. Bulletin of the Department of Agriculture. Agriculture. DOUGLAS FIR PITCH MOTH. 13 shake " in larch above a few feet from the ground is practically nonexistent, since this tree, more than any of our conifers, is, if healthy, immune to insect attack, except to the foliage, and, if at- tacked, is more able to repulse the onslaught from the outset, " Lightning " has been included in the same category with " wind- shake " as a cause of pitch seams in Douglas fir. The theory that lightning is a causative agent refutes itself by mere examination of the damaged materia
. Bulletin of the Department of Agriculture. Agriculture. DOUGLAS FIR PITCH MOTH. 13 shake " in larch above a few feet from the ground is practically nonexistent, since this tree, more than any of our conifers, is, if healthy, immune to insect attack, except to the foliage, and, if at- tacked, is more able to repulse the onslaught from the outset, " Lightning " has been included in the same category with " wind- shake " as a cause of pitch seams in Douglas fir. The theory that lightning is a causative agent refutes itself by mere examination of the damaged material. It is the lower two-thirds of the tree trunks which are seriously pitch seamed, while the upper part is almost invariably free from the defect, and it is not reasonable to assume. Fig. 7.—Development of a " pitch seam " only four years after the emergence of the Douglas fir pitch moth. Note the enormous growth the tree put forth to cover the wound. Greatly reduced. (Original.) that the electric spark would persistently leave the tops untouched and so frequently injure only the part below the branches. Another point in this regard is the fact that judging from the location of the seams in the trunks the trees could not have been of very great size when the defect occurred. A casual stroll in the woods will convince the most heedless observer that it is not the younger trees which are most subject to lightning. It is evident from the foregoing that infestation of a tree by the Douglas fir pitch moth does not result in immediate financial Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original United States. Dept. of Agriculture. [Washington, D. C. ?] : The Department : Supt. of Docs. , Govt. Print. Off.
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectagriculture, bookyear
