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WHITE GRUBS IN WISCONSIN FOREST TREE NURSERIES. R. D. SHENEFELT and H. G. SIMKOVER. Jour.
Forestry 48:429-34. 1950.

PROTECTING MACHINE PLANTED TREES FROM WHITE GRUBS. R. D. SHENEFELT, H. R. LUBERG, and
R. C. Doson. Tree Planters’ Notes 20 :14-17. 1955.

WHITE GRUB DAMAGE TO YOUNG PINE PLANTATIONS. J. G. WATTS and JOHN B. HATCHER. Jour. Econ.

Ent. 47 :710-11. 1954.

U.S. GOVERNMENT PRINTING OFFICE: 1961

» Return to the Forest and Tree Health Publications

» Alphabetical Listing of FIDL Publications
» Return to the St. Paul Field Office

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these apparently do not normally act as effective controls. Mammals and birds also eat the
grubs, and skunks may greatly reduce populations in local areas. Attempts to control white
grubs through the use of bacterial milky disease of the Japanese beetle have not been
successful.

Preventive Control (See pesticide caution below)

An application of insecticide before planting seed or seedlings may be needed to prevent
extensive damage by white grubs. In forest nurseries 8 pounds of chlordane per acre,
thoroughly worked into the soil, has given excellent control. A maintenance dosage of 1 to 1
1/2 pounds per acre is needed every 2 years. Dieldrin applied at the rate of 1 1/2 pounds per
acre, followed by 1/2 pound every 2 years, may be substituted for chlordane.

Preventive control under field conditions is advisable if the grub population is one or more per
2 square feet. A grub population of 2 per square foot has caused high tree mortality. Areas
with such a high rate of infestation should not be planted without control measures. Since
young grubs are difficult to detect, even when they are present in considerable numbers, very
careful observations must be made when sampling for damaging grub populations.

Protection of young seedlings re-quires a fast-acting chemical that will repel or kill the grubs
before the roots are cut and the seedling dies. An aldrin solution of 1/2 to 1 percent, applied to
the root systems of seedlings during planting, has given good results. The chemical can be
applied by a sprayer attachment on planting machines or by dipping the roots of hand-planted
stock.

Applied Control (See pesticide caution below)

Once a plantation is established, control measures are extremely difficult and expensive. The
insecticidal solution must penetrate several inches of soil rapidly and kill the grubs before they
cause additional damage. This is seldom possible.

Insecticide dust or granules broadcast from either ground machinery or aircraft are not
effective because the insecticides generally penetrate only the upper layers of soil and do not
reach the root zone where the grubs are feeding.

Insecticide should always be applied before planting where damage is likely to occur, in either
nursery or field.

Caution: Pesticide recommendations in publications from 1975 or earlier may no longer be
valid. Some pesticide products may not be registered anymore or may not be available to the
public for use. For current recommendations, consult your local forest
pathologist/entomologist, county agricultural agent, or state extension agent about
restrictions and registered uses of particular pesticides.

References

WHITE GRUBS IN FOREST NURSERIES OF THE CAROLINAS. H. R. JOHNSTON and C. B. EATON. U.S. Bur.
Ent. and Plant Quar. E-486, 9 pp. 1939.

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Forest Insect
& Disease
Leaflet 63

U.S. Department
of Agriculture
Forest Service

November 1961

White Grubs in Forest
Tree Nurseries and Plantations

By Charles F. Speers and Donald C. Schmiege!

' Forest entomologists, Forest Service, U.S. Department of Agriculture. Mr. Speers is stationed at the
Southeastern Forest Experiment Station, Asheville, N.C. ; Mr. Schmiege at the Lake States Forest
Experiment Station, which is maintained by the U.S. Department of Agriculture in cooperation with
the University of Minnesota, St. Paul, Minn.

White grubs of the genus Phyllophaga and related genera live in the soil and feed on roots of
plants. This feeding can sever or girdle roots and cause injury or death. Root feeding of the
grubs causes the principal injury to plants. Minor injury to hardwoods and pines is caused by
foliage feeding of the adults, which are often called May or June beetles.

