The IRMS has a new layout. The Helicoverpa table has been combined with the Aphids & Mites table. In the current era of GM cotton, aphids, mites, mirids and silverleaf whitefly are no longer secondary pests. More often than not, it is this range of pests that require intervention with foliar insecticides to protect cotton yield and quality. For 2011/12 there are no changes to window dates or product windows. However, the endosulfan and spinosad windows have been removed due to the discontinuation of supply of these products. Witholding periods (WHP) for products no longer appear in the IRMS, however are included within the Guide. Refer to pages 157–158, Tables 44 and 45, for full listings of product re-entry periods and withholding periods.
Ratification of the IRMS prior to the start of each season is the responsibility of Cotton Australia’s TIMS Committee. A Troubleshooting sub-committee is empowered to act on TIMS’ behalf during the cotton season to respond to emergency requests to vary the IRMS. The Troubleshooting sub-committee has a clear process for handling requests. The process is detailed on page 67. For further information contact Greg Kauter at Cotton Australia, phone 02 9669 5222.
- Monitor pest and beneficial populations.
- Use recommended thresholds for all pests.
- Monitor fruit retention.
- Comply with all directions for use on product labels.
- Avoid repeated applications of products from the same insecticide group, even when targeting different pests. Rotate between groups.
- Do not respray an apparent failure with the same product or another product from the same insecticide group. Rotate to a different group.
- For all pest species, aim to use the most selective insecticide options first, delaying the use of broad spectrum insecticides for as long as possible.
- Control weeds and cotton volunteers in fields and around the farm all year to minimise pest hosts.
- Pupae bust cotton as soon as possible after harvest.
Many products used in cotton for insect and mite control are efficacious against more than one important pest. In every population of every pest species there will be a small proportion of individuals with the ability to survive an insecticide. The IRMS aims to assist users to;
- Lower the risks of inadvertent selection of resistance in pests that are not the primary target of the insecticide application.
- Delay the evolution of pest resistance to key chemical groups, by minimising the survival of individuals with resistance.
- Manage entrenched resistance problems, such as the now widespread resistance in cotton aphids to neonicotinoids.
Aphids reproduce asexually. All the progeny of a resistant individual will be resistant. Once resistance is selected in a population it can quickly dominate and give rise to new, entirely resistant populations. While there has been very low use of neonicotinoid insecticides against aphids during recent cotton seasons, resistance in cotton aphids to this insecticide group has become widespread. Resistance has been inadvertently selected in two ways. The first has been through the widespread use of neonicotinoid seed treatments and the second is through the use of foliar applied products targeting mirids. Even when aphids are present at very low levels, resistance is being selected. All currently available insecticide seed treatments contain a neonicotinoid. Where a seed treatment is used, avoid all early season uses of foliar neonicotinoid products. There is cross resistance in cotton aphids between pirimicarb and dimethoate/omethoate. Even though these products are in different insecticide groups, the use of one will select for resistance to both. It is critical that a gap be observed between the early season use of pirimicarb and the late season use of dimethoate/omethoate. Where dimethoate/omethoate is used at the end of one season for late aphid control, be vigilant in controlling cotton volunteers during the winter to minimise the risk of resistant populations being present on farm in the following spring. When choosing an aphicide, consider previous insecticide choices for mirids as well as for aphids and rotate chemical groups.
Pupae busting is a critical tactic in delaying resistance to all insecticides targeting Helicoverpa armigera, including Bollgard II. It is the last line of defence. Individuals that have survived the insecticide selection pressures of the cotton season can be controlled before they have the chance to mate and enrich the starting population of the next season with their resistance. Pupae busting should be a priority post harvest operation on all cotton farms. The IRMS recommends pupae busting as soon as possible after harvest. For Bollgard II crops, follow the pupae busting directions in the product’s Resistance Management Plan, page 81. Currently the frequencies of resistance to all insecticides for the control of Helicoverpa species in cotton are low.
Mites There are three species of mite that are commonly found in cotton. Only the two spotted mite causes economic damage and has a history of developing resistance to miticides. While current resistance levels are low for all products, resistance can be selected very quickly. Avoid consecutive sprays of the same miticide. If mite numbers rebuild after a miticide application, rotate to a product from a different chemical group. Once cotton is ~8 nodes, thrips cease to be a pest and become veracious predators of mites. Where thrips are preserved, they can provide sustained suppression of mite populations at below damaging levels.
Mirids aren’t known to have developed resistance to insecticides in Australian cotton. Currently there is no resistance monitoring program for mirids. However it is possible that resistance could develop and the principles underlying the IRMS should be followed in making mirid control decisions. Many of the products registered for mirid control in cotton are also registered for the control of other pests. It is critical that mirid control decisions also consider sub-threshold populations of other pests that are present in the field. Using dimethoate/omethoate for the control of mirids can inadvertently select for both dimethoate/ omethoate and pirimicarb resistance in aphids. Use of clothianidin (Shield) for mirid control can inadvertently select for imidiacloprid (multiple trade names), acetameprid (Intruder) and clothianidin (Shield) resistance in aphids, as all products belong to the neonicotinoid chemical group. When selecting an insecticide for mirid control, consider the options that are left open for subsequent aphid control, in case the need arises.
SLW is a relatively new pest in cotton. Currently there are only a few products available for its control, each with a very high risk of resistance. Refer to the SLW Threshold Matrix, page 29, for industry recommendations on the best way to utilise the products available with the lowest risk of developing resistance. To delay the development of resistance, ENSURE ONLY A SINGLE APPLICATION OF ADMIRAL OCCURS WITHIN A SEASON. SLW has not been incorporated into the IRMS because the use patterns of the available chemistries and the thresholds for the pest require that products be used in windows based on crop growth stage and rate of SLW population growth rather than the use of calendar dates. The SLW Threshold Matrix is designed to minimise the need to intervene with chemical control as well as to delay the development of resistance.
