Chapter III: Part 3

The native chestnut tree is properly regarded as the best forest tree remaining in a large quantity in Pennsylvania. The presence of the deadly chestnut tree bark disease throughout eastern and central Pennsylvania counties, and the actual and immediate necessity for a concerted and active warfare against this parasitic disease in order to prevent the threatened total extermination of the chestnut tree in the Keystone State, naturally awakened the editorial fraternity and other advocates of forest conservation to the great importance of aiding in the fight to control and eradicate the disease.

It is admitted by scientific authorities that had the necessary work towards stamping out the blight been inaugurated by other states at the proper period, Pennsylvania’s extraordinarily heavy loss could have been confined to a minimum. It is believed however, that the Commonwealth has already sustained a loss through the partial destruction of chestnut, aggregating a total of $70,000,000, of which enormous amount Eastern Pennsylvania timber owners suffered the heaviest burden. The proverbial “ounce of prevention” was sadly ignored, and hence, the deplorable conditions that rapidly followed this costly neglect of duty. Although the Keystone State has ceased its activities in its efforts to save this invaluable species of trees from destruction, the National Department of Agriculture and a dozen other states are continuing the work with renewed energy, confidently believing that the interests of timber owners and the public in general deserved such recognition and protection. Many taxpayers who were compelled to wage warfare against the spread of the blight at their personal expense report gratifying results, thus again demonstrating that by prompt action and thorough work, the parasite might have been controlled and these extraordinary heavy financial losses averted.

Oliver D. Schock, Assistant Superintendent, was in charge of this important publicity department. Grateful acknowledgments are due to the newspaper editors for their continued and liberal co-operation. It is equally gratifying to know that there was but little, if any unfavorable criticism by the press of the entire State of the methods pursued by the Commission in combating the blight.

Report of
Samuel B. Detwiler
General Superintendent Pennsylvania Chestnut
Tree Blight Commission

OBSERVATIONS ON SANITATION CUTTING IN CONTROLLING THE CHESTNUT BLIGHT IN PENNSYLVANIA.

By SAMUEL B. DETWILER,

GENERAL SUPERINTENDENT OF THE PENNSYLVANIA CHESTNUT TREE BLIGHT COMMISSION.

INTRODUCTION.

In view of the continued rapid spread of the chestnut blight, and the great damage sustained through this relentless parasite, it is important at the present time to have more complete information on the possibility of controlling its spread. It is now an established fact that the disease exists in China, and that it was probably introduced into America from the Orient. This disposes of the theory that the blight is caused by a native fungus, originally a saprophyte or weak parasite, which gained vigor, or appeared to gain vigor because of the decadence of the native chestnut trees from the effects of drouth and winter injury. It is evident that it would be difficult, if not impossible, to control a native fungus of wide dissemination, with predisposing factors in its favor. But even the most severe critics have acknowledged that foreign origin of the parasite affords “at least some basis for the fight for control.”[9]

[9] Clinton, G. P. Science 36: pp. 907-914, Dec. 27, 1912.

HOW THE BLIGHT SPREADS.

The pathological investigations of the Commission have shown that wind, water (rain), and birds are the principal agencies in disseminating the blight. A single spore thread may produce from 100,000,000 to 200,000,000 pycnospores, and even a small canker produces dozens of spore threads in a season. A single perithecium has been observed to eject ascospores almost continuously for a period of 26 days, at the rate of 4.7 spores per second. Insects assist by making wounds through which the spores of the fungus enter the bark, and also, to some extent, by distributing the spores locally. The ejection of ascospores into the air following rain, and the washing of pycnospores down the trunks and into the soil during rain, appear to be the principal agencies in spreading the disease. Birds have been proved to carry spores in great numbers, and undoubtedly are responsible for a certain proportion of infections, at least, of advance infections.

The planting of diseased nursery stock in regions free from the blight appears to be one of the principal agencies in spreading the disease to great distances. The disease was probably introduced into this country on nursery stock, and in the early years, nursery stock apparently played the most important role in getting the disease quickly and firmly established. This point is well illustrated by a shipment of three chestnut trees sent from a New Jersey nursery into Western Pennsylvania in 1912. Through a misunderstanding, these trees were not held at the State line for inspection, but were carried direct to their destination. When the inspection was made, the disease was found at two places on one of the trees, although the nurserymen claimed to have carefully examined the trees before shipment. At Warren, Warren county, Pennsylvania, 11 out of a shipment of 12 nursery trees purchased in 1910 were found affected with the blight in 1912. In Elk County, 34 diseased nursery trees were found in a young chestnut orchard, and the disease had already reached adjoining native chestnut trees. In Somerset County, there is evidence to support the belief that an infected area covering about one-third of the county spread originally from diseased scions grafted on native trees. There are many similar occurrences outside of Pennsylvania.

All observers have noted that the blight advances by attacking widely separated trees far ahead of the generally infected territory. In Pennsylvania, the main spread of the blight has been from the southeastern corner of the State. During rains and immediately following, when the spores are being ejected, the wind is usually from the south or east, thus tending to carry the spores north and west. At least, it is a matter of common observation that the southern and eastern edges of woodlots very frequently show the first infections.

