My weeds have become resistant to my usual herbicide, what do I do?

When a herbicide that worked for years suddenly gives poor control, the most common cause is herbicide resistance, not a fake product, though both are possible. Resistance builds up when the same chemical, or chemicals with the same mode of action, are used on the same field season after season. The surviving weeds breed and pass on resistance until the population no longer responds. The fix is to rotate modes of action: stop using that chemical family and switch to a different one, ideally one not used on that field before. Use tank-mixes of two different modes where the label allows, so any weed surviving one is hit by the other. Add non-chemical pressure too: timely sowing, a dense competitive crop, a pre-emergence herbicide, crop rotation with a different crop and herbicide system, and removing weed escapes before they seed so the seed bank does not refill. Always confirm the product was stored well and is within date, and use only herbicides recommended for that crop at the label dose and timing. Check with your local KVK, which often knows which products are still working in your area, and remember the wrong herbicide can kill the crop.