The concept of combining an herbicide and a fertilizer to “kill two birds with one stone” may be good in theory but may not work in every situation. Several potential problems exist when using this approach.
The first is that the timing for herbicide application and fertilizer application are usually not in sync. Some weed and feed products contain preemergence herbicides that control weeds as they germinate and are best applied before late February depending on weather conditions. Fertilizer applications for warm-season grasses such as bermudagrass should not go on until the first of May. See the problem? The two really need to be applied at different times; so, using a weed and feed blend on bermudagrass in later winter/early spring is not advised.
Second, the selection of formulations for weed and feed blends is much more limiting than if one were choosing only a fertilizer. Fertilizer formulations are much more diverse because fertilizer companies make many more types. Most companies that produce weed and feed products only make one type, not allowing one to consider special nutrient needs that may have shown up in a soil test, i.e., a need for less or more phosphorus. Once again it is obvious that the best approach would be to apply weed killer and fertilizer separately. (Note also: Types of weed killer used in weed and feed blends is also limited compared to the many formulations available without fertilizer.)
Third, there is more chance of over-application or misapplication of the weed killer.
Because tree and shrub roots can also absorb many of the herbicide products, care in applying the herbicide is very important. In fact, many of the herbicide products state that they should not be applied where roots of desirable trees or shrubs are growing. Research has shown that the roots of many tree species extend well beyond the dripline of a tree. So how does one apply an herbicide to turf areas with trees growing in or near them? By using separate fertilizer and herbicide products and avoiding weed and feeds. Another common problem is overthrow of the product into areas that have sensitive plants growing in them such as flower and shrub beds. This is usually a result of using the wrong equipment such as the use of a broadcast spreader rather than a drop or gravity spreader. Once again, it makes good sense to apply products separately allowing for more accurate rates and distribution.
And fourth and last, why treat healthy grass with something it does not need and could potentially weaken it? By the way, a weakened turfgrass is more likely to have weed problems.
Spot treat only the weed prone areas.
The real way to address weed problems is to start with improving turf management. A vigorous, healthy lawn can choke out most weeds. For information on recommended turfgrass management practices see HLA-6420 – Lawn Management in Oklahoma.
