April 1 2005 12:00 AM

The battleground is the front lawn that you’re doing your best to maintain. The enemy is those pesky weeds that attempt to thwart you at every turn.

The weed is a resilient adversary that continually uses guerilla war tactics to undermine our pursuit of maintaining a beautiful, vibrant lawn. Whenever you make a move to eradicate them, it seems others are on the sidelines waiting to take over. And before you turn your head, a bare patch of land is quickly infested.

But it doesn’t have to be that way; the weed can be defeated. There’s an array of weapons and techniques at your disposal. How and when you use them can be the difference between victory and failure.

First, let’s define exactly what we mean by a weed. It’s been said that a weed is a plant out of place. Using that definition, a tree in a peanut farm would be considered a weed! While a tree in such a situation might be welcome, the weeds we hope to control are not as benign. In most cases, they are unattractive, compete with other plants for space, light and nutrients, can promote disease and harbor unwanted insects.

Weeds are generally categorized as grassy, broadleaf or woody. Since woody weeds are usually not a problem for turf, for the purpose of this article we will focus on grassy and broadleaf weeds. Grassy weeds, like crabgrass, emerge from seed as a single leaf with blades that are longer than they are wide. Broadleaf weeds, like dandelion and clover, emerge from seed with two leaves.

The war on weeds starts with the proper use of herbicides. There are two main types of weed control at your disposal: a pre-emergence and a post-emergence herbicide. The pre-emergent is used prior to the weeds emerging from the ground; post-emergence controls are applied after weeds rear their ugly heads.

One of the biggest nuisances on turf is crabgrass. It usually appears in the summer and crowds out the fine turf it replaces. With the signs of the first cold weather, it turns a purplish color and dies. Unfortunately, not before it has laid down some of its seed below the surface of the soil. The following year, this crabgrass seed will begin to germinate. It will take time for it to pop through the soil, but when it does it will crowd out the turf it replaces.

Since you want to stop these crabgrass weeds before they grow, it’s best to start with a pre-emergent herbicide. However, timing is crucial; if you’re late with the application, you lose the herbicide’s full effectiveness. If you apply the pre-emergent very late, it will not be effective at all.

Here’s how a pre-emergent herbicide works: Once the application is made, the herbicides form a chemical barrier over the soil, preventing germinating weeds from breaking through that chemical barrier. So once you put down the herbicide, be careful not to disturb the soil. Disrupting that chemical barrier provides an opening and an opportunity for weed seeds to germinate.

A pre-emergent provides good control for many annual grassy weeds and is a great weapon for keeping crabgrass at bay. It also can control some broadleaf weeds, but not all.

Regardless of what type of herbicide you’re using, and what type of weed you’re trying to eradicate, if you don’t use the herbicide properly, you are doomed to failure. Most of what you need to know is right in front of you. Herbicide labels contain information about application timing, rates, soil conditions, and how to activate it. Effective weed control begins with something as simple as reading the label of the product you’re using.

In order for a dry or granular pre-emergent herbicide to effectively form that protective barrier, it needs to be activated by water. For best results, irrigate immediately following application; this activates the herbicide. Since all weed seeds don’t germinate simultaneously, you’ll need to give the herbicide a few weeks to gain maximum effectiveness. As pre-emergent herbicides vary in their residual period, it’s important to check the product’s label.

Since no single herbicide provides control of all weeds, you need to identify what types of weeds you are trying to control. It lays the groundwork for all your efforts to follow. Are they annuals, biennials, or perennials? More than likely, you’re dealing with all three.

Consequently, it’s probably best to use a product effective in controlling broadleafs, mixed with one that works well on controlling grassy weeds. Generally, two or more active ingredients provide improved control compared to just one. But it’s imperative that you use the right herbicide for the right weed, otherwise you can do more harm than good.

