INSECT DAMAGE AND CONTROL
, 7 min reading time
There are many insects that damage turf. They vary by location and with the predominant turf species in the region. In this article, we will concentrate on common turf insects in the midwestern US on cool-season grasses.
While weeds are a continuous problem that we have to deal with every year, insect damage is not as common. You may go 5 years or more without experiencing any significant damage. But when it does occur, the damage can be significant and may even destroy an entire lawn. For weeds, we have pesticides called herbicides that can selectively control the weeds. For insects, there are insecticides. These are different chemicals than the herbicides and must be chosen and timed carefully to achieve insect control. They may also be quite toxic to humans and must be used carefully according to label specifications. As with all pesticides, read the label carefully and follow all safety recommendations.
Insecticides can be difficult to use. Sometimes they are applied directly to the insect when they are feeding on the grass, but often they must be applied at a time when the insect is not visible. The insect may also be protected from the chemical by the soil, or they may be protected in the sheath of the grass and may be difficult to reach with the insecticide. This requires a thorough knowledge of the insect’s lifecycle and feeding habits, as well as of the characteristics of the insecticide being applied.
The most consistent insect damage in the Midwest comes from the white grub (Figure 1). The term white grub does not pertain to a single insect species, but to a group of insects that have a larval stage in their life cycle referred to as a white grub. The adults, which generally do not damage turf, lay their eggs in the grass and they hatch into the larval (grub) stage. These grubs live in the soil just below the crown of the plant and feed on the roots. Once they mature, they change into adults and leave the area. The best way to identify the damage is to reach down and try to pull the turf up. If the root system has been severed, it will come up easily and you can observe the grubs on the surface of the soil.
The damage to the roots is not necessarily fatal to the turf. If there is enough moisture, the grass will recover. When the damage coincides with a drought period, however, the damage can be fatal to the turf stand. Even in situations where there is not enough feeding damage to kill the grass, mammals like skunks and racoons that feed on the grubs can do serious damage (Figure 1).
In the Midwest, the masked chafer is the most likely species to cause damage to turf. The Japanese beetle that was generally recognized as a problem in the northeastern US, has also been more prevalent in recent years. The largest of the group is the June Bug that is often found on screen doors in May and June. It produces a very large white grub. The masked chafer and the Japanese Beetle grubs are most active in mid-August through late September, whereas the June Bug grubs do damage in mid-summer. Luckily, June Bug damage is quite rare. In my 45 years at Iowa State University, I only saw the damage a few times. Masked Chafer damage generally occurs somewhere in the state each year.
Figure 1. White grubs below the turf. The second slide shows the damage racoons can do looking for grubs. In the lower picture, the masked chafer is above and the Japanese beetle below.
The Bluegrass Billbug is another common turf insect in the Midwest. The adult female uses its large snout to burrow into the sheath tissue of Kentucky bluegrass just above the crown of the plant. It then deposits an egg in the sheath. Later the egg hatches and the larvae eat down through the crown and kill the plant. The larvae then emerges into the soil, forms a pupa and then an adult which moves off the area. The damage is identified by reaching down and grabbing some grass tissue. If it breaks off easily at the crown and feeding damage is visible, it is likely billbug damage. The presence of the larvae in the soil will confirm the diagnosis. Egg laying occurs in the spring, usually around mid-April. Feeding damage takes place in early August. The damage is often not apparent until the feeding is over and the insect has left the turf.
Once the egg is in the sheath, it is protected from insecticides and applying an insecticide when the feeding damage is occurring is usually not very effective. The adults have to be killed in the spring before egg laying. This timing will vary by location, but it is usually in mid to late April. Once the eggs are laid, the insecticide will not work.
Figure 2. Bluegrass billbug adult and larvae. The last picture shows damage on Kentucky bluegrass turf.
The Chinch Bug and the Greenbug Aphid are surface feeders. They feed above ground on the leaves. They are both quite active in the Midwest, although they tend to be intermittent and years may go by that they are not reported. Both of them do their damage by sucking juices from the plant. They are very small and you have to get down close to the turf to see them. It takes a lot of them to do serious damage, but they can suddenly show up by the millions if conditions are right. The chinch bug is a small reddish to black insect (Figure 3). Their feeding damage generally occurs in full sun and they tend to avoid the shade. The greenbugs are small green insects (Figure 4). Their damage generally appears in the shade pattern of trees, although you may also find them in full sun. Chinch bugs tend to be more active in dry years, while the green bugs are more common in wet years. Both are easily killed by insecticides, but you have to recognize that they are there before the damage occurs. Often, they do their damage before we notice them and then it is too late to treat.
Figure 3. Chinch bug on grass plant and feeding damage on Kentucky bluegrass lawn.
Figure 4. Greenbug aphids on leaf and feeding damage on Kentucky bluegrass lawn.
There are many insecticides for use on turf. The carbamates and the organophosphates are among the most widely used, but they are toxic to humans. They also have a very short residual and must be applied to the insect when they are feeding. They are generally the best materials for billbug control in the spring if you can hit the adults before the eggs are deposited. They work on grubs, but it is difficult to get them down into the soil where the grub is feeding.
There is a newer material available to homeowners for grub control. This is Merit (imidacloprid) which is derivative of nicotine and much less toxic to humans. This material must be applied in late June to early July well ahead of when grubs are feeding. Timing is critical so read the label carefully and apply the material at the best time for your location. My experience has been very positive on my tests with this material.
Nick Christians, University Professor of Horticulture, Emeritus, Iowa State University
books: http://www.amazon.com/Nick-Edward-Christians/e/B001H6SB7A/ref=ntt_dp_epwbk_0
turf blog: http://www.iaturf.blogspot.com/
Fundamentals of Turfgrass Mgt. 5th ed http://www.wiley.com/WileyCDA/WileyTitle/productCd-1119204631.html
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