Economics of summer weed control.

Aims: To test various chemical options for summer weed control; measuring their efficacy, the amount of soil moisture conserved, and follow-up crop yield. A full season cost-benefit could then be produced. Summer rains were widespread in 1990, and summer weed sites were plentiful. Trial 90A3 Location: Avondale. This site had adequate moisture for most of the summer. Weeds were growing well when sprayed, and were readily controlled. (df. Wongan Hills). 2,4-D/diuron gave excellent control at the time of spraying but follow-up germinations marred the result. Trial 90M6 Location: Merredin. All treatments have failed at this site. Large doublegee and melons dominate each plot. Clover is also present om significant numbers. 1-1.21/ha glyphosate + 1-2g/ha Ally would be required before sowing. The weed density was such that sub-soil moisture was not measured on this site. Trial 90N6 Location: Newdegate Research Station. This site was the only one where summer weed control was probably not necessary. the site was a wheat stubble, and volunteer wheat was the dominant weed. these quickly ran to seed and died off. thus they would not have interfered with seeding. the site also became very dry and thus any fallowing effects was minimal. Overall yields were so low that any yield benefit from the fallowing was not cost effective. 90WH12 Location: Wongan Hills. This site dried quickly after each germinating rain, and by the time of spraying the weeds were under moisture stress. Thus the Roundup was much less effective than at Avondale as it was not translocated effectively by the target plants. Sprayseed was very effective when applied at a sufficient rate (1-1/ha), but 500 ml/ha was not adequate. Again 2,4-D/diuron was initially effective but the end result was marred by later germinations