Summary of a Report Made to the FAO European Forestry Commission
PROTECTION of the forests against harmful insects and diseases is one of the main problems before the U.S.S.R. Forestry Department. All forest protection work is based on the premise that measures for combatting harmful insects and diseases must be closely related to all of the Forestry Department's other work. In practice, this can be realized because the over-all control of all U.S.S.R. forests by a single administrative center permits the use of the Forestry Department's common administrative machinery for the organization of forest protection work.
However, for specific and special forest protection work there is also a special agency consisting of experts in forest pathology, each of whom serves five or six forest collectives. These are specialists with particular training in forest entomology and forest phytopathology.
The Forestry Department particularly stresses forest prophylaxis to keep the forests healthy and to create the conditions to discourage the spread of noxious insects and diseases; and planning, management and silvicultural practices are directed to this end.
Administrative policy takes into account the way in which insects and diseases may, in given circumstances, endanger the sound development of the forests. Planned measures are given effect by the units which carry out forest operations and exploitation in the field, in consultation with the forest pathology specialists, and they are aimed at the complete restoration of the forests, as well as to the creation of conditions discouraging the spread of harmful insects and diseases.
The fundamental prophylactic measures for preventing the spread of harmful insects and diseases are given in Regulations on the Sanitary Minimum in the Forests. It is compulsory to follow these regulations in forest administration and forest exploitation.
Regulations on the Sanitary Minimum in the Forests establishes sanitary felling as compulsory. This applies to all felling in the forests and aims at the removal of trees liable to lead to population increases in harmful insects or the development of fungus diseases, and also aims at lessening forest fire hazards. For this reason sanitary felling includes the removal of dead timber and of trees whose trunks harbor insects such as bark beetles (Ipidae, Cryphalus), longhorn beetles (Cerambycidae), and oakborers (Buprestidae), clearing of damaged trees and of charred remains, slash and stumps which endanger adjoining healthy forests.
Likewise, one of the regulations forbids leaving unbarked timber in the forests over the summer. This rule obliges all logging camps to remove all timber felled in the autumn and winter period outside forest limits before 1 May; if the cut cannot be removed during this period, the timber must either be left barked or else stored by methods which preserve it from serious attack by insect pests. Timber accumulated in the spring-summer period must be shipped out of the forest no later than three weeks after felling, or otherwise also be barked or given appropriate preservative treatment.
In the past, the absence of proper sanitary methods in the forests has often created conditions favoring the mass increase of harmful insects and the spread of plant diseases, and therefore the application of these sanitary measures in the forests is now given exceptional significance.
Measures in the forest
Measures comprise a whole complex of agro-technical and protective measures promoting sound, well-developed forests and creating conditions discouraging the spread of harmful insects and diseases. Healthy forests are naturally resistant to big attacks. One of the preventive measures particularly widely encouraged is the protection of useful birds and attraction of insectivorous birds to the forests by erecting nesting-boxes. This latter work is made a supplementary assignment of the Forestry Department with the participation of the collective organizations and particularly schools.
The organized fight against harmful insects and forest diseases is based on systematic inspection for the appearance of symptoms or the spread of insects and diseases, timely notice of the outbreak of infection centers, and their correct diagnosis. For this purpose, field surveys, aerial surveys, investigations of mass increases in needleand leaf-eating insects, and forest-pathological inspections are carried out. Systematic field survey and initial notice of the appearance of one or another insect or disease are the duty of the government forest wardens.
Aerial reconnaissance is the task of the fliers of the forest air warden bases; in every flight over forest areas they must watch for the appearance of large-scale damage in the forests which is visible from the air. Such cases of damage must be immediately reported. Air reconnaissance supplements ground surveys and is especially important in the vast forest concentrations of the North, Siberia, and the Far East, where regular air patrol service is used for detection of forest fires.
Ground and air surveys, however, only reveal infection centers when defoliation is already fairly advanced. Research has been devoted to the problem of working out a survey method which would ready detection of the mass increase of defoliating insects at the very earliest stage, so that control measures could be started before serious damage or loss to the forests has been caused. Such a method, called stationary inspection, has been devised by the Soviet entomologist, A. P. Ilynsky. Widely practiced by the Forestry Department, the method is described in a government publication entitled Surveying for Defoliating Broadleaf Insects in the Forests and the Prognosis of their Mass Increase.
