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 Complete Final Report

This project has addressed issues that have emerged with the widespread adoption of Bollgard II cotton, and the resulting reduction in insecticide use. Specific objectives and outcomes are described below.

1)      The fit of new insecticides into integrated pest management. Selection of insecticides can have a big influence on both control of the target pest as well as on beneficials, and the risk of secondary pest outbreaks. We found that low rates of fipronil provided strong efficacy against mirids, with or without salt, and were significantly more selective that the full rates of fipronil against beneficials, though still with a risk of flaring mites. Low rates of indoxacarb alone provided poor efficacy against mirids but the addition of salt or canopy oil boosted this to efficacy equivalent of the full rate with low risk to beneficials or risk of flaring mites. Altacor (rynaxypyr) a new insecticide for Helicoverpa control was highly efficacious and selective against many beneficials indicating a good IPM fit. These results have been made available to industry via the Cotton Pest Management Guide, to assist pest manager in spray choices, and to industry to help in registration, thereby ensuring availability of new insecticides or uses of insecticides to industry.  

2)      Defining the pest status of emerging pests

a)    Management of thrips on seedling cotton. Tobacco thrips, Thrips tabaci, is still the dominant species. It was controlled moderately well at some sites but poorly at others, which could indicate resistance. At some locations the western flower thrips, Frankliniella occidentalis, is also abundant and poorly controlled by available options indicating insecticide resistance. Control of thrips is problematic because damage is often cosmetic, plants will recover without loss, and because thrips are also predators of spider mites. Nevertheless in cooler regions, where control is justified, management of WFT may be difficult. Monitoring of thrips population composition early in the season and determination of resistance profiles for both WFT and T. tabaci has been initiated in conjunction with Dr Grant Herron (NSWDPI) and CSD.

b)    Late season pest damage from thrips and jassids. These pests often build to levels causing significant damage to leaves on maturing cotton. We found that late season damage to leaves is only likely to reduce yield in crops with high yield potential and if the damage is very severe and prolonged before cut-out. High yielding crops are likely more affected but even they show strong compensation at yield levels up to 14 b/ha.

c)    The effect of mirid sprays on secondary pests. We found that controlling mirids with the most popular insecticide (fipronil) increases the risk of causing mite outbreaks, which would then require additional control. Our results also suggest that in some situations Bollgard II crops are more at risk – this deserves further investigation. Nevertheless, the results highlight the need to have good mite sampling protocols in place in Bollgard II crops especially if OP’s, SP’s or fipronil are used to control mirids.

3)      Develop a new aphid sampling strategy and thresholds. These were developed and extended to industry. They will provide a more rational basis for deciding when the occurrence of this pest justifies control and when beneficials are providing adequate control. This information has been linked with new information on the aphid borne disease cotton bunchy top, to provide pest managers with a holistic approach to managing both the pest and the disease.

4)      Sporadic pests. Information and publication to help manage the pale cotton stainer was completed and will help industry to manage this pest in the future. In particular thresholds for lint damage are now available. These indicate that for stained locks the threshold is >50% of bolls with all locks damage, and for tight-locked bolls it’s > 20% of bolls with all locks damaged. We also studied the feeding behaviour and have a better understanding of the damage symptoms.

This project has provided new information to help pest managers to make better decisions about management of emerging pests. Outcomes have been largely delivered to industry through a range of presentations, published resources and the WWW. Benefits to the industry are more rational decisions on the need to control pests, and awareness of risks for different control options. This will contribute to reduced pesticide use with flow-on economic, social and environmental benefits.