72 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 16 
A single application, while greatly reducing the amount of injury and 
giving fair commercial control, failed to prevent injury amounting to 
nearly ten percent of the total number of plants involved. The second 
application for 1922 gave results distinctly inferior to that made a week 
earlier, while the plats treated after this time were not greatly superior 
to those receiving no treatment at all. 
In 1921, on the other hand, where the infestation was much more 
severe, two early applications were necesary to secure results comparable 
to those secured with a single one during 1922. Three applications were 
required in 1921 to insure a perfect stand, while treatments made late 
in the season were correspondingly less effective than in 1922. 
This difference in degree of control shown by the mercuric chloride 
treatment during two seasons when the pest was unequally abundant, 
suggests that a certain amount of caution may not be out of place in 
adapting this method to the treatment of cabbage seed-beds. If three 
applications were required during 1921 to give the same results secured 
the following year with but two treatments, might not even three dosages 
prove inadequate during one of those seasons which may be expected to 
occur periodically when the insect is present in overwhelming numbers. 
In any case, until the method has been given a trial during such a 
season, it is probably not wise to advise its unqualified substitution for 
the cheesecloth screen. 
Table 1. Control of Root Maggot in Cabbage Seed-Bed During 1921 
(Mercuric chloride used at rate of 1 ounce to 10 gallons water) 
Plat 
Row 
Number of 
applications 
per row 
Date of 
final 
application 
Number of 
plants 
counted 
Number 
infested 
Number Percentage 
clean clean 
plants 
1 
1 
5-2 
210 
63 
147 
70.00 
2 
2 
5-10 
196 
17 
176 
91.19 
3 
3 
5-18 
167 
0 
167 
100.00 
1 
4 
4 
5-26 
190 
0 
190 
100.00 
5 
5 
6-4 
193 
0 
193 
100.00 
6 
6 
6-12 
240 
0 
240 
100.00 
7 
1 
5-10 
239 
78 
161 
66.94 
8 
2 
5-18 
235 
25 
210 
89.36 
2 
9 
3 
5-26 
203 
24 
179 
88.17 
10 
4 
6-4 
204 
17 
187 
91.66 
11 
5 
6-12 
312 
30 
282 
90.38 
12 
1 
5-18 
191 
120 
71 
37.17 
3 
13 
2 
5-26 
200 
86 
114 
57.00 
14 
3 
6-4 
166 
82 
94 
56.62 
15 
4 
6-12 
236 
145 
91 
38.59 
16 
1 
5-26 
170 
108 
62 
36.47 
4 
17 
2 
6-4 
184 
92 
92 
50.00 
18 
3 
6-12 
250 
155 
95 
38.00 
5 
19 
1 
6-4 
172 
132 
50 
29.07 
20 
2 
6-12 
232 
173 
59 
25.43 
6 
21 
1 
6-12 
268 
206 
62 
23.31 
Check 
1245 
902 
334 
26.82 
