I8 MISC. PUBLICATION 657, U. S. DEPT. OF AGRICULTURE 
and young plantations, more expensive methods of protection are Justi- 
fied than can be practiced in the forests or natural stands of reproduc- 
tion. Under certain circumstances the use of insecticides and special 
tools or appliances are feasible, as is a considerable amount of hand 
labor. Soraci (395) in 1987 published a circular on control of insects 
in the nursery. 
INSECTS FEEDING ON ROOTS 
Some of the most serious nursery pests, and the most difficult to con- 
trol, are insects that feed on the roots. White grubs, certain weevils, 
and termites are among the worst offenders, with minor damage by 
wireworms and borers. Soil poisons or fumigants offer the best possi- 
bilities for control, but in their use there is always danger of injuring 
the seedlings. Experiments by St. George (370) indicated that @¢ is 
dangerous to use crude white arsenic or lead a senate as a soil poison in 
seedling nurseries, since the arsenic will remain in the soil and continue 
to cause injury for a number of years. 
White Grubs 
The best control of white grubs has been obtained with commercial 
carbon disulfide injected into the seedbeds, but flooding the infested 
area with 50-percent miscible carbon disulfide has given some success 
on small areas. In the use of either form of the chemical, the results 
vary in different soils and under different soil temperatures and mois- 
ture conditions. Since the grubs go deep during the winter and soil 
temperatures are too low for successful control, these methods can 
be used only during warm summer weather when soil temperatures are 
high and when the larvae are feeding within a few inches of the sur- 
face. Y oung seedlings are more susceptible to chemical injury than 
older ones, but under certain conditions older stock may be damaged. 
It is therefore advisable to test the chemicals on a small area of the 
same soil before large-scale control is undertaken. 
Straight carbon disulfide injected into the seedbeds at the rate of 1 
pint per 100 square feet is, under many nursery conditions, an effective 
control and causes negligible chemical injury to pine seedlings. The 
depth of penetration of the chemical depends somewhat on the nature 
of the soil. 
In addition to being extremely poisonous, the vapors of carbon 
disulfide are highly inflammable and explosive and will ignite at 
temperatures as low as 212° F. 
To obtain maximum grub control and minimum chemical damage to 
the seedlings in sandy “soil or sandy loam, the following conditions 
must be complied with: (1) The soil should be moist, loose, and friable 
(conditions suitable for cultivation) with a moisture content of not 
more than 15 percent. Do not water within 1 hour after treating and 
do not treat immediately before or after rains, as such conditions re- 
sult in severe chemical injury to the seedlings, (2) the temperature of 
the upper 6 inches of soil must be 78° F. or ‘above for successful con- 
trol of the larvae, (3) the chemical should be injected into holes 3 to 4 
inches deep, spaced 6 by 6 inches apart, at the rate of 1.2 cc. per hole. 
