Aug. 1,1924 
The Greenhouse Leaf-Tyer 
157 
Even though there has been no 
opportunity to test this treatment on 
a commercial scale, the indications are 
so promising that it seems desirable 
to include the use of nicotine dust in 
the control program. The plants are 
not injured, and the moths and some 
of the younger larvae hit by the dust 
are killed. Moreover, because of the 
ease of application many florists will 
no doubt prefer to use the dust rather 
than fumigate with hydrocyanic-acid 
gas. 
SUMMARY AND CONCLUSIONS 
The preceding data bring out certain 
features which may be used as a basis 
upon which to formulate a definite 
control program. Briefly summarized, 
the life-history studies show that this 
insect breeds practically without inter¬ 
ruption, and that all stages are likely 
to be found in greenhouses throughout 
.most of the year. The destruction 
-of plants is due to the feeding of the 
larvae, which later increase the injury 
by tying themselves up in the foliage 
prior to pupation, thus causing further 
disfigurement and consequent decrease 
in commercial value. The pupae are 
well protected by the formation of the 
pupal case within tied leaves lined 
with a rather tough silken cocoon. 
The adults are nocturnal in habit. 
The results of the control experiments 
indicate (1) that the adults may be 
successfully controlled by fumigation 
with hydrocyanic-acid gas, or by dust¬ 
ing with a 5 per cent nicotine sulphate 
dust; (2) that the eggs are impervious 
to contact insecticides; (3) that the 
larvae succumb to the effects of arsenical 
poisons when applied either in the dry 
or liquid form, and (4) that the pupae 
are virtually immune from all artificial 
control measures, except hand picking, 
because of their protection and resist¬ 
ance. It is evident, therefore, that an 
effective control program necessitates 
simultaneous direction of efforts against 
the susceptible stages, which are the 
adults and larvae. 
RECOMMENDATIONS 
In case of a heavy existing infesta¬ 
tion the following drastic control 
measures are recommended: Fumigate 
after dusk twice at intervals of seven 
days with hydrocyanic-acid gas, using 
1 ounce of sodium cyanide per 1,000 
cubic feet of air space, with an exposure 
lasting for one hour. The first fumi¬ 
gation will operate against all moths 
which are present at the time of fumi¬ 
gation, and the second will kill all 
moths which have emerged since. The 
day following the first fumigation the 
plants should be treated with the 
arsenical insecticides as outlined in the 
paragraphs below. 
When it is not feasible to fumigate 
with hydrocyanic-acid gas, persistent 
dusting with a 5 per cent nicotine 
sulphate dust is recommended. 
For plants which are well developed 
and of large size, or growing in per¬ 
manent beds, dusting with a dry 
mixture consisting of 1 part of calcium 
arsenate or arsenate of lead and 9 
parts of superfine sulphur is very 
effective, and should be applied by 
means of a modern type of hand 
duster or blower gun. This treatment 
has the advantage of sifting the 
insecticide through the webbing which 
the larvae spin, as well as poisoning 
the leaf surface on which they feed. 
It possesses the additional advantage 
of overcoming the unsightly deposit 
which follows the application of liquid 
arsenical sprays. 
For low-growing or potted plants, 
spraying with lead arsenate or calcium 
arsenate solution, prepared by dis¬ 
solving 1 ounce of the powdered form 
in each gallon of water used, is re¬ 
commended. Spray solutions are de¬ 
sirable for the treatment of the smaller 
plants because the entire plant may 
be dipped directly in the solution or 
else sprayed with a knapsack or 
compressed-air sprayer, an angled 
nozzle being used so that the spray 
can be directed to all surfaces of the 
infested foliage. 
The most important considerations 
in controlling the larvae or caterpillars 
are promptness and thoroughness in the 
applications of the poison, especially 
to the under side of the leaves where 
the larvae feed. Since the young 
larvae are less resistant to the insec¬ 
ticides soon after hatching and before 
they become webbed-in on the leaves, 
they can be more easily destroyed at 
this stage and, moreover, there is 
less risk of the plants becoming 
seriously disfigured. After the webbing 
is formed it is difficult to coat the 
foliage with a liquid spray because 
the silken fibers prevent the insecticide 
from reaching the leaf. It is also 
imperative that the plants be kept 
constantly covered with the spray. 
In case of a light infestation, or one 
which is discovered in its incipiency, 
going over the plants daily and 
picking and destroying any that may 
be found will prove effective. 
