General Tips On Using Preemergent Herbicides

Most of the following tips refer to preemergent herbicides. However, some apply to the application of any herbicide.

1. Preemergence herbicides generally do not control established perennial weeds, even if applied prior to seedling emergence. This is because these weeds generally produce seeds that germinate over many weeks of any one season. Several very important exceptions to this situation exist.

2. Tillage prior to application allows better penetration and distribution of the herbicide into the soil.

3. Application of herbicides to moist soils is preferable to dry soils.

4. Following application, all of the preemergence herbicides must be activated by 0.5 to 1 inch of rainfal or irrigation, or must be mechanically incorporated to become fully effective. They must be applied early enough so that the herbicide can be activated and incorporated by irrigation or rainfall before weed seed germination.

5. It is preferable that preemergent herbicides not be applied to new transplants until the soil is settled by irrigation or rainfall and there are no cracks in the soil leading to the roots of the transplants. Still, try to make preemergent herbicide applications as soon as possible after planting.

6.  As of this writing, no preemergent herbicide is recommended or labeled for use in greenhouses or other enclosed structures.

7. Apply any type of granular herbicide to dry foliage. Granules that stick to wet foliage may cause injury.

8. Do not apply granular herbicides to herbaceous plants with whorls of leaves that channel granules to a growing point at their base or the plant may be severely injured.

9. Most preemergent herbicides are more effective and last longer when placed under an organic mulch.

10. Most preemergence herbicides can be safely applied over the top of most ornamentals, even during active growth. There are some exceptions; refer to the labels.

11.  Applying the same herbicide time after time can result in a buildup of herbicide-resistant weeds. Use combinations of herbicides and periodically switch the herbicides used.

12. Aside from nonselective vegetation killers, no one herbicide controls all weeds. Some work best on broadleaf weeds and some work best on grasses. Very few provide good control of nutsedge.