Homegrown: More on Japanese beetles

I'm still seeing the notorious Japanese beetles in my gardens, but hope they will be in retreat mode soon. Becki Lynch, Linn County Master Gardener, offered more on this recent scourge:

The summer pest to beat is the Japanese Beetle, once again.  One would think with the heat and drought, there would be fewer of them, but, unfortunately, that is not the case.  The Japanese Beetle was first found in the US in 1916, and although the Eastern US has a natural control for them in their soil-inhabiting protozoa, the Midwest is not as fortunate.  They are a serious pest as the grubs feed on the roots of grass, thus killing sections of lawn, and the adults feed on over 300 types of plants.  Although they do not necessarily kill the plant, they severely damage and destroy the foliage and blooms.  Some of their favorites are roses, hollyhocks, linden and crabapple trees.

In case you're not sure what a Japanese Beetle looks like, think of a small, square shaped copper/bronze glinted black bug.  You will find them on blooms and foliage quite easily, and one of the easiest ways to control an adult is to simply knock them off into a bowl of soapy water.  It's quite easy to do this early in the day.  Another method of control is by using a contact spray.  A number are available, and are organic and leave the environment very quickly.  However, they will kill everything they touch, such as bees, so it's best to use sparingly when beneficial insects are not around.  Some people use beetle traps, but research has found the traps attract more beetles than they catch.  So, if desperate, go ahead, but do not expect a highly successful deterrent.

Finally, there are some trees that are not attractive to the beetle, such as box elders, lilacs, and oaks, so you can make some choices when choosing your trees.  Unfortunately, many of us have beautiful, mature trees that were present when we moved to our homes, so this step isn't really an option.

The other method of control is through elimination of the grubs that develop into the beetle.  Look for patches of brown grass areas, and they seem to prefer the roots of strawberries.  The best time to control an infestation of grubs is from mid-July through September through a granular application which will not allow them to develop into the beetle. The beetles emerge in late June to early July and are active for approximately 6 – 8 weeks before they die.  They will lay up to 60 eggs in that time frame, and the grubs will grow to almost 2 inches.

Thus, now is the time to check out your property and address any problems.  By being proactive this year – perhaps you can get ahead of the problem for next year!

For additional information, please refer to the reference article below --

Japanese Beetle Management

Copyright ©  2012  Regents of the University of Minnesota. All rights reserved.

The Japanese beetle (JB) is a serious pest of turf and ornamental plants. Grubs feed on the roots of grass and adults feed on the foliage of more than 300 plant species. Japanese beetles were first found in United States in 1916, after being accidentally introduced into New Jersey. Until that time, this insect was known to occur only in Japan where it is not a major pest. It is controlled in the eastern United States by soil-inhabiting protozoans that are not present in Minnesota. There are two biological control agents, the fly Istocheta aldrichi and the tiphid wasp, Tiphia vernalis, but they do not control infestations.

There are a number of related beetles in the family Scarabaeidae that feed on the roots of grasses. In Minnesota, JB is the worst pest, so you need to identify grubs to species as the life history varies and management is not the same for all species. A management program consists of identifying grubs to species, determining grub numbers, identifying thresholds, timing pesticide application to smaller grubs, and monitoring the treated area for results.

Japanese beetle adults are approximately 3/8 inches in length with a dark metallic green head and metallic dark tan wings. Key characteristics for adult JB are two white rear tufts and five white lateral tufts of hair (Figure 1).

adult Japanese beetleJapanese beetles have two white rear tufts and five white lateral tufts of hair. Adults found on plants.

adult Japanese beetle

Japanese beetles have two white rear tufts and five white lateral tufts of hair. Adults found on plants.

adult False Japanese beetleFalse Japanese beetles lack the five white hair tufts along wing margin. Adults rarely seen.

adult False Japanese beetle

False Japanese beetles lack the five white hair tufts along wing margin. Adults rarely seen.

adult rose chaferRose chafer are a light green tan color with long legs. Adults found on plants.

adult rose chafer

Rose chafer are a light green tan color with long legs. Adults found on plants.

adult May/June beetleAdults found at lights.

adult May/June beetle

Phyllophaga species

Adults found at lights.

adult masked chaferAdults do not feed so not found at lights or plants.

adult masked chafer

Adults do not feed so not found at lights or plants.

adult black turfgrass AtaeniusThe smallest species found in turf with high organic matter.

adult black turfgrass Ataenius

The smallest species found in turf with high organic matter.