Grub damage to forest tree seedlings in nurseries has been recognized as a problem in this
country for at least 50 years. Not until the early 1940's, however, did it become evident that
grubs might also threaten forest plantations. Damage to plantations in the Lake States was
generally restricted to small acreages, according to early reports. Serious injury to larger areas
was reported in 1953 when 8,000 acres in South Carolina were heavily attacked.

Because grub populations tend to build up on open land that has been idle for a year or more,
preventive measures may be needed before these areas are planted.

Host Trees

White grubs normally feed on roots of many plants and do not especially prefer roots of trees.
All coniferous and hardwood stock are readily attacked, however.

Damage

Heavy grub damage is generally first noted in the late summer and early fall when formerly
healthy appearing seedlings turn color and may die. The symptoms are similar to those of
drought injury. A gentle tug on such seedlings will pull them up and reveal that lateral and
taproots have been chewed off or girdled (fig. 1).

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F- 494653
FIGURE 1.-Root injury on pine seedlings caused by feeding of white grubs. Aisa
healthy seedling ; the other seedlings show varying degrees of grub damage.

Survival of discolored seedlings depends on their original vigor, the nature and degree of
injury, and weather conditions. Seedlings injured during dry weather are much more likely to
die when dry conditions continue than when cool, wet weather follows. Even with cool, moist
conditions the trees may not be able to produce new rootlets and recover before the tops dry
out. Generally, coniferous stock is more severely injured and makes a slower recovery than
hardwood stock. Damage is most severe on light soils.

Description

Adults of the Phyllophaga genus, which contains over 100 species, are robust, oval, brown or
brownish-black June beetles (fig. 2).

Larvae are milky white. They have six prominent legs. The head is brownish and armed with a
strong pair of jaws. The body is strongly curved, all the hind parts are shiny, and the body
contents show through the skin. White grubs vary in length from one-eighth inch when first
hatched to over an inch when full grown (fig. 3).

Pupae have the general appearance and size of adults. They vary from yellowish to brown,
growing darker as transformation to adult proceeds. Pupae, inactive in the soil, do not feed.

Eggs are pearly white and oval when first laid and are about one-tenth of an inch long. Later
they become cream colored and spherical.

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F-494655 F-494654

FIGURE 2.—Adult stage of the white FIGURE 3.—A full-grown white grub.
grub, commonly known as a June beetle.

Life History

Life cycles of the various Phyllophaga species vary from | to 4 years. In the South the species
may have a 1-, 2-, or 3-year cycle, the 2-year cycle being most common. In the North Central
States they have a 2- or 3-year cycle. Further north the cycle may be 3 or 4 years, although the
3-year cycle is most common in the Lake States. Different species in the same locality may
have different cycles. Also, part of a single brood may emerge at the end of the second year
and the remainder of the same brood at the end of the third year.

There is a continual overlapping of broods, with emergence much heavier in some years than
others. Because of this overlapping, an overwintering population may consist of adults that
have not taken flight from the soil and larvae of several sizes.

The female beetles lay their eggs at depths of 2 to 6 inches in the soil 8 to 10 days after mating.

Several eggs may be laid in a single mass, with each egg in a small ball of dirt. They hatch in
2, or 3 weeks. Egg laying continues over a period of several weeks during spring and summer.

Grubs, hatched from the eggs, feed first on organic matter in the soil, but soon attack the
tender roots of seedlings and other plants. After hibernating in the soil during the winter at
depths determined by temperatures and frost levels, the grubs resume feeding when plant
growth starts.

Adults of most Phyllophaga species emerge from the soil at dusk on warm evenings and fly to
the foliage of trees. Here they mate and feed until dawn, then return to the soil.

Natural Control
White grubs are very sensitive to lack of moisture. They move up or down in the soil as
moisture conditions change, in an attempt to remain in a habitat with optimum moisture.

Protracted drought causes heavy larval mortality, especially among the newly hatched larvae.

Although the grubs have enemies, such as insect parasites and predators and fungus diseases,

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