Although some chestnut tree pathogens and pests specialized for the genus Castanea, most of them are common with the tree’s close relatives, the oaks. A number of diseases and pests can be found in chestnut trees grown in semi-domesticated conditions; the significance of such diseases and pests is determined by natural factors, but it considerably increases or decreases under intensive growing conditions in professional plantations.
Chestnut blight (Endothia parasitica [Murr.] Anders.) is the chestnut tree’s most serious disease. This fungus infects the branches and trunks, killing their phloem tissue and cambium. The fungus’ orange fruiting bodies develop by breaking through the bark. Infections most often occur in injuries, but they can also develop at forkations and bark creases wihout any visible injuries. The disease in the tree shows as dry foliage during summer time, which also
stays on in winter. The fungus mostly spreads downwards in the older branches and the trunk. Above the infected areas, the tree begins to dry out, the bark crackles, and the crown decays. Below the infection, however, strong shoots sprung up, which usually fall victim to the downward-spreading disease the next year; these sick chestnut trees with their broom-like branches look quite characteristic within forest stands and scattered areas.
The pathogene originated in East Asia and spread throughout the world with the domestication of Asian chestnut tree species. The American and European chestnut species did not develop resistance against this pathogen; therefore, the pathogen’s destruction of native chestnut species is unparalleled on these two continents.
Endothia parasitica has been considered a closure pathogen since 1971; that is, it must be eliminated by the strict observance of government regulations. In Hungary, the reoccurance of the pathogen can occur during the spring migration
of birds, since this pathogen -- which became widespread in Italy in 1940 and Yugoslavia in 1949 -- are spread by birds towards the North. It is necessary to employ continuous chemical protection against the pathogen in industrial-sized orchards. In case of a full-blown disease, quarantine is mandatory.
Another pathogen, a fungus named Melanconis modonia also plays an important role in the bark death of Hungarian chestnut trees. Its domestic occurence was first reported by Hausz (1972). This fungus has two conidium-like side forms, of which Coryneum perniciosum occurs most frequently on dead chestnut tree branches. It infects trees through injuries, and according to our observations, it damages saplings through their graftings in nurseries. Its damage is not significant in older or stronger trees. Since the fungus appears on all decayed, ligneous parts of a chestnut tree, it used to be considered the pathogen in the so-called ink-disease -- a
mistake, which still persists in today’academic literature.
Melanconis-caused infections on smooth-trunk, young trees look similar to the bark-decay symptoms that Endothia can trigger; therefore, it is important to mention Melanconis modonia, so that it can be considered when determining the causes of bark decay in chestnut trees. Bark infected by Melanconis modonia sinks in and becomes brownish red, but on the surface, there are no orange-colored fruiting bodies, only black lentil-like conidium bodies, as well as black cone-like stromas, which break through the barks. The conidia are dark in color and are multicell. Melanconis-caused damage can be prevented by keeping the chestnut trees in good shape, although the necessary protections implemented against Endothia also provide some protection against bark-death caused by Melanconis.
The longest-known chestnut-tree disease leading to tree death is „sudden oak death,” of which pathogens were successfully identified at the
beginning of the last century. There are two main pathogens of the chestnut tree’s phytophtora disease, both of which trigger similar symptoms: Phytophtora cambivora and Phytophtora cinnamoni. These pathogens are not found in Hungary.
Phytophtora cambivora has been known to be the pathogen of the „sudden oak death” disease of chestnut trees in Europe since 1971, while Phytophtora cinnamoni was discovered in chestnut trees in the United States in 1932. Since then, it has also been proved to occur in most the chestnut-growing European countries. This latter pathogen also appears in a number of other plants. Since the involved parasites do not constitute breeding bodies in their developmental phases, differentiation between the aforementioned two Phytophtora pathogens is difficult.
The disease attacks the phloem tissue and the cambium of the chestnut trees’ roots and root collars about 10-20 centimeters above ground; as a result; they begin to wet-rot. Although
this disease received its „ink disease” name after the ink-black color of the tannic acid which becomes oxigenated after seeping through the tree, it is not a characteristic symptom of the disease. Other types of decays and mecahnical injuries on the chestnut tree can also result in liquids, which become black in color due to oxygenation. In addition, in case of certain phytophtoric diseases, no tannic acid is generated. The general characteristics of the disease are the following: the leaves of sick trees become yellow and ultimately fall down, the fruits remain tiny, and the nuts are forced to prematurely drop out of the cupules, the latter which dry onto the trees and remain on them even during winter time. In an accute stage of the disease, the trees dry out and wither away due to root decay.
Since 1971, no such pathogen has entered our country due to regular inspections by Hungarian control agencies. In other countries’ experiences, the effectiveness of chemicals against the
pathogens is meager. In case the disease appears in Hungary, large-scale destruction can only be prevented by planting resistant trees in endangered areas.
The chestnut tree’s most common disease is „leaf spot” (Mycosphaerella maculiformis) . Since the fungus’ summer conidium form is Cylindrosporium castaneaé, this disease has become known as cylindrosporium leaf spot disease in the academic literature. In Hungary, the occurance and biology of the pathogen was researched by Krenner (1944). The symptoms of the disease are usually appear in June as tiny white spots on the leaves, which increase in size and turn brown over time. The pathogens, which spend the winter in the white spots of the fallen leaves, re-infect the new leaves during spring time. By the end of the summer, the spots cover the entire leaf, which ultimately turns yellow. If the weather is rainy and humid, and there is great temperature fluctuation, the
infection is followed by defoliage.In case of a dry and warm August, the infected leaves roll up, the arteries twist, and the dead leaves dry on the tree until defoliage.
