Every season is different when it comes to pest and beneficial insects in vegetable crops. There are some pest species that are significant every year while others can go from almost insignificant to causing major problems from one season to the next.
This year pressure from Heliothis (both Native Budworm, Helicoverpa punctigera, and Corn Earworm, H. armigera) has been very low across south-eastern Australia. This is great news for growers of susceptible vegetable crops such as lettuce, sweet corn, beans, tomatoes and eggplants. However, it is important not to forget just how damaging this pest can be in these crops if it is not detected and managed early enough, so we encourage growers to be prepared to monitor this pest throughout spring and summer next season.
We recommend the use of pheromone traps to get an early warning of the arrival of adult Heliothis. Once adults have been detected in the traps it is necessary to follow up with direct searching in susceptible crops. Look for moth eggs and small caterpillars, as well as the range of beneficial insects that parasitise and prey on the eggs and larvae. The key predators of Heliothis in south-eastern Australia are typically damsel bugs (which we have seen a lot of this year) and predatory shield bugs. We also often see a high level of egg parasitism occurring in IPM crops as a result of naturally occurring populations of Trichogramma parasitoid wasps.
Plutella (diamondback moth) pressure is now dropping right back on many farms across south-eastern Australia. We are no longer seeing continual movement of adult Plutella moths into vegetable crops from outside sources such as drying out canola crops and this means that growers need only manage local populations rather than face constant pressure from external sources.
There has now been plenty of time for beneficials to build up in IPM brassica crops and from now on, in many cases, these beneficials will be able to take care of much of the remaining Plutella. Where pressure is low and populations of beneficials are well established, applications of Bacillus thuringiensis (Bt) based products such as Dipel or XenTari should be all that is needed to keep on top of both Plutella and Cabbage White Butterflies.
Putting aside the group 28 products such as Belt and Coragen when Plutella pressure drops at this point in the season helps to ensure that these valuable products are not over-used and helps to delay the development of insecticide resistance.
As milder autumn weather approaches we need to keep an eye out for aphids in many vegetable crops. Aphids are starting to show up in outdoor lettuce and brassica crops and we are seeing examples of various protected vegetable crops where aphid populations are already well established. The decision as to whether an aphicide application is necessarily should always take into account the levels of aphid predators and parasites in the crop. If aphids are detected at a low level in the crop, it is often best to delay making this decision for about a week, in order to gauge whether the population of aphids is actually increasing or whether predators and parasites are stepping in to provide an adequate level of control.