Herbicide damage is an ever increasing challenge for much of the cotton industry due largely to:

. the increasing complexity in the farming system (with a wide range of herbicides used),

. the increasing trend to minimum/zero tillage (using more herbicides for fallow weed control),

. difficulties in controlling fallow weeds (eg. fleabane and feathertop Rhodes grass), and

. increasing climatic uncertainty (need to treat weed flushes in a shorttime frame and maintain soil moisture).

Continuing herbicide damage is threatening the profitability of the cotton industry and in some areas may threaten the viability of the industry. Unfortunately, there is no easy solution. Crops generally will recover from herbicide damage, but in many instances with delayed maturity and reduced yields.

Over the last 3 years, CRC Project 1.01.49 has been developing a valuable

herbicide damage data set which will be expanded in the new project. This data

set currently gives detailed it Iformation on 2-4-D, bromoxynil, dicamba, MCPA,

glyphosate, Spray. Seed and Starane damage, with data from other phenoxy

herbicides to be added soon. Work is needed on the implications of lower rates of

2,4-D and multiple damage events and to further expand the range of herbicides and rates included in the database now available on the web.The 2nd part of the project involves the development of a readily assessable weed

control threshold for cotton. The threshold is essential if the industry is to fully realise the value of herbicide tolerant cotton.

The threshold based on the Critical Period for Weed Control was an important

outcome from project CRC 126 and a large step forward. The shortcomings of this threshold are that it

* is based on single weed types and does not integrate across types, and

* is based on a visual estimation of weed species and density which are difficult and time consuming to accurately measure over a whole field, where weeds are often patchy.

The next step is to develop a user-friendly, readily applied weed control threshold based on weed biomass, which integrates weed species and density.