20 CIRCULAR 639, U. S. DEPARTMENT OF AGRICULTURE 
from within. Even under these conditions the walls and top are of 
much benefit from the standpoint of hornworm control. Many of 
the moths which emerge within shades go to the walls, where they 
remain inactive during the daytime. The majority seek shelter in 
the shade corners, where they may be found clinging to the cloth or 
to a post. A beneficial practice is to inspect the inside of shade 
walls each morning and kill all moths found. 
The tops and side walls of shade structures are a great protection 
not only against hornworms but also against budworms, grasshoppers, 
and several other tobacco insect pests. “Any breaks in the cloth should 
be patched promptly, and all possible efforts should be made to keep 
the fabric intact throughout the growing season. The side walls 
should be fastened closely to the ground and should be so constructed 
that the cloth will not tear where it comes in contact with the posts. 
The practice of raising the walls to permit the entrance of wagons 
and farm implements is not to be recommended. The cloth-covered 
gates that provide entrance to shade fields should be kept closed as 
much as possible, and especially during the night and early part of 
evening when the moths are active. 
Efforts are being made to find a hornworm insecticide that is safe 
and efficient, and which leaves no disfiguring residue on the cured 
tobacco. No such material is yet available. The poison which comes 
nearest to fulfilling these requirements is paris green, the main 
disadvantage of which is its severe burning qualities. If this arsen- 
ical is not used with extreme caution, its application may cause more. 
harm than benefit to a crop of shade-grown tobacco. Owing to the 
hazard involved, it is considered advisable to omit applications of 
paris green on tall tobacco until after the valuable middle leaves 
have been harvested. The few hornworms that usually occur on shade- 
grown tobacco previous to this time should be picked off by hand. 
Paris green is appled by means of rotary hand dusters. The 
dust gun ‘nozzle is held in the center of the space between the tobacco 
rows so that the dust drifts through the foliage and settles on the 
leaves. When applications are made to tall tobacco the nozzle of 
the dust gun is directed upward at an angle of about 45° and to the 
rear of the operator (fig. 22). Applications of undiluted paris green 
are made at the rate of about 1 pound per acre. Higher dosages of 
the poison are made only at considerable risk to the crop. It is a 
difficult matter, however, to maintain an even distribution of paris 
green with a maximum dosage rate of 1 pound per acre. 
The burning hazard of paris green may be somewhat decreased by 
mixing 1 pound of the poison with 6 pounds of hydrated lime. The 
mixture should be applied at the rate of about 4 pounds per acre. 
In this manner a smaller quantity of paris green is applied than 
when the poison is used undiluted. Paris green or mixtures of this 
arsenical and lme should be apphed to the tobacco foliage only 
when it is dry. 
j CONTROL ON SUN-GROWN TOBACCO 
The 1-to-6 mixture of paris green and lime previously mentioned 
may also be used to combat hornworm attacks on sun-grown tobacco, 
but its use is not entirely satisfactory. The poison and lime should 
be thoroughly mixed and appled with an efficient rotary duster. 
On sun-grown tobacco the applications may be made while the fohage 
