Growing oilseed rape without neonicotinoid-based products poses real challenges for growers this season. Paul Spackman discovers what the ban means for four farmers.
Business as usual despite ban
The 2014-15 season will not be the first time Richard Cotton (pictured below) has grown oilseed rape without an insecticidal seed treatment, so he hopes it will be business as usual despite the neonicotinoid ban.
Mr Cotton, who farms 1,200ha of cereals (wheat, barley and oats), oilseed rape and grassland with his sons near Exeter, says his relatively simple establishment system for the 200ha of oilseed rape has worked well, producing an average yield this harvest of 4t/ha, up to 5t/ha on the best land.
He normally sows a 50:50 split between bought-in treated seed and untreated home-saved seed and like other growers, believes strong early establishment is key to success. “We’re on light, sandy land and have favourable climate, which really helps.”
For the past two years, oilseed rape has been established straight into wheat or barley stubble using a seeder unit mounted on a Sumo Trio cultivator and then rolled within 24 hours.
Varieties this season are unchanged and are split evenly between hybrids and conventionals that include Quartz, Excalibur, Flash and Expower.
Drilling is normally from 20-31 August, with seed rates of about 2-3kg/ha for hybrids and 3-4kg/ha for conventional varieties. “We might go a bit higher, up to 5kg/ha, for later-drilled home-saved seed, but it really depends on the variety. We aim for establishment of 50-60 plants/sq m going into winter.”
A clomazone or metazachlor-based pre-emergence herbicide is usually applied primarily to tackle hedge mustard.
Flea beetle is the biggest early pest challenge and Mr Cotton says this can normally be controlled by using an early pyrethroid at the cotyledon stage, followed by a second spray if required.
“We want to get as good establishment as we can and so far what we’re doing seems to be working, so I see no reason to change it.”
Worries about reliance on pyrethroids
Half the oilseed rape grown on Doug Taylor’s 450ha farm near Folkestone is from untreated seed and he is not unduly concerned by the loss of neonicotinoid-based treatments. However he is worried about the possible knock-on effects of the industry’s extra reliance on pyrethroid sprays.
“We’re about 150m above sea level, so peach potato aphid has not been an issue, and in 25 years we’ve never really seen any difference in yield between bought-in treated seed and home-saved untreated seed. Crops normally average 3.5-4t/ha. We have our own rotary cleaner and use only the larger seed.”
But he knows over that time flea beetle and aphid resistance to pyrethroids has not been an issue, whereas it is increasingly now. “Pyrethroid resistance is a bigger threat to us than the loss of neonicotinoids.”
Mr Taylor is growing 90ha of Trinity, ES Alegra, Cabernet and Catana plus some Pioneer W21 oilseed rape this season and says getting crops established quickly is key to beating pests.
Most rape follows winter barley, which usually allows a fortnight to prepare ground for drilling, he says. Barley stubble is given a light cultivation with a Vaderstad Carrier to encourage volunteers to germinate before spraying-off with glyphosate.
All rape is sown in mid-August at 80 seeds/sq m. “That’s fairly early, but because most land is quite high, we get away with it. If drilling goes beyond late August we don’t get good enough establishment to see it through winter.”
Drilling is done with a farm-adapted power harrow drill featuring four winged tines that cultivate down to 150-200mm, double-disc coulters to sow three rows behind each leg and a press wheel to consolidate soil. This is followed by an extra pass with ring rolls.
“It’s a nice, simple system that gives us a good, firm seed-bed and ensures seed goes in at an even depth on any soil type.”
Untreated seed normally emerges one to two days earlier than treated seed, which gives it an advantage against pests. Pre-emergence herbicides are restricted to specific fields, as some chemistry can slow rape emergence, he says.
To make the system work, Mr Taylor knows it is crucial to get pyrethroid sprays on early, as soon as cotyledons emerge.
Along with Hutchinsons agronomist James Short, he closely monitors flea beetle pressure and applies a second pyrethroid when needed, typically at the emergence of the first or second true leaf.
Make best use of varietal vigour to combat pests
The loss of neonicotinoids has prompted a number of tweaks to oilseed rape agronomy at the 1,220ha Revesby Farms near Boston.