In order to learn more about the spread of the blight, two areas in the region of general infection, one in the Mahoning Valley in Carbon County, and the other in the vicinity of Topton Mountain, in Berks county, were studied in the spring of 1913 by Mr. J. Wesley Sitler, a field agent of the Chestnut Tree Blight Commission.

By J. Wesley Sitler, June, 1913.]

STUDY OF BLIGHT CONDITIONS IN THE MAHONING VALLEY.

In the Mahoning Valley, all timber tracts on an area about 7 miles square were mapped on a large scale topographic sheet, (Fig. 1). In round numbers this investigation covered about 50 square miles of land which varied widely as to elevation and geological formation. Spot infections of blight were accurately located on the map, and each spot was studied in detail as to the percentage of surrounding infection, slope, exposure, soil, character of the stand of timber, and surface features. Originally chestnut oak and yellow pine occupied the steeper upper slopes, while the more gentle and fertile lower slopes were covered with a stand consisting of 50 to 70 per cent. chestnut, with a mixture of red oak, maple, and white pine. Very little chestnut grew in the valleys where the forest consisted of heavy stands of white oak, white pine, red oak, and maple. All of the flat bottom land and much of that along the lower slopes has been cleared for farming, so that part of the area studied consisted of woodlots with trees varying in size from small coppice to 20 inches in diameter. The area is traversed by several ridges extending northeast and southwest, and the poor rocky soil of these ridges, particularly north of the Mahoning Valley, is covered with young coppice of oak and chestnut, or with scrub oak brush. Forest fires frequently burn over the ridges and the young growth is therefore in poor condition.

At present no tract can be found on the area studied that is entirely free from blight, but the chestnut trees south of Mahoning Valley are diseased more than the stand north of the valley. The southern slopes of the ridges, also the south and east portions of exposed woodlots, are more seriously infected than the northern exposures. There are thousands of cicada wounds in twigs of all species growing in these woods. These wounds were made during the invasion of 1911. It is very common on chestnut to find such wounds infected, and the cicada has thus undoubtedly aided in the general distribution of the blight throughout this region.

Every tract of chestnut timber showing the presence of blight, when carefully examined, shows that the disease appears in spots. By careful observation, the source of infection for the entire spot can be traced to one or more badly infected trees which evidently bore the original infection of that particular area. Such a tree or group of trees is commonly referred to as an infection center, because from such centers the disease advances in all directions. The age of these centers can be determined quite accurately from the appearance of the original infection, by the concentric rings of cankers and by the age of water sprouts and shoots at base of cankers. Generally, the older the infection, the further it has spread from the center.

Many of these infection centers have been carefully worked over, but nothing definite can be said as to characteristic elevation, soil conditions, exposure, or character of woods. Probably 90 per cent. of these centers are found in the shallow depressions at the heads of gullies; or, where a ridge slope forms a terrace-like flat. However, it is evident from a large number of observations, that such centers develop under any surface conditions favorable to the growth of chestnut. They are found on well drained gravel slopes, dry knolls, steep rock slopes, and in low fertile flats.

The spread of the blight seems more rapid in young coppice growth of nearly pure chestnut, than in a chestnut stand of large trees. In old stands the percentage of infected trees decreases abruptly from the infection center outward. Often, a distance of twenty rods will take one from an area of 40-50 per cent. infection to a zone of one-fourth per cent. and beyond that no infection may be found. In coppice growth the decrease is more gradual and a zone showing less than 8-10 per cent. infection can seldom be found on a tract with an infection center. The abundance of bast miner galleries in the bark of young smooth-barked chestnuts probably explains the wide and even distribution of the blight in such stands.

The importance of wind as an agent in disseminating blight cannot be positively stated, but from observations made in this locality there seems more evidence favoring wind distribution than any other factor. The result of a large number of comparative observations show that:—

1. A large number of infections are in wounds made by cicadas and are usually uniformly distributed around a blight center.

2. New infections are generally scattered through areas of young shoots growing up after fire.

3. Freshly cut stumps with their new sprouts show a high per cent. of infection even where the surrounding woodland is little affected.

4. Trees standing in exposed places, such as isolated trees in fields, and trees along southern edges of timber tracts, show a high per cent. of infection.

Very little can be said about birds as carriers of blight. Numerous scattered spots of infection show signs of having been started by bird distribution. However, the observations gave little reliable evidence on this point. Many spots have a large, dead-topped tree standing near the center. Often these trees have been infected on the lower branches, longer than any of the surrounding trees. The dead, snaggy tops show no evidence of death from blight. There is reason to believe that birds were attracted by the open snag and carried the spores which later started the infections in the lower branches.

This locality furnishes numerous opportunities for comparing the percentage of infected trees on the north and south slopes. The stand of chestnut is similar on the two slopes. The results of detailed examinations show that there is more blight on the south slopes. Also, many of the woodlots show a higher per cent. of infection on the southern borders. To strengthen these observations several miles of the Blue Ridge, (lying north of the Mahoning Valley, and not included in the area studied), were also worked over, (Fig. 2.) This ridge is higher than any other within the limits of area studied, and shows the typical high percentage of blight on the south slopes, up to the summit. Immediately across the summit, northward, the number of blighted trees decreases. However, at the base of the north slope in almost pure chestnut, it increases but does not average more than 60 per cent. of the amount of infection at the base along the south side. There is a general decrease in the amount of infection on each successive ridge to the north.