Japanese beetle larvae or grubs are “C” shaped and live in the soil and feed on grass roots. JB was recorded to feed on the roots of corn, beans, tomatoes, and strawberries.

Grubs can be identified to species by the pattern of hairs on their brown hind ends (raster). Using a 10-power hand lens, you can see that the hairs on the raster of Japanese beetle form a small “V” shape just below the anal slit (Figure 2).

Grubs chew off grass roots and reduce the ability of grass to take up enough water to withstand stresses of hot, dry weather. As a result, large dead patches of grass develop in grub infested areas. These dead patches can be rolled back like a carpet to expose the lack of turf roots. Grubs can be found in adjacent green areas. Early recognition of the problem can prevent this destruction. Starlings and crows, as well as moles, shrews, and skunks may be seen digging up grubs, also damaging the turf.

Grub populations between 7 and 15 per square foot can cause significant damage to non-irrigated turf. Irrigated turf can withstand a higher grub count because the increase in water compensates for the roots chewed off by the grub.

Adults emerge from the soil in early July, feed, mate, and lay eggs. In July adults are noticed feeding on vines, linden trees, roses, and many other ornamentals. Activity is most intense over a 6 to 8 week period, after which the beetles gradually die off. Individual beetles live about 60 days. Over 2 months females can lay a total of 60 eggs.

JB adults feed in full sun at the top of plants, moving downward as the leaves are consumed. Odors emitted from beetle-damaged leaves causes beetles to aggregate. Also, adults release an attraction pheromone that causes them to aggregate. At dusk, this pheromone is no longer produced and the females fly to turf to lay eggs. Females burrow 2 to 3 inches into the soil and lay their eggs. The grubs grow quickly and by late September are almost full-sized (about 1 inch long). When the soil cools to about 60°F in the fall, the grubs begin to move deeper. Most pass the winter 2 to 6 inches below the surface, although some may go as deep as 8 to 10 inches. Grubs feed again in May when ground temperatures are above 50°F (Figure 3).

Adults fly long distances to food plants; so adult infestations do not indicate turf infestations. Timing of pesticide treatment is important. Insecticides for grubs can be applied from May through mid-June, when recently overwintered grubs (larvae) start feeding. However, these grubs are large and may be difficult to kill. Starting in mid- June most grubs are in the pupal stage and insecticides are not effective. In early July adults emerge to feed on plants, mate, and then at night fly to grass to lay eggs. The best time to apply insecticides for grubs is from mid-July until early September. Granular applied insecticides distributed on soil with a spreader are usually the best insecticides for JB (Figure 3).

If many adults are feeding on leaves in an area, it does not indicate a grub infestation in the turf. Before applying an insecticide for grubs, make sure you have a large infestation. Look for areas of brown turf and search in adjacent green areas for grubs and pupae. Insecticides are needed to control grubs and adults if the damage is extensive. Irrigating after applying an insecticide improves its insect control. However, a significant rainfall shortly after the application may reduce the insecticide's concentration below effective levels. Infestations should be checked one week after an insecticide is applied, especially if the original grub population was high. If after 10 days the grubs are still alive, apply a different product. Also, read the label carefully for cautions about their use (Tables 1 and 2).

The best time to apply insecticides for grubs is from mid-July until end of September. Granular applied insecticides distributed on soil with a spreader are usually the best insecticides for JB. There are conventional insecticides that kill grubs (imidacloprid) and biorational insecticides that conserve beneficial insects in turf (halofenozide and Acelepryn). In trials in Ohio milky spore disease (Bacillus popillae) has not been as successful in killing JB grubs as was reported in the 1960's. A beneficial nematode, Heterorhabditis bacteriophora, attacks JB grubs. Nematodes are microscopic parasitic roundworms that transport and feed on bacteria. When they find a grub, the nematodes penetrate the larva and inoculate it with bacteria, which quickly multiply within the grub's body. The nematode then feeds on the bacteria. Nematodes need to be applied to soil at night and the soil must be irrigated daily to kill it moist so the nematodes stay alive.

