By Greg Hutson
By their very definition, weeds are unwanted plants that are usually unattractive and compete for water, nutrients, and sunlight with the desired turfgrass. This makes protecting landscapes from weeds even more important as you are also protecting the investment your clients have made in their properties.
The most effective and environmentally friendly weed control and management plans include several control strategies.
Cultural controls that promote an aggressive, healthy, dense turf
Cultural controls are field management practices that reduce the incidence of weed infestations. Whenever you see weeds, it could be an indicator of weakened turfgrass. The first and best defense against weeds is to promote an aggressive, healthy, and dense turfgrass. A healthy, dense turfgrass on the surface typically indicates a healthy root system. This allows the desired turfgrass to outcompete weeds for water and nutrients in the soil while the top growth creates a dense canopy that blocks sunlight from weed seeds.
Cultural controls include:
- Appropriate planting dates
- Ensuring the desired plants get the required sunlight
- Proper drainage
- A comprehensive soil, fertilization, and nutrient-management program
- Proper irrigation management
- Bed mulch and tree rings
- Proper mowing techniques such as mowing in different directions and the height of the cut
- Sharp mower blades. Dull mower blades tear the leaf blade, causing injury, which weakens the plant and increases the chances of disease occurrence.
Chemical control involves the use of control products to manage weed populations. To effectively control a weed population by chemical controls, you must know the type, the life cycle and the growth habits of the weeds that occur in your area.
Essentially, there are three types of weeds:
- Broadleaf weeds such as dandelions, chickweed, henbit, clover, and Virginia buttonweed.
- Grassy weeds such as crabgrass, annual bluegrass, torpedograss, and dallisgrass.
- Sedges include yellow nutsedge and purple nutsedge.
After you have identified the weeds you intend to target, you will need to choose the type of control product to apply. When applying control products always read and follow the product label.
Using a pre-emergent control product is a cost-effective and proactive way to eliminate weeds before germination. Pre-emergent control products are applied prior to weed emergence and inhibit the germination of weed seeds.
The two commonly used formulations of pre-emergent weed control products are liquid and granular. The formulation you choose should be based on advantages and limitations of each formulation (cost, effectiveness, and safety) as it relates to your target, weather conditions, and application methods.
Whether using a liquid or a granular product, your application equipment must be properly calibrated. This ensures that the proper amount of product is applied over the target area as instructed on the product label. Before liquid applications, you should inspect your spray equipment. Inspect hoses and fittings to make sure there is no leakage, which could cause injury to the desired turfgrass. Screens and nozzles should be clean and clear of any debris.
Whether using a liquid or a granular, it is critical to the effectiveness of the product to consider and implement the following application tactics:
- The timing of application is critical and should be based on soil temperatures. Spring and summer weeds require a minimum soil temperature of 55 degrees for three consecutive days. Fall and winter weeds will germinate when soil temperatures drop below 68 degrees.
- Split applications increase the length of control.
- Whether you use a liquid or a granular control product, watering in immediately after application increases the effectiveness and residual of the product. If the product remains on the surface, the sunlight will break down the active ingredient of the product, which lowers performance of the product.
- Do not apply to saturated soils. When the soil is saturated there is little to no pore space, therefore the product cannot move into the soil. This means it remains on top of the soil and could easily be washed away in the runoff to non-target areas by rainfall or irrigation.
Post-emergent control products are used to control weeds after they have germinated. Types of post-emergent products include:
- Contact herbicides cause injury or kill the plant where the product comes into contact with the plant. To be effective, the entire plant must be thoroughly covered with the product. Applied correctly, they are usually fast acting, and are effective in controlling annuals, biennials and young, seedling perennials.
- Systemic herbicides are absorbed through the leaves or roots and move throughout the plant. Therefore, application to part of the plant will usually kill the entire plant. Systemic herbicides are slower acting, but are very effective against most plants and are recommended for hard to control perennials.
- Selective post-emergent products are used to control weeds without damaging the desired turfgrass.
- Nonselective post-emergent products are used to eliminate or injure all plants, both desirable and undesirable. Glyphosate is an example of a nonselective control product.
To maximize the effectiveness and efficiency of post-emerge products, consider the following:
- Post-emergent products are most effective when applied to young weeds that are actively growing.
- Post-emergent products are generally more effective in warmer temperatures. The product label will specify a minimum temperature at which the product is most effective.
- Post-emergent products formulated or applied with surfactants or adjuvants (per label instructions) provide greater leaf surface coverage and a greater potential for herbicide absorption into the plant.
When applying control products always read and follow the product label.
Always be cautious when treating your landscape with control products.
- The applicator should wear the appropriate Personal Protective Equipment (PPE) as directed in the product label.
- Use properly calibrated equipment. The applicator must operate at the exact speed or rpms to deliver the proper labeled rate.
- To avoid product drift to non-target plants, weather conditions should be favorable to the safe application of the product.
- Be cautious when applying control products near trees. Avoid applying within the drip line. Surface-feeding roots can be damaged and application in these areas can result in the translocation of the product throughout the tree causing injury or death.
Mechanical or physical controls
Mechanical or physical controls either eliminate weeds or make the environment less favorable for seed germination.
Mechanical controls include:
- Mowing. However, mowing is a temporary control and usually not acceptable as a long-term solution to the property owner.
- Hand pulling/hoeing/digging. Also temporary controls that are labor intensive and not cost effective.
- Mulching. The most effective control as it creates a lasting physical barrier that blocks sunlight needed for weed germination and survival.
Greg Hutson is a regional franchise advisor at U.S. Lawns and is a graduate of Mississippi State University.