Healthy grass is beneficial both aesthetically and environmentally. Grass can be attacked by various insects as can any other plant. Grubs are often the most invasive pest for grass. These pests feed on the roots of grass thereby depriving grass of their method to sustain life. Damage from grubs can be treated and prevented with proper identification and various treatment methods.
Grubs are beetle larvae. According to Penn State University the grub body is a dirty white soft form with six legs and a brown head. Grubs lay on their sides in the shape of a "C" once exposed. Depending on the beetle species, grubs can be various sizes; the Japanese beetle grub and the Northern masked chafer reach 1 inch in length for example. The hairs, spines and bare spaces found on the grub are called a raster and are usually found on the underside near the rear end. These markings help further identify the grub species. Northern masked chafers have a random pattern while Japanese beetles have a V-shape pattern. Other grub species have different identifying characteristics.
Lawns attacked by grubs exhibit various signs depending on the severity of the infestation. The most common signs are the large uneven patches of dead lawn. Spongy sections of sod can often be found nearby; sections that can be rolled up similar to carpeting also indicate grubs. If these signs appear between April and May or September and October this is another indication of grub presence. Animals such as skunks, crows or moles may suddenly appear to be digging into the lawn; these animals eat grubs and will dig up the yard to reach them. Removing a 1 square foot area at multiple locations helps determine the extent of the problem according to Penn State University. Grubs can be found at a depth of around 4 inches into the soil.
Identifying the severity of the problem involves timing and random sampling. Grub samples should be sought around mid-August when the grubs are growing, recommends Cornell University. Random sampling can be controlled by mapping the property on paper, then placing markings 10 feet apart to guide the sample taking. Cornell University adds that areas where grubs were evident previously should also be included in sampling. Samples are gained by cutting squares at the marked locations and peeling the sod away; grubs will be found underneath the sod. The number of grubs per square foot indicates the severity. Between six to 10 grubs per square foot indicates treatment should be considered; more than 10 grubs per square foot indicates immediate action is required.
Affected lawns can be treated using chemical and natural methods. Curative chemical methods should be used between August and September, states Missouri State University. Penn State warns against treating lawns too early since the treatment will miss the egg laying cycle of the beetles. Recuperative chemicals are used to kill off existing grubs. These chemicals must reach depths greater than 1/2 inch into the soil to be effective. Treatment should begin five weeks after beetles are spotted. Natural methods for treating grass include drying the grass out during July and August to stop the eggs from hatching. Nematodes can be used to attack grubs from the inside out because they are digested by the grub and then feed off of the grub from the inside out.
Lawn care begins with proper maintenance. Maintaining adequate water supply for the lawn depends on the location and the season. Overwatering invites grubs. Overfertilizing can also increase the chances of grubs because the grass grows too quickly and then is weak.