Over the past 10 years the rapid uptake of IPM and transgenic cotton has allowed a dramatic reduction in the use of insecticides in cotton. However, new technologies bring new challenges, and amongst these for Bollgard II® cotton and IPM systems is the emergence of pests that were previously controlled by insecticides applied against other pests. A further challenge is the potential for high retention in Bollgard II® crops which may affect compensatory capacity and potentially limit yield through premature cut-out. This project has addressed four broad areas of relevance in the Bollgard II® era.

1) The effect of aphids on cotton photosynthesis and yield.

Our research has shown clearly that aphids can reduce the photosynthetic rate of cotton, resulting in reduced yield and development. A statistical relationship predicting yield loss from aphid densities has been developed and used to produce look-up charts to estimate potential yield losses from this pest. This relationship will be used to enhance the CottonLOGIC decision support tool.

2) Effect of insecticides and miticides on predators and parasites.

A table summarising the effects of all currently available insecticides and miticides on beneficial predators and parasites was developed and updated regularly with data from this project, as well as that from collaborators. This table (IPM Supporting Document 1 ‘Impact of insecticides and miticides on predators in cotton’) has been widely distributed and used throughout the industry and served as a template for other crops.

3) Effect of early damage on Bollgard II® and UNR cotton.

We found that cotton can recover from damage by thrips through a process known as ‘accelerated ontogeny’. This is when the plant ceased development of damage leaves early in order to speed up the development of new, undamaged leaves to recover leaf area. This information will be used to update thrips compensation routines under development in the OZCOT cotton simulation model. A range of experiments were co-ordinated with the Cotton Extension Team. Outcomes from experiments were (i) Bollgard II® cotton varieties can compensate as well as or better than conventional varieties (ii) cotton with early retention levels of 80-85% showed no indication of premature cut-out and treatments to manipulate plant growth to avoid this problem did not increase yield but did cause delay iii) UNR cotton is less able to compensate for early damage than cotton on conventional 1 m beds (iv) in conventional cotton in a cool region (Hillston) later tip damage, at nodes 6 or 8, carries a higher risk of delayed maturity. Outcomes of this research have been extended to industry and have also increased IDO and crop manager’s knowledge of cotton compensation and provided valuable additional research data

4) Emerging pests and late season damage.

We found that late season damage to younger leaves (i.e. removal of the top 25 cm or top 6 main stem leaves) may have a greater effect on yield than expected. This raises questions about l for leaf damaging as opposed to fruit damaging pests and should be investigated further. We also investigated the effect of jassids on cotton yield and found a initial experiment showed a negative linear relationship between jassid density and yield. This should be investigated further.