Winter OSR crops – time to check their GAI

Teagasc tillage advisors are actively encouraging farmers with winter oilseed rape (OSR) crops to check their Green Area Index (GAI) values as a matter of priority.

GAI can be used to determine the amount of nitrogen that should be applied to OSR crops over the coming weeks in order to maximise yield.

Co. Laois-based advisor Veronica Nyhan said:

“Step one is to download the GAI app on to the user’s phone. Open it and then take a photo of the crop in question.

“The photo can then be submitted and the GAI figure is returned within a very short space of time. This process should be repeated at a number of locations in order to develop an average GAI figure per field.

All the photos and GAI information received can be forwarded to the farmer’s computer from the field.

Agronomy update

Nyhan was one of the contributors to this week’s Teagasc winter crop agronomy webinar. Featured within her report was a progress update on a field of winter OSR sown out near Stradbally, Co. Laois.

The crop in question, which was sown out on September 11, 2020, is being grown for seed.

Nyhan commented:

“The crop has a current GAI value of 1.1. The target is to increase this figure to 3.5 at flowering. Every full unit of GAI is equivalent to a nitrogen content in the crop’s leaves and stem of 50kg.

Getting the GAI figure to the appropriate level will require a total nitrogen application of 210kg/ha. This can be applied over three splits: an application of 50kg in mid-March, 100kg at the end of March and the final 60kg at seed-fill in early April.

OSR crops in east Cork also featured on the webinar. Here again establishment rates were good. But the threat of early leaf spot was highlighted. In such instances, the immediate application of a suitable fungicide was advised.

In total contrast, a winter OSR crop featured in Co Wicklow had been heavily grazed by pigeons. The average GAI was 0.4. In this case, the immediate application of nitrogen was advised.

Provided the crop has a strong root system, the prospect of it responding well to nitrogen is very good.

Another general point to come out of the webinar was the need for growers to look out for signs of boron deficiency. If the problem is identified, the immediate application of a proprietary spray is strongly advised.