Advancing splatter gun technology for rangeland weeds

To determine whether more rangeland weeds could be susceptible to low-volume highconcentration herbicide applications (e.g., splatter guns), trials were initiated on gamba grass (Andropogon gayanus), rubber vine (Cryptostegia grandiflora), prickly acacia (Vachellia nilotica), and Chinee apple (Ziziphus mauritiana). For gamba grass, a rate response trial (0, 9, 18, 27, 36, 45 and 54 g a.i./L of mixture) of glyphosate has shown that 100% mortality can be achieved at rates ≥ 36 g a.i./L of mixture. A rubber vine trial is comparing the effect of timing of applications (between December and May) of two herbicides. Six months after treatment (MAT), Grazon™ Extra (triclopyr/picloram/aminopyralid) recorded the highest (i.e. December application) but most variable efficacy (0-80%) compared to 40-70% for Brush-off® (metsulfuron-methyl). The optimum way to spray plants using Hotshot™ (aminopyralid/fluroxypyr) is being investigated in a prickly acacia trial. Preliminary results, six MAT suggest that more severe damage occurs if the amount applied is calculated on the basis of the whole surface area of plants (i.e. both sides), but spraying from one side appears to be sufficient. For Chinee apple, a screening trial of five herbicides and two rates is showing that Brush-off® (metsulfuron-methyl) and Stinger™ (aminopyralid/metsulfuron-methyl) are the best performing herbicides, but only on smaller plants (< 2 m high) and at the highest applied rates 12 MAT. While promising, the variability in results indicates that many factors may affect efficacy, including the health, size and density of plants, herbicide choice and mixture/application rate, presence/absence of biological control agents and climatic conditions.