Zoysia Grass Weed Control

A good thick zoysia grass lawn is a natural defense against weeds. This does not mean, however, that weed seeds do not regularly blow onto your lawn. They do. They are merely waiting for enough bare moisture, and light to sprout and grow. This is true for both annual weeds and perennial weeds. Annual weeds sprout and grow, flower, seed, and die within one year. Perennial weeds sprout from a seed as well, but the weed plant continues to grow and spread for more than one season (even though the top may die back in the winter).

Weeds enter a lawn for one reason: your lawn is not growing well. With a zoysia grass lawn, weeds usually enter voids like dead spots, damaged turf, or large areas that have died due to drought (i.e., near tree roots). Zoysia grass is very slow to spread, and weeds have plenty of time to drift onto exposed soil and germinate. Your trouble may be different. A zoysia grass lawn will thin because of soil compaction, cold damage, insect/disease damage, flooding, steep slopes (causing dry soil), lack of fertilizer, or irregular pH. The best defense against weeds is to concentrate primarily on maintaining a thick, well grown stand of zoysia grass and secondarily on weed control.

TIP: Neighboring lawns, woods, and adjacent untended areas produce enormous numbers of weed seeds that blow into your lawn. If possible, mow or cut these areas before they produce seeds.

Types of Weed Control for Zoysia Grass Lawn

There are two ways to control weds in a zoysia grass lawn: as the weed seed germinate (pre emergence weed control) and after the weeds have already sprouted and are growing (post emergence weed control). When using weed control products, always make sure the product(s) are approved for zoysia grass and follow the labeled directions. Do not apply more than the recommended rate; it will not give you better results and may injure your zoysia grass.

PRE EMERGENCE WEED CONTROL: Usually sold as a dry, granular product in 10-30 pound bags. May be labeled as "crabgrass control" although it will stop other weeds as well.

POST EMERGENCE WEED CONTROL: Usually sold as a liquid concentrate you spray from a pressurized sprayer or a hose end sprayer. May be labeled as a "broadleaf weed killer" or "grassy weed killer".

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 return from seed each year, a pre-emergence weed control will remove from your zoysia grass 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 form (with or without fertilizer)that your spread using a fertilizer spreader. It is important to spread the chemical over the entire area 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 active the chemical (unless otherwise stated on the bag). Once activated, the weed controls create a chemical barrier in the top few inches of your lawn that will kill weeds as they germinate. Do not turn your soil, core aerate, or disturb the soil after treating or you will disrupt the chemical barrier and open the soil to weed seed 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, products will either treat grassy weds like crabgrass or broadleaf weeds like chickweed. Choose the weed control spray that best fits your needs. You may need to purchase one spray for grassy weeds and one spray for broadleaf 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 young and actively growing. If the weed is dormant because of cold weather or drought (i.e., not using the metabolic process), is may not die. Spray on a still day when air temperatures are between 60-80 degrees and the grass is dry. Avoid spraying during the 4 to 6 weeks in the spring when your zoysia grass is turning green. Post-emergence weed controls are sometimes available in a granular form that you apply with a fertilizer spreader when the grass is wet. The dry particles need moisture to adhere to weed leaves. Again, avoid using these products in the spring when your zoysia grass is turning green.

WARNING: Weed controls have dramatic and damaging effects on ornamental trees, shrubs, and plants growing in or near your lawn. This is true for pre-emergence and post-emergence weed controls. For instance, some post-emergence sprays are absorbed by tree roots and can cause the leaves to burn or defoliate. Read the product label carefully for directions and never spray underneath shallow-rooted trees and shrubs like Dogwoods and Boxwoods.

There are other post-emergence weed controls like Round-Up that are non-selective. The term non-selective means they will kill all vegetation including zoysia grass. The trick is that non-selective weeds sprays are absorbed through plant leaves. During the winter months when your zoysia grass is born, you can carefully spray green weeds without affecting the dormant zoysia grass. WATCH OUT. Be very cautious and make sure the zoysia grass leaves and stolons have not emerged during a winter warm spell. Even then, spray only the weed and expect some zoysia grass in the vicinity to be killed as well.

