In the UK we grow around 130,000 hectares of vegetables, valued at £690 million. Supermarkets and processors demand high quality unblemished vegetables, so tackling pests effectively is of paramount importance for any vegetable grower. Considering the increasing demands of retailers, it has however become more difficult on two counts - the demise of several key active ingredients in the armoury plus the increasingly widespread resistance to other actives. It is still important in vegetable crops to try and use insecticides with different modes of action within the programme in order to reduce the build-up of any further resistance.
Brassicas can be infested by up to 49 different pests according to AHDB. Pests affect quality and yield through direct feeding, transmitting viruses and contaminating produce. The most frequent pests in brassicas are aphids, whitefly, caterpillars particularly Diamond Back Moth, and cabbage root fly. The Pesticide Usage Survey for outdoor vegetables confirms this - 39% of all insecticides applied were targeted at caterpillars, 37% against aphids, 6% against diamond back moth, 5% for aphids and caterpillars, 3% against mealy cabbage aphid and 9% against a range of other pests. Pre-planting drench treatments to control cabbage root fly are not included in the survey but virtually all conventional crops are treated to control this pest, with the exception of root brassicas where crop covers are used widely.
Campaign Manager for horticulture, Dr. Tim Lacey of Bayer CropSciences says that next year, the loss of the neonicotinoid seed treatments and the second year since the loss of pirimicarb’s brassica recommendations will have a massive effect on how aphid pests are controlled in brassicas and will require a rethink of strategies. “Neonicotinoid seed treatments (such as Cruiser – thiomethoxam) offer 6 to 12 weeks protection against aphids and nothing can emulate that length of protection now.”
The new insecticide cyazypyr (VeriMark 20SC) from FMC can be used as a drench to plant modules in cauliflowers, broccoli, cabbage and Brussels sprouts and will give some protection against aphids but for a short period after planting. Tim also reports that the future of Plenum (pymetrozine), now sold by Adama, is in jeopardy as its approval expires on 30 January 2019. “There will be a use up period next year but it is likely that there will not be enough material for the whole season for cabbages, cauliflowers and Brussels sprouts.”
Tim points out that brassicas are a diverse crop - some are short term, being in the ground between 40 to 60 days whilst others such as Brussels sprouts are long term crops , being in the ground 100 to 150 days. “Their needs are different but most suffer from aphids at some point. Two insecticides from Bayer will inevitably feature more broadly next season – Movento (spirotetramat) and Biscaya (thiacloprid). Movento is a ketoenol insecticide with unique two-way systemicity to control hidden pests within the foliage. It will be the backbone of the program now and has just been reregistered. It has recommendations for aphids and whitefly in broccoli, cabbage, cauliflower, collards and kale, with EAMUs in parsnips, swedes, turnips and carrots. It can be used in IPM as it is safe to beneficials. Two sprays can be applied in brassica crops with the latest application being 7 days before harvest. ”
Movento works best when crops are growing and pests are actively feeding. It is not a knock- down product, taking a few days to control populations. Interestingly, despite being specific to sucking pests, it has been shown in trials to have some effect on reducing Diamond back moth populations. Biscaya however can provide quick knockdown when crops are more open and aphids exposed. It is a neonicotinoid insecticide controlling aphids in broccoli, Brussels sprouts, cabbage, cauliflower and other crops. Just 2 sprays can be applied and its Harvest Interval is 7 days. (21 days on kale and collards)
But Tim also some optimism as Bayer has just submitted the data package to CRD for a totally new aphicide from a new chemical group. “This will hopefully hit the market in 18 months time,” he says. Corteva also have the new product isoclast or Closer registered in Ireland and anticipated for UK soon for use against sucking pests. Vegetable specialist for HLHutchinsons, Peter Waldock says “Isoclast was looking very good in our trials. It has minimal impact on beneficials so fits in with IPM programs. It has systemic/ translaminar properties and fast feeding cessation which will reduce virus transmission. It remains active for 10-14 days.” Peter also added that Movento gave the best results when applied ahead of aphid population build up and said it was the best treatment for whitefly.
Other insecticides in brassicas to consider are Steward (indoxacarb) which is now sold by FMC and aimed at caterpillars. Diamond Back Moth (Plutella xylostella) (DBM) has become a real problem in the UK vegetable crop, as well as the small cabbage white. DBM is a migrant species which arrives from the Continent and can complete its life cycle in our weather conditions. It may also survive the winter in warm locations.This pest was a particular problem in 2016,” says Dr. Rosemary Collier of Warwick University. “Another migrant, the Silver Y moth was also a problem last year but mainly on lettuce. Controlling pests is a major challenge with fewer effective chemicals available due to legislation or resistance. Growers will need to use IPM approached where possible and make sure they try to use different products with different modes of action which is challenging with fewer products from which to choose.” Rosemary is interested in the contribution of biopecticides and these are being evaluated in the AHDB SCEPTREplus project.
According to Certis IPM Manager, Selchuk Kurtev biorationals will have a greater part to play as they are moved out of the protected environment to the field. He says that use of these products is preferable in the Kale crop which is more often than not eaten fresh or in a smoothie. “Kale is now seen as a super food and is consumed fresh. Any pests or indeed pesticide residues would be unacceptable. Whitefly can hide within the nooks and crannies of its leaves. Other brassicas also suffer whitefly and caterpillar infestations. Certis can offer several biorational options including BotaniGard with an EAMU anticipated soon (an entomopathogenic fungus Beauveria bassiana GHA) for whitefly control, Majestik (maltodextrin) for the control of spider mites and white fly in all outdoor and protected crops and Spruzit (natural pyrethrums for caterpillars). “Spruzit had a wide range of brassicas added to its label in October 2018. It can now be applied 4 times in a program. Botanigard can be used in an IPM system, has a zero harvest interval and low chance of resistance and works best in warmer conditions.”
“Growers spend time and effort creating field boundaries to encourage beneficials and we would say that our biorational solutions are sympathetic to this, allowing naturally occurring predators to increase. Majestik is a physically acting product, taking care of adult whiteflies and allowing natural predators to tackle nymphs and scales. As a company Certis have been able to replicate performance of these biorationals from the glasshouse to the field.” Selchuk mentions that half the pending European registrations are naturally derived biorationals indicating their growing popularity.