Southern New Mexico's Major Turfgrass Weed: Khakiweed Herbicide Control Options and Seed Germination.

Multiple experiments were conducted in Las Cruces, NM, USA to test post-emergent herbicide control (Experiment 1) and optimum seed germination timings for khakiweed (Alternanthera pungens Kunth) (Experiment 2). For experiment 1, herbicides were applied to evaluate long-term herbicide control options. Treatments selected for post-emergent control were chosen from previous research conducted at New Mexico State University. The treatments consisted of Speedzone (PBI Gordon), Pendulum Aquacap (BASF), and a tank mix of Speedzone and Pendulum. The same treatments were replicated in 2010 with the addition of Battleship (Helena) and Monument (Syngenta). The following treatment rates were applied: 1. 0.62% carfentrazone-ethyl , 28.57% 2,4-D, 2-ethylhexyl ester, 5.88% mecoprop-p acid, 1.71% dicamba acid (1.25 kg product/ha), 2. pendimethalin (3.3 kg ai/ha), 3. 37.84% dimethylamine Salt, 4.45% 1-methylheptyl ester of fluroxypyr, 4.07% triethylamine salt (1.41 kg product/ha), 4. 2-pyridinesulfonamide (.15 kg ai/ha), 5. tank mixture of treatments 1 and 2, and 6. untreated control. Thirty days after treatment, two treatments had higher control than untreated:  treatment 1 = 68% control and treatment 5 = 80% control. However, 60 days after treatment, four treatments had higher control than untreated: treatment 5=66%, treatments 1 and 2=63%, and treatment 3=56%. For experiment 2, khakiweed seed was field planted beginning 23 March 2010 to determine optimal germination timing for southern NM. Khakiweed seed was collected from established stands in 2009 in Las Cruces, NM. One hundred seeds, as estimated by mass, was applied weekly to bare soil plots, measuring 0.5m by 1.0m.  In 2010, initial field germination was observed on 11 May (soil temp 16 C). Peak seed germination occurred during the first week of June (soil temp 22 C), and germination continued until 21 September (soil temp 20 C). These results indicate herbicide control with single post-emergence application timing is not successful and may require additional techniques to obtain adequate, long-term control. Pre-emergence herbicide control may provide an additional control option, but should be targeted prior to 11 May (16 C) for Las Cruces, NM populations.