There are distinct differences in the moisture conditions in this region. The stream valleys often have a clay loam soil too heavy and moist to support chestnut. We find all variations in soil and moisture from these valleys to the dry, rugged ridges where chestnut oak and scrub oak form most of the stand. The amount of infection apparently does not depend on soil moisture, as is shown by the percentages on the infection map. Tracts lying in the valleys show similar percentages of infection to those on higher ground. The theory that chestnut trees growing on or near limestone soils are resistant to blight is not supported by these observations. A belt of limestone borders Lizard Creek Valley on the south, and the per cent. of infection is as high in that region as elsewhere. Infection centers have been found near limestone quarries, where the roots of the chestnut penetrated to bed rock.

INFECTION POINTERS.

1. Each successive ridge shows a decrease in the number of old infections, from the Blue Ridge northward.

2. There is more blight along the south slopes than on the adjacent north slopes.

3. Recently cut stumps with their sprouts show a high per cent. of infection even where adjacent tracts are clear of blight.

4. Centers of infection are found under all conditions. Slope, exposure, drainage, rock formation, and fertility of the soil seem to have no relation to origin of infections.

5. A large number of infections one and two years old began in wounds made by cicadas in 1911.

6. Wind appears to be the most important factor in the dissemination of the blight. Birds may be factors as carriers of the original infecting spores, but cannot be blamed for the local distribution of the blight around an infection center. This distribution is very uniform, which presumably would not be the case had birds been the principal carriers of the disease. In young coppice growth much wounded by cicadas, the wounds on the twigs are the chief points of entrance for the disease. Results of accurate counting show that on certain tracts 80 to 90 per cent. of new infections began in such wounds made by the 17-year cicadas during their invasion of 1911. Many new infections are at and near the bases of young sprouts, and there is little cause to believe that these were due to birds, since they are usually about the same age and at points that birds are not likely to frequent. Also, this condition exists on exposed north slopes little visited by birds. The most plausible explanation seems to lie in the hypothesis of wind dissemination. This explains the numerous infections starting in cicada stings; also the rapid spread over a tract of young sprouts; the common occurrence of new infections on trees standing alone, in exposed places. The greater quantity of infection on south slopes appears to be due to the fact that the prevailing winds are southerly and easterly during the periods when ascospores are extruded in greatest numbers.

STUDY OF BLIGHT CONDITIONS ON TOPTON MOUNTAIN, BERKS COUNTY.

The highest point of this mountain rises about 600 feet above the base, the summit being 1,230 feet above sea level. The long axis of the ridge runs about 15 degrees north of east, the east end of the ridge terminating abruptly. The area studied comprises about 2,000 acres, about 600 of which are cleared, and the balance bears a dense stand of timber which is mainly coppice growth between 10 and 25 years old. On the summit, and the upper and middle slopes, chestnut is the predominating species, forming 80 to 90 per cent. of the stand. Below this is a zone in which chestnut and chestnut oak constitute the stand in about equal proportions. At the base of the mountain there is a narrow, irregular belt of tulip, butternut, red oak, and ash, with a very low per cent. of chestnut.

Strips four rods wide were run north and south across the mountain, and also in an east and west direction over the top and along the sides. Observations were made of all the chestnut trees on each strip acre. In this way the tract was gridironed, and a fairly comprehensive idea obtained of the relative amount of blight in the various portions of it. (Fig. 3).

Scale 2.75 inches—1 mile.

6/6-yr blight center, upper figure is per cent. of infection on an area within 50 feet radius or more of the center.

Lower figure is the approximate age of the original infection.]

The infection nowhere runs less than 3 per cent., and it was impossible to find an acre with less than this amount of blight on it. On most of the ridge the percentage of diseased chestnut runs from 17 to 30 per cent., although there are spots where it is much higher. The centers of infection are not confined to any characteristic slope or environment. Generally, the blight has spread over larger areas on the summit and south slope than on the north slope. The centers along the south slope and summit show more trees killed by the blight than those of any other part of the mountain. This is doubtless due to a more rapid spread of the blight in these situations. Scattered dead trees are less common along the north slope than elsewhere; however, several centers containing a dozen or more large trees entirely killed are found on the north slope.

The blight is so uniformly distributed between the centers that it was difficult to determine the facts relative to the dissemination of the disease by wind. However, most of the infected areas show a wider zone of distribution east and north of the infection center, giving the areas of thick infection an egg-shaped outline, with the oldest infections nearest to the western boundary. No definite information was obtained on this tract concerning the part played by birds as disseminators of the disease.

The south slope of the ridge is more dry and barren than the north slope. The only springs found there are near the eastern end of the ridge, and a few small springs are scattered along the lower portions of the south slope, but these are below the zone of chestnut growth. The north slope is a more gradual incline, and there are numerous shallow dips resembling miniature gullies. Some of these are moist enough to support alder bushes and several species of moisture loving ferns; also trees of the lowland types, such as tulip and maple, are quite common in these depressions. Most of these dips contain springs, but not all of them; however, there are numerous small springs scattered all along the north slope of the ridge. Most of these are well down toward the base, but several are well up toward the summit. So far as could be ascertained, no relation exists between the thickly infected areas and moisture conditions.

