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Another point that should be brought out here is that the four trees treated with carbolineum in the experimental plot in 1913-14 were not attacked during the summers of 1914 and 1915, and only a single larva was found in them during 1916. This would indicate that carbolineumtreated trees are not readily selected by the females for oviposition, provided untreated trees are available. This point will be further investigated by the writer.
* In determining the infestation of the treated trees, not all the 14,000 trees were examined. Rows were selected in different parts of the block and every tree was examined carefully. In this way 1161 trees were closely scrutinized and not a sign of borer work could be found. The figures in the table are based on the result of this examination. In the second examination a single larva was found at work on one of the treated trees, but as this was the rare exception the fact has been ignored in the percentage column.
TABLE 4. RESULTS OF EXPERIMENTS OF 1915-16
* Only 1560 trees were examined, but these were selected rows and the percentage of infestation is fairly accurate,
The results of the treatment of the second block of about an equal number of trees are shown in table 4. In this block the results were extremely interesting, showing most conclusively the effectiveness of the carbolineum treatment. The writer visited this nursery and showed the owner the method of treatment but did not further supervise the work. In treating the trees on the following day the workmen failed in many cases
- he did not know the exact shown by the percentage of infestation found on June 23. During the and wherever sufficient material was applied most of the larvæ were killed. The trees then readily outgrew the injury. The carbolineum had
to cover the base of the trees with the material, and also failed to apply it sufficiently high on the trunk. As a result all the infestations, amounting to nearly 1.3 per cent, occurred either at the base or above the highest point of treatment. This is well shown in figures 126, 127, and 128.
Another interesting point in connection with this block is in regard to the check row. This row, running through the center of the block, contained 639 trees. When the owner saw the excellent results in the treated trees, he asked himself why he should not save most of the trees in the
FIG. 128. TREE SEVERELY INJURED AT BASE, DUE
TO LACK OF TREATMENT THERE check row. Therefore on June 3, 4, or 5 date - he treated 555 of these trees, leaving some at either end as a true check. The treatment, even at this late date, had a marked effect, as first week in June all the larvæ were still at work in the cambium layer, no apparent effect in retarding growth.
Method of application of carbolineum After many trials it was found that the simplest method of application of carbolineum was by the use of cotton waste. Carbolineum is noninjurious to the hands, and each workman carried a small quantity of the material in a dipper or a tin can. The cotton waste was dipped into the material and then rubbed carefully up and down the trunk of the tree. It is usually not necessary to go higher than four or five feet, but great care should be exercised to see that the base of the tree is well treated and all parts of the trunk are well covered. At the same time the material should not be allowed to run down to the roots. After the trees are pruned workmen can apply the material at a very rapid rate.
It is preferable to make the application on a warm day, as under this condition the carbolineum is thinner and may be more easily applied.
Cost of treatment It was at first thought that the cost of the treatment might prevent its use under nursery conditions, inasmuch as poplars are not very highpriced stock. In one nursery a careful account of the entire cost of treatment was kept. This was as follows: Labor, treating 14,000 trees . .
$18.50 Carbolineum, 7 gallons at go cents.
6.30 Total cost ...
$24.80 Total cost per tree.
$0.00177 It is thus seen that the cost per tree is extremely small, not exceeding two-tenths of a cent -- a practically negligible charge.
The poplar and willow borer is a European pest recently introduced into America and at present widely distributed in the northeastern United States. It is proving a serious pest not only in nurseries but also wherever willows or poplars are grown.
A very effective means for control of the insect is the use of carbolineum ayenarius. In nurseries this should be applied by hand during the latter part of March or the first week in April. The work can be done most advantageously just after the trees are pruned.
In setting out poplar trees they should be treated with carbolineum in order to insure the destruction of all larvæ present. This can be done either in the fall or in the spring while the trees are dormant.
The item of cost has been shown to be extremely small, not exceeding two-tenths of a cent per tree under nursery conditions.
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