Along with length, strength, micronaire and leaf content, the colour grade of cotton is a critical component of the set of characteristics used to assess the overall quality of a sample of cotton, and thereby determine its value. The current ‘base grade’ for colour for Australian cotton is Middling (31). If the colour grade falls to even the next lower grade of Strict Low Middling (41) then a significant discount to the value of the cotton will be applied. Wet, cloudy weather at harvest, a factor beyond a grower’s control, is one of the main causes of deterioration in the colour grade. The extent of the impact of wet weather on colour grade may also be influenced by a range of factors including presence of honey dew, the type / source of the honey dew, crop architecture, crop stage (degree of boll opening), amount of sunshine following the wet and cloudy weather that the crop is exposed to, trash levels in the seed cotton, the moisture of the lint when harvested and the length time between harvest and ginning.

Honeydew studies conducted as part of CSP 1401 “Enhancing IPM in cotton systems” provided information on honeydew characteristics and behaviour under various weather conditions and was followed by a pilot study on the effect of rainfall on cotton colour during 2015/16. This study showed that extended exposure of cotton to rainfall had a marked negative effect on colour. The two-year project herein was developed to continue research into the factors affecting cotton colour in the field and reports on the results of the pilot project and further investigations into the impacts of weather, sooty mould, fungicides and effects on yarn quality.