?   Imidacloprid – use from July until early September. It has minimal risk to mammals and fish.

?   Halofenzide – use from July until end of August. It mimics an insect hormone and is best applied when adults are active and laying eggs. Minimize thatch since heavy thatch will prevent the insecticide from penetrating to the area where insects are feeding.

?   Chlorpyrifos – is only available to golf courses. It is generally not considered a top choice due to the high binding ability of the active ingredient to the thatch. It is a good choice for adult Japanese beetle control, but is available only to nurseries and golf courses.

?   Milky spore disease – is caused by the bacteria Bacillus popilliae and is sold under the names of Japidemic Doom and Milky Spore. Recent trials with these formulations have not reduced Japanese beetle grub numbers in turf.

Removing beetles by hand may provide adequate protection for backyards, especially when beetle numbers are low. The presence of beetles on a plant attracts more beetles. Thus, by not allowing beetles to accumulate, plants will be less attractive to other beetles. One of the easiest ways to remove Japanese beetles from small plants is to shake them off into jars filled with soapy water.

With all insecticidal products, foliage and flowers should be thoroughly treated. The application may need to be repeated to prevent reinfestation. Follow label directions and avoid spraying under windy conditions. Never spray when bees are foraging. Be sure the insecticide is registered for use on the plant or crop you intend to spray. If it is a food crop, note the minimum number of days that must be observed between the date of the last application and the date of harvest.

Different chemicals are used on adults when feeding on foliage. Foliar sprays of contact insecticides kill adults and offer immediate knockdown, such as carbaryl, acephate, pyrethrins, and pyrethroids. Examples include pyrethroid products such as cyfluthrin (Tempo, Bayer Advanced Lawn & Garden Multi-Insect Killer), bifenthrin (TalstarOne, Onyx), deltamethrin (Deltagard), lambda cyhalothrin (Scimitar, Spectracide Triazicide), esfenvalerate (Ortho Bug-B-Gon Garden & Landscape Insect Killer) and permethrin (Spectracide Bug Stop Multi-Purpose Insect Control Concentrate and other brands). Both pyrethroids and carbaryl provide around 2 weeks of protection. For adults, repeated applications may be necessary because of the relatively short residual effect of the pesticides. Insecticides that are advertised as organic usually do not kill adults. Formulations with pyrethrins and PBO (piponeryl butoxide) are more effective. Neem products such as Azatrol may provide about 3-4 days deterrence of feeding. Insecticidal soap, extracts of garlic, hot pepper, or orange peels, and companion planting, are generally ineffective (Tables 1 and 2).

Soil-applied imidacloprid is systemic and translocated around the plant and kills adults when feeding on foliage. However, when adults feed on petals of shrub roses rather than the spiny leaves, imidacloprid is not effective. Soil-applied imidacloprid used on linden or basswood trees or any plant visited by bees or beneficial insects, can potentially kill any bees or beneficial insects feeding on the pollen and nectar in the flowers.

Pheromone traps contain a lure with the scent of geraniums and rose (geraniol) and the sex pheromone of the JB female. The pheromone is very powerful and will call in beetles from a few thousand feet. Research demonstrated that more beetles fly toward traps then are caught; resulting in surplus beetles that feed on your plants. Think twice before purchasing and installing a pheromone trap. Some growers have set pheromone traps over basins filled with soapy water with a white bottom (opaque white plastic bag) to increase the size of the area to catch beetles. Some testify that these pools fill with beetles that drown in the soap and reduce the numbers in the area. If you are really frustrated with JB numbers, please try this method and see if JB numbers on your plants are reduced.

common name

trade name

target

class

comments

imidacloprid

Merit, Grubex, Menards Grub Control

grubs

neonicotinyl

Low toxicity to mammals.

halofenozide

Mach2

grubs

IGR, insect growth regulator; diacylhydrazine

Conserves adult predators.

chlorantraniliprole

Acelepryn

grubs

insect muscles

Conserves adult predators. Environmentally friendly. Available to professional applicators.

trichlorfon

Dylox

grubs

organophosphate

High toxicity to birds, fish. Do not use nearer than 100 yards from water. Available for homeowner use. Not effective in pH 8 water.

