In Bollgard® II cotton 2-5 sprays are required to manage mirid and stinkbugs every season. An industry survey revealed that growers are 'insurance' spraying when mirid numbers are below suggested thresholds. One main reason for insurance sprays is possibly a lack of confidence in the relationship between mirid numbers and fruit loss. The development of a plant based management strategy (through detailed studies on mirid numbers, fruit loss and yield) could increase growers and consultant’s confidence in making decisions on mirid management, therefore reducing insurance sprays. The main objectives of this project was to develop a plant based management strategy for mirids and to develop selective management options for mirids and stinkbugs to fit with the existing IPM systems.

Through this project, a plant based management strategy for mirids has been developed. This strategy will consider two major factors; mirid damage rates (per cent fruit loss per mirid per week) and retention levels. The action threshold for a plant based management strategy is determined as ≥ 80% retention at up to the 14/15 node stage. Thereafter, the threshold is 60 – 70% retention. Retention levels should be determined by assessing the 1st and 2nd position bolls of all nodes up to the 14/15 node stage. Thereafter, retention levels can be assessed for the top 5 nodes. A plant based threshold should be considered in association with per cent fruit loss for each mirid. It should be considered that two per cent fruit loss per week will occur for every mirid above the base population.

When pale cotton stainer feed on young bolls (up to 15 days old), they can cause up to 40% yield loss. The germination rate of seed from damaged bolls is significantly reduced, by up to 30% compared to the control. This finding from the glasshouse trials needs further research in field conditions to confirm the result.

When salt is mixed with low rates (100 mL/ha) of Shield® (clothianidin), mortality is increased by 25% compared to the low rates of Shield® alone, which is similar to the full rates (250 mL/ha). Shield® and salt mixtures also reduced the impact on benficials significantly. However, caution needs to be exercised when using Shield® against mirids if aphids are present in the field, as aphids are capable of developing resistance against Shield®.