Aphid control in brassicas

With the foliar aphicide toolbox being limited to start with, and further reduced by the limited stocks of Plenum (pymetrozine) ahead of its withdrawal, this puts increased pressure on the fundamental building blocks of aphid and whitefly control, Movento (spirotetramat) and Biscaya (thiacloprid).  Understanding how to get the best out of these products in order to stretch sucking pest control through the expanded season has never been more important.

Breaking the aphid lifecycle

Typically, Biscaya should be used for quick knockdown of populations, while Movento is there to help prevent populations from building up, explains Matt Garnett, Bayer’s commercial technical manager for Lincolnshire.

“Timing is key. Movento’s two-way systemicity means it should only be applied when plants are actively growing, and pests are feeding. Application when plants growth is limited (e.g. during drought or extreme hot or cold weather) will limit its ability to move in the plant and be taken up by the pests,” he says.

“Always aim to apply it early in the infestation: that way its mode of action preventing lipid synthesis can stop development of the pests and effectively break their lifecycle.”

Use Biscaya to target aphids in open canopies, and time applications to make the best use of its rapid knock-down effect to thin out aphid numbers, he adds.

“Biscaya is translaminar in leaves and has some systemicity too – but the key for best efficacy is trying to target pests directly.”

Climatic conditions

Aphid pressure was high earlier in the year, and although levels have dropped away reflecting the typical summer population dip, they are expected to rise again from late August as a further generation benefits from warm and wet conditions producing plenty of lush growth.

With limited insecticide options, it is critical that pests are stopped before they become established in the crop – but without wasting any sprays. Growers will need to continue to monitor their crops carefully over the coming weeks to determine when aphid and whitefly populations are building, and to deploy Movento and Biscaya effectively at the right time.  

Integrated pest management

Trying to avoid the need for insecticides by using cultural controls, such as more tolerant varieties, considering crop hygiene in surrounding fields and managing the green bridge from one crop to another is important in any season, Mr Garnett notes. “But it will have added significance in the absence of neonicotinoids and the limited armoury of foliar sprays meaning that it will be impossible to use solely chemical solutions for control.”

Growers also need to be cautious of the impact of other agronomic activities on beneficial insects such as ladybirds, lacewings and hoverflies, which prey on aphids. Ensuring crop protection applications and other activities minimise the impact on these crucial allies is becoming increasingly important.

“Broad spectrum pyrethroids, which can reduce beneficial insects, can be swapped for more species-specific caterpillar sprays where practical, and it’s helpful to know that Movento has a very strong beneficial safety profile too,” adds Mr Garnett.

Looking to the future, he also recommends that growers consider the use of biological crop protection products to help get the balance right.

Controlling aphids in 2020

Historically using neonicotinoid seed treatments meant growers were able to plant a crop with the assurance it would need little attention for two months, but this is no longer the case.

As a result, careful field observation, an in-depth understanding of aphid life cycles, and clear understanding of how to make best use of the available insecticide options as well as alternative methods of control are now imperative to protecting crops from aphid attack.  

For further guidance, Mr Garnett advises growers to follow pest intelligence services including ABC’s Brassica Alert, AHDB Aphid News and AHDB Pest Bulletin, in addition to regular articles on the Bayer blog.