Spraying for insect pests in wet weather

Before spraying for insect pests, consider the size and density of the pests when you detected them and the impact of weather conditions post spray when deciding whether to spray or not in a La Nina summer.

If wet weather is threatening, you may decide to spray immediately in case the weather sets in for an extended period of time. In these cases, consider options that:

  • are less likely to flare pests, such as those that kill their predators and parasites
  • have a long period of activity post spray.

For example, in soybean, a virus-based biopesticide such as VivusMax might be a viable option for helicoverpa (provided larvae are small, i.e. = 7mm), as the wetter conditions will hasten the secondary infection and spread of the virus, and beneficial insects attacking helicoverpa will be preserved. If high helicoverpa pressure is detected, consider a more selective pesticide such as indoxacarb, which has a much longer period of activity than a methomyl-based product, and which is far less likely to flare secondary pests such as aphids and whitefly.

However, for other pests – in particular the problematic bean podborer in mungbeans – prompt action may be needed at flowering as larvae are very difficult to control at a later date once they are inside the pods.

Learn about the chemical control of insects and how to choose the right insecticide.

Reducing your spray costs

Pest management costs can be reduced by avoiding the temptation to spray pests if the at-risk period for a pest is still some time away. This is especially true for podsucking bugs, which are not a threat until pulse crops reach the podfill stage. Unless there is extreme adult pressure, pulse crops can compensate for pre-podfill damage and young nymphs inflict very little damage.

Panic spraying your crop too early with non-selective pesticides can also flare secondary pests and kill beneficial insects, which may further reduce your yields.

You can keep costs down by only spraying the part of the crop infested with the pest. This particularly applies to red shouldered or Monolpeta beetle, which often emerges in plague numbers after heavy rain, but which is often most abundant along the edges of crops.

Also consider...