Since the disease occurs annually -- although the extent of the damage varies from year to year -- the defense against leaf spot determines how the spraying of pesticides is organized in chestnut orchards. The different species’ susceptibility to the to the disease is varied. Among the domestic species, the Iharosberényi 2 is especially resistant to the disease, while the Kőszegszerdahelyi 2 and 29, as well as the Nagymarosi 22 species are mildly sensitive to leaf spot.
Of the several foliage diseases, which have a smaller significance for Hungarian chestnut growing, oak mildew infects the most trees (Microsphaera alphitoides) (Körtvély, 1974). The extent of the damage is most significant in younger trees in nurseries: as a result of the disease, the shoots of the young trees become short-jointed, and exhibit
growth delay and sensitivity to frostbite. With regards to older trees, the fungus usually infects only the tip of the shoots. The pathogens spend the winter in the shoots and infect the leaves from there. The mildew coating only becomes apparent in mid-summer. The fungus grows on the top of the leaves. The infected leaves fall back in development, the distance between their vessels shrink, and the vessels themselves become curly. Since in the nurseries the disease occurs only in Kőszegszerdahelyi 2, particular attention must be paid to its prevention in that particular specie.
Among the the pests that attack the chestnut tree’s shoots and foliage, the most damaging is the larva of the polyfag moth specie – already well known from other host plants. The most frequently occuring pests are the winter moth (Operophtera brumata) and the motted umber moth (Erannis
After laying its eggs, another pest -- the oak roller weevil -- rolls up the chestnut leaves into a barrel shape, in which its larvae develop. The insects swarm from the end of April to the middle of June, and during their feeding season, they damage the tree’s flower buds. Nevertheless, the damage caused on the foliage is not significant.
In the leaves of the chestnut tree, the larvae of the oak-leaf-mining moth, also called the Tischerid moth (Tischeria ekebladella), dugs white, see-through mines. The moth lays its eggs into the leaves between May and June. The larvae chews on the inside of the leaf, causing white spots in them.
The oak aphid (Myzocallis castanicola) damages the tree by sucking on the apex of the tree’s young shoots and leaves. This specie of aphid, which is native to Europe and North America, also damages Hungarian chestnut
trees. Although the leaves do not roll up as a result of the aphid’s suction, it delays the growth of shoots in nurseries, and causes significant damage in graft-shoot hosts in young plantations. The spraying of pesticides during the shoots’ growth period can effectively limit the damage.
The chestnut weevil (Curculio elephas) most often damages the chestnut tree’s fruits. According to Hungarian observations, the insect swarms around in chestnut orchards around August 20th (Sifter, 1971). The swarming is the strongest in sunny weather around noon. The females lay their eggs into the chestnut’s cupules or around the peduncle joints. The larvae feed on the inside of the nuts, and leave only nutchips and excrements behind. During the ripening of the chestnuts, they chew their ways out of the nuts and retreat into the ground, where they turn into pupas the following July. Since the larvae can also develop inside the acorn of a turkey
oak, the closeness of turkey oak forests near chestnut plantations poses the danger of spreading the pests to chestnut trees. Sifter and Bürgés (1971) developed a warm aerosol-like plant protection method for the protection of older chestnut orchards. Regular soil work in closed industrial plantations does not create favorable living conditions for the pest, so their significance will most likely decrease in such areas. Choosing the right time for the mechanized harvest of the evenly ripening chestnut fruits can also limit the individual numbers of the overwintering larvae. The reason is that the chestnut weevil breeds mostly in areas where the fruits are not regularly harvested, or where there are a lot of trees with small fruits, which remain in the undergrowth of untilled chestnut grove soil. The larvae of the chestnut weevil can only chew itself out of the fallen nut. If the harvest was thorough, the weevil only leaves the produce during storage. Chemical protection will be possible on the smaller grafts
Chestnuts can be damaged by several types of moths. In Hungary, the most common is the acorn moth (Laspeyreisa splendana) and its subspecies (Bürgés, 1973: Gál, 1973). The damage caused by its grayish-yellow larvae is similar to that of the chestnut weevil. The damaged crop can be recognized of the characteristic webs spun among the nutchips and excrements by the larvae.
The acorn moth causes about 5-41% of the damage occuring in western Hungarian scattered plantations. Since its occurance does not decrease in plantations, regular protection against them is necessary.
The chestnut’s protection is determined by sprayings against Endothia bark-death and micosphaerella leaf spot, as well as against other pests.
Prior to the tree’s development of new shoots, it is necessary to use a wash containing unorganic copper against Endothia-caused infections. The shooting of
the chestnut occurs relatively late, in the second half of April; it is then necessary to protect the plant against the ascospores of the micosphaerella leaf spot with mancoceb-conatining substances -- supplemented by trichlorphon -- against insects that tend to damage the tree’s shoots and foliage.Until the next budding period in the second half of June, only two or three more sprayings are necessary, primarily against micosphaerella leaf spot. In case of rainy weather, it is also necessary to protect the plants against micosphaerella leaf spot during the summer shoot-growth season. In addition, starting at the beginning of August, it is important to protect the plants against chestnut weevils and acorn moths by spraying the plants with substances conatining methylsinphos, prolate, or trichlorphon, three times every other week. To protect the plants against micosphaerella leaf spot and Endothia, fallen leaves and tree branches need to be sprayed with DNOC after defoliage.