July is the perfect month for tillage farmers to accurately assess the level of grass weeds across their fields.
In turn, this will allow them to put an integrated pest management (IPM) control plan in place.
It’s a case of identifying the weeds present and recording their location in specific fields.
Identification is easier when grass weeds are headed out, but if growers are not sure, they should contact an agronomist for help.
Hand roguing can be done if the population is small. Alternatively, growers can desiccate larger areas if seeds have not already been set in the head.
If they suspect the existence of a resistance issue, then they should contact their local Teagasc advisor to arrange testing.
Herbicide-resistant grass weeds
The results of herbicide resistance testing from 2022 samples submitted by Irish tillage farmers to Teagasc paint a worrying picture.
Greater than 70% of black grass or Italian ryegrass samples tested were resistant to both ACCase and ALS herbicides.
It was also found that poppies were resistant to ALS and/or hormone type (2,4-D) herbicides.
If growers suspect that they may have herbicide resistance in grass or broadleaved weeds (specifically black grass, Italian ryegrass or poppy) in their fields, they should use the free testing service available through Teagasc.
This then allows growers to identify an effective herbicide programme to be used in conjunction with integrated weed management strategies.
Collecting samples
Good sample collection is essential for successful testing; the following sampling procedures should be followed.
For grass weeds, cut-off the mature seed heads directly into a paper envelope, or bag. Gently rub the heads or shake vigorously inside the envelope. This process should be carried out in a secure area away from the field to prevent seed escape.
Seeds should be collected on dry days. But if damp, allow them to dry, away from sunlight, before threshing.
For broad-leaved weeds, farmers should cut-off the mature heads directly into a paper envelope, or bag, and keep the paper envelope open for couple of days to allow further drying of the heads.
Seeds can also be collected by covering the top of the weed plant with ‘party bags’. This will allow the seeds to fall into the bag and not onto the soil and makes the collection of seeds much easier.
Farmers should collect seeds when they are ripe and easily fall from their seed heads. Mature seeds will germinate rapidly.
Seeds sampled too early or from intact heads will be unripe/immature and will not germinate.