Among the diseases of fruit crops, one of the most dangerous is a bacterial burn. Pears suffer most from this disease: three-year-old trees die in three months. The causative agent is the bacterium Erwinia Amilovora. The apple tree is less susceptible to the disease. On it, a bacterial burn develops more slowly, the tree dies, as a rule, in the second year after infection.
Until recently, it was believed that in Russia this fruiting disease was not detected. However, in the south of the country, pear plantations with affected trees were discovered not so long ago. And recently, photos of fruit trees with obvious signs of a bacterial burn have begun to appear on various garden forums. Above you see just such a photo. The author of the photo lives in the Krasnodar Territory.
The incidence depends on the variety, the age of the tree, the juiciness of the tissues and spring meteorological conditions. The disease manifests itself most severely when the air temperature in the spring is warmer than average. Warm rains especially contribute to the rapid spread of the pathogen, which leads to the fall of flowers. Infection of branches can occur from the end of May to June in the rainy season. Hot summers usually slow or stop the disease.
Symptoms of infection can be observed on all above-ground tissues, including flowers, fruits, shoots, branches, and in a stock, near the grafted union on the lower body. Symptoms are generally easy to recognize and distinguish from other diseases.
Signs of the disease appear when the pears bloom. Infected flowers suddenly fade, become light or dark brown. The infection spreads down from the stalk and the bark becomes watery and dark green. Leaves turn brown or black, but usually remain on the infected branch throughout the growing season.
The characteristic signs of infection with the Erwinia Amilovora bacterium were continuous blackening and curling of leaves, the death of bark, shoots. First, the leaves on one shoot turn black and curl, then the disease spreads throughout the skeletal branch, and in an intensive course it covers the entire plant.
A more significant sign confirming the spread in the garden of a pear burn is the nature of the defeat of leaves and shoots. Blackened leaves do not fall, but remain on the branches; shoots with leaves look like scorched by a fire, hence the name - burn.
Cortical necrosis occurs with extensive spots with a clearly defined dying zone. Sites of dying off are accompanied by cracks, the crust in these places shrinks.
Infected shoots often form a “shepherd’s hook” at their tips.
The degree of spread of infection depends on the variety of affected plants. Trees of unstable varieties die. Partially resistant varieties carry the disease in a more or less severe form. The surviving plants in the third or fourth year after infection can restore productivity.
A distinctive feature of the garden with burned plants was a huge number of wasps. It can be assumed that in the first half of the growing season, before the fruits appeared, one of the essential elements in the diet of wasps was exudate (mucous fluid), secreted by plants in this disease.
Infection can also spread in the root zone, which leads to the death of trees. Rhizome does not show typical symptoms of this disease. They are sometimes mistaken for root rot.
Affected parts of the plant (flowers, fruits, branches, shoots) have droplets of milk or amber color on the surface.These drops contain millions of bacteria that can infect new plants. Insects can spread bacteria. When bees or flies visit infected flowers or the fruits of their body may be covered with bacteria. Rain, wind, fog can also transmit bacteria from diseased to healthy parts of plants.
Of course, for a strict definition of the disease, it is necessary to conduct detailed and systematic observations of the development of the disease in the next season from the time of flowering plants. It is also necessary to experimentally confirm the infectious onset of a bacterial burn, isolate and accumulate the pathogen, conduct its microbiological studies, microscopy and serodiagnosis.
Nevertheless, some measures can now be recommended to limit and treat the disease.
First of all, in the winter it is necessary to carry out a thorough sanitary pruning: the affected shoots are cut off by 15-20 cm below the infection site. The cut points, pruning tools (secateurs, saws) are treated with disinfectors. Cut branches are burned without fail.
In addition, with the beginning of the growing season, multiple treatments with Bordeaux fluid are carried out (up to nine sprayings). The most effective treatments performed in phenophases: the promotion of inflorescences, pink bud, flowering and its end. Eradicating insecticide treatments are also carried out to destroy insect vectors - wasps, flies, aphids.
But advice on treating pears from a bacterial burn with Bordeaux liquid may not work today. This is because the disease today has a fulminant form. The gardener does not immediately notice the signs of the disease and begins treatment too late. Experts note that in laboratory studies in the affected parts of plants are several types of pathogenic fungi and bacteria that cause burns. Together, they strike our trees.
In warm and humid weather, pathogens fall on flowers, young twigs of fruit trees, and from there they spread with great speed not only in your garden, but throughout the district with flies, wasps, cicadas, aphids and other insects. Bacteria enter the vessels of the tree through the thin skin of twigs and we see how they turned from green to brown in one night.
Copper sulfate (Bordeaux liquid) in modern conditions can not cope with these pathogenic fungi and bacteria. He can stop the disease, but he can’t afford to kill pathogens with copper sulfate.
Experts advise to pay close attention to pears (and other fruit trees) in the period from the beginning of sap flow to flowering. Usually it is 2-2.5 weeks. Inspect all branches and trunks. Are there any cracks oozing white juice on them? If there is, then clean them and treat with Ofloxacin. It is a bactericidal, antibacterial pill. Ofloxacin is sold at the pharmacy. Dissolve two tablets in a bucket of water and spray the tree. But the cleaned cracks must be tied with a cloth dampened in Ofloxacin solution so that the drug can penetrate inside and disinfect the bursted sections of the cortex.
Not only Ofloxacin, but also Ampicillin has a similar effect on pathogenic organisms that cause a burn. Two or three treatments in 1.5-2 weeks each of these drugs or both together will have a preventive and therapeutic effect on your trees.
It was not for nothing that I drew your attention to the role of insects in the spread of destructive bacteria. To prevent a bacterial burn and its development, it is necessary to disinfect bees, flies, aphids and other carriers of the disease. How to do it? Fitolavin will help - a fungicide of contact and systemic action. For bees, it is not toxic, but penetrates deep into plant tissue and stays there for a long time. You can use Fitolavin together with Skor. Skor is an antifungal drug. Together with Fitolavin, it will also cope with pathogenic fungi and bacteria.
Change preparations for spraying every one and a half to two weeks - Fitolavin, Skor, Tsineb, Ridomil Gold, Acrobat.
Not only old trees, but also young ones die from a bacterial burn. Pears are mainly susceptible to this disease, but bacteria can also affect apple trees, hawthorn, quince, mountain ash, raspberries.