White Grubs Weevils

A nicely manicured lawn has a lot of attributes for your landscape. It adds to the value of the property, it provides cooling and protection from soil erosion, and can be a great play surface. Unfortunately, I am not the proud owner of a front lawn so lush and full that it could pass for a green carpet, but I do the best I can in the heat and dryness of the summers in northern California. Our biggest problems for turf in my area has little to do with insects, and a lot to do with dryness and heat, and at times the accompanying fungus infection. We do have some of the typical lawn insects, but not in very big numbers. However, in many parts of North America insects can be a huge threat to landscapes and turf, and it is the beetles we'll focus on here.

Our goal in these articles is primarily to help you, the homeowner, understand how to identify what the culprit is when you see pest problems, and decide how to go about the non-chemical fixes to at least reduce that problem. Often, a pesticide may be needed to manage a pest problem, but it is often best to leave this area of pest management up to those who are trained and licensed to apply these products. The Pest Management Professional makes his living by understanding the pests and the products for controlling them, and you can find a list of many of these "PMP's" in your area by going to the heading on this website entitled "Find a Pest Management Company".

While there are likely many kinds of beetles which cause you grief in your landscape efforts, those that attack your turf in earnest will boil down to two families of beetles, the Scarabs and the Weevils. We generally call the larvae of the scarabs “white grubs” and the adult beetles “June beetles”, but the family Scarabaeidae is most properly called scarabs. This is a pretty flashy family of beetles, including the astounding Rhinoceros beetles that can be up to 6 inches long, the incredible golden and silver scarabs found in the rainforests of Latin America, and other kinds with brilliant colors of all kinds. Unfortunately there are some nasty derelicts in this family too, such as the Japanese Beetle, which devastates turf and ornamentals alike, and feeds rampantly on fruit and flowers.

The family of Scarab beetles also includes some great curiosities, and one of these is the “dung” rolling beetles. As key players in recycling leftover stuff, it is the role of the dung beetles to recycle animal waste, and they do so by packing animal feces into a large, round ball, and then rolling this off to some underground chamber created by the adult beetles. Here they bury the dung and eggs are laid on it, with the dung serving as the food of the larvae. The adult beetles often are brilliant colors of metallic green, blue, or rainbow hues. Other scarabs that may be called dung beetles are also some turf pests, and these are small scarabs called the Turfgrass Ataenius, which can occur in great numbers in your lawn, feeding on the roots of the grasses.

The weevils are in the beetle family Curculionidae, and they are not nearly the terror on turf that the white grubs are, and there are only a few species of weevils, called Billbugs, that are pests of turf. However, rather than let the weevils off the hook here, keep in mind that these guys make up for it by being big problems in other areas, such as the boll weevil on cotton, or the various grain weevils that infest stored grains and legumes. We’ll spend most of our time in this article on the scarabs and the white grubs.

It depends somewhat on where you live in North America as to the beetle YOU think is a “June” beetle. Out west, along the Pacific Coast states, we have a number of species of big scarabs called the “Lined June Beetles”, and these may be our most noticeable June Beetles. A smaller brownish-orange kind is in a group called the “masked” chafers, and this is another that I commonly see flying around and coming to my porch lights on July evenings. They get their common name from the black “mask” across the front of their head, and throughout the eastern United States the Northern and Southern Masked Chafers are a major lawn problem.

While some of the larger June beetles require 2 or 3 years to complete their life cycle, the masked chafers need only one year. The adult beetles emerge from the ground in late spring and early summer to mate and lay their eggs. The adult beetles do not feed, so they live only a short time. The larvae, the “white grubs”, then feed in the soil for the remainder of the summer and when weather cools they dig deep into the soil and spend the winter in their last larval stage. The adult beetles are active only at night, so it may be common for you to find them at your porch lights in the summer, an indication that your lawn may be the one producing these insects.

Some of the largest June Beetles are also called May Beetles, even though those “month” designations are not necessarily indicative of when you’ll see them. These big insects are light brown to dark brown in color, and it is their big larvae that are most often referred to a white grubs. Typically a scarab larva assumes a “C” shape, with the darker head and long legs at the front end, and the curved white body widening as it moves toward the back end, giving it a bit of a bulbous appearance. There are over 150 different species of these May and June Beetles in North America, but no more than 10 species will be problems for ornamental lawns. The adult beetles also feed, but on the leaves of nearby trees, especially oak trees, and if their numbers are high they can produce some noticeable damage to your trees.

