While it may be hard to believe, most weeds blow into your lawn as seeds and sprout the minute they find enough bare soil, moisture, and light to grow. This is true for both annual weeds and perennial weeds. Annual weeds sprout, grow, flower, seed, and die within one year. Perennial weeds will sprout from a seed as well, but the plant continues to grow and spread for more than one season.
Unfortunately, all Kentucky bluegrass lawns weaken during the hot Southern summer and a thinning lawn is the perfect place for a weed seed to germinate and grow. Consequently, your ultimate goal should be to grow as thick , luscious lawn that will naturally prevent weed seeds from germinating. There are two ways to accomplish this. First, correct fundamental problems like poor drainage and soil compaction that make growing a dense lawn difficult at best. Second, do not neglect your lawn maintenance. Kentucky bluegrass lawns need to be nurtured during the summer and a couple of weeks without water or mowing can be devastating. The best defense against weeds is to concentrate primarily on maintaining a thick, well-grown stand of Kentucky Bluegrass and secondarily on weed control.
Types of Weed Control for Fescue Grass
Pre-Emergence weed controls: kill immature weeds immediately after they germinate and before they emerge from the soil surface. Since annual weeds like annual bluegrass and henbit die and return from seed each year, a pre emergence wed control will eradicate them from your Kentucky Bluegrass grass lawn over several seasons. At the same time it will prevent annual and perennial weed seeds that blow into your lawn from emerging. Most pre emergence products are sold in a granular from with or without fertilizer that you spread using a fertilizer spreader. If is important to spread the chemical wall to w all at the recommended rate. Areas that are not covered by the chemical will not be protected. After spreading the product, irrigate your lawn with at least .5 inches of water to activate the chemical (unless otherwise stated on the bag). Once activated, pre emergence weed controls create a chemical barrier in the upper inches of your lawn that will prevent weed seeds from germinating. Do not cultivate, aerate, or disturb the soil after treating your lawn or you will disrupt the chemical barrier and open the soil to weed infiltration. Pre emergence weed controls are usually effective for 2-3 months, depending on the temperature and amount of rainfall.
Post-emergence weed controls: kill weeds that are already growing in your lawn. These products are referred to as "selective" since they are targeted at specific annual and perennial weeds listed on the label. Usually, controls will either treat grassy weeds like crabgrass or broadleaf weeds like chickweed. Choose the weed control spray that best suits your needs. You may need to purchase a spray for each category of weeds. In most cases, post emergence products are designed to disrupt one of the weed's critical metabolic processes and should be sprayed when the weed is actively growing. If the weed is dormant because of cold weather or drought it may not die. Post emergence products are most often sol in liquid spray. The liquid sprays are very effective when weeds are young and actively growing. Spray on a day when your air temperatures are 60 to 80 degrees and the grass is dry. Avoid spraying during the 4-6 weeks in the spring when your Kentucky Bluegrass grass is greening up. Post emergence weed controls are sometimes sold in granular form that is spread with a fertilizer spreader when the grass is wet. The dry particles need the moist to adhere to the weed leaves.
Another group of post emergence weed controls are the non selective sprays such as Round-Up. The term non-selective means they will kill all vegetation including Kentucky Bluegrass grass. The trick is that non selective weed sprays are absorbed through plant leaves. During the winter months when your Bermuda grass is brown, you can carefully spray green weed without affecting dormant Kentucky Bluegrass grass. WATCH OUT!
When to apply weed controls
When it comes to weed control in a Kentucky Bluegrass lawn, timing is critical. Pre-emergence controls have to be applied before weeds seeds germinate or they are useless. Post-emergence weed control sprays and granules have to be applied when the weeds are young and actively growing. With weed control, it is always better to be a little early than a little late.
Under normal conditions, a well-grown Kentucky Bluegrass lawn will remain weed-free with two applications of granular pre-emergence weed control (late winter and early fall) and spot treatments of problem weeds in mid-winter and early summer.
Late winter: Apply a pre-emergence weed control without fertilizer when the soil temperature reaches a consistent 50°. This is usually February/early March, when Forsythia is in bloom. This application will control annual weeds and perennial weeds that germinate in the spring. Do not aerate for 3 months after you apply pre-emergence weed control because it will affect the chemical barrier. Irrigate after applying unless other wise instructed on the bag. Be sure not to use a pre-emergence weed control that contains fertilizer. If you fertilize now, you might stimulate your lawn to break dormancy during a warm spell, only to be damaged by freezing temperatures soon thereafter. Also, do not apply pre-emergence weed control if you are planning to seed, sod, or reseed Kentucky Bluegrass in the spring. It will prevent the seed from germinating and slow root growth.
Spring and Summer: Begin treating weed outbreaks as soon as you see them with a post-emergence weed control spray approved for use on Kentucky Bluegrass. Weeds will die quickly when they are young and actively growing. Spray on a calm day when the air temperature is 60-80°. Avoid spraying newly seeded or sodded Kentucky Bluegrass, however, until you have mowed at least twice.
If your lawn is still overrun with weeds in mid-spring, consider using a combination fertilizer/ post-emergence weed control (granular form) when you fertilize in early April. Apply pre-emergence weed control without fertilizer 2-3 months after your late winter application to control the annual and perennial weeds that continue to germinate into the summer. This is usually around June 1st. If your lawn is mostly weed-free, you can skip this application.
Early fall: Apply pre-emergence weed control (without fertilizer) to Kentucky Bluegrass lawns when soil temperatures drop to 70°. This is usually mid-September in the upper south and late September in the middle South. Do not apply pre-emergence weed control if you are planning to seed, sod, or reseed your Kentucky Bluegrass lawn in the fall. It will prevent Kentucky Bluegrass seed from germinating.
Winter: This is usually in late November/early December. If your lawn is mostly weed-free, and weeds do not usually blow in from surrounding areas, you can skip this application. Use a product approved for use on Kentucky Bluegrass and apply at the rate recommended on the bag. Irrigate after applying unless otherwise stated on the bag.
During the winter, treat winter weed outbreaks as soon as you see them with a post-emergence weed control spray approved for use on Kentucky Bluegrass. This is usually in January and February. Most of your problems this time of year will be from annual weeds like annual bluegrass and henbit. Spray on a warm after-noon (air temperature is at least 60°) when the weeds are young and actively growing. It may take two applications to kill them.
