possible after each variety was mature. The actual harvest dates were September 13 & 26 and October 3 & 18. Harvest date was based on soybean visual observations of maturity, by variety. The early maturing varieties were harvested first and the full season varieties were harvested last. Results: Early season weed control was excellent. However, cocklebur and waterhemp emergence late in the season did become an issue of concern. No post emergence herbicides were used to control these late emerging weeds, again because weather conditions did not favor herbicide application at the time the weeds should have been treated. The yield data would suggest that the late emerging weeds were not overly competitive. Several plots within the study did suffer from excess water and this resulted in poor stands. We could not obtain yield data from all plots due to the poor stands that existed in them. This was more of a problem with the soybeans in the second planting than with the earlier planted soybeans. The yield data is shown in Table 2. Yield data from the May 23 planting showed that there was no significant yield differences between the early maturing Mars (1.5) and the late maturing Denver (4.5) soybean varieties. There was more variability in the performance of the June 13 planted soybeans. The early maturing soybean varieties performed significantly less than they did when planted early. With the exception of the Cleveland variety, the fuller season varieties performed as well in the late planting as they did in the earlier one.
Figure 1 graphically illustrates the way the different soybean maturity groups performed. Conclusion: Soybean maturity group did not play a significant roll in soybean seed yield performance when the soybeans were planted on May 23. The later planted (June 13) soybeans exhibited more seed yield variability and the earlier maturing varieties did not produce satisfactory yields in comparison to the fuller season varieties.
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