Some 200ha of oilseed rape will be drilled this autumn and farm manager Peter Cartwright says making best use of varietal vigour will be crucial to ensure crops establish quickly and stay ahead of potentially higher pest pressure throughout the season.
Hybrids (mainly DK Extrovert and Popular) make up 80% of the farm’s rape area, with home-saved Quartz accounting for the rest. “Autumn and spring vigour has always been a key driver for us, but even more so this year.”
While he is keen to get crops away quickly, Mr Cartwright will not drill too early. Conventional varieties typically go in from 20 August and hybrids from the 25th. “We usually get better yields from drilling slightly later and if we drill too early, there is a danger we are establishing plants when flea beetle is more active.”
Crops are sown using a 3.5m seven-leg Spaldings Flat Lift cultivator adapted with two Vaderstad coulters a leg. Coulter depth can be controlled precisely, which ensures seed is placed into moisture, giving more uniform establishment, he says.
Seed rates are normally about 40 seeds/sq m for hybrids and 80 for conventional varieties, although these may be increased 10% for crops at extra pest risk (for example, near woodlands or certain headlands).
“We normally double-roll by overlapping our 12m rolls, but this year we’ll try two passes with the second one at a 45deg angle to the first.”
This firms soil more effectively, improves seed-to-soil contact, conserves moisture and makes it harder for pests to move in and around the soil.
Seed-bed nitrogen is being increased from 25kg/ha to 30kg/ha and all seed will be treated with Hypro-Duet and a growth promoter to aid establishment and early development.
In addition, no pre-emergence herbicide will be applied, as Mr Cartwright believes this may slow establishment. Instead, a post-emergence metazachlor-based herbicide will be applied with an insecticide such as Hallmark (lambda-cyhalothrin).
Aphid-monitoring systems are used and a follow-up insecticide, such as Plenum (pymetrozine), will be applied when needed, normally towards mid-October.
“Until now we’d been using Cruiser seed treatment and a spray for aphids and had not needed anything for flea beetle. But we’ve seen a lot of adult beetles in rape and our pollen-and-nectar mix has been hammered quite badly, so it looks as if numbers are building.”
Get OSR crops away quickly
Early establishment of oilseed rape into a good seed-bed is the key to coping without neonicotinoid-treated seed this year for Jim Cargill, who farms 400ha of mixed arable 30 miles south of Aberdeen.
Cropping includes first wheats (Horatio, Viscount and Istabraq), winter and spring barley, OSR, seed potatoes and daffodil bulbs.
Oilseed rape is normally treated with Cruiser (thiamethoxam) to tackle flea beetle, but this autumn he will be relying on getting his 40ha of Mendel away quickly together with an early pyrethroid spray.
“We hope to be able to establish the crop in mid-August and will go on with the first pyrethroid at the cotyledon stage. Hopefully it’ll do the job, but so much depends on the weather and how quickly harvest progresses. It’s normally a pretty tight turnaround to get land ready for rape drilling, but luckily harvest is a week or two earlier than normal this year, which gives us a decent chance.”
To help speed up crop establishment, Mr Cargill is switching from a plough-based system to direct drilling this year after trialling a Sumo Trio last autumn.
“Flea beetle is a real issue in years when the crop goes in late and establishment is more difficult, as the last two seasons have proved. Provided the weather is suitable for direct drilling on our medium loam and heavier land, we should be OK, but if it isn’t, we may need to rethink.”
The latest Mr Cargill will drill oilseed rape is the first week in September and if it goes beyond that, he says the crop will simply not be grown. “I’ll probably put land down to winter or spring barley instead.”
Seed rates of about 2.5kg/ha are likely to be used, which is similar to previous years, he says.
“We’re increasingly looking at varietal resistance as sprays disappear, which means we’re being forced into a situation where we’re not necessarily growing the highest-yielding varieties anymore. Our rape yields are normally about 3.7t/ha, so we’ll wait to see what happens next season.”
We’ll be following the fortunes of our four growers throughout the season – to see how their different strategies pay off and how their crops fare. Our next update will be published in the December issue of Crops magazine.