New survey aids growers in fight against wild oats

The first wild oat survey for 20 years has shown an increasing incidence of the winter wild oat (avena sterilis ssp. ludoviciana) in some regions and higher occurrence of resistance to herbicides in this species than in the common wild oat (avena fatua).

Ruth Stanley, country manager at off-patent crop protection manufacturer Life Scientific, says wild oats have become the forgotten enemy.

Most competitive

Its actually our most competitive grass-weed, on a potential yield loss/plant basis.

Just one wild oat plant/square metre can reduce yields by as much as one tonne/hectare in winter cereal crops, and 0.6t/ha in spring cereals.

With increasing numbers of growers asking about wild oats, NIAB weed biology specialist John Cussans says: We felt it was really time to provide an updated picture of wild oat herbicide resistance and also a general picture of where we are with wild oats currently across the UK, so we asked for wild oat samples to be submitted after harvest, along with a detailed questionnaire.

NIAB and Life Scientific collaborated on the survey which saw 105 samples submitted by growers or agronomists 97 of these were viable for testing for their susceptibility to pinoxaden (for example Axial Pro) and iodosulfuron/mesosulfuron (for example Niantic).

Of the samples, 70% contained the common wild oat and 30% the winter wild oat or both, says Mr Cussans.

When people have looked at the winter wild oat in the past they have found about 10% of wild oat populations containing it so it was surprising to find 30%.

Distributed Samples were distributed in a band across central England, with winter wild oats accounting for half the population in some areas, he adds.

Why it seems to have gone under the radar is difficult to tell.

However, it is difficult to tell the two species apart you can only discriminate between them when the seeds are being produced on the adult plant. (See Identifying wild oats panel) According to the survey, common wild oats tend to be more prevalent in rotations containing more spring and break crops, whereas winter wild oats tend to be seen more in rotations where there is a lower proportion of spring crops and break crops, says Mr Cussans.

We had 11 samples that were from continuous cereal rotations and either 100% or 99% of wild oats in these scenarios were winter wild oats. Reasons for an apparent increase in wild oats are both cultural and chemical, says Ms Stanley.

There are several factors. Min-till and direct drilling have become more popular.Burial increases the dormancy of wild oat seeds.

With min-till and direct drilling, seeds are left on the soil surface which increases germination, particularly when soil is moist.

Also, there has been a reduction in the use of ALS chemistry, traditionally used to control black-grass, but growers worried about reliance on this chemistry for black-grass control have forgotten that these herbicides are actually very effective at wild oat control.

Resistance

Examining herbicide resistance in winter and common wild oats, Mr Cussans found that 10-15% of populations showed resistance to ACCase inhibitor pinoxaden, with no great difference between wild oat species.

Five to 10% of common wild oats showed resistance to ALS herbicides compared with 10-15% of winter wild oats.

The initial findings point to cases of resistance in both species to both Axial Pro and Niantic, with the study confirming the occurrence of resistance is indeed higher in the winter wild oat. Ms Stanley adds: Although were getting more and more reports of wild oats as a problem weed, its reassuring to know from these survey results and the resistance testing, that ALS chemistry such as Niantic and Cintac still work and have a valuable place in the herbicide programme to provide efficient control.

Its important to ensure correct product application to prevent decreased sensitivity in the field, so we continue to get the best performance from these herbicides.