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Drought-fuelled pests threaten winter feed crops


Drought-fuelled pests threaten winter feed crops

20 March 2013

As farmers across the country grapple with drought recovery plans and dry conditions, Ravensdown’s George Kerse Business Manager Agrochemicals is warning about the impact of insect pests on winter feed.

“As if the lack of moisture was not bad enough, the consistent extremely dry conditions mean insect pests are becoming a real issue for farmers.

The current dry conditions will have already reduced the amount of autumn-saved forage for winter feed, so specialist winter crops are becoming more important ensuring adequate feed for animals to prepare for next season.

Plants can usually tolerate one or two stresses. However, when there are multiple stresses acting simultaneously, like we are seeing now on brassica crops, crop damage and major yield losses are a real threat.

The focus should be on removing the controllable stresses; such as insect pressure and plant nutrition. Obviously, moisture is required to increase the plant nutrient status. But the removal of insect pressures on the plant enables more energy to be put into increasing both quality and quantity of the final winter yield.

With the increase in dewy mornings, comes the increased risk of insects as the moisture creates an ideal habitat for the insects while the temperatures are still warm.

When it comes to choosing insecticide and control methods, it’s a case of ‘horses for courses.’ So for example, contact insecticides can be used, but ideally should be mixed with a systemic insecticide to ensure good control of insects not directly contacted by the chemical.

Know your enemy #1 Aphids

At present aphids seem to be the major problem. Contact insecticides, like chlorpyrifos (Toppel 500) can be useful at early crop growth stages and before aphid populations have established. At more advanced crop growth stages and where populations of aphids have already established, it is advisable to use a systemic aphicide, such as dimethoate (Rogor). Pirimicarb (Pirimisect) can also be a good option, because it does have a combination of contact, translaminar (moves to the underside of the leaf) and fumigant action, and is safe for the pest’s predators like lacewings and ladybirds.

Know your enemy #2 Caterpillars

Populations of diamond back moth or white butterfly caterpillar are also on the increase and it is important to get these under control early. It is much more difficult to get control when populations have built up to a high level and generations start to overlap. For control of these caterpillars the use of a specific insecticide such as lambda-cyhalothrin (Halex) is advised.

Where there are mixed populations of aphids and caterpillars, a tank mix of Halex with Rogor or Pirimisect will provide better control. The use of a suitable wetting agent such as Widespread is highly advised as brassica leaves can be difficult to wet due to their waxy surfaces.

Timing of application to reduce crop damage from these insects is critical and needs good crop monitoring. In warm, dry weather, it can only take a few days for insect populations to go from an annoyance to a real threat. Good crop monitoring is needed, walking the paddock at least once a week and at even closer intervals when insects are found as populations could explode very quickly to damaging levels.”


Concerned farmers can call Ravensdown on 0800 100 123.

About Ravensdown:

100% farmer-owned Ravensdown is Australasia’s largest fertiliser co-operative, providing farmers with the tools, advice and inputs to lift their production and lower their environmental footprint.


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