This article originally appeared in the Aug. 2005 Ag News and Views newsletter.
As you probably know, it's now too late in the summer to spray for most pasture weeds. There are a few exceptions, but most weeds in pastures should be sprayed in the spring when they are young and actively growing. That said, you can do something now that will improve your weed control program next year.
Now is a good time to inventory your weed situation. One thing is for sure - if you have a lot of weeds in a certain place this year, you'll probably have them again in that place next year. Right now, weeds are large enough to see and most will have seed heads or fruiting parts that make them easier to identify. This greatly aids in inventorying the weeds.
How should one conduct a weed inventory? First, identify the species and abundance of each of the weeds you want to control. The abundance rating system can be as simple as few, many, scattered or "more than I can shake a stick at." Mark this information on a field map and highlight areas where there are hard-to-control weeds or particularly high numbers of weeds. Be sure to accurately identify areas where you might be able to spot spray difficult-to-control weeds and save some money by not spraying the entire field.
Next, identify areas on the map you don't want to spray or where you don't want to spray certain herbicides. Examples are areas where you want to maintain clovers or areas with certain wildlife foods. In these areas, you may want to avoid herbicides altogether or use herbicides that are not as harsh on the plants you want to keep. For example, if you want to keep clovers in an area, don't use Grazon P+D. As an alternative (although not as good from a weed-control perspective), you can wait until the clovers produce seed and spray with something like 2, 4-D. This herbicide program will not be as effective because you're not spraying at an ideal time for 2, 4-D to work, but it will control some weeds and not wipe out the clovers.
After you have inventoried the situation, sit down and work out a spray plan and budget that includes the correct herbicides to use and when to use them. Many of the weed control failures we see are due to using incorrect products for the targeted weeds or spraying at the wrong time.
Creating a spray plan now, when the weeds are easy to identify, can be very valuable in controlling weeds at the least cost in the spring. It can ensure that you spray what you want to spray, where you want to spray it, to control what you want to control.