MISSOURI BOTANICAL GARDEN BULLETIN 21 
CoMMON NAME TREATMENT FREQUENCY 
Hollyhock rust ....... Permanganate of potash 
(2 tsp. saturated solu- 
tion diluted in 1 qt. 
WEILER) iiss Fb oe 5 04 ve 
Lilac powdery mildew. Sulphur ...........---- 
Mignonette spot ...... Bordeaux mixture...... 
Lettuce downy mildew. Sulphur .........-..--. 
Onion smut .......... Formaldehyde treatment 
Of “BOI seh en ees 
Palm spot and tip burn Bordeaux mixture...... 
Peach curl ........... Lime-sulphur .......... 
Peach brown-rot ..... Self-boiled lime-sulphur. 3 times in winter 
Potato late blight..... Bordeaux mixture...... 5 times 
Potato scab .......5.% Bordeaux mixture...... 5 times 
Primrose diseases ..... Bordeaux mixture...... 
Privet twig-blight ..... Lime-sulphur ........-- Early spring 
Rose black-spot ...... Ammoniacal copper car- 
Honwkte si. oe Ve a tes 
Rose powdery mildew.. Sulphur ...........-++- 
Snapdragon wilt ..... Bordeaux mixture...... 
Tomato leaf-spot...... Bordeaux mixture...... 
Verbena powdery mil- 
op ME ee Potassium sulphide..... 
Violet leaf-spot ....... Bordeaux mixture...... ‘ 
Water-lily spot ....... Soda Bordeaux (effective 
in removal of algal 
growth as well).....- 
The use of chemicals for destruction of insect pests had 
its origin with the advent of the Colorado potato beetle, 
about 1870. The spread of this insect was so rapid that it 
was feared that growing of potatoes was doomed. A trial 
of spraying the tops with Paris green succeeded so well that 
it gave rise to the use of chemicals for the control of other 
rapidly increasing insect pests. At present the methods of 
control have developed so as to embrace the majority 
of injurious insects and have relieved the plant world 
to a certain extent of the depredation caused by these para- 
sites. 
The application of chemicals for control is based upon 
the understanding of the feeding habits of the insects as 
well as partially upon the life histories and internal struc- 
tures of their bodies. The insects may be divided into two 
oups according to their feeding habits—the chewing and 
the sucking. The former have biting mouth parts con- 
structed to eat the foliage, and usually may be killed by 
an application to the foliage of stomach poisons. The best 
of such poisons are Paris green (5 ounces Paris green, 1 
pound lump lime, 50 gallons water) ; arsenate of lead (2 
pounds to 50 gallons water) ; and hellebore (1 ounce to 
1 gallon water). Of these, the arsenate of lead is the most 
