Changes in varieties, biotechnology, boll weevil eradication, and other developments in cotton production have potential to affect optimal planting date. Objectives of this study were to evaluate yield and maturity response of modern cotton varietiesto planting date under current production conditions. The location of the study was the LSU AgCenter Northeast Research Station, Saint Joseph, LA. The soil type was Commerce silt loam, and the test was non-irrigated. A split plot design was used, with planting dates as whole plots and varieties as split plots. The 2003 planting dates were March 25; April 8, 16, and 28; May 9 and 20; and June 2. Planting dates in 2004 were March 25; April 5, 15, and 28; May 6, 21, and 27; and June 11; however, only the first, third, sixth, and eighth planting dates are reported. Six varieties were used in 2003, namely Deltapine DP 555 BG/RR, Deltapine DP DeltaPEARL, Phytogen PSC 355, Stoneville ST 4892BR, SureGrow SG 215 BG/RR, and SureGrow SG 821. Eight varieties wereplanted in 2004, with Deltapine DP 444 BG/RR, Phytogen PHY 410 R, Stoneville ST 5599BR, and FiberMax FM 960 BR added to the set planted in 2003 and the SureGrow varieties excluded. Open boll counts were taken prior to defoliation in 1 m of row for all varieties in 2003, and in 1.5 m of row for four varieties in 2004. Cotton was spindle picked to measure yield. Lint percent was obtained by ginning all seedcotton from the plot in 2003. In 2003, significant differences in percent open bolls did not exist among varieties within planting dates until the May 27 and June 11 dates, when DP 555 BG/RR was significantly less open than PSC 355, ST 4892BR, and for the June 11 planting date, less open than SG 821 as well. A significant variety by planting date interaction occurred on lint yield. Varieties generally yielded well at early planting dates, and DP 555 BG/RR and DP DeltaPEARL demonstrated the largest decline in yields with the later planting dates. Both of these are considered full season varieties, an assertion supported by the percent open boll results for DP 555 BG/RR. They may not have had sufficient heat units to mature bolls and reach their full yield potential at the later planting dates. In 2004, some variation in the relationship of varieties in percent open bolls was evident among planting dates. However, DP 555 BG/RR was significantly lower than the varieties with the highest percent open bolls when counts were made for planting dates 1 and 3. In contrast to 2003, the yields were relativelylow at the first planting date for all varieties, but were high when planted April 15 or May 21. Seedcotton yields were relatively low for all varieties when planted June 11. Significant interaction between variety and planting date was present in seedcotton yield. Although differences among varieties were not significant at any planting date, three early-season varieties, FM 960 BR, PSC 355, and DP 444 BG/RR each improved in seedcotton yield ranking relative to other varieties when planting was delayedfrom May 21 to June 11. The two years of data suggest that time required for maturation may be the most important factor in varietal response to planting date, with full season varieties more adversely affected by late planting than early maturing varieties. The optimal planting window in Northeast Louisiana is considered to be mid-April to Mid-May. Results of reported planting dates from 2004 validate this window, although 2003 data suggest that earlier planting may be acceptable when in-season conditions are favorable.
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