Beyond herbicides for grass weed control

Thumbs up for spraytopping

Grass control by herbicides alone is not sustainable in the long term. Grass weeds in a pasture/crop rotation are more likely to succumb to an integrated approach using cultivation, grazing and rotations as well as herbicides. Fewer herbicides, and non-selective ones, may be the way to go.

These are some of the messages coming out of continuing research by Western Australia Department of Agriculture scientists at Katanning. Research trials used year-about pasture/crop rotations. During 1993 trials, shallow cultivations (tickles) and consecutive applications of glyphosate reduced ryegrass levels in the following crop by 50 per cent. Plots treated with effective grass herbicides during the pasture phase and spraytopped in spring had grass levels in the crop of only onehundredth of untreated plots.

Increasing resistance with selective herbicides?

Although 1994 trials indicated that a treatment of residual grass control and an in-crop application of grass selective herbicides gave fewer weeds in-crop and high grain yields, growing resistance to herbicides means that these treatments may have a limited life span. It is possible that grass selective treatments can hasten the build-up of resistant grass populations.

The answer is likely to lie with an integrated approach, according to research officer Alexandra Wallace. She said grass control during the crop year could be through herbicides, cultivation or seed collection at harvest. Spraytopping has been achieving good results.

"Spraytopping for grass seed-set control reduced grass density in the following crop, even in plots which appeared grass free," Ms Wallace said.