A few other important scarab species exist, such as the smaller European Chafer and the Asiatic Garden Beetle, and these two kinds are exotic imports in North America, being native to Europe and Asia, respectively. They occur primarily in eastern states, but where they occur they can do serious damage to lawns. The European Chafer, in particular, can be terribly destructive due to the extended period of time in which the larvae may be actively feeding, beginning very early in the spring.

The final scarab player is the notorious Japanese Beetle, currently still confined to the Northeast states in the U.S. It can hitchhike though, and now and then will be discovered in other parts of the country, having hitched a ride in the wheel wells of aircraft or in road vehicles crossing the country. It is another exotic invader to North America, originating in Asia, but found in the U.S. since 1916. The adult beetles are easily identified by the reddish-copper color of their wings, the shiny dark green of their thorax, and the presence of white tufts of hairs along the sides of their abdomen. The adult beetles can cause terrible damage to flowers, fruits, and vegetables, feeding in masses of many beetles on the same flower or fruit.

The larvae of the Japanese Beetle feed on the roots of many kinds of plants, grasses included, and there have been infestations in lawns where as many as 122 larvae were present in each square foot of the turf, sawing off the roots of the grass and killing the lawn. The late-stage larvae live through the winter buried deep in the soil, and they move back to the surface in very early spring to begin their feeding, continuing well into the fall to cause maximum damage to turf.

Controlling White Grubs

Control of any pest problem begins with determining that you actually have the pest you think you do, and this means finding a way to collect them. It helps, also, to understand the habits of white grubs so that you can inspect for them or attempt to control them at a time when you will be most successful. The larvae move up and down in the soil in response to moisture and temperature, and may end up as deep as 2 or 3 feet down, particularly in the northern states where the soil freezes well below the surface. So, if you are trying to sample for the larvae you need to either pick a time of year when the temperature is mild and the soil is moist, at which time the larvae would be most likely to be in the root-zone of the turf, or water the lawn to encourage the larvae to make the trip upward. For white grubs you then can use a sharp tool to cut out a section of the lawn and peel it back to expose the roots. If the conditions are correct for the larvae to be feeding you should be able to see these white grubs very easily. The turf can then be rolled back into place without harming it from the cutting.

One resource you should use in your geographic area is your University Cooperative Extension Service, and you can find their websites quite easily on the internet. The importance of white grubs varies widely across the country, and one of the variables is how many grubs it takes to warrant trying to control them. This is referred to as the “threshold” level for the pest, and for white grubs it would be a count of how many larvae are present in each square foot of the turf. For very sensitive or important turf, such as a golf green, that threshold level might be only 1 larva. But, for hardier turf that does not need to look so manicured the threshold level might be much higher, perhaps 10 grubs per square foot. The meaning here is that an infestation below the threshold level, for your geographic area and turf type, would not warrant going to a huge effort to eliminate the insects. The small amount of damage they would cause would be minimal.

So, stay in touch with your local Extension Service, check their advice on the need for control, and identify the actual presence of the pests. Brown patches on your lawn could be caused by lots of other things besides insects. If you find you do need a control program it would be good advice to contract with a licensed pest management company. These folks have the training to use insecticides correctly, they have the equipment to apply the materials to a large expanse of lawn, and they have access to products that you might not on the retail shelves. These products may require that the user be certified or licensed.

Your home remedies for control could include some non-pesticide options. One material that can be effective on Japanese Beetle larvae, and to some extent on some of the other white grubs, is called Milky Spore. This material is composed of bacteria, apparently native to North America, which feed on beetle larvae, and in areas infested with Japanese Beetles this material likely is available in retail stores. There are also a number of kinds of parasitic flies and wasps that are known to feed on white grubs, but at this time you may not be able to find these commercially. One family of wasps is called the Scoliidae, and releases of this wasp in Hawaii have shown success in reducing populations of the Oriental Beetle there.

So, the take-home lesson here, hopefully, is that white grubs can definitely be a problem for your lawns, but quite often they get blamed for the damage you see when the cause is something else. If you suspect an insect problem you should sample in the proper way to determine if it truly is there, and if so then you need to decide if the level of the pest population is high enough to warrant going to a control program.

Source: BugBattalion New Jersey