Aphids and whitefly alert for brassica crops
Some aphid species have appeared a month earlier than forecast and whitefly have already been spotted on overwintered brassica crops. Growers are therefore advised to step up vigilance and be ready to take action to protect produce quality.
Last summer, as in 2009, whitefly numbers reached epidemic levels in Lincolnshire. UAP agronomist Dan Hayes saw infestations begin in late May to early June; about a month earlier than usual. This year he has already started to see adults laying eggs in overwintered crops: “It’s a clear sign this year’s crops could again be at risk of early infestation.”
The Rothamsted Insect Survey has already recorded first catches of peach–potato aphids at the Starcross, Wye, Silwood Park, Broom’s Barn and Writtle trap sites and Dan has found the first in Lincolnshire crops. “These are a month earlier than forecast so the effects of the cold winter may have been outweighed by the warm dry spring.”
Where crops face pressure from either or both of these sucking pests he advises control programmes based on Movento (spirotetramat). He has found its two-way systemicity to be highly effective against these pests which hide in the growing points of brassicas or are concealed by the canopy. “Timing is key though and you need to deploy the two permitted sprays for best effect according to the main target.”
To control whitefly Dan uses the first spray during early infestation to target the larvae. Under sustained pressure he follows with Biscaya (thiacloprid), for further suppression and resistance management, and holds the second spray back until late August to early September to maximise protection of harvestable produce. If control has to begin in June he advises adding a Plenum (pymetrozine) spray between Biscaya and the second Movento.
Dan says last year this new approach achieved excellent control and dealt with any aphids present. “Marketable yield of Brussels sprouts was vastly improved. Button quality was saved from contamination and they were bigger too. It also made harvesting much more operator friendly as there weren’t any clouds of whitefly coming off crops.”
Should the main target be aphids – particularly mealy cabbage aphid – a subtly different approach is needed. “Early on when the crop canopy is more open they can be reached with other chemistry such as Biscaya. It’s therefore best to keep the first Movento spray until mid season when the crop has thickened up and you need to start protecting harvestable parts.”
Bayer’s Dr Richard Meredith adds that Movento is a ‘generation-breaker’, not a ‘knockdown’ product. “It’s two-way systemicity works with the plant’s vascular system so it has to be applied when plants are actively growing and pests are actively feeding. It takes a few days to start taking effect with duration of protection lasting two to three weeks so expect a slower start followed by a very thorough finish.”