Bacillus popilliae

Milky spore, Japademic, Doom

grubs

bacteria

Not shown to be effective in Ohio State tests.

Heterorhabditis bacteriophora

 

grubs

bacteria and nematodes

Water before and daily after application.

common name

trade name

target

class

comments

carbaryl

Sevin

adults

carbamate

High toxicity to bees, earthworms; moderately toxic to birds, fish. Do not use adjacent to water. Available for homeowner use.

bifenthrin

Talstar, Menards Insect Control, many other names

adults

pyrethroid

High toxicity to honeybees, birds, fish. Do not use nearer than 100 yards from water.

cyfluthrin

Tempo, Bayer Advanced Lawn & Garden Multi-Insect Killer

adults

pyrethroid

High toxicity to birds, fish. Do not use adjacent to water.

lambda-cyhalothrin

Scimitar, Spectracide, Triazicide

adults

pyrethroid

High toxicity to fish.

permethrin

Astro, Spectracide Bug Stop Multi-Purpose Insect Control Concentrate

adults

pyrethroid

High toxicity to fish, bees. For home lawns only.

esfenvalerate

Ortho Bug-B-Gon Garden & Landscape Insect Killer

adults

pyrethroid

High toxicity to honeybees. Odor may be a problem in public places.

deltamethrin

DeltaGard

adults

pyrethroid

High toxicity to birds, fish. Do not use adjacent to water.

chlorpyrifos

Dursban

adults

organophosphate

High toxicity to birds, fish. Not available for home lawns.

common name

trade name

class

comment

bifenthrin

Talstar

pyrethroid

For use in containers.

imidacloprid

Marathon

chloronicotinyl

For use in containers.

Carefully select plant species that Japanese beetle adults do not like to feed on, when retrofitting or adding to your landscape or golf course. Certain common landscape plants are inevitably attacked and may be poor landscape choices (Table 3). The nursery industry can reduce Japanese beetle numbers in cultivated areas or containers by eliminating grasses that the grubs feed upon.

Plants that attract beetles

Plants seldom damaged

American chestnut?American elm?American linden?American mountain ash?apple?birch ?black cherry?cherry

flowering crabapplegrapeshollyhockhorse chestnutNorway Mapleplumroseswalnut

flowering crabapple

grapes

hollyhock

horse chestnut

Norway Maple

plum

roses

walnut

American elderarborviateblack oakboxeldercommon lilaceuomymusfirgreen ash

American elder

arborviate

black oak

boxelder

common lilac

euomymus

fir

green ash

hemlockhollyjuniperpinered maplered oakrhododendronscarlet oak

hemlock

holly

juniper

pine

red maple

red oak

rhododendron

scarlet oak

silver maplesprucewhite ashwhite oakwhite poplaryew

silver maple

spruce

white ash

white oak

white poplar

yew

Bloetscher, B. et al. 2001. Management of turfgrass pests, weeds, diseases, and insects. Ohio State University Extension Bulletin L-187.

Bradenburg, R. and M. Villani. 1995. Handbook of Turfgrass Insect Pests, Entomological Society of America. 140 pages.

Cranshaw, W. 1997. Turfgrass Insects in Colorado and Northern New Mexico, Colorado State Cooperative Extension, ISBN 1 889143006. 38 pages.

Krischik, V. and M. Ascerno. Revised 2000. Managing Lawn and Turf Insects, University of Minnesota Extension Service, item FO-1008-F. 12 pages.

Villain, M. and H. Tashiro. 2001. Turfgrass Insects of the United States and Canada, Cornell University Press, ISBN 0801418143. 391 pages.

This publication was produced in cooperation with the Minnesota Department of Agriculture, the College of Food, Agricultural and Natural Resource Sciences, and University of Minnesota Extension.

In accordance with the Americans with Disabilities Act, this material is available in alternative formats upon request. Please contact your University of Minnesota Extension office or the Extension Store at (800) 876-8636.