Tillage update: Oilseed rape crops have wintered well
Teagasc is confirming that winter oilseed rape crops have wintered well.
Plant numbers are good in most crops around the country with Green Area Index values ranging from 1.7 to 2.8.
Teagasc tillage specialist, Shay Phelan, commented: “A Green Area Index value of 1.7 represents a saving of 75kg of applied nitrogen fertiliser per hectare.
“In order to calculate Green Area Index figures, it’s simply a matter of growers downloading one of the apps currently available onto their phones.
“[Oilseed] rape represents one of the most profitable tillage crops that can be grown in Ireland.
"This is why every step must be taken to ensure that the highest possible agronomy standards are achieved.”
Phelan explained that it starts with good weed control through the use of pre-emergence herbicides.
“August and early September can be busy times on tillage farms. And it’s easy to put off the implementation of weed control measures in newly established rape crops until later in the season," he continued.
“This is a mistake. The best time to control weeds in rape is through the use of pre-emergence herbicides from the 'get go'.
“This approach ensures that weeds never get the opportunity of establishing a foothold within the crop.”
Disease threat for oilseed rape
Two of the main disease threats that confront winter oilseed rape crops grown in Ireland are light leaf spot and sclerotinia.
Light leaf spot is very much a wet weather disease and must be controlled in the early spring.
Infections, if left uncontrolled can reduce final crop yields by up to 20%.
The objective is to protect the early flower buds that appear from the middle of February onwards.
Growers can check for the presence of light leaf spot by incubating a number of rape leaves that have been placed in a plastic bag for 24 hours.
It’s simply a case of placing the bag in a hot press or airing cupboard.
The onset of sclerotinia coincides with petal fall taking place within rape crops.
Petals falling on to stems creates an environment within which the disease-carrying fungi can grow.
If the petals are falling to the ground within crops, then the issue is averted.
There is no cure for sclerotinia. Fungicides can only be used to prevent the disease gaining a foothold in the first place.
It is essential to get a fungicide on to crops as soon as those early petals start to fall.
Taking this approach will cut down the risk of sclerotinia infections becoming problematic in the first place.
There are a number of risk factors associated with the predisposition of rape crops to a sclerotinia infection.
In cases where crops are growing in fields that have never been used to grow oilseed rape before, the threat is usually low.
But if it’s a case of a farmer making a long-term commitment to oilseed rape within a rotation, then the priority must be to prevent the disease getting a foothold in the first place.
Meanwhile, clubroot continues to become an increasing threat to oilseed rape crops grown in Ireland.
The main source of infection is brassica species included in cover crop mixes.
One way of avoiding the problem is to select rape varieties that are clubroot resistant. However, this approach brings with it a yield penalty.
