Pre-emergence vs post-emergence herbicide, which one should I use?

Pre-emergence and post-emergence herbicides are used at different times and do different jobs, and in most crops you get the best, cheapest control by using both rather than one. A pre-emergence herbicide is sprayed on the soil within 1 to 3 days of sowing, before weeds and usually before the crop come up. It forms a barrier in the top soil layer that stops germinating weed seeds, so it needs a moist, well-prepared field and must not be disturbed by hoeing or heavy irrigation right after. A post-emergence herbicide is sprayed after weeds have already emerged, usually at 15 to 35 days depending on the crop, and is targeted to the weeds present, so you can pick a grass killer, a broadleaf killer, or a broad-spectrum product to match what you see. The two work together: pre-emergence knocks down the first big flush so the crop gets a clean start, and post-emergence cleans up escapes and later flushes. Use only herbicides recommended for your specific crop, follow the label dose and timing exactly, and check with your KVK, because timing windows are strict and the wrong product or wrong stage can fail or damage the crop.