Blame it on the grubs!
Blame it on the grubs!
Diagnosing turf problems can present a challenge. Whether the problem stems from an insect or a mower, it all just looks like brown grass. Unlike damaged ornamental plants, there is not always an obvious clue that pops out, such as powdery mildew on lilacs, or Japanese beetles on roses.
Turf problems make us dig for clues and work hard for our answers. There are some steps
we can take to narrow the field of problems that might be causing an unhealthy lawn.
First, try to determine if the problem is living or nonliving. Living problems include disease, insects or weed infestations.
A nonliving problem might involve soil compaction, drought, or herbicide damage. You can distinguish living from nonliving by looking at the large picture of the lawn. Ask yourself these questions: How much of the lawn is affected?
Do you see the problem in only the shady or sunny areas? Is it near the pavement or confined to one sprinkler zone?
Chances are that if a problem is stretched across the entire lawn, it’s an abiotic, or nonliving, cause. Not many insects
or diseases can destroy a lawn in just a few days. So if the problem is widespread, you need to dig a little deeper into
the past to find out what has happened that may have caused the problem. Here are two common complaints that often indicate a widespread problem:
“My lawn looks discolored”
Ask the homeowner to get up close and look at the individual blades. Most lawns are made up of many types of grass, and each variety expresses problems differently. If the lawn is looking speckled, the homeowner is most likely noticing that different varieties have different hues of green, and when mixed together, there can be a spotted appearance across the lawn. Often one type of grass will take over a section of lawn and that monoculture will look off-color compared to the rest of the lawn. Ask if there has been any cold weather recently. Turf varieties express cold weather effects differently; some don’t change color, some turn brown, and others turn purple when cold weather hits.
Ask if there has been any fertilizer applied. Yellow or lime-green grass may indicate nitrogen deficiency. If the entire lawn is evenly brown, it’s most likely a lack of water. If the lawn is brown in long rectangular patches, it’s probably fertilizer burn.
“My lawn doesn’t seem to be growing, it’s thin and wilted looking”
Ask when it was planted and what type of seed was used. Fescues can take up to 4 weeks to germinate and grow slowly after that. In an established lawn, ask when the soil was last tested. Even if the lawn is being regularly fertilized with nitrogen, it may suffer from lack of a different nutrient. Worse yet, if the pH is not within 6.0-6.5, the plant can’t take up the nutrients it needs, despite that fact that the soil may be holding the proper amounts.
Soil compaction is a hidden problem. Lawns that get a lot of traffic in one area, such as a path from the driveway to the house, or an area around the grill may suffer compaction. Depending on soil type, compaction can happen quickly with regular traffic. Turf is thin and wilted in compacted soils because it can’t get the air and water it needs.
If the problem is not widespread, but confined to a small section of the lawn, and that section hasn’t had any special treatment, you may be dealing with a disease or insect.
Start this approach by looking for patterns. If the pattern is perfect, like a straight line or a perfect curve, then you probably have another abiotic problem, such as a leaking mower or lawn that was scalped while turning the mower.
But if the pattern is more like circles or patches, you may have a disease. Color is important at this time. Is the circle or patch yellow or brown? Does it have a smoky gray to purple hue to it? Is it extremely green? Is the entire circle discolored, or just the center or the outside ring?
Once you’ve checked the overall appearance, get closer. Is the entire leaf blade discolored or are there lesions or streaks? If obvious lesions or streaks are present, are the lesions circular or hourglass-shaped? Do they stretch across the entire blade or are they dotted here and there along the blade? Do they have a halo around them of a different color? Do the streaks have a different color on the outside compared to the inside?
After you’ve answered these questions, you can easily diagnose leaf diseases with any quick reference book. If you need more information, tug on the grass and see if it pulls up easily. If it does, then you may be dealing with a root or crown problem. Root problems don’t usually have neat, obvious leaf lesions, but more of an overall discoloration of the entire blade. Check the roots for dark brown or black colors or swollen areas like nodules.
If the roots look healthy and white, then you may be dealing with a crown rot. In this case, the turf will pull out of the ground easily but leave the roots behind. The crown, or the area where the turf plant touches the ground, will look brown, black or yellow. Once you’ve determined whether you have a leaf, root, or crown problem, a quick check with a reference book will help you make your final decision.
Insect damage may be the easiest to determine. There are 3 types of insects; those that feed on leaves, those that feed inside the crown, and those that feed on roots.
Most insects that cause problems on turf grass are a problem in the larvae stages. So if you see the adult stage of a turf eater, you’re too late for control. One exception to this is the chinch bug. These leaf feeders suck sap and leave turf looking browned and burnt. This looks a lot like drought stress. Presence of the actual insect will help you decide between the two problems.
Other leaf feeding insects include the larvae of cut worms and sod webworms. Both of these larvae will chew the grass blade entirely, leaving a very small brown patch of missing or dead turf. If you see dead spots in the lawn covering anywhere from 1-10 inches, look for the presence of a cut worm or sod webworm somewhere below.
Crown feeders are larvae that burrow into the growth point of the plant and chew around the crown. In this case, the entire leaf blade will fall over as if it has been cut. If you’re raking up leaf blades but you haven’t returned clippings to the lawn recently, you probably have crown-feeding larvae, probably billbugs.
Finally, there are the root feeders. These are white grubs that chew the roots leaving large brown patches across the lawn. Grubs get blamed for most lawn damage by homeowners, because this is the problem they hear the most about. However, the only sure fire way to know if a lawn really has a grub problem is to pull up the turf and find the grubs. If you don’t see any white larvae, keep digging for clues—there could be other problems present.
The best way to beat turf problems is to know your enemy. Become familiar with the life cycles of the diseases and insects in your area. If the current environmental conditions are not right for the damaging stage of the organism, then you can rule that problem out completely. For example, you’re not likely to see snow mold damage in August, or drought stress in May. You won’t see fresh grub damage in April, or chinch bug damage in October, so keep looking for clues and asking questions, as there’s probably something else going on.
Finally, bear in mind that humans are the biggest turf pathogen. More likely than not, it’s what people aren’t telling you they did that’s causing the problem. Who among us would confess to leaving the sprinkler on for 4 days? “Naw, it wasn’t me, it must have been the grubs!”