The extensive Eucalyptus plantations created in many countries have so far suffered relatively little from attack by insects or diseases, and even such damage as has been caused has apparently been generally insignificant. But it is evident that the establishment of pure Eucalyptus plantations on a large scale creates a risk of possible serious attacks that could result in a dangerous setback to the economic use of these quick-yielding species. The following paper gives only a brief description of present conditions and is obviously incomplete. Readers are invited to submit supplementary information to the Forestry Division of FAO.
Nurseries and young plantations have suffered severe damage from termites. There is a considerable literature on general eradication methods so that it is sufficient to mention that aldrin, parathion and DDT (chlorinated carbohydrate) as well as spraying with sulphur and especially with HCH, have given excellent results. In East Africa, principally in the dry regions where termites endanger Eucalyptus plantations up to 3 to 4 years old, HCH powder and dieldrin are used for protection around individual plants (15 grams per plant); but it is evident that the larger the area of soil treated, the more effective is the treatment, as the moment the roots spread beyond the treated area, they are attacked. In making plantations, very vigorous and healthy plants must be used and planting should be at a sufficiently close spacing so that, after an attack, an adequate number of plants still survive. Eucalyptus maculata seems to be more resistant than other species, while E. citriodora, E. saligna and E. maideni are very sensitive.
In Malaya, the same method is used. E. deglupta is the more resistant. In Brazil, white arsenic, lead arsenate and sodium arsenate have been tried with success by mixing them with the soil around the planting holes at a proportion of 3 to 4 percent. Lead arsenate and white arsenic are the most effective, but the latter is the most economical. HCH (0.45 percent Isomer gamma) has given even better results than arsenic, a concentration of 6 grams to 100 grams of soil being the best. Equally good results are obtained by mixing HCH with the soil in the earthenware pots in which plants are raised: DDT, on the contrary, has proved almost totally ineffective. In Brazil, E. alba, E. resinifera, E. paniculata and E. punctata have proved the most resistant species to termites.
The genera Atta and Acromyrmex have proved to be very noxious in South America and represent the greatest danger to plantations and nurseries. Although these genera are present in nearly all areas, they seem to be less prevalent in low sandy or permanently cultivated lands. In Argentina, it is considered that the presence of 50 anthills per hectare will justify the cost of operations to destroy the pests before planting Eucalypts. In fact, effective control of these insects is difficult and costly. If only four or five nests remain, these are sufficient to result in grave damage.
The ants injure the leaves and the buds seriously enough to cause the death of a plant. This necessitates constant inspection during the second and third years following planting. Many insecticides have been used, either in gas or liquid form, to destroy the ant hills. To be effective they must penetrate into the fungus food crop and kill the queen. Sulphur dioxide, either pure or mixed with arsenic, carbon disulphide (approximately from 60 to 200 cubic centimeters per ant hill according to its size) are both insufflated or blown into the anthill by means of a special instrument. Methyl bromide is much used in Brazil and requires only a receptacle with a tube which penetrates into the ant hill (approximately 3 cubic centimeters per square meter of ant hill; 1 kilogram per 30 ant hills). A mixture of methyl bromide and 20 percent chloropicrine or methyl bromide and 80 percent of carbon disulphide is also used. HCH is used either as a powder which is injected by pressure into the middle of the ant hill or as a liquid; the best results are achieved by 200 grams per ant hill of the powder at 20 percent (2.4 percent Isomer gamma) or especially with a mixture of 100 grams at 50 percent (6 percent Isomer gamma) dispersed in 10 liters of water. Chlordane and lindane are used dispersed in water or sprayed on the ground or even onto the plants. Aldrin (1 to 2 kilograms per hectare), endrin and especially dieldrin are effective. The latter is insufflated under pressure at a density of 2 to 5 percent into the center of the ant hills or well placed all around the ant hills to prevent the ants from leaving them. In Brazil, placing the insecticide around each plant in a ring of bamboo has also been tried with success.
This weevil, Australian in origin, is certainly up to now one of the insects which has caused most damage to Eucalyptus plantations. Gonipterus scutellatus has been found in New Zealand, South Africa, Southern Rhodesia, Kenya, Uganda, Mauritius and Madagascar. It mostly attacks Eucalyptus maideni, E. viminalis, E. globulus, cam camaldulensis E. robusta, E. citriodora and E. smithii. On the other hand, E. saligna, E. cladocalyx, E. melliodora, E. crebra, E. fastigata, E. paniculata and E. maculata seem to be resistant. There is a considerable literature on this insect and the methods of its control, and it is sufficient to point out here that it is attacked by a hymenopterous parasite Anaphoides nitens, also of Australian origin, which has been spread generally with success, and its dispersion is rapid. For example, in the Island of Mauritius, Gonipterus scutellatus attacks are now only sporadic and isolated.
In South Africa, success has been practically complete except at high and dry altitudes (from 1,300 to 2,000 meters) where this parasite, though very resistant, does not thrive. Nevertheless, even here satisfactory results have been achieved except in certain cases with E. viminalis. The success of this control varies greatly from one area to another, particularly on high plateaus, and local climatic conditions and soil have a definite influence. A certain equilibrium has now been reached, but this can be upset, for example, by a year of drought or by an increase in competition among the trees. This biological control has proved very economical and efficient, and only in very rare cases it is necessary now to abandon plantations of E. viminalis.