The data collected lead to the belief that the infection is distributed without any regard to elevation. For instance, along the base of the north slope high percentages of infection are found. Similarly, an increase in the percentage of blight is found half-way toward the summit. While the summit seems to support more infection than any other portion of the mountain, there is no reason to suppose that this is due to elevation. The stand here is almost pure young chestnut coppice, and the conditions appear to be more favorable to the rapid spread of the disease in such stands. The base of the south slope supports coppice growth similar to that found at the summit, and here the per cent. of infection compares very closely with that along the summit.

RESULT OF OBSERVATIONS.

No definite cause for the areas of high and low per cent. of infection was determined. The highest percentages of infection are found on the summit and on the south slope of the ridge. Also this portion of the area supports more old infection than any other part of the mountain. In part, this may be due to the higher percentage of chestnut on the summit and south slope, and to the fact that most of it is young coppice. Such stands appear very susceptible to the disease. The theory that varying chemical elements, derived from the rock strata, affect the amount of infection is not supported by any evidence gathered in this work, for on the three general rock formations of this tract, as well as along the edge of the adjacent limestone, high and low per cents. of infection seem equally common. No evidence sheds any light upon the belief that the distribution of disease is along any definite compass direction. If there is any proof at all toward this end, it lies in the fact that infections on the south are more uniformly distributed than on the north. It is probably true that the advance infections came from the south and crossed the mountain northward, but areas of thick infection are not confined to any character of topography, slope, or elevation.

The accompanying maps give in detail the percentages of blight found in the Mahoning Valley and Topton Mountain areas.

RATE OF INCREASE OF BLIGHT IN EASTERN PENNSYLVANIA.

The southeastern corner of the State has a higher percentage of infection than any other portion of the State. The rapid increase of the blight is well shown in this section by the record of 1,637 trees on tracts in the vicinity of Philadelphia, which were examined for blight in October and November, 1910, December, 1912, and August, 1913. In 1910, 31 per cent. of these trees were infected with the blight, and 29 per cent. were doubtful. In 1912, 79 per cent. were infected, and in 1913, 88 per cent. If we include the 29 per cent. doubtful trees with the 31 per cent. certainly infected in 1910, the total becomes 60 per cent. This makes the annual increase in infection approximate 10 per cent. per annum. In this connection it is interesting to note that on the du Pont estate at Kennett Square, Pa., where tree surgery methods, supplemented by spraying with Bordeaux mixture, have been in use for the past two years, the progress of the blight has been materially delayed. Mr. R. E. Wheeler, forester for the estate, believes that these methods will save the trees under treatment for at least five years more, and probably for a much longer time.

Cross section of the Blue Ridge Mountain, showing altitudinal distribution of the chestnut blight on north and south slopes]

Tree surgery without spraying has had little effect in delaying the progress of the blight after it attacks a tree. In a large orchard of Paragon chestnuts, in Northumberland County, in a block of 9,612 trees, 4 to 15 years old, thoroughly examined in the winter of 1911-12, 194 infected trees were found, (2 per cent. infection), 103 of which were so badly diseased that they were cut out and burned, and 91 trees were treated by surgical methods. In the winter of 1912-1913, this same block was again carefully gone over, and 1,064 infected trees were found, (11.2 per cent. infection), 325 of which were marked for removal, and the balance for surgical treatment. The rate of increase in this case was over 500 per cent.

INFECTION CENTERS ON THE ADVANCE LINE.

In applying sanitation measures for the control of the blight, it is not practicable to use tree surgery methods and spraying, (except possibly in orchards), but only to cut out bodily every infected tree and to sterilize the stumps. When the blight is generally distributed through a region, as is the case in southeastern Pennsylvania, it is manifestly impossible to eradicate the disease by sanitation methods without also practically eradicating the host. A detailed study of spot infections as they occur on the western advance line of the disease is therefore of more interest than the conditions which exist in the generally infected territory.

On the advance line, as in the eastern part of the State, there is no rule for the location of an infection center, nor is there any rule as to the part of the tree which is attacked first by the disease. It is true, however, that on the western advance line more infections occur on isolated trees and on the edges of timber tracts than elsewhere, and that the majority of infections first appear in the tops of trees. Likewise, in its spread from tree to tree around a center, the blight shows no general rule, except that the trees immediately adjoining a primary infected tree are most apt to show the first secondary infection. The following tabulation gives the details of 175 infected trees in a spot infection of 271 trees, located at Orbisonia, Huntingdon County, Pennsylvania, studied in 1911 by Mr. R. C. Walton.

TABLE I.

DETAILS OF INFECTION AT ORBISONIA, PA.