The method rests on the fact that mass increase of defoliators starts up in concentrated areas where conditions are most favorable for the insects. Such forest areas represent insect 'reservations' where the first foci of infection begin; the kinds of insects harbored depend on the tree species. A. P. Ilynsky has deduced factors which appear to govern a mass increase in the population density of insects, on the basis of which quantitative and qualitative indices for outbreaks of harmful insects have been compiled; the quantitative correlation of the site, fecundity of the females, rate of egg-laying and survival of the larvae, the absolute and relative insect population of the forest and the coefficient of increase.
By systematic inspection of the same area, calculation of the number of insects at particular stages of development, determining the heaviness of the oviposition, and by estimating the indications of the rising coefficient of increase, reliable judgments may be made on the insect's condition and the dynamics of its increase. A prognosis of the increase or the extinction of a mass increase of these insects can be made by comparing the indices over a consecutive period of years.
The stationary inspection is supplemented by general reconnaissance, which is now being carried out as a matter of routine under the forest warden service by the rangers in those forest concentrations where the presence of particular insect pests is most likely. The survey is made during the period when it is easiest to detect signs of the presence of the particular insects.
To calculate the spread of forest insects and diseases and determine the indications of the danger of their mass increase, forest pathology inspections are made both by Forestry Department specialists and interregional forest pathologists and by special inspection teams. The inspections provide the basis for the particular forest protection counter-measures to be undertaken, and are carried out in keeping with methods prescribed in special instructions.
Of the measures for the extermination of defoliator attacks, dusting and spraying, especially from the air, has been particularly highly developed. In 1954, the area covered by aerial control was four times greater than the area covered over the entire period from 1937 to 1947. The airplane has considerable advantages over any ground equipment whose use in the forests is usually complicated and difficult, and in recent years there has been a greater availability of highly effective chemicals such as DDT and hexachlorane preparations in the form of dusts which have proved especially useful in combatting forest insects, particularly defoliators. The DDT dust is usually applied in concentrations of 5-10 percent and hexachlorane of 12 percent.
In the defoliator group the most important insects are Dendroctonus pint, Dendroctonus sibiricus, Porthetria monacha, Butalis piniarius Tenthredinidae, Porthetria dispar, Nygmia phaeorrhoea, Malacosoma neustria, Tortrix viridiana and Opthera brumata. There is a whole series of other harmful insects causing defoliation to conifers and broadleaved species, resulting in serious damage to forest production during years of mass increase in population density.
Chemical attack and aerial dusting with DDT and hexachlorane are widely practiced against this whole group during the period when the insect is in the earliest larval stage. As a rule, after the first three stages of growth, larvae and caterpillars acquire resistance to the chemical preparations, in proportion to the stage of growth, so that aerial attack in such periods becomes less effective.
The amounts used in aerial dusting of defoliators is 15-20 kilograms of DDT and hexachlorane per hectare, increasing to 25 kilograms in cases where the dusting is delayed (late in the season) or when the forests treated are particularly severely infected or damaged.
When treatment is timely and properly carried out, aerial dusting can lead to complete elimination of danger, since the destruction of the insect larvae and caterpillars generally amounts to not less than 95 to 98 percent.
Air operations, like other extermination measures, are always preceeded by a forest pathology survey, and the specific control project is drawn up on the basis of the survey's results. Special attention is paid to the condition of the insects and the activities of beneficial insects; predators and parasites of the noxious host are likewise taken into account with the aim of causing as little destruction of useful parasites as possible. The determining factor for achieving this aim is to concentrate the operation in that phase of the mass increase of the harmful insects either when the natural parasites show signs of reaching satiation point or when the larvae and caterpillars are in the earliest stages of growth; the majority of the beneficial insects generally attack the noxious hosts during later phases of development.
In recent years, chemical air attack has also yielded good results in combatting Melolontha hippocastani, which in a number of the regions of the U.S.S.R. has been found to cause serious damage to seedlings, saplings and shrubs in forest plantations and forest nurseries. Aerial dusting is done with hexachlorane during the summer period before the females deposit their eggs in the soil.
In recent years, other chemical measures have been devised for the protection of seedlings, saplings and shrubs and nurseries against larvae and caterpillars of harmful insects inhabiting the soil and damaging the roots, and are now widely applied in forestry practices.
In former years, many promising attempts to create new forests ended in failure because of the depredations of this group of harmful soil-infesting insects, which are more difficult to deal with because their larvae are less accessible than the defoliators.
