|Are foraging bees vulnerable to nionicotinoid seed dressings ?|
Phil Jarvis; What are the pests that oil seed rape plants are vulnerable to?
Dr Alastair Leake; Spring and autumn sown rape crops are attacked by a range of pests. These include the peach potato aphid, which spreads beet yellows and turnip yellows virus, pollen beetles, cabbage seed weevil, brassica pod midge, cabbage stem flea beetle, mealy cabbage aphid, cabbage stem weevil and rape winter stem weevil.
Phil ; Are there practices farmers can employ that don’t involve seed dressings or spraying?Alastair ; There are a number of cultural techniques farmers can employ to help control pests, but many are not practical or have other consequences. Delaying drilling after ploughing by 5 weeks reduces the “green bridge” effect, but results in backward crops; converting to a min-till establishment system increases the number of beneficial predators but exacerbates the ”green bridge”.
Phil ; So why do growers prefer to use nionicotinoid seed dressings ?Alastair; The most effective means of protecting the emerging seed is to use a nionicotinoid seed dressing. This removes the need for an insecticide spray for 6 weeks post drilling. In a crop of autumn rape, this would provide protection for August and September when many other non-target insects would still be active in the field. After 6 weeks the crop should be monitored regularly and where thresholds are exceeded a spray applied. Trials have indicated this approach can add an extra 0.3 t/ha to yield worth approximately £150/ha to the farmer.
Phil; Farmers are concerned that any ban on these seed dressings will affect yield and reduce food production. What are the alternatives to using nionicotinoid seed dressings?
Alastair; Rather than treat the seed, many growers will be forced to spray emerging crops. The return to the widespread spraying of these non-selective insecticides would be considered by many to be a retrograde step.
There are two other groups of insecticides available and approved for use on OSR. These are the synthetic pyrethriods (e.g. cypermetherin, deltametherin) and the carbamates (e.g. pirimicarb). The former group are highly toxic to bees, the later moderately toxic. A high proportion of the of the peach potato aphid population is resistant to pyrethroids and the vast majority resistant to pirimicarb, so there is little left in the armoury for dealing with virus vectors. The problem of resistance is becoming greater and greater as active ingredients are withdrawn leading to the more widespread and greater frequency of use of the remaining few.
Phil; How should growers deal with pollen beetles later in the season when oilseed rape is flowering?
Alastair; Dealing with pollen beetles is particularly tricky as they infest the crop just pre-flowering, at the green/yellow bud stage. HGCA run a migration forecast scheme and there is a well defined system for determining threshold levels, above which sprays should only be applied. Some work has been done growing turnip rape around the headlands which flowers a little earlier than OSR and acts as a trap crop. Where a threshold is exceeded pyrethroids can be sprayed, or Thiacloprid, which is a neonicotinoid and has escaped the proposed ban. Spraying for pollen beetle should be limited to the green/yellow bud period when economic damage can be done, but ceased by flowering time, as the pollen beetles may be helpful with pollination at this point. There is a code of practice which sets out how spray operators can minimise the effect their activities may have on bees.
Phil; When will this ban on nionicotinoids take place?
Alastair; The ban on the three nionicotinoid actives affected by the EU decision is likely to come into force by the end of the year, which means that this autumn’s crops can still be treated with a seed dressing.