========================+=========================+=======
| |Number.
------------------------+-------------------------+-------
Origin of tree, | Coppice, | 136
| Seedling, | 89
------------------------+-------------------------+-------
Slope, | Gentle to medium steep, | 5
| Gentle to steep, | 24
| Gentle, | 6
| Steep, | 79
| Very steep, | 0
| Medium steep, | 61
------------------------+-------------------------+-------
Aspect, | North, | 108
| Northeast, | 16
| Northwest, | 41
| North to northwest, | 7
| North to northeast, | 3
------------------------+-------------------------+-------
Location, | Lower slope, | 23
| Middle slope, | 152
+-------------------------+-------
| Along road, | 76
| Near road, | 28
| Away from road, | 71
------------------------+-------------------------+-------
Moisture, | Dry, | 28
| Damp, | 37
| Dry to damp, | 69
| Medium dry, | 13
| Medium damp, | 20
| Windy, dry, | 8
------------------------+-------------------------+-------
Density of forest, | Dense, | 72
| Medium dense, | 97
| Rather open, | 6
------------------------+-------------------------+-------
Infection on benches, | | 36
------------------------+-------------------------+-------
Orientation of lesions, | North, | 34
| East, | 29
| South, | 14
| West, | 21
| Northeast, | 29
| Southeast, | 10
| Northwest, | 9
| Southwest, | 5
------------------------+-------------------------+-------

The most important practical point in the study of spot infections, however, is the location of the secondary diseased trees with reference to the original center of infection. Where a careful study has been made, it has always been apparent that the disease spreads from an original center of one or two trees to trees in the immediate vicinity, as illustrated in the accompanying diagram, which is an example of a typical small spot infection, (Fig. 4).

PROCEDURE IN ERADICATING SPOT INFECTIONS.

SCOUTING.

The principal obstacle met in applying sanitation methods for the control of the chestnut blight is the high cost of locating spot infections. The cause of this lies in the great extent of territory which must be covered, and difficulty in securing competent and reliable scouts at reasonable salaries. Experience has proved, however, that thorough scouting can be done at a moderate cost under efficient supervision. Rapidity and efficiency in scouting vary with the size and density of the stand, the proportion of chestnut, the topography and location of the tract, and the prevalence of blight. The records of the Chestnut Tree Blight Commission show that between October 3 and June 30, 1913, it required 11,651 days of labor to scout 738,881 acres of timber, notify timber owners of infections found, and supervise the work of removal. This is at the rate of 63.41 acres per man per day, with the average of 2.07 infections found, and 1.49 infections removed per man per day. The average day, (not including time consumed in going to and returning from work), consisted of 8.2 hours spent in the field, .4 hour lost on account of rain, and .4 hour lost on account of sickness and leave. With thoroughly experienced and practical men under competent crew leaders, an average of 100 acres or more per day can be covered, unless the spot infections are very large and numerous. In thick infection, one man can make thorough tree to tree examinations of from 2 to 5 acres, depending on the character of the timber. However, on the basis of past experience, it appears to be more practical and economical to locate the boundaries of the spot infection, and eliminate all of the chestnut trees within and immediately adjoining the spot infection, instead of eradicating only the diseased trees. This plan reduces the amount of tree to tree inspection required, and one man should be able to scout at least 50 acres per day, even when spot infections are numerous. It has been found that a crew of two or more men can accomplish more and obtain better results than in the case of men scouting alone, except in a country where the woodlots are very small and scattered.

In scouting, rapid and thorough work depends upon the experience and capability of the crew leader. The size of the crew depends on the character of the timber to be scouted and the ability of the crew leader to handle men. Except in a very heavily timbered area, three men constituting a crew will usually accomplish more than a larger crew. There is an added advantage in a small crew in that two or three men can find accommodations near to their work where a larger number of men cannot, and must consequently spend more time on the road to and from work. In large tracts of woodland, the best plan is to establish a camp as headquarters for several crews. A camp is too expensive for a small crew, but for a number of men it is economical, and has the advantage of keeping the men close to their work.

The tracts must be scouted systematically. The best plan is to go back and forth parallel to the backbone of the ridges, each man inspecting a strip 50 to 100 feet wide. In large bodies of timber four or five men can work together advantageously, each man being separated by the distance best adapted to viewing all the trees in the strip between himself and the men on either side of him. The man on the outside marks the edge of the strip either by breaking branches on the underbrush of species other than chestnut, or by marking tree trunks with yellow lumber crayon. Unless eradicated as found, diseased trees are located by pacing to the strip boundary at right angles and marking a tree on the line with crayon to indicate the location of the diseased tree. If a cutting-out crew closely follows the scouting crew, there is less waste of time and effort than where the scouting crew attempts to eradicate the infections as found, unless infections are very few and limited to single trees. With the cutting-out crew following the scouting crew, there is the additional advantage that they may locate diseased trees missed by the first crew.

The greatest aid to efficient scouting is a pair of good field glasses. They often make it unnecessary to climb doubtful trees, and are of further usefulness in the hands of an experienced scout, because they enable him to locate many diseased trees from a high point of land or from tree tops. In such cases compass sights are taken on the diseased trees, and an assistant is dispatched to locate them. Such scouting, however, cannot entirely take the place of more detailed examination.

It has also been demonstrated that more and better work in scouting can be done in the fall and winter, after the leaves have fallen. In August and September the majority of new infections become plainly visible on isolated trees, but in dense woods the foliage makes it difficult to locate small infections. After the leaves have fallen, however, more light is admitted, and a scout can see for comparatively long distances through the bare tops, even in dense woods. The dead leaves on girdled branches are conspicuous throughout the winter and early spring, and where cankers have not yet girdled the parts, the increased light makes them much more prominent than in summer. Winter scouting has the disadvantage of fewer hours of daylight and occasional loss of a day or two on account of snow storms that tend to hide the cankers on the trunk and branches. If the snow becomes very deep it is not easy to examine the bases of the trees sufficiently, and the snow also greatly interferes with the proper treatment of the blighted trees.

