Fact Sheets

Growers are reporting variable control of annual ryegrass with clethodim. Poor performance of clethodim can be attributed to cold and frosty conditions. In 2013 and 2014 trials to examine the effect of frost on clethodim treatment of annual ryegrass were conducted under controlled conditions using a frost chamber to mimic a frost event. Key Message Frost events in the few days before or after Clethodim application can reduce activity of the herbicide on annual ryegrass. Clethodim efficacy tends to be reduced more substantially by frost where ryegrass populations have evolved resistance to this herbicide.

Disc seeding system design and settings influence pre-emergent herbicide behaviour and can play a critical role in minimising crop damage. Ideal set-up of disc seeding systems, to maximise weed control with pre-emergent herbicides whilst minimising crop damage, requires an understanding of how the products interact with the crop and the distribution of weed seeds in the seedbank, as well as knowledge of soil type, likely rainfall and surface residues. Using pre-emergent herbicides is not cut-and-dry!