In New Zealand, Gonipterus scutellatus attacks Eucalyptus globulus and E. viminalis, to a lesser degree E. radiata and E. gunnii and not at all E. linearis and E. amygdalina. The introduction of Anaphoidea nitens has also been a success in this country.
Also reported in New Zealand is a Coccid which has caused serious damage mainly to Eucalyptus globulus, E. viminalis, E. qunnii and E. macarthuri, while E. amygdalina, E. oblique, E. stuartiana, E. eugenioides are attacked to a lesser degree. This insect is to be found on the branches and principal veins of the leaves and discharges a liquid on which there develops a fungus of a distinctive black color. However, due to a Coccinella, Rhizobius ventralis, imported from Australia and to a fly, Pseudoleucopis benefica, and a lepidopterous insect, Stathmopoda melanchra, this pest does not now present a great danger to Eucalyptus plantations.
This insect is a coleopterous Cerambycid originating in Australia and spread over South Africa on Eucalyptus globulus, E. diversicolar and E. saligna. E. paniculata, E. fastigata and E. cladocalyx are not affected. In Southern Rhodesia, it occurs on E. saligna and E. botrioides, although E. camaldulensis and E. citriodora are not affected. In Chile and in Argentina, it is found on E. globulus and E. viminalis, and in the East Mediterranean region on E. globulus and E. camaldulensis. Felled trees are subject to attacks, as are standing trees in poor condition, or young trees from 15 to 20 centimeters in diameter in not very favorable situations (Cyprus, Israel). The larva of the insect bores a tunnel in the wood, making it unusable and, by destroying the cambium, causing the death of the tree. The methods employed in Cyprus against this insect are the felling and burning of affected young trees. Trap trees are employed in South Africa. In Israel, important work has been done in the treatment of Eucalyptus poles immediately upon felling.
Various other insects attack Eucalyptus in South America but none are of great importance from the point of view of destructive power. As regards Brazil, mention may be made of two Lepidoptera, a Geometrid, Thyrinteina arnobia, which can be destroyed with DDT 2 ½ percent; and a Lymantrid, Phassus giganteus which hollows out galleries where lianes touch the tree. The following Coleopters, which are also reported from Brazil, are listed in order of importance: Sternocolapsis quatordecimoostata especially on E. citriodora, E. alba and E. maculate while E. globulus is not attacked, and E. saligna very little. It is treated with HCH powder (1 percent Isomer gamma) or liquid (250 grams of powder 12 percent Isomer gamma dispersed in 100 liters of water). Costalimaita ferruginea which comes from the cotton plant and attacks in particular E. citriodora; it can be treated with HCH in powder (1 to 1.5 percent Isomer gamma). Colaspsis quadrimaculata and Bolax flavolineatus. These last two are of lesser importance.
In Argentina, Gonipterus gibberus is reported; against this is employed HCH at 10 percent or chlordane at 6 percent. Biological control measures against this pest are in the course of development. In Argentina also, the larva of a Coleopter, Dyscinetus gagates, eats into the bark of young plants causing their death. Dieldrin or chlordane are employed to fight it.
Argentina and Brazil report a Thrips, Isoneurothrips australis originating in Australia, which destroys the inflorescence of Eucalypts.
In Ecuador, larva of a Cerambycid, Paramallocera ilinizae, has been found to bore into the bark and the cambium, sometimes causing the death of the tree.
In New Zealand the most important insect is a Chrysomelid, Paropsis dilatata, which has caused great damage in South Island on plantations of E. globulus, E. radiata, E. viminalis, E. regnans, E. gunnii, E. obliqua and E. eugenioides. Against this no biological means of destruction have yet been found, in spite of various trials A Chalcid, Rhicnopeltella eucalypti, which attacks solely branches of E. globulus, has resulted in the plantations in several regions having to be abandoned as no means of destruction have been found to date. Lastly, there is a Psyllid, Rhinocola eucalypti, infested successfully by a Eulophid, Pteroptrix maskelli and a Tortricid, Eucolapsis brunnea.
Apart from damping-off fungi, many other diseases are reported but on the whole are of little importance. For instance, in South America there is Gommosis of Eucalyptus citriodora which causes injury and decay of the collar; a tumor of the stem of the young plant due to a species of Cylindrocladium, and Ganoderma sessile which attacks the injured trees.
Botrytis cinerea is reported in various countries: in Portugal and Argentina on E. camaldulensis; in Brazil, on E. citriodora, E. botrioides, E. alba; Kenya on E. globulus, E. camaldulensis; in Italy, on E. globulus. This is not, however, of great economic importance. It attacks the seeds in the nurseries or the very young trees which are not in good condition. In South Africa, attacks of Ganoderma colossum are reported especially on E. maculata and E. paniculata; of Lembosiopsis eucalyptina on the foliage of E. delegatensis and E. globulus; of Stereum hirsutum on the stool shoots of E. globulus, bringing on an infection of the shoots and, subsequently, decay of the heart, also on E. diversicolor of over 40 years, and on the shoots of old stumps of E. saligna. The latter is avoided by limiting the rotation to less than 30 years and cutting the stumps to the ground.
In Italy, the Belgian Congo, and in South America, the fungus Cercospora eucalypti is reported on Eucalyptus leaves. In Morocco, Hypoxylon mediterraneum lives particularly on Quercus suber but attacks also E. camaldulensis, E. gomphocephala and E. robusta. In Cyprus a canker is reported which seems to be connected with the presence of Phoracantha semipunctata.
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