Indaziflam and imazapic applications to jointed goatgrass (<i>Aegilops cylindrica</i>) spikelets and cheatgrass (<i>Bromus tectorum</i>) seeds inhibits plant establishment

Abstract Indaziflam (Rejuvra ® ), a preemergence herbicide first registered in vine and tree nut crops, was recently approved for applications to rangeland for winter annual grass control. Indaziflam controls cheatgrass ( Bromus tectorum L.) for at least 3 yr, and control can extend into a fourth and fifth year; however, it is very difficult to find indaziflam residues in the soil 2 yr after application. Indaziflam could be absorbed by seeds still retained on the plant and on the soil surface in sufficient concentrations to stop establishment. To test this hypothesis, B. tectorum seeds and jointed goatgrass ( Aegilops cylindrica Host) spikelets were treated with indaziflam and imazapic at rates from 5.4 to 175 g ai ha −1 using a greenhouse track sprayer delivering 187 L ha −1 . Treated seeds were planted into field soil, and plants were allowed to grow for 21 d under greenhouse conditions. Growth was compared with growth of non-treated controls. In addition, a second set of treated seeds were exposed to rainfall 1 and 24 h after treatment and rainfall amounts ranging from 3 to 24 mm to determine whether rainfall impacted herbicide performance. Bromus tectorum was so sensitive to indaziflam that establishment was eliminated at all rates. Imazapic inhibited B. tectorum establishment with an ED 90 of 67 g ai ha −1 . Indaziflam effectively inhibits A. cylindrica establishment with an ED 90 of 7.4 g ai ha −1 compared with imazapic with an ED 50 of 175 g ai ha −1 . Indaziflam’s impact on A. cylindrica establishment was not significantly impacted by rainfall, indicating that the herbicide was absorbed to the seed coat. These findings support the hypothesis that indaziflam’s long-term control could result from its ability to inhibit establishment of seeds retained in the canopy and those on the soil surface at the time of application.