Using IPM in brassica crops
Over the next few months, white butterflies will be seen dancing above brassica crops. This often signals it is time to contact a spray contractor to apply an insecticide. Instead of doing this, consider contacting your local PGG Wrightson (PGW) Technical Field Representative (TFR) to look at the crop.
With increased scrutiny around pesticide use, making sensible decisions around insect control is better for the wallet and for the future protection of the environment, as well as delaying the development of resistance to chemicals.
Integrated pest management (IPM) helps control several insects that damage brassica crops. IPM strategies include cultural, physical, and biological control measures alongside the use of registered chemicals.
Cabbage white butterfly
When looking to control cabbage white butterflies, it is important to scout paddocks before spraying as it is not the butterflies themselves that damage the crop, but rather the caterpillars that emerge from the eggs the butterflies lay. Even in warm weather, it takes approximately eight to ten days for the eggs to hatch. During this time, no damage is being done, so a chemical spray is likely unwarranted.
Before reaching the decision to apply a chemical, scout paddocks to check for the presence of beneficial insects such as parasitic wasps and hoverflies. If present in high enough numbers relative to the white butterfly caterpillar population, beneficial insects take care of the problem themselves. This does not provide 100 percent control, as for beneficials to be present in the crop, some insect pests must be there to maintain their own population. If they have the upper hand though, the economic justification for spraying is not valid. There are some tell-tale signs that a PGW TFR is trained to identify and can help guide these decisions alongside farmers.
If the decision to spray has been taken, IPM is still relevant. There are a range of registered chemical options, each with differing levels of impact on both the target pests and the beneficial insects. The worst decision at this point would be to use a broad-spectrum insecticide that will remove the beneficial insects along with the pests. By doing so, this gives the next generation of cabbage white butterflies the opportunity to establish with no beneficials to aid in the control, leading to a greater problem than already present.
Be mindful of both the impact on the environment as well as protecting the pesticides currently available as this allows the continued control of insect pests into the future. Making informed decisions about the most appropriate chemical to use, and when to apply it, are both good tools in helping achieve this.
To incorporate integrated pest management techniques into your crop management programme, contact your local PGG Wrightson Technical Field Representative.
