TITLE:

Weed Management in Irrigated Cotton-Cropping Systems Using Roundup Ultra in Roundup Ready Cotton at AG-CARES, Lamesa, TX 2001.

AUTHORS:

             Wayne Keeling, John Everitt, and Danny Carmichael, Professor and Research Associates

MATERIALS AND METHODS:

             Plot Size:                                     8 rows X 300’, 3 replications

             Planting Date:                             May 9

             Varieties:                                    Paymaster HS26, Paymaster 2326RR, and Paymaster 2326

BG/RR

             Systems:                                      Conservation Tillage (Terminated Rye and Rye-Sorghum-

Cotton Rotation) and Conventional Tillage

              Irrigation:                                    13” for season (based on 0.75 ET)

             Application Dates:                      Preplant Incorporated (PPI)

                                                                              Conventional Tillage                  April 10

                                                                              Conservation Tillage                  April 16

                                                                 Preemergence (PRE)                               May 9

                                                                 Postemergence-topical (POST)  June 5

                                                                 Postemergence-directed (PDIR) July 23

             Harvest Dates:                            October 1

RESULTS AND DISCUSSION:

Two irrigated conservation tillage cotton-cropping systems were compared to conventional tillage. Those included: 1) terminated rye cover crop and 2) sorghum-cotton rotation. Each system included two weed management systems: 1) Treflan PPI fb Caparol PRE + cultivation and 2) Prowl PPI fb Roundup Ultra POST and PDIR using a hooded sprayer. Weed escapes, mainly Russian thistle (tumbleweeds), were hoed as needed. Roundup Ultra was used preplant to terminate the rye and to control winter weeds in the rotation system. Both Roundup Ready and stacked gene (BG/RR) varieties were planted in the Roundup treated plots. Cotton lint yields were determined and net returns calculated using input costs (Table 1).

Table 1. Comparison of conservation and conventional tillage weed and insect management systems using Roundup Ready and Roundup Ready/Bollgard varieties at AG-CARES, Lamesa, TX 2001.                

                                                                                                                                 Gross Returns 

System                                                                                                          Yield                  Net Returns^*   

                                                                                                                     (lb/A)                 ($/A)

Conventional Tillage

1)   Treflan fb Caparol + cultivation                                         635 bc             75            

2)   Treflan fb Roundup Ultra (RR)                                                      759 a               104

3)   Treflan fb Roundup Ultra (BG/RR)                                                 716 ab             64

AVG.                 703                   81

Conservation Tillage (Terminated Rye Cover) 

1)   Prowl fb Caparol + cultivation                                                        625 bc             96

2)   Prowl fb Roundup Ultra (RR)                                                          685 abc           82

3)   Prowl fb Roundup Ultra (BG/RR)                                                   731 a               84

AVG.                 680                   87

Conservation Tillage (Rye-Sorghum-Cotton Rotation)

1)   Prowl fb Caparol + cultivation                                                        719 a               124

2)   Prowl fb Roundup Ultra (RR)                                                          724 a               130

3)   Prowl fb Roundup Ultra (BG/RR)                                                   759 a               98

                                                                                           AVG.                 734                   117            

^* Net returns to land, management, and risk. Based on yield x loan price with no government payments included.

Highest average yields and net returns were produced in the sorghum-cotton rotation system. In both conventional tillage and terminated rye systems, higher yields were produced where Roundup Ultra was used in-season to control weeds in place of cultivation. Because of extremely low bollworm pressure, no yield advantage resulted from the stacked gene variety.

This test area was not replanted following the hailstorm in late May. The terminated rye, and especially the sorghum residue, gave some degree of protection from the hail and the decision was made not to replant.

Pigweed control was excellent in the Prowl fb Roundup Ultra plots, but some Russian thistle were not controlled. When planting into residue, a burndown herbicide (Roundup Ultra or Cyclone Max) at planting may be valuable to control small, emerged thistles that grow quickly and may not be easily controlled by Roundup Ultra under hot, dry conditions.