Discussion at the recent Teagasc virtual crop walk discussed the growing grass weed problems. There was a time, not so long ago, when this discussion might have centred around wild oats, annual meadowgrass and possibly sterile brome.

Now these discussions focus on blackgrass, canary grasses and a range of brome grasses, plus the presence of herbicide resistance in a number of grassweed species.

During the discussion, Jimmy Staples of Teagasc reported that a grower had to destroy five acres of a moderately infested crop because roguing the blackgrass was impossible.

To leave it intact would take the land out of effective cropping for very many years. The tragedy in this action is that it might have only taken 5m2 to be removed in the previous crop to help prevent the problem from building.

Grassweeds are a growing menace for tillage farmers. It is no longer feasible for growers to allow a problem to increase, as effective herbicides are running out of road on some of these weeds.

Resistance in wild oats

Wild oats are a particularly good example. There is now quite an incidence of resistance to the main graminicides, but, so far, this is mainly confined to the southeast.

This shows that the continued use of a single active will inevitably select for resistance and if that one initial resistant plant is not removed, it will allow a whole new problem to develop.

Jimmy emphasised the need for growers to be extremely conscious of any grass weed in a field that they do not recognise. This takes vigilance to find it in the first instance, but this is a classical case of where 'a stitch in time saves nine'.

We might not have wild oats as a universal problem or sterile brome or canary or blackgrass if the first occurrences had been rogued rather than tolerated.

While burning off the crop is an extreme action, to not do so would have even greater consequences, especially as much of the infestation is already resistant to most herbicides.

Various actions to reduce infestation were discussed, including delayed planting date in these fields, early autumn stubble cultivation to grow out seeds, occasional ploughing, etc, but the Teagasc view, like mine, is that zero tolerance is the only sensible attitude to grass weeds and blackgrass in particular.

Grass

Having to put land down to grass may also seem like a tough decision, but the lower the infestation level the quicker it can come back in cropping safely.

Also, the bigger the infestation when going down to grass the longer it will need to be undisturbed to get the population to drop low enough to be cropped again. Weeds like blackgrass are not problems to play with.

Even grass has its limitations. Jimmy commented that it is common to see blackgrass growing and producing seed heads in the early months of a new reseed. So this too has to be managed in order to prevent further seed set in the early years in grass.