2006 Annual Report 4d.Progress report. This report serves to document research conducted under a Specific Cooperative Agreement between ARS and Mississippi Agricultural and Forestry Experiment Station. Additional details can be found in the report of the inhouse project 6402-21000-004-00D, Develop Soybean Genotypes and Management Systems for Early Season and Strees Environments. OBJECTIVES: 1. Optimize management practices for the production of early-maturing soybeans in Mississippi. 2. Evaluate foliar fungicides for control of Asian Rust and other late-season diseases. 3. Determine the impact of percent defoliation on yield of determinate and indeterminate soybeans 4. Optimize wheat/soybean double cropping systems for Mississippi producers. Objective 1: Three early soybean cultivars were planted on 30 March, 19 April, 9 May and 25 May 2005 using three seeding rates: 4, 6 and 8 seeds per ft of a row equivalent to 104,000, 157,000 and 209,000 plant/acre, respectively. Seeding rate and planting date had significant effects on soybean yield and yield components (Appendix 1). Generally, the interaction between planting date and seeding rate, and between planting date and cultivar was significant. However, no interaction occurred between cultivar and seeding rate suggesting that seeding rate affected the cultivars similarly. For the early planting date, higher seeding rate increased yield, but the effect of seeding rate was generally not significant when seeding occurred after the first week in May (Appendix 1). The yields for the late March and mid April planting dates were higher than the May planting dates, but the best planting date for the late MG III and early IV cultivars was the 19 April planting, whereas 30 March was the best planting date for the late IV cultivar. The number of pods produced by individual plants was consistently higher for the 4 seeds per ft plots compared with the 8 seeds per ft plots because of increased branching, and this perhaps compensated for the low plant population in terms of yield. The number of seeds per pod did not vary among seeding rates but differences in seed weight occurred when planted on 30 March. At this planting date, increasing seeding rate enhanced seed weight; a reflection of the number of pods per plant and suggested that the higher the pod number the lower the individual seed weight. Seed weight also decreased consistently as planting date delayed due primarily to the relatively shortened seed filling duration when planting was delayed. Objective 2: Fungicide efficacy. A comprehensive research program has been instituted to evaluate 16 different foliar fungicides for control of Asian soybean rust and other foliar diseases of soybean using single and sequential applications. Treatments include strobilurin, triazole, and other classes of fungicides. This research is being conducted at 6 locations in Mississippi. In addition, nine triazole fungicides are being evaluated alone and mixed with pryaclostrobin. To date, these studies have been instituted at 4 locations and more may be instituted if soybean rust moves into the major soybean growing area of the state. All trials to date have been conducted as preventative trials because no soybean rust has been detected in Mississippi as of this report. Curative trials will be conducted, if rust is detected prior to the end of the growing season. Data collected during the 2005-growing season and prior to establishment of this cooperative agreement indicate that yield responses to foliar fungicides will be higher with strobilurin fungicides than with triazole fungicides in the absence of rust. Therefore, triazole fungicides will likely not be profitable unless rust is a concern. Fungicide timing. Studies have been initiated to apply various fungicides at R1, R3, R5, R1 fb R3, R3 fb R5 and R1 fb R3 fb R5 application timings. Headline, Folicur, and Headline SBR were selected to represent strobilurin, triazole, and tank mix categories of products. This study should generate valuable data that can be used to determine the benefit of applications made prior to and after the optimal R3 to R4 growth stage. Because rust was not present at the test location, this trial is preventative in nature. It is unlikely that this test can be conducted as a curative trial during the 2006 growing season due to the absence of soybean rust in Mississippi. If soybean rust moves into the growing area, studies may be conducted to determine how late in the growing season soybeans need to be protected against soybean rust to maintain maximum yield potential. Studies conducted during the 2005 growing season and prior to the establishment of this cooperative agreement suggest limited benefit to sequential fungicide applications and that R3 is the optimum application timing for yield enhancement in the absence of soybean rust. Objective 3: Two separate studies have been initiated at the Delta Research and Extension Center in Stoneville, MS, for the 2006 growing season. Studies are designed to emulate a defoliation event caused by soybean rust that is late brought into check by a fungicide application. Soybean rust infections begin in the lower canopy and defoliate plants from the ground upwards. Treatments applied after detection usually results in percentage of the lower canopy being defoliated and top foliage being protected. Determinate and indeterminate soybeans of similar maturity were planted in the first study. The lower 50% of leaves were removed at R1, R3, R5, and R6. Yields will be taken and yield reductions due to defoliation determined. Asgrow AG4403, a widely planted indeterminate soybean variety, was planted in early April. Plants were defoliated 30 or 60% at R1, R3, R5, or R6. With this study, we should be able to compare the effects of heavy and light defoliation events at various growth stages. As with the earlier study, soybean will be harvested and yield reductions due to defoliation determined. Objective 4: Double-cropping soybean [Glycine max (L.) Merr.] after harvesting wheat (Triticum aestivum L.)  is an important production system in the mid-southern USA. A major problem with this system is the low soybean yield due to the delayed planting of relatively late-maturing cultivars typically utilized. Field studies were conducted at Stoneville, MS, (33o26' N lat) to evaluate the seed yield and net returns from early soybean maturity groups grown in a double-crop system under limited irrigation, and to compare the results with those from a full-season system. Soybean cultivars from maturity group (MG) III, IV and V were used. Double-cropped soybean yields ranged from 2055-3767 kg ha-1 and were 10-40% lower than their full-season counterparts. For both systems, the average yield and net returns from group IV, in particular the late IV cultivars, were among the highest, whereas those from groups III and late V were generally the lowest. The net returns from the full-season soybean averaged $85 to 274 ha-1 higher than those from the double-cropped soybean; however, the net returns from the double-cropped wheat more than compensated for these differences. The 3-yr average wheat yield was 5170 kg ha-1 and accounted for more than 60% of the combined net returns from the double-crop system. These results indicate that yields and net returns from double-cropped MG III or IV soybean could be equal or greater than MG V cultivars, but the late IV provided the highest yield and economic return. The data further indicated that wheat-soybean double-crop system using MG III or IV under limited irrigation was more profitable than the full-season soybean system. For detailed report Agronomy Journal 98:295-301.