Weeds are opportunists. They will find bare spots or places where your grass is weak, and they will exploit them to their advantage.
Perennial weeds (weeds that grow from their roots every year) can spread and make a lawn unsightly. Annual weeds (weeds that die at the end of the season and reseed the next year) can leave bare spots that are vulnerable to runoff.
No matter what weeds you have, the first line of defense is preventive practices. Try these options to get at the root of the problem first, before resorting to herbicides.
1. Prevention practices.
Mow high. Do not mow grass shorter than recommended for the species you grow. Mowing at 3 inches or higher helps grass shade out weeds and encourages a thicker, more competitive turf. See other sections of this site to make sure that you are using the right grass species, fertilizing and watering correctly, and generally doing all you can to encourage healthy grass.
2. Reduce compaction.
Pay special attention to heavily used areas and sections next to pavement. Weeds can gain a foothold in these spots and spread to the rest of the lawn if it is weak. Repair bare spots by raking in seed in early spring so that the new grass can compete with the weeds that are sure to come up. This can be tricky though. When you seed, you can’t use traditional preu-emergent crabgrass products because these will keep your grass seed from germinating just like the crabgrass seeds.
There are however a couple of products and strategies to avoid this situation and keep the spring crabgrass germination
If lawn is thin, fertilize it properly ,with quality fertilizers ,to improve density.
3. Let the weeds be your guide.
If weeds dominate an area, it’s likely that there is something wrong with either the growing conditions or your lawn practices. Dense stands of prostrate knot weed are a good sign of soil compaction. Don’t just pull out the weeds. Relieve the compaction. Violets (Viola SSP.) are a good sign of low light levels. One solution might be to seed shade-tolerant fine fescues or new shade and drought tolerant hybrid blue grasses.
If you use herbicides…
Use the right product at the right time. Follow label directions and try to spot treat areas with the weeds only using the right liquid concentrate weed control. The best and most economical way is in a pump sprayer. You usually mix a very small amount with water and spray. This saves lots over time.
Use granular weed control products only on lawns with lots of weeds throughout. Some products are better than others for certain types of weeds. Applying at the right time, and allowing the weeds to take in the weed control is critical. Usually this is done while the grass is wet or damp to help the granules stick to the weed. 24-48 hours without rainfall is best.
To avoid volatilization and drift, which release pesticides into the air, do not spray when temperatures are high or it is windy.
To help prevent polluted runoff, do not apply pesticides when heavy rains are expected or the ground is already saturated or frozen. You will also get a better result.
Sprayers should be triple rinsed with a spray tank cleaning solution to avoid residual left over when you use the sprayer for other products.