70 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 16 
might be effected; for, if the insect did not appear in sufficient numbers 
to threaten a serious outbreak after the first treatment, the subsequent 
applications might be omitted. With screening the total yearly cost is 
fixed irrespective of the abundance of the pest. On the other hand, the 
screen, if properly constructed, insures complete freedom from maggot 
injury as well as affording protection in a large measure from certain 
other pests, such as the flea beetle, besides stimulating the plants to more 
rapid growth than where produced in the open. 
In the use of mercuric chloride certain precautions must be observed. 
If the first application is made too soon, just as the young plants are 
pushing through the ground, there is danger of severe burning. In 
some cases fifty percent or more of the plants so treated have been lost 
in this way. This risk, however, is greatly reduced when the first ap¬ 
plication is deferred until the young plants are well through the ground. 
If three or four days or even a week is allowed, there appears to be com¬ 
paratively little danger unless the season is unusually backward and 
the germination very uneven. After the first application even excessive 
doses appear to have little effect on the plants, although occasionally 
a slight stunting is noticed from which, however, the plants quickly 
recover. 
Although a number of materials were tried out on cabbage seed-beds 
in the course of this work, only one of the tests with mercuric chloride 
Plan and Treatment of Experimental Plats 
Plat Row Seed-bed Times treated Date 
1 1 -- 1 -— 5-2 
2 - 2 — 
3 -— 3 — 
5-10 
5-18 
1 
4 
5 
6 
4 
5 
6 
5 - 26 
6 - 4 
6-12 
7 
8 
9 
10 
11 
1 
2 
3 
4 
5 
5-10 
5-18 
5 - 26 
6 - 4 
6-12 
12 
13 
14 
15 
1 
2 
3 
4 
5-18 
5 - 26 
6 - 4 
6-12 
16 
17 
18 
1 
2 
3 
5 - 26 
6 - 4 
6-12 
19 
20 
1 
2 
6-4 
6-12 
21 
Check 
6-12 
Fig. 1. Diagram showing arrangement of plats in 1921 cabbage-maggot exper¬ 
iments, with respect to number and frequency of applications for each mateiial to 
be tested. 
