The first virus-transmitting aphids of the season have been reported in brassica and lettuce crops. The detection of the peach-potato aphid (Myzus persicae), potato aphid (Macrosiphum euphorbiae) and grain aphid (Sitobion avenae) at sites across eastern England signals the need to start monitoring crops in preparation for protection against virus.
The unseasonably cold weather in January and February served to delay aphid flights compared with recent years, but its value to crop protection is likely to be limited. The cold and dry spring means many crops are behind where they could be expected to be while aphid numbers are likely to increase quickly as temperatures begin to rise.
The Rothamsted Insect Survey may give growers an indication of pressure, but the reality is that once aphids are found within crops, programmes will commence. The main consideration is what product to apply that delivers the necessary level of control based on the anticipated pressure. This will differ between crops. In some cases, application restrictions such as maximum number of times a spray can be applied in a given length of time or season and the need to observe pre-harvest intervals mean that the choice of products will be limited.
The withdrawal of insecticides with good knock-down performance has also forced a change in practice with the focus shifting to more preventative tactics. One consequence of this is that crops need to be inspected more frequently so sprays are timed for best effect while the need to consider how conditions can influence product performance has also risen in importance.
Where aphids are deep within crops such as with some brassicas and headed lettuce then contact-only insecticides may struggle to deliver control unless penetration is sufficient to ensure the product being applied comes into direct contact with the pest.
This highlights the need to inspect crops closely. In some situations, a systemic insecticide, such as Movento (spirotetramat), will be the most suitable, but restrictions on the number of times these products can be applied to a crop during a season means they can’t be the default method of control.
This is just one example of the nuances that exist in seeking to achieve insect control in field vegetables and salad crops. Another is the increasing significance that moisture can have on performance as is nozzle choice in supporting coverage.
Good application is now considered essential to effective performance. This is partly because of the increasing role given to biologicals in a programme. Success is often heavily influenced by the actions of the spray operator whereas with conventional insecticides, the product could be relied on to deliver much of the control. Conditions such as leaf wetness at spray time are as important as application technique.
In short-duration leafy salad crops, such as baby leaf, an application of Movento can be enough to provide control through until harvest. Where there is a need for longer protection, Movento can be alternated with Tracer (spinosad) or the biological insecticide, Flipper (fatty acids C7-C20).
Flipper is a relatively new form of insecticide. Getting the best from it has been a learning experience for all users with Bayer investing in detailed guidance on mixing to avoid issues with hard water to application practices to support performance. Application rate is important with all products. With Flipper, Bayer recommends a minimum inclusion rate of 1%, equivalent to 1 litre of product to 100 litres of water. In field vegetables, many growers have reported a 4% inclusion rate to be effective.
Achieving season-long protection, especially through periods of high pressure, can mean relying on a few choice products. How protection is maintained during times of low pressure, however, has become fundamental to both retaining the stronger products for use during periods of high pressure and also keeping populations in check.
No grower wants to find themselves fighting a swarm of insects, so managing numbers where possible can relieve much of the stress. With just two applications of Movento and three of Tracer per crop, programmes need to be structured carefully. Biologicals such as Flipper, which can be applied to outdoor leafy vegetables up to nine times per crop, are a valuable means of balancing a programme.
The AHDB aphid forecast cab be seen here: https://ahdb.org.uk/aphid-forecasts
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