Tillage farmers are being advised to avail of a free testing service to check for herbicide resistance in grass or broad-leaved weeds in fields.
The period between now and harvest is the perfect time for growers to walk through their crops and assess how well weeds were controlled this year.
If weeds are present, the fundamental question to be asked is – why?
There may be a number of reasons why weeds were not controlled such as delayed herbicide application, poor herbicide choice, inappropriate herbicide rate or poor weather at herbicide application timing.
If one of these scenarios explains why weeds are present in a crop, then this is a valuable lesson for next season.
Herbicide resistance
However, if there is no obvious reason for the presence of weeds then there may be a weed resistance issue developing.
The results of Teagasc herbicide resistance testing from 2022 paint a worrying picture.
The work confirmed that greater than 70% of blackgrass or Italian ryegrass tested were resistant to both ACCase and ALS herbicides.
In addition, poppies were found with resistance to ALS and/or hormone type (2,4-D) herbicides.
If farmers suspect that they may have herbicide resistance in grass or broad-leaved weeds (specifically, blackgrass, Italian ryegrass or poppy) in their fields, they should use Teagasc’s free testing service to check it.
This will allow the identification of an effective herbicide programme to be used in conjunction with integrated weed management strategies.
Testing
Good sample collection is essential for successful testing.
A useful technique to gather seeds is to cover the top of the 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.
Identification and mapping of problem weeds should be carried out now with ripe seeds collected in mid-July to early August (mid/late-June for winter barley).
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 seeds escaping.
Seeds should be collected on dry days. But if damp, allow them to dry, away from sunlight before threshing.
For broad-leaved weeds, 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.