In the third article in this series focusing on getting the best out of your oilseed rape crop, we track the progress of OSR crops throughout the UK.
Most crops of winter OSR have experienced a bizarre phenomenon this season. A series of hard night frosts reversed strong autumn growth, while increased attacks from pigeons have reduced some previously good looking crops to stems and leaf crowns.
With hopes of spring triggering green shoots of recovery, growers and agronomists will have to take extra care to preserve new leaf growth for as long as possible through the growing season, James Southgate, Syngenta field technical manager, advises.
He says: “In the short-term, growers should focus on keeping pigeons away and providing crops with the early nutrition they need to get them growing, then as they move quickly towards flowering, it will be important to maximise green leaf retention.
“Amistar [azoxystrobin] should be applied at the yellow bud to early flowering stage, as plants switch from their vegetative to reproductive stage. This timing will also give early protection from sclerotinia infection.
“The rapid development of OSR crops this season means we are likely to see plants go through their growth stages and flowering period relatively quickly, which will limit their individual exposure to sclerotinia infection.
“Where growth within fields is variable, the overall flowering period could be protracted.
“The second-spray Amistar programme after three weeks will ensure most plants are treated at the optimum time and will provide leaves with extra protection against late disease infection.”
Preventing early leaf loss from post-flowering diseases, including Alternaria, will be more important than ever this season to boost yield, predicts Mr Southgate. He says green leaf is far more efficient at capturing sunlight and converting energy into oil than either the stems or pods.
The effectiveness of this action could be enhanced by careful spoon-feeding of nutrition to encourage leaf development, since most crops where leaves have been stripped by frost and pests currently have limited carbohydrate reserves.
Trials show a late foliar N feed, at or around flowering, applied just as the first leaves start to show signs of senescence stress, can prolong green leaf and boost yield.
Sclerotinia can cause serious yield losses in OSR crops, as much as 50% in those seriously affected. However, the good news is it is a relatively weak pathogen which typically requires decaying plant material or damage to stems to get into the plant, followed by a ‘perfect storm’ of conditions during flowering to cause widespread infection.
Although sclerotinia has only been a significant problem in two of the past 10 years, growers are nevertheless advised to take action to insure against losses, bearing in mind to deliver a guaranteed return on investment the treatment must offer more than sclerotinia protection alone.
In addition to controlling sclerotinia, Amistar offers green leaf and plant health benefits. Syngenta says it has been shown to consistently provide an economic increase in yield and oil content over untreated crops.
Verticillium wilt has become increasingly common where oilseed rape crops have been grown repeatedly in the rotation. It is believed inoculum is introduced through infected seed and, once in the soil, will remain there to infect future OSR, with weed species perpetuating its impact.
The disease results in whole plants dying back and shedding seed before harvest, or weakening stems and making them susceptible to lodging and breaking.
Healthy OSR plants are said to be better able to fight off the pathogen or at least resist its effects until later in the season, allowing the seed to be harvested.
As well as fungicidal activity, Syngenta says Amistar enhances plants’ green leaf and photosynthetic activity and stimulates stress-reducing free radicals within cells, which can boost performance.
Growers report the impact of verticillium wilt is reduced in treated crops, even where there has been a historical incidence of the disease.
This season, the Syngenta iOSR initiative will encompass soil sampling and testing to help identify the extent of potential verticillium wilt infection and validate the results of this process with observations of what actually happens in the field prior to harvest.
Pollen beetle seriously damage green flower buds of oilseed rape plants when they burrow into petal sheaths in search of pollen before flowers open. The key point is a damaged flower is a lost seed pod.
Thresholds for treatment have been revised in recent seasons, with ADAS now saying crops with a high plant count are more susceptible to damage. This is because they typically have less opportunity to produce supplementary flower buds from branches to compensate for damage, compared to those with lower plant populations.
This season, a significantly greater proportion of crops have high plant counts, because growers used higher seed rates to compensate for potential autumn and winter pest losses.
Establishment was good and winter survival has been excellent. Furthermore, some crops which advanced well in winter are moving to the green bud stage early, although cold weather and relatively short days mean they are unlikely to come into flower soon. Crops could therefore remain in the highly susceptible green bud stage for an extended period.
Reliable insecticide performance is critical to protect the crop through to flowering. Where damage is seen and thresholds are reached while the crop is at green bud stage, Syngenta says growers should spray as soon as possible with Plenum, which it says provides the highest level of pollen beetle control and persistency but has no resistance issues.
Where pyrethroid resistance is common, resistance action advice is not to spray any pyrethroid product. Once crops are in flower, beetles move onto open petals to reach pollen without damage.