Don't risk resistance: destroy your crop residue

Successful crop destruction and volunteer cotton control is an important part of meeting grower requirements in the Bollgard® 3 Resistance Management Plan (RMP).

Effective removal of cotton between seasons helps reduce the risk of Helicoverpa spp. resistance to Bt proteins, and prevent pests and diseases from overwintering.

Reducing the resistance risk:

Volunteer and ratoon Bt cotton can impose additional resistance risks as they extend the amount of time Helicoverpa spp. are exposed to Bt proteins outside the growing season.

Under the Bollgard® 3 RMP, as soon as practical after harvest, cotton crops must be destroyed by cultivation, root cutting or herbicide so that they do not continue to act as hosts. In Central Queensland, Bollgard® 3 crops must be slashed or mulched (and controlled to prevent regrowth) within 4 weeks of harvest.

Growers must also ensure that volunteer and ratoon cotton plants are removed as soon as possible from all fields including fallow fields, Bollgard® 3 crops, conventional cotton and refuges.

Preventing overwintering:

Maintaining a farm that is free of weeds, including volunteer and ratoon cotton plants, breaks the green bridge needed for pests and pathogens to overwinter until the following season. These unwanted plants can harbour a starting number of pests that increase the likelihood of pest outbreaks in subsequent crops.

Volunteer and ratoon cotton plants can also act as reservoirs for plant viruses such as cotton bunchy top (CBT), which is spread by the aphids that overwinter on these plants. Previous CRDC-supported research, conducted by DAF, found around 4 out of 10 volunteer and ratoon cotton plants alongside roadsides in cotton growing regions were infected with CBT.

Several years ago, Central Queensland had significant CBT outbreaks with yield losses of up to 40 per cent. The low but continued detection of CBT in CRDC-supported industry disease surveys highlights the importance of continued perseverance in controlling volunteer and ratoon cotton to minimise the risk if conditions favour a CBT outbreak.

Destroying ratoons while maintaining soil moisture

Ratoon cotton is best managed post-harvest through effective root cutting and mulching, with a follow up pupae busting operation or cultivation if required. However, this may not be the preferred option in dryland systems, or in the limited irrigation scenarios that growers are currently facing, where management decisions are focused on conserving soil moisture.

Herbicide options: 

Three herbicide options are available for the control of large volunteer or ratoon cotton plants amongst stubble or in fallow. These herbicides are registered for both optical booms and broadacre application enabling all growers to make use of these options.

Water as a crop-destruction tool:

CRDC-supported research has been underway for the past three years to develop and assess alternative methods to the use of metal discs to minimise moisture loss. AquaTill Injeticide is a new technology that incorporates herbicide with ultra-high pressure water jets to cut through the main stem at ground level. Initial trials found this technology had potential as an effective crop destruction method, with further trials incorporating fluroxypr successively providing more robust control.

The Dryland Cotton Research Association (DCRA) has been working with the manufacturers of AquaTill Injeticide towards registering the technology as a new method of herbicide application. A registrant is on board to expand the Fluroxypyr 400 product label to include AquaTill Injeticide as a new method for controlling cotton regrowth.

For interested growers, demonstrations will be set up across cotton growing regions this season. For further information, contact Annabel Guest of DCRA.

Want to know more?

• View the Bollgard 3 RMP (found within the Cotton Pest Management Guide).
• Visit CottonInfo's stewardship page.
• Read the Australian Cotton Production Manual (see the IPM and resistance management, plus the managing cotton stubbles/residues chapters).  
• View the ‘Using ultra-high pressure water cutting for cotton termination – progress from three years of development’ online presentation.