Products are formulated to be used on a specific weed at a specific time of year. Correctly using herbicides means knowing when they are most effective, and using the least amount necessary to achieve weed control. It’s truly a case of where less is more. Incorrect application and use of herbicides can damage lawns, kill plants, harm trees, and is just a downright waste of money.

Depending on the product, pre-emergent herbicides are effective six to 12 weeks. A second application will be needed about nine weeks after the first to ensure season-long control.

Now that you’ve dealt with weeds that can be controlled before they emerge, it’s time to go after the weeds that can only be dealt with after they emerge. Pre-emergent herbicides will help keep annual weeds like crabgrass in check, but will not stop perennial broadleaf weeds like dandelions from infesting your lawn. That’s when you’ll need to use a post-emergence herbicide.

Broadleaf weeds present a different set of problems. One dandelion plant can make thousands of seeds that can survive for years in the soil. Usually the best way to control this family of weeds is by applying herbicides once the weeds have emerged. Post-emergence herbicides can be found in liquid or granular form. Since the goal is to target visible weeds, they are often applied with a spray. They only kill weeds that are already present when the herbicide is applied. They do not prevent weeds from germinating and developing in the lawn later in the season. For best results, treat broadleaf weeds in the spring or fall when the air temperature is somewhere between 65 and 85 degrees.

Post-emergence herbicides are available in two forms: contact and systemic. A contact herbicide kills the part of the plant it comes in contact with. A systemic herbicide attacks the whole plant. You must also consider whether you’ll need a selective or nonselective herbicide. One targets specific weeds (selective), the other kills anything green (nonselective).

Controlling established weeds depends greatly on getting the herbicide onto the unwanted weed and then keeping it there long enough so it’s absorbed by the plant. Irrigation or rain can reduce effectiveness. It’s also best not to mow the lawn before treatment because you want to spray as much foliage surface as possible. Some products include surfactants to help the active ingredient stick to the surface of the weed. They can also be added to the spray tank.

Weeds need to actively be growing so the herbicide can be absorbed and translocated to the root of the weed. Uniformity and application rate will be the difference between success and failure. Make sure to calibrate and test all sprayers and nozzles before you start. Since in all likelihood you won’t eliminate the weeds in just one season, keep thorough records of all the sites and the treatments you make.

It’s important to avoid treating weeds on windy days because many herbicides can injure ornamental plants. Drift or misdirected herbicide can kill the very plants you’re trying to save from weeds. For best results, avoid mowing or watering lawns for at least 24 hours after applying either liquid or granular post-emergence herbicides. If you’re using a granular product, it’s best for the lawn to be wet before it’s applied. The moisture helps the granules stick to the weeds. Whenever possible, avoid any herbicide applications in July or August. Not only do you run the risk of damaging the lawn, but weed control is also much more difficult to achieve during these peak summer months.

Knowledge of your enemy is your best weapon in the war against weeds. That includes knowing the life cycle of the weeds in your region to help you plan a long-term strategy to control them.

When using an herbicide, it is essential to rapidly establish turf where the recently killed weeds once stood by reseeding the area before new weeds invade. If weeds keep getting the upper hand, you might want to rethink your strategy. Maybe you should be looking at more aggressive plants that resist weeds. You could be helping the weeds by fertilizing or watering too much.

If you’re trying to maintain a weed-free lawn, you might be setting your sights too high. Many experts will tell you that it’s better to tolerate a few weeds than making numerous applications of herbicides in a futile effort to eliminate all weeds.
Herbicides should be one tool in a total weed control program. Ultimately, the best way to keep weeds from being established is the development and maintenance of a dense, flourishing lawn. Healthy turf prevents sunlight from reaching weed seeds ready to germinate, and minimizes the available space to establish themselves in the first place.

The first step in winning any war is by knowing the ways of the foe you are about to face. He may not have been talking about weeds, but in his military treatise “The Art of War,” Sun Tzu put it best: “If you know the enemy and know yourself, you need not fear the result of a hundred battles… your victory will not stand in doubt.”