536 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 17 
adding an amount of dry glue equivalent to two per cent of the weight of 
the lime sulfur solution used. The glue should always be added in solu¬ 
tion and prior to the acid otherwise little good is accomplished. 
Experimental Work 
Sulfur in the colloidal form particularly the hydrophilic solution, is 
more dangerous to foliage even than lime sulfur solution. At high tem¬ 
peratures (80°-95° F.) 1 per cent and 0.8 per cent concentrations injured 
almond foliage, which is quite resistant to sulfur. Peach foliage was 
slightly yellowed at 0.5 per cent although apricot, plum, apple and 
orange were uninjured at this concentration over a period of two weeks. 
The maximum temperature during this time was seldom over 80°F. 
Since sulfur has been commonly used at the rate of five pounds of the 
material to 100 gallons (approximately 0.6 per cent concentration), a 
comparison at low temperatures of the standard spray of lime sulfur 1 
per cent plus five pounds of sulfur and colloidal sulfur solutions 0.6 
per cent was made. The results given in Table II show almost perfect 
control for all three colloidal sulfur solutions while the lime sulfur solu¬ 
tion plus free sulfur dropped to 90.6 per cent and the ground sulfur, to 
44.9 per cent. These striking results were intensified by the low tem¬ 
perature at which the work was conducted and show the superiority of 
the colloidal form especially over dry sulfur, under conditions where 
sulfur in the coarser form is not very active. Experiments at higher 
temperatures showed less difference but even then the colloidal forms 
were always superior. Good control was also obtained in laboratory 
experiments at concentrations as low as 0.06 per cent, one-tenth that at 
which the data are given. The weaker concentrations offer the possi¬ 
bility of treatment for plants that are quite susceptible to sulfur injury. 
Little difference will be noted in the adaricidal value of hydrophilic and 
hydrophobic solutions when extended over a period of nine days; al¬ 
though for shorter periods the difference ranged from eleven to thirteen 
per cent. 
Under California conditions where most of our control work on red 
spider is done at high summer temperatures, it is doubtful if colloidal 
sulfur solutions could be economically substituted for lime sulfur solution 
containing free sulfur, at least until an inexpensive process of manu¬ 
facture is established. Finely divided precipitated sulfur either as a 
paste or in the dry form may be a more satisfactory form than true 
colloidal solutions. The latter, however, may find a place for use in the 
early spring or in regions where low temperatures retard the oxidation 