In the work done by the Commission, the law required that the owner of diseased trees be notified to remove them within 20 days. A map or written description giving the location of the diseased trees on the tract, was also required by law. On private land the scouts kept field notes on the location of all diseased trees, blazed each tree to the wood and marked a serial number on it with black lumber crayon; on the side opposite from the blaze, a yellow manila tag was attached to the tree. These tags bore a printed notification that the tree to which one was attached must be cut in 20 days, with directions for treatment and a warning against starting forest fires; they also bore the serial number of the tree, the name of the scout, and the date when attached. In this way the trees were easily identified later when approached from any direction, and by means of the “location sheet” giving the direction and distance of each diseased tree from some fixed point, it was not difficult to find the trees. The “location sheet” was made out in duplicate, one copy being handed to the owner of the tract, with a written request to remove the trees within the 20 days granted by law. The duplicate copy was sent to the field office, the scout retaining his note book. Some system of this sort is necessary when the cutting out is not done by the scouting force, but it is cumbersome and very expensive. Frequently, it required more time to fulfill the requirement of the law than would have been necessary to treat properly the diseased trees on a tract. Much time was consumed also in very detailed inspection of the trees around a blight center, so that apparently healthy trees would not be cut, since the law provided that healthy trees ordered to be cut, must be paid for. Not only was this very detailed scouting a waste of time in the light of recent investigations, but it resulted in decreased efficiency of control because so many of the trees permitted to remain, in reality were infected. Although no disease could be found on them at the time, the disease developed fully after the spot was treated, necessitating several re-examinations before all infections could be removed.

METHOD OF ERADICATING A SPOT INFECTION.

There are many points to be observed in removing diseased trees in spot infections, if the disease is to be permanently wiped out. The main point to keep in mind is the fact that the fungus propagates itself more readily as a saprophyte than as a parasite, so that unpeeled logs, strips of healthy bark and chips from diseased trees or nearby healthy ones, if left in the woods, are almost certain to become infected. The principal object is to do the work in a thoroughly sanitary manner at a reasonable cost. An experienced man acquired “tricks of the trade” that enabled him to do the work much more thoroughly and in less time than an inexperienced hand can do even a poor job. Great care was necessary in supervising the work of removal carried on by the individual owners, since each spot infection practically meant training a new man to do the work, and unless an experienced man was constantly on the spot, the work would seldom be done properly. On State forest reserves and in cases of forced removals, the work was done by employees of the Commission, and it was found that it was done at less cost and much more effectively than was usually the case elsewhere.

The removal of an infected tree is best done as follows: First: Where the ground beneath the tree is covered with a dense growth of brush, this growth should be cleared away so that the chips and branches may be easily picked up. Small chestnut or chinquapin trees or sprouts should be cut flush with the surface of the ground and the tops burned.

The stump should be made as low as possible. The bark should be first removed from the lower 3 or 4 feet of the trunk to an inch or more below the surface of the soil. If felled by sawing, peeling may be done after the tree has been cut down. During the fall and winter the bark is difficult to remove, and if the stumps are cut low, it is easier and cheaper to split off the sap wood and attached bark with an axe. In any case the stump and all exposed roots must be cleared of every particle of bark, and all bark removed must be carefully collected and burned.

Typical small spot infection, near Dry Run, Franklin County, Pa., showing original center and secondary infected trees. If all chestnut trees within 35 feet of the nearest diseased tree cut in 1911 had been removed at the time of the first cutting, and all stumps properly sterilized, it would have prevented the appearance of the new infections of 1912 and 1913.]

After the tree is felled, all portions above the stump which show mycelium or pustules of the blight must be peeled of bark or the entire piece cut out. This diseased material, the brush from the tops, the bark, and portions of the felled chestnut trees which are not peeled and which it is not intended to utilize must be burned.

After the stump is peeled, if fire can be made over it without injuring the surrounding trees, and without danger of forest fires, the brush and refuse is best piled over the stump and burned. The fire must entirely consume or deeply char all of the material; no uncharred ends of branches and small twigs can be allowed to remain without grave chances of reinfection. If it is impossible to make the fire over the stump without injuring the surrounding trees, the sides and top of the stump and exposed roots should be thoroughly coated with creosote.

Portions of infected trees which show no evidence of the blight should not be permitted to lie unpeeled in the woods over twenty days, but may be safely handled and shipped with the bark on, if shipped as soon as cut. If the logs from the diseased trees are not removed from the woods within twenty days from the time the trees are felled, they should be peeled and the bark burned, or else the entire trees burned. Wood from diseased trees to be used where exposed to the weather must be peeled, or the fruiting bodies are almost sure to appear on the dead bark and become a source of infection. Fire wood, if kept under dry cover, need not be peeled.

