In this section:
Pests that refuse to go away
A change is needed
The Northern Adelaide Plains is an economically significant, horticultural region, that has a concentration of major pest problems affecting most growers. This can be a costly situation because of high pest control expenses and frequent reductions in marketable harvest due to insect pest and disease damage. In fact a modest estimate for costs and losses to the industry each year is about $25m and up to $80m in a severe season.
The problems at Virginia are due to a combination of factors:
- high pest pressure emerging from poorly managed weeds and old crops
- failure to control all these pests because of pesticide resistance and a lack of knowledge about the most effective ways to use pesticides
- poor timing, assessment and improvement of pest management decisions because very few growers are regularly monitoring pest and disease levels in their crops
- too few growers have realised the benefit of a range of non-chemical strategies to reduce pest pressure and control pests, or lack the support to implement them
Insecticide resistance is a very big issue
Most growers at Virginia are familiar with the problem of pests becoming ‘immune’ to insecticides. This is called insecticide resistance. There is a long history of insecticide resistance issues with pests such as Western Flower Thrips (which spreads Tomato spotted wilt virus) and Greenhouse whitefly. Two Spotted Mites (or ‘spider mites’) have now also become resistant to Vertimec on many farms. Other potential resistance problems are lurking on the horizon with pests like Bronze Mites that can cause problems in tomatoes and Broad Mites in capsicums. There is a new disease affecting many tomato crops interstate called Yellow Leaf Tomato Virus that is spread by whitefly. Green peach aphids can be an issue for capsicum growers under some circumstances.
If an insecticide (or fungicide) is not rotated properly with other insecticides from a different chemical group, or is otherwise not used according to the label rates and conditions, high levels of resistant insects are likely to develop. Once resistant insects breed and reach a critical level they will become uncontrollable when weather conditions are suitable – which can be year round in a greenhouse!
Once pests are resistant to an insecticide it is usually not possible to use that insecticide again as a reliable control measure. It becomes a lost weapon in the fight against pests. There are some exceptions:
1) Where a farm is far enough away from other farms with resistant pests a grower may manage to prevent the onset of critical levels of resistance in their pest populations if they have a very well run pest control program with effective chemical rotations.
2) Sometimes when the insecticide has not been used for a lengthy period of time the resistance levels drop enough to start using the chemical again on a less frequent basis and rotated with insecticides from a different group. This strategy may be possible in the case of Vertimec resistance in Two Spotted Mites. However resistance will return very rapidly if the chemical is used inappropriately again.
Resistance is not however the only cause of pest control failure and may not even be the most common. This booklet looks other possible reasons for poor pest control results and shows how to identify and deal with them.
Without major change the current situation will ensure that a large number of growers remain trapped on an expensive, and often ineffective, insecticide treadmill as they battle to protect their crops. In fact resistance problems are likely to increase.
Major change is effective change
Information in this booklet describes how you can deal with pest issues and includes basic information about key greenhouse pests. Improving pest control outcomes requires a program covering all the key areas. To be effective the program needs to be designed, managed and adjusted from time to time by the grower or a consultant. Time spent on this may create some extra cost at first, but the gains more than outweigh the losses very quickly. This is not hard to see when we know that between $25m and $80m is going down the drain every year.
Improved pest management practices make it easier for growers to harvest more from produce their crop that meets market specifications. Quite a few growers have already proved this for themselves and highly recommend these practices to other farmers as the following quotes demonstrate:
- Emmanual (Virginia - capsicums): Just improving my spray coverage has made a huge difference and helped me to improve on expenses and losses. I do think full IPM with beneficials is the way to go, but we need more support and research to make it truly reliable. This is how I want to grow my crops and we’re getting there, but the big thrips problem in Virginia makes it very hard
- Paul (Perth W.A. - cucumbers): We tried and tried and then when we got the right consultant it all came together with the Western Flower Thrips and predators. It is a bit more expensive, but more than makes up for itself in improved yields
If all of the region’s farms implement an appropriate pest management program with good farm hygiene and spray practices, pest levels will probably reduce by close to half in the first year and continue to drop steadily each year after that for some time. Disease levels, especially tomato spotted wilt virus and any other diseases spread by insects, would reduce to the same degree. It is obviously worthwhile co-operating to achieve this goal as soon as possible.
So to find out how to save a lot of the money and time you may be spending on pests and diseases take a close look at the information that follows. If the information is unclear or incomplete for your needs seek expert advice from an agronomist or other expert advisor.
