Direct-drilling winter cereals and getting the resultant crops well established in the autumn are key to control the rising problem of wild oats seen in the past two seasons.

Wild oats have been largely kept in check by blackgrass herbicides, but two very wet autumns and an increase in winter-emerging wild oats has seen the weed become a bigger problem.

Add in the fact that winter-emerging wild oats seem to be developing resistance to contact herbicides more quickly than their spring cousins and the problem is exacerbated.

John Cussans, weed expert at crop consultant Niab, says taking the two types together, germination and emergence can stretch from September through into early July and so control measures need to start early.

“Growers should be looking at wild oat control in the autumn as they can no longer leave control until the spring,” he told a recent briefing.

See also: Why farmers battling wild oats should identify the species

Four-point plan

Mr Cussans has put forward a four-point plan to help growers cope with control of both species of wild oats, following the principles of integrated weed management.

1. No-tillage, fallow and non-cropped periods

Wild oats seeds are actively eaten by birds and beetles, so leaving the relatively large seeds on the soil surface can result in a massive reduction in viable seeds.

Conversely, cultivations soon after harvest increase wild oats in the following crop.

“If possible and if there is high wild oat pressure, leave the seed on the surface for as long as possible,” he says.

Seed losses can be as much as 50% over seven days from bird and beetle feeding.

2. Cultivations

Wild oat seed can emerge from much deeper than other seeds such as blackgrass, so effective cultivations to bury seeds need to be deep – and ideally inversion, such as good, deep ploughing.

“Growers should either use inversion (ploughing) or do nothing. Moving from little cultivations to no-till will bring big benefits,” he says.

Cultivations after harvest can result in four to five times as many wild oats in the following crop.

3. Biosecurity

Although most wild oat seed is shed pre-harvest, combining is still a major cause of seed movement within fields and potentially between fields. So cleaning of machinery is very important.

4. Crop competition

In the case of spring-emerging wild oats, dense crop canopies suppress late germination and so help weed management.

So early drilling could be advantageous for wild oat control, although not for the control of blackgrass.

Two wet autumns

Mr Cussans says the wild oat burden has increased over the past two seasons as two wet difficult autumns have left open crops rather than big crop canopies, while the window to treat actively growing wild oats was very narrow in cold, dry springs with little active weed growth.

Poor control also has come with the emergence of a new type of wild oat, in addition to the common spring-emerging wild oat, Avena fatua.

This new winter-emerging wild oat, Avena sterilis (subspecies ludoviciana), was first recorded in 1910-12 in the UK, probably in contaminated imported grain from the Mediterranean area, and was recorded as an arable weed in 1926.

The two wild oats are very difficult to tell apart and can only be easily identified from the seed.

Common spring (fatua) individual seeds shed separately or easily fall apart.

In the winter (ludo) plant there is often a small third seed and rarely a tiny fourth seed which doesn’t have the “wild oat” awn, and pairs of seeds are shed together and stay as a unit.

Rotations

Mr Cussans says that the winter wild oats are encouraged by cropping dominated by winter cereals, while spring wild oats are associated with more diverse rotations and spring cropping.

In a survey across the UK, 30% of wild oat samples taken contained ludo seed, and across a central-southern band of England it is well over 50% of the samples, suggesting that ludo is becoming more of a problem.

In addition, he is beginning to see the relatively slow development of resistance to selective contact herbicides such as acetolactate synthase (ALS) inhibitors, and the ludo wild oats do seem to be developing herbicide resistance more quickly.

However, while the resistance problem may be building, it is nowhere near the resistance problems seen in other grassweeds such as Italian ryegrass.

The speakers were attending a briefing to celebrate 60 years of Avadex use in the UK