The present practice requires that at the time of planting, seedlings must be protected with hexachlorane by one of the three following methods: powdering of the roots; submersion in suspensions; or powdering of the planting holes.
Hexachlorane protects the roots against damage for a period of two to three years and plants show no negative reaction when transplanted if certain conditions have been observed. A concentration exceeding 12 percent hexachlorane must not be applied to the soil immediately surrounding or touching the roots of the seedlings. In dry regions it is better to use suspensions or to powder the planting hole, whereas in the forest and partly in the plains-forest zones, direct powdering of the roots may be used. Planting with the application of hexachlorane should be done in the early spring while there is a great deal of moisture in the ground, in order to reduce the negative effect of hexachlorane on the plant.
DDT dust preserves the roots against damage for a two to three month period, and its use for chemical protection is therefore recommended only in years when the threat of beetles is particularly great.
In powdering the root systems of transplanted one-year seedlings 0.16-0.30 grams of hexachlorane (12 percent dust) or 0.5-1.0 grams of DDT (6.5 percent dust) per seedling is used. In the planting of two-year seedlings the amount of dust for each specimen is proportionately increased 1.6 times.
For immersion of roots in suspensions 0.2-0.4 grams of hexachlorane (12 percent dust) or 0.7-1.6 grams of DDT (5.5 percent dust) are used per one-year seedling. For preparation of suspensions for 1,000 seedlings, 200-400 grams of hexachlorane or 700-1,500 grams of DDT powder are taken, mixed thoroughly with a bucket of compost or of top-layer humus-treated soil and, constantly mixing, a bucket of water is poured into the preparation.
The powdering and immersion of roots in suspensions may be done by hand, as well as by mechanical means during planting operations, and likewise in planting tree grafts or shrub stock.
In powdering the planting holes, the amount used for each hole is 0.25-0.50 grams of hexachlorane (12 percent dust) or 0.7-1.5 grams of DDT (5.5 percent dust).
As regards dosage rates, the minimum is applied when the larvae present in the soil are in the first stage, under dry growing conditions, for the trees and shrubs that are more sensitive to hexachlorane such as Larix, Pinus, Betula, Tilia, Quercus, Malus, Cerasus, and Acer platanoides. The maximum rate is applied when the larvae are in the third stage of growth, for humid-growing conditions, for carbonaceous soils, and to trees and shrubs less sensitive to hexachlorane such as Ulmus, Fraxinus, Populus, Robinia, Caragana arborescens, Rhus cotinus and Evonimus.
In using dust of other hexachlorane or DDT content, a revision of the proportions is made.
To free the soil entirely from harmful insects, it is treated with 12 or 25 percent hexachlorane dust. The dust is introduced with the aid of a sowing machine or by hand sprinkling over the surface before the sowing or planting, and subsequently covered to a depth of 10-15 centimeters. When dust is sprinkled by hand, it should be mixed with a small quantity of damp sand to avoid blowing off or raising dust clouds in windy weather.
The quantity of dust to be introduced depends on the nature of the soil, and the insect's form or stage of growth. When the larvae, caterpillars or other insects present are for the most part in the formative first and second stages of growth, 60-80 kilograms of 12 percent dust per hectare are used; with a predominance of insects in the second and third stages, 100-120 kilograms are used. If the 25 percent hexachlorane dust is introduced, the amount used is reduced proportionately.
For clay soils the amount per hectare is increased 1.5 times; for black soils, 2 times.
It is advisable to introduce the hexachlorane into the soil in the spring, as this gives the best results. When the soil is heavily infested, it is advisable that the application be made in good time, a year before planting or sowing forest stocks.
With such application to the soil, it is also advisable, where areas are limited, to add steam, i.e., to introduce the hexachlorane dust in the spring and then, during the year, treat the soil with steam, repeating the treatments at suitable intervals. Soil sterilization should preferably be carried out once every four or five years.
At present research is being done on techniques of applying hexachlorane to reduce the amount of dust needed. The scientific research organizations are also working on further advances in chemical and control methods of combatting forest insects, and in particular on the aerial method of fine dispersion sprinkling of forests with DDT, hexachlorane and other chemical emulsions, and methods using toxic chemical systems.
At the same time research is in progress to work out methods for utilizing beneficial insects in combatting harmful forest insects.
(Article translated from an original Russian text.)