Even the most intractable and costly grass weed problems can be overcome with the right management, the necessary determination and sufficient time.
Understanding, commitment and flexibility are the main keys to success.
Because they produce fewer seeds per plant, wild oat infestations tend not to build-up as fast as those of other annual grassweeds. However, their highly competitive nature means that even small populations can be extremely damaging.
At the same time, the pre-emergence herbicides increasingly being relied upon for annual grass weed control in cereals tend to give limited control of wild oats because many plants may only emerge in the spring, especially after a cold winter.
Equally, all the most effective wild oat herbicides are either ACCase or ALS inhibitors that present a particularly high risk of metabolic resistance development.
In contrast to other annual grass weeds, fewer effective non-chemical means of controlling Wild Oats mean it is vital to make the most of the available herbicide options.
Autumn pre- and early post-em herbicides used to control other annual grass weeds can give useful control of winter and any autumn-emerging spring Wild Oats. But if spring wild oats are a significant element of the population then spring post-em treatment will be required.
Enhanced metabolic resistance is the commonest type and this can reduce the efficacy of most ACCase and ALS inhibiting herbicides. However, where target site resistance is identified in UK wild oats it currently only tends to affect ‘fops’. So ‘dims’ (cycloxydim) and ‘dens’ (pinoxaden) as well as mesosulfuron/iodosulfuron and pyroxsulam mixtures should be the preferred treatments.
Delaying post-cereal harvest cultivations for as long as possible will allow freshly-shed Wild Oat seeds on the soil surface to lose their viability through germination, predation and fungal attack; the longer the delay, the greater the benefit. Incorporating freshly shed seed can induce dormancy for up to six years.
Rotational ploughing is generally less effective at controlling wild oats than other annual grassweeds both because they can emerge from greater depths and as it is more likely to bring their longer-lived seeds back to the surface.
Also less effective, because of the weed’s protracted germination pattern, is delayed autumn sowing, although it may have some benefit in making wild oat seedlings more sensitive to frost.
Non-cereal break crops provide excellent opportunities for Wild Oat control with a range of other herbicides, such as clethodim and propyzamide.
In their early growth stages Wild Oats are very susceptible to competition, so competitive crops like winter oilseed rape and winter beans can be very valuable in assisting other control measures.
Late-spring sown crops like peas and linseed can also help by allowing the greatest possible time for pre-planting Roundup control, while potatoes and sugar beet offer both this and useful in-crop chemical or mechanical control opportunities.
It is essential that any Wild Oat plants emerging before drilling are effectively destroyed with Roundup. Sufficient time should, therefore, be allowed in the establishment programme for the greatest emergence.
This will be especially important when ploughing after several years of non-inversion tillage as it can result in substantial wild oat emergence from previously buried seed.
Later-sown spring crops provide particular opportunities to destroy Wild Oats before drilling, with the least possible soil disturbance at planting minimising weed emergence within the crop.
Wild oats confined to distinct patches or parts of the field should be contained by hand-rogueing or patch-spraying with Roundup. This needs to be done in June before seeds start shedding.
Hand rogueing will be impractical in badly infested areas and, at 2-4 man hours/ha, may be time-consuming. But both it and patch spraying are likely to be justified by the extent to which they limit weed seed return and the yield impact of even relatively low wild oat populations.
This will be most important if herbicide resistance has been confirmed or is suspected in order to prevent the development and spread of resistant wild oat patches.
Avena fatua – seeds separate when mature and are shed singly.
Avena sterilis ssp. ludoviciana – the two to three seeds within each spikelet remain attached together and are shed as a unit.
Avena fatua - Awn present on 3rd seed in spikelet (and 4th seed if present)
Avena sterilis ssp. ludoviciana - Awn absent on 3rd seed in spikelet (and 4th seed if present)