One of the most important time saving items is to peel the lower portion of the tree before felling, and it is still more important to cut the stumps as low as possible. Bark remaining between buttresses and deep crevices of stumps can be removed very readily by chipping down from a position directly over the low stump, which is not possible in the case of high stumps. A rake and a large coal-burner’s basket included among the tools used in burning, are very useful in cleaning the chips from the ground. Before starting the fire, all the leaves and debris for a considerable distance around the place where the material is to be burned should be raked into a pile on which the fire is started. The bark and small particles of wood are raked together as soon as the brush is piled, instead of waiting until all the tops are burned. In this way, no large quantity of leaves and fine rakings are left until the end to smoulder for a great length of time before burning, and thus increase the danger of forest fire.

All possible care should be taken to prevent injury to surrounding chestnut trees and sprouts in felling the infected trees. Observation has shown that nearby trees are too frequently injured through carelessness, and the wounds are very apt to be a point of reinfection. Experience has also shown that unbarked stumps of blighted trees and green tops which are permitted to lie for a month or two on the ground are almost certain to become infected. The spores germinate on the sappy surface of the stump, and the mycelium grows downward through the cambium, and in the course of a year or two reaches the sprouts which come up around the base of the stump. In the case of the tops and particles of bark and wood, the decaying bark appears to be a very favorable seed-bed for the development of the spores that reach any portion of this material. It must be impressed on the workmen that the stumps must be peeled clean, and every particle of the diseased tree must be either burned or utilized in such manner that no opportunity is given for the saprophytic growth of the fungus.

It has been found that painting the thoroughly peeled stumps with creosote is effective in keeping the stumps free from the pycnidia of the blight fungus, but is not so desirable as hard burning over the stumps. In an experimental cutting at Wildwood Park, Harrisburg, 55 per cent. of burned stumps later showed blight, while only 23 per cent. of the creosoted stumps showed any signs of it. However, it is possible that in the future, many of the creosoted stumps will become diseased.

The results of an extensive experiment at Anderson Station, Mifflin County, are given below. This experiment deals with the efficiency of burning over stumps as compared with creosoting stumps. The stumps in Table II were peeled at various times during January, February, and March, 1913, and cold creosote applied with a brush. The cost of creosote and labor of application was approximately one-fifth of a cent for each six-inch stump, cut low. The data given below are the result of an inspection of these stumps made December 12, 1913.

Center of spot infection at St. Mary’s, Elk County, Pa. This tree was infected at least four years prior to the time the picture was taken.]

TABLE II.

RESULTS OF CREOSOTING PEELED STUMPS.

=========+========+=========+==========+========+========+==========
| Number | Average | Number | Point |Diseased| Pycnidia
| of |height of| of | of |bark on | on wood
Number. |vigorous|vigorous | diseased |disease | stump. | of stump
|sprouts.| sprouts | sprouts. | on | |(creosoted
| | (feet). | |sprouts.| | portion).
---------+--------+---------+----------+--------+--------+----------
1, | 14 | 5 | | | Yes |
2, | 8 | 5 | 1 | Base | Yes |
3, | 8 | 5 | | | |
4, | 6 | 6 | | | |
5, | 4 | 4 | | | |
6, | 4 | 5 | | | |
7, | 5 | 6 | | | |
8, | 3 | 3 | | | |
9, | 12 | 5 | 1 | Base | Yes |
10, | 7 | 7 | | | |
11, | 4 | 6 | | | |
12, | 3 | 5 | | | |
13, | 1 | 3 | | | |
14, | 6 | 6 | | | |
15, | 2 | 5 | | | |
16, | 5 | 3 | | | |
17, | 2 | 4 | | | |
18, | 6 | 5 | | | Yes |
19, | 2 | 4 | | | |
20, | 4 | 3 | | | |
21, | 4 | 6 | | | |
22, | 6 | 7 | | | |
23, | 10 | 7 | | | Yes | Yes
24, | 3 | 5 | 2 | Base | Yes |
25, | 1 | 4 | | | |
26, | 3 | 4 | 1 | Base | Yes |
27, | 8 | 5 | | | |
+--------+---------+----------+--------+--------+----------
Average, | 5.2 | 5.2 | 0.035 | | |
| | |of sprouts| | |
| | | | | |
| | | 0.148 | | |
| | | of stumps| | |
---------+--------+---------+----------+--------+--------+----------

No pycnidia were found on wood of peeled stumps after creosoting, except in one case, where a large area of inner bark adhered to the stump at time of creosoting, and later raised up, exposing an untreated wood surface. The inner side of this bark and the uncreosoted area of wood were covered with pycnidia. Creosote painted on thick bark at the base of stumps or on an exposed root does not appear to hinder the growth of the fungus. Hence, since stumps can be peeled but a very short distance below the soil, especially in winter, it is believed that creosoted stumps are more apt to have infected sprouts after a few years than burned stumps. The danger point is at the ground line, and exposed roots and the crotches at the collar between roots are especially liable to have areas of bark that are missed in peeling. If this bark becomes affected, it brings the disease very close to the young sprouts that spring up around the stumps, and sooner or later causes infection.

The stumps in Table III were burned in December, 1912. The data given below are the result of an inspection made December 12, 1913.

TABLE III.

RESULTS OF BURNING OVER PEELED STUMPS.

