The implementation of Integrated Pest Management and use of Bt varieties has drastically reduced insecticide sprays on cotton farms. This enabled the industry to focus on agronomy, leading to continued growth in yields and profitability over the last 20 years. However, there are still ongoing challenges being faced by growers each season concerning sustainable pest management. Our research in this project focused on some of the more complex issues growers face that occur from the interactions between multiple biotic and abiotic factors that can be unique to each season. We aimed to generate new knowledge to support IPM adoption and potentially reduce the risk of IPM dis-adoption that we see as a growing threat to the future sustainability of cotton. What we achieved in this project included:

• • Further contributions to Table 4 of the Cotton Pest Management Guide, evaluating the effects of new pesticide compounds on non-target species (predators and parasitoids) and ranking them according to the standard that is now a well-known IPM resource.
• • We examined insecticides specifically aimed at controlling silverleaf whitefly (SLW) given the increased likelihood of resistance to some commonly used products. In both years the impacts of the insecticides were not significantly different from each other or the unsprayed control. However, our trials did show that predators and parasitoids, if not interfered with, can control pest numbers.
• • We tested an app that assessed SLW nymphs on leaves to make SLW monitoring more time efficient. The app captured about 51% of the variance of the nymphs on leaves. However, with refinement, these types of tools will become increasingly important for monitoring pest populations.
• • We conducted experiments to examine the effect of early season pest damage on yield of BGIII cotton and compensation for early fruit loss by plants. We simulated pest damage by tipping and removing fruit from the lower and mid-canopy fruiting branches. Tipping of cotton between nodes 5 and 7 or loss of fruit from the lower six fruiting branches (FB 1-6) in a portion of the crop (33%) did not result in significant yield loss or a delay in maturity. However, fruit loss from fruiting branches in mid- canopy (FB 7-12) and/or a higher proportion of the crop (100%) has the potential to incur greater yield loss and significantly delay maturity. The potential for loss was greater in higher yielding crops. Our results suggested that low levels of insect damage could be tolerated, which has implication for mirid management and future research.
• • There was no significant compensation for losses but the severity and timing of damage changed fruit development and contribution to yield within plants. In undamaged plants, the contribution to yield by bolls from the plant core (FB 1-12, Position 1&2 bolls) was 65%, contribution from bolls on vegetative branches was 21% and 14% from bolls on the remainder of the plant (FB 13+ and FB1-12 P3 bolls). This pattern remained when only every third plant was damaged (FB1-6 or FB 7-12) but damage to FB 7-12 or to more plants (100%) shifted yield contribution to vegetative branches and upper canopy in roughly equal proportions. The most extreme damage (FB1-12 x 100%) shifted 51% of fruit and yield production to the upper and outer canopy, and 33% to vegetative branches.
• • We conducted experiments to test the effect of cloudiness and mirid damage (both simulated and actual damage via mirids themselves) on cotton yield. Our findings showed that plants can compensate for both factors in this controlled environment, and there was no impact on bolls and lint weight at the end of the season.
• • We attempted to link changes in whole invertebrate communities to the cumulative application of multiple insecticide products across a season (via the BDI, beneficial disruption index). This exploratory approach showed that BDI is only one of many factors that influence community turnover and change and our experimental design could not unpick these interacting factors.
• • Endemic pest issues are further compounded by the continued threat of exotic incursions. During this project, we contributed to the Australia-wide response to the arrival of fall armyworm. This species has established in maize at ACRI and is already being attacked by parasitoids. We also contributed to the cotton industry plans to respond to future threats like blue disease.
• • An incentive-based approach to enhance IPM best practice that focussed on exploring the economic benefits of IPM to individual growers, especially long term; and encouraging realistic expectations of yield based on seasonal constraints. In consultation with Mr Ben Simpson (CRDC) and Ms Janine Powell (AgEcon) we developed a survey instrument to identify whether an IPM approach to growing cotton is costly (or whether there is no correlation in cost), however, the survey itself was not conducted

Our work during this project supports the importance of early season crop management which can greatly impact on outcomes at the end of the season and beyond. The use of pesticides to control thrips, cutworm, wireworm and mirids is likely to increase the risks of resistance development and can negatively affect beneficial species. In some years that risk may be manageable and in others it may not. Furthermore, plants can compensate for certain levels of pest damage, even when combined with other factors (such as physiological fruit loss and cloudiness). Capacity-building of growers and consultants as well as a re-evaluation of what knowledge tools are required will help in these complex scenarios.

Our team faced many challenges throughout this project, beyond the risk of extreme seasonal weather events. Both the impacts of Covid-19, staff changes and personal crises influenced the timing and success of some experiments but we implemented contingency plans wherever possible. Furthermore, we see the need to better understand the complex interactions between the crop, insects and abiotic processes in order to answer pertinent industry questions and improve on current IPM practices.