IPM CONTROL OPTIONS FOR KEY TURFGRASS INSECT PEST
IPM CONTROL OPTIONS FOR KEY TURFGRASS INSECT PEST
JAPANESE BEETLE Contents:
Introduction
Japanese beetles
are considered to be a major pest of both turfgrasses and
ornamental plants in the Mid-Atlantic region. They are native to
Japan and were first identified in 1916 in New Jersey. Japanese
beetles are in the Scarabaeidae family and their common
name, white grub, describes the larval stage of this insect
family.
Identification
Japanese beetle: Popillia japonica (Newman). The
adult
male beetle is .3-.5 inches long; the female is slightly larger.
The beetle is roughly oval in outline (from above). The head and
prothorax are greenish bronze, and the wing covers are brownish
bronze with green along the sides and center. Twelve white tufts
or hair are present along the sides of the abdomen and at the tips
of the wing cover. Antennae are platelike. The legs are long, with
heavy claws.
Eggs are round, become oval after absorption of soil moisture, measuring less than 1/16" across. White grubs are white, C-shaped, and will have 6 legs. Their size will vary from .4 " as first instar to 1" for third instars. They have a distinctive V-shaped rastral pattern.
Distribution
The Japanese beetle is an Asian native, which was first reported in the U.S. at Riverton, New Jersey, in 1916. It is common in all states east of the Mississippi River, except Florida, Mississippi, and Wisconsin. It has also been found in Missouri, Minnesota, and California. Because of the ease of shipping grubs with nursery stock and soil, potentially this species could be found about anywhere in the U.S. including, Hawaii and Puerto Rico. Adults are highly mobile and frequently hitch rides in airplanes and cars. The larvae are distributed in transported soil and nursery stock.
Hosts
Adult Japanese beetles attack more than 300 species of plants including many trees, ornamental shrubs and vines, fruits, flowers, vegetables, and weeds. Adults feed on foliage and fruit, while larvae feed on roots, especially those of grasses, vegetables, and nursery plants. Females prefer to lay eggs in warm, moist soil where turfgrasses are exposed to full sunlight.
Life Cycle
In Maryland the Japanese beetle has one generation per year and overwinters as third instar larva in the soil. Adult emergence occurs over a 3-4 week period from late June to mid-July and adults may live for 4-6 weeks. Adult beetles are attracted to one another due to the production of both aggregation and sex pheromones. Females will burrow into the soil (2-4") and lay their eggs. Egg laying occurs during July and August with a reported 75% of eggs laid by mid-August.The larval or white grub stage will extend from late August through the fall and into the spring (late May). There are 3 instar stages for white grubs; the first and second instar stages are normally completed within 5-7 weeks. The third instar stage occurs by fall and the larvae will remain as third instars until late May. They will overwinter at a soil depth ranging from 4-8 inches. As soil temperatures warm in the Spring they will return to the soil surface (less than 1" depth) by the beginning of April. Prepupa and pupa development will occur in June.
Damage
Larvae feed on grass roots and may move up into the thatch layer after consuming the total root system. In Kentucky bluegrass, populations of 6-8 grubs per square foot may kill turf during August-October. Because of the good growing conditions in spring counts of 10-15 per square foot. ft. may cause no damage symptoms. Clump grasses such as tall fescue tolerate higher summer populations but in mixed tall fescue/bluegrass sod, grubs will selectively kill out the bluegrass component.This root feeding injury gives the turf a spongy feeling when walked upon and after heavy feeding the roots are severed and sod can be easily rolled back and the grubs observed. Without irrigation the turf will turn brown, die and usually not recover. Some improved varieties of Kentucky bluegrass with extensive underground stem systems will have better recovery prospects.