When to Apply Weed Control on a Zoysia Grass Lawn

Zoysia grass is usually so thick and dense that they will remain weed free with two applications of granular pre-emergence weed control applied in late winter and early fall. Supplement this program by spot-treating problem weeds with a post-emergence weed control spray (approved for use on Zoysia grass) in early spring and summer. I have included two "optional" pre-emergence weed control applications for people trying to renovate a very weedy lawn and people that live near a major source of weeds like an old pasture.

LATE WINTER: Apply a granular pre-emergence weed control when the soil temperature reaches a consistent 50 degrees. This is usually late February/early March, when the Forsythia is in bloom. Make sure the product is approved for use on zoysia grass and apply at the rate recommended on the bag. Do not core aerator or mechanically dethatch for 3 months after you apply pre-emergence weed control as it may affect the chemical barrier of the control. Irrigate after applying unless otherwise stated on the bag. Do not use a pre-emergence weed control that contains fertilizer. IF you fertilize now, you might stimulate your zoysia grass to break dormancy, only to be damaged in the next hard freeze.

LATE SPRING and SUMMER: Apply granular pre-emergence weed control without fertilizer around June 1 to control annual and perennial weeds that continue to germinate during the summer (optional application). Most zoysia grass lawns will be thick, healthy, and weed free, and they will not need this application. Use a product approved for use on zoysia grass and apply at the rate recommended on the bag. Remember not to core aerator for 3 months after (using lazyman gold or lazyman aerator is fine) you apply pre-emergence weed control because if may affect the chemical barrier of the control. Irrigate after applying unless otherwise stated on the bag.

Begin treating weed outbreaks with a post-emergence weed control spray approved for use on zoysia grass as soon as your lawn is completely green and soil temperatures reach 75-80 degrees. This is usually in mid to late May. Do not spray weed control during March/April when your zoysia grass is turning green because it may harm your lawn. Most sprays should be used when the air temperature is 60-80 degrees (check the product label) and weeds are actively growing.

If your lawn is overrun with weeds in mid-summer, consider using a combination fertilizer/post-emergence weed control when you fertilize around July 1. Follow the labeled instructions. Most products should be applied when your lawn is wet.

EARLY FALL: Wait until soil temperatures drop to 70 degrees to apply granular pre-emergence weed control (without fertilizer) to your zoysia grass lawn. This is usually September 15 in the upper South and October 15 in the lower South. If you think you will forget, you can apply pre-emergence weed control when you fertilize in early September but you will be sacrificing some effectiveness. This application will control weeds like annual bluegrass to germinate in the fall and winter.

Either way, make sure the pre-emergence product is approved for use on zoysia grass and apply at the rate recommended on the bag. Irrigate after applying unless otherwise stated on the bag. This application will late 2-3 months.

WINTER: Apply a pre-emergence weed control without fertilizer 2-3 months after your fall application (optional application). This is usually in late November/early December. Most dormant zoysia grass lawns will be thick and weed free, and they will not need this application. Use a product approved for zoysia grass and apply at the rate recommend on the bag. Remember not to core aerate for 3 months (lazyman gold or lazyman aerator are okay to use any time) after you apply pre-emergence weed control because it may affect the chemical barrier. 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 zoysia grass. This is usually in January and February. Most of your problems this time of year will be from annual weeds. Spray on a warm afternoon when the air temperature is at least 60 degrees. It may take two applications to kill the weeds during the winter. You can also spray during winter with a non-selective weed control like Round-Up. Make sure your zoysia grass is completely brown and spray only the leaves of the weeds. Be very careful because zoysia grass stolons and rhizomes are often green during mild winter weather. Even then, expect some zoysia grass around the weed to die.