==========+========+========+===========+========+========+=========
| Number |Average | Number | Point |Diseased| Pycnidia
| of | height | of | of | bark | on
|vigorous| of | diseased |disease | on | wood
Number. |sprouts.|vigorous| sprouts. | on | stump. | of
| |sprouts | |sprouts.| | stump.
| |(feet). | | | |
----------+--------+--------+-----------+--------+--------+--------
1, | 4 | 3 | 0 | | |
2, | 8 | 6 | 3 | Base | Yes |
3, | 2 | 2 | 0 | | Yes |
4, | 4 | 4 | 0 | | |
5, | 6 | 6 | 1 | Base | Yes | Yes
6, | 7 | 4 | 0 | | | Yes
7, | 3 | 3 | 0 | | |
8, | 2 | 4 | 0 | | |
9, | 5 | 4 | 0 | | |
10, | 0 | 0 | 0 | | |
11, | 3 | 4 | 0 | | |
12, | 4 | 3 | 0 | | |
13, | 1 | 1 | 0 | | |
14, | 4 | 3 | 0 | | |
15, | 4 | 7 | 0 | | |
16, | 3 | 6 | 0 | | |
17, | 4 | 4 | 1 | Base | Yes | Yes
18, | 4 | 4 | 0 | | |
19, | 4 | 5 | 0 | | |
20, | 1 | 6 | 0 | | |
21, | 3 | 5 | 0 | | |
22, | 2 | 3 | 0 | | |
23, | 4 | 4 | 0 | | |
24, | 2 | 2 | 0 | | |
25, | 3 | 5 | 0 | | |
26, | 0 | 0 | 0 | | |
27, | 2 | 4 | 1 | Base | Yes |
28, | 6 | 4 | 0 | | |
29, | 6 | 6 | 2 | Base | Yes | Yes
+--------+--------+-----------+--------+--------+--------
Average, | 3.5 | 3.9 | [10]0.078 | | |
| | | | | |
| | | [11]0.17 | | |
----------+--------+--------+-----------+--------+--------+--------

[10] Sanitation well done—stumps well peeled, well burned or creosoted, and refuse burned.

[11] Sanitation fairly well done, but stumps not thoroughly peeled or burned.

One very heavily burned stump, cut close to ground, had an area of diseased bark at crotch between roots, and a diseased sprout (No. 27). The least charring was always in crotches between roots at or near the soil line. Heavily burned stumps have weak sprouts or none, as a rule, about one stump out of twenty having no sprouts. Creosoted stumps usually have more and stronger sprouts than burned stumps.

Creosoting is cheaper than burning over the stump, on account of the labor saved. While it is apparently effective where the peeling and creosoting are well done, burning is safer, although more expensive. A gallon of creosote costs about 15 cents and will treat from 50 to 100 medium sized (10”-15”) stumps, varying with the height of the stump and the temperature of the air and creosote. The creosote may be profitably used where other trees will be injured by fire or where there is great danger of starting forest fires. Other methods of treating the stump have been tried, such as spraying the stumps with crude oil or kerosene and then burning them, after peeling. The stumps have also been buried under a mound of soil through which the sprouts had to penetrate. These treatments are less efficient and more expensive than creosote and cannot be recommended.

COST OF ERADICATION.

The cost of eradication will vary greatly according to the conditions. If an average of 50 acres is scouted per day per man, at a labor charge of $2.50 per day to include the cost of supervision, the cost of scouting an acre is 5 cents. In a region of much blight, the cost of efficient scouting will run four or five times this amount unless the plan is adopted of determining only the edges of a spot infection, and then cutting out all of the chestnut trees inside of the area regardless of whether or not they show visible signs of the blight. This seems to be the most sensible plan, since the results of reinspection show that it is the trees inside of the edges of the spot infection which in almost every case show reinfection. It will save money not only in scouting, but in future control. On the Pennypacker forest reserve in Perry County where the infections were thickly scattered, the cost of scouting and removal in 1911 and 1912 on 1,620 acres was 73 cents per acre, or 52 cents per diseased tree, and this is probably the lowest figure for which the work can be done. The most expensive part of the work is the peeling of the stumps, and here a great deal can be saved by following the proper methods. In a large spot infection, the cost can be reduced considerably because of the concentration of the work. A spot infection of 822 trees, ranging up to 18 inches in diameter on the stump (average 6 inches) was cut out at a cost of $70.50 or 8.58 cents per tree. This included peeling not only the stumps; but all merchantable portions of the trees, burning the brush, sterilizing the stumps, and cleaning up thoroughly. This cost, however, does not include scouting, which in this case can be figured at 2 cents per tree. The total area of this spot was about three acres, so that the total cost of scouting and eradication was approximately $29. 00 per acre. In all but very small spot infections, enough material is produced to pay for doing the work.

In Mifflin County, three men treated 2,341 clumps of six-year-old chestnut sprouts at an average cost of 20.3 cents per clump. Each man averaged 15 clumps per day; cutting, peeling, cleaning up and burning were very carefully done at a cost of 16.3 cents per clump. Scouting, creosoting, and loss of time from bad weather cost an additional 4 cents per clump. The average acre contained 205 clumps of chestnut sprouts, with an average of 5 five-inch sprouts per clump; 29 clumps per acre or 14 per cent. were diseased. The cost of thorough sanitation thus amounted to $5.89 per acre. The average daily wage was $2.40, including the cost of board and supervision.