Generally, treatments are recommended when grub populations exceed 6-8 per square foot ft. However, moles and skunks may destroy turf and because of these small mammals treatment thresholds can range as low as 4-5 grubs per square foot. In this situation the grubs do not kill the turf; the animals destroy the sod when they dig for the grubs. Cultural conditions may also affect treatment thresholds such as turf type, amount of irrigation or time of year. If bluegrass turf areas are frequently irrigated during the July-August stress periods, populations as high as 20-25 grubs per square foot may not produce damage until the irrigation is stopped. Kentucky bluegrass, perennial ryegrass and fine fescues are the most sensitive to grub feeding damage. Whereas, tall fescue and warm season species such as zoysiagrass and bermudagrass can tolerate moderate to heavy populations during the hot dry conditions that often kill Kentucky bluegrass. Mixed populations of masked chafers and other grub species are common throughout the species range.
Biological-Biorational Control
Japanese beetle grubs are infected by many species of bacteria, fungi, protozoans and nematodes. Few of these have commercial possibilities but together they are one of the major grub population regulators in established turf pastures and meadows. In many older communities problems rarely occur particularly where turf has been established for 8-10 years or more. The highest risk of grub damage occurs in new lawns 2-5 years of age or newly disturbed sites reseeded to turfgrasses. We suspect that these new housing landscapes that were developed from farm fields or wood lots that lack a grub pathogen complex. These pathogens haven't had the opportunity and time to develop because the Japanese beetle and other important grub species generally avoided their habitats. In short no hosts, no microbial control agents. However once these grub populations become established for several years, key pathogens and other biological agents (parasitoids and predators) also become well established and thus help maintain low grub populations.Various biological and biorational control options include milky disease, nematodes, and insect growth regulators.
Milky disease, Bacillus popilliae, is the first option in the Mid-Atlantic area for low to moderate maintenance turf situations such as home lawns, public parks, school grounds, and housing developments, etc. This bacterium is long living, species specific, self perpetuating, easily applied and best adopted to the Mid-Atlantic region. Success in New York and New England areas has been limited due to cooler soil temperatures and a shorter grub season.
This bacterial disease only controls the Japanese beetle grub and requires the presence of moderate grub populations in order to increase the soil spore counts and spread the disease to untreated areas. Spores can remain viable for 20-30 years once established in a lawn. However, at the economical rates of application recommended by the manufacturer, effective control may require 2-4 years.
We do not recommend the granular formulations as they have not been proven effective to date. The spore dust product, "Doom" is recommended for newly established turf. Areas with 10 or more years of turf coverage may already have naturally infected soils. Remember that this disease works most efficiently when grub populations are moderate to high. This situation usually occurs in new housing developments Some occasional damage can be expected regardless of the spore levels in the soil and age of the turf.
The milky disease is not compatible with insecticides. Generally insectides kill the grub population that is required to increase and maintain the soil spore counts. Fortunately the spores will remail viable after an insecticide treatment and continue to increase in later years when the grub populations return.
The entomophathogenic nematode, Heterorhabditis bacteriophora , has shown good activity against white grubs and is commercially available as Cruiser.
A new product which mimics the insect molting hormone, ecdysone, and causes premature molting is Mach 2 (halofenozide). This product has shown consistent and excellent control for a number of white grub species.
Cultural Control
Females prefer to oviposit in moist soils that are high in organic matter. Avoiding irrigation during egg laying in July will increase mortality of eggs. However, the use of irrigation during August-September can mask larval feeding damage.
Chemical Control
Insecticidal control may be warranted if threshold levels of 6-8 grubs per square foot exist. Improved control will occur if the following conditions are met; proper timing of insecticide application, sufficient irrigation after application (1/2") and removing excessive thatch layers (more than 1/2"). The preferred timing for a majority of the recommended insecticides is in late summer to early fall when damage is first noticed. The other time period is in the Spring from April to mid-May.The following insecticides have labeling for white grub control however a number of these products have restrictive labeling and may require a certified applicator to apply them.
Organophosphates: Dylox, Proxol, Mocap*, Mainstay, Crusade*, Oftanol*, Triumph*, and Diazinon*
Carbamates: Sevin and Turcam*
*Restrictive Labeling
A new product for white grub control which was released in 1996 is Merit. This product can be applied earlier in the season (May-early August) due to its longer residual activity. However, it does not perform well on later instar or on older grubs and is not recommended for application after mid to late August in this area.