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Importance of refuge management for dryland growers

While there are still many new cotton growers entering the dryland cotton industry, now would be a good time to remind ourselves why refuge management is so important, understand how it can impact farming operations and recognise why it’s a good idea to start planning now.

In a nut shell, or a cotton boll so to speak, the purpose of a refuge is actually part of a numbers game against our industries arch enemy, the cotton bollworm (Helicoverpa Armigera and Helicoverpa Punctigera). Even though the Australian cotton industry has significantly reduced the dryland cotton grower’s reliance on cotton pesticides, the war against the cotton bollworm is not yet won. The potential for this pesky insect to develop resistance to genetically modified cotton varieties is a major concern for growers, and the major reason why the Monsanto Bollgard II® Resistance Management Plan (RMP) was developed.

The numbers game begins when we plant a refuge. The purpose of a refuge crop is to produce large numbers of the Helicoverpa moths that haven’t already been exposed to the Bacillus thuriengensis(Bt) proteins, found in Bollgard II. The aim of the game is to produce moths in the refuge crops that will spread out and mate with moths from the Bollgard II crops – therefore reducing the risk of resistant moths meeting and mating with each other.

To make sure that we have the most productive and effective refuge crop, there are three basic principles to remember. One is to minimise the exposure of Helicoverpa to the Bt proteins; secondly to produce susceptible individuals to mate with any resistant moths to dilute possible resistance; and thirdly, remove any resistant moths at the end of the cotton season.

To achieve this there are a number of very specific measures a dryland cotton grower should adhere to.

The first is timing. Remembering that the purpose of a refuge is to provide sufficient numbers of Bt susceptible moths to mate with Bt resistant moths, it is crucial to produce the moths at the same time. In accordance with the Resistance Management Plan (RMP), dryland growers must plant their refuge in the two week period prior to Bollgard II planting.

We need to make sure the refuge moths are the first hatched and flying about. The destruction of the refuge crops is another important timing measure; it is recommended that refuges should preferably be left uncultivated for at least two weeks after harvest to allow any pupatingHelicoverpa to emerge. Ideally refuges should be left uncultivated until the following October.

Another measure is location. There is no use planting the refuge too far away – we want the dating and mating process of the Helicoverpa to be easy. For the RMP to work, the best location for a refuge crop is as close as possible to your Bollgard II crop and at least within 2km.

Size is also an important measure. We have to make sure that we produce enough Helicoverpa to cover any moths emerging from Bollgard II crops and different refuge crops will produce different numbers of moths per hectare. Luckily the Cotton CRC has determined the moth productivity of different refuge options and it can be easily calculated using the Bollgard II refuge calculator.

Finally, one of the most important measures that are crucial to the effectiveness of your refuge crop, is the control of volunteer and ratoon cotton. The control of volunteer and ratoon cotton is a key component of the RMP and can be managed through cultivation, spraying and pre-watering. For more information refer to the volunteer and management guide.

One of the easiest and best ways to avoid Bollgard II volunteers is to not plant refuges in fields where Bollgard II has been grown in previous seasons. And remember that it is much easier and less expensive to handle seedling volunteers in refuge crops as opposed to established plants.

There are other specific measures (such as pupae busting, trap crops and spray limitations) in theResistance Management Plan (RMP), that we have not covered but remain vital in preventing resistance development. There have also been a number of changes to the RMP this year and all growers need to fully aware of their obligations in managing resistance. To be aware of your obligations you must read the RMP, available here. And remember that if you need some clarification with interpreting the RMP, contact your Technical Service Provider or Monsanto Regional Business Manager.