Guidance on aphid control in strawberry

From effective monitoring, natural predators, biological control products and even garlic, Scott Raffle outlines potential ways to control aphid in strawberry crops from our latest research.

AHDB Project SF 156 screened a number of crop protection products for controlling potato aphid in strawberry, including Hallmark (lambda-cyhalothrin), Calypso (thiacloprid) and Chess (pymetrozine). Of these, Hallmark, with or without the wetting agent Silwet, offered best control (100%) when applied by knapsack sprayer. Calypso and Chess are no longer approved on strawberry.

Although effective, as a synthetic pyrethroid, Hallmark is very harmful to beneficical and predatory insects, so growers need alternatives. In a subsequent trial, Batavia (spirotetramat) and a coded product gave durable control for up to three weeks, but Batavia is restricted in use to very-early-season or post-harvest sprays. Alternative forms of management and control are needed.

Natural control

The project demonstrated that the naturally occurring aphid predators Aphidius ervi and Praon volucre offer control of aphids in strawberry, but A. ervi needs temperatures of >8^oC and P. volucre > 12^oC to be effective so may not work so rapidly to contain rapidly rising spring populations of aphids.

Further survey work on the effect of natural predators on aphid control in commercial strawberries demonstrated that commonly occurring predators such as Aphidius and Praon species, as well as lacewings and hoverflies, will peak in number in July, thereby helping to reduce aphid populations. However, the aphid numbers peak in June, so growers need to find additional control methods for early in the season.

Planting garlic in strawberry bags under tunnels, regularly cutting their leaves and placing them in the crop canopy reduced numbers of strawberry aphids in a one-year trial. There was no effect on numbers of predatory mites. Thrips numbers were unaffected. The strong scent given off is thought to act as a repellent to a number of pests. These trials only ran for one year, so it is too early to make bold recommendations on these results.

Guidance for growers resulting from this work:

• Improve the coverage and penetration of the plant (particularly the undersides of leaves) when applying control sprays and adopt one of a range of techniques to assess the level of coverage they are achieving

• Apply control products to existing aphid populations in the autumn to reduce spring populations. Avoiding the need to spray aphids in spring will reduce possible adverse effects on natural and biological control of aphids and other pests

• Carefully monitor both aphid numbers and their associated natural enemies within crops to determine the need for control sprays. Do not treat all fields the same. Consider the species of aphid prevalent and the damage it may cause, including plant virus spread

• Follow resistance management guidelines on control product labels and rotate between products with different modes of action. Populations of some aphid pests, such as the melon and cotton aphid (Aphis gossypii), have developed resistance to certain products

• The control products Hallmark and Batavia both provided effective control in this project. Hallmark is generally incompatible with most predators, although a single application had no adverse effects on Neoseiulus cucumeris in this project. Batavia’s compatibility with naturally occurring and introduced predators is unknown, but use early in the season to meet the harvest interval (14 days before the start of flowering)

• Natural predators can be relied upon to gain control by late summer, but use other control measures early in the season, for example boosting numbers of parasitoids with early releases of commercially available products

• Consider early-season releases of Aphidius ervi to control potato aphid when daytime temperatures exceed 8°C regularly for at least part of the day. Praon volucre is currently only available as part of a mix of parasitoid species (including also ervi) and may also be considered for releases when daytime temperatures exceed 12°C regularly for at least part of the day

• If planning to test garlic intercropping to control aphids, plant a hard-neck variety such as ‘Violet’ in autumn for control the next year. For maximum effect, consider planting at a spacing of every 1 m. When garlic is established, snap leaves at least fortnightly and lay on the strawberry crop

• Always consult a BASIS-qualified agronomist before choosing to use crop protection products

Access more information and the latest research project report: