Among the bacterial diseases of fruit crops one of the most dangerous is bacterial burn. The causative agent is the bacterium Erwinia Amilovora. Pear suffers most from this disease: three-year-old trees die in three months. The apple tree is less susceptible to it - on it a bacterial burn develops more slowly, the tree perishes, as a rule, in the second year after infection.
Bacterial burn on a pear Until recently, it was believed that in Russia this fruit disease was not detected. However, in the south of the country, pear plantations with affected trees were discovered not so long ago. And recently, no different garden and garden forums began to appear photos of fruit trees with clear signs of a bacterial burn. 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 richness of the fabrics and the spring meteorological conditions. The disease is most pronounced when the air temperature in the spring is warmer than average. Warm rain especially contributes to the rapid spread of the causative agent, which leads to abscission of flowers. Bacterial burn branches can occur from the end of May to June during the rainy period. Hot summer usually slows or stops the disease.
Symptoms of a bacterial burn can be observed on all above-ground tissues, including flowers, fruits, shoots, branches, and in the rootstock, near the graft union on the lower body. As a rule, the symptoms are easy to recognize and distinguish from other diseases.
Disease symptoms appear when pears are in bloom. Infected flowers suddenly fade, become light or dark brown. The infection spreads down from the stem and the bark becomes watery and dark green. The leaves turn brown or black, but usually remain on the infected branch throughout the growing season.
Bacterial burn on a pear. The characteristic signs of a bacterial burn were continuous blackening and twisting of the leaves, dying bark, shoots. At first, the leaves on one shoot turn black and curl, then the disease spreads throughout the skeletal branch, and with intensive flow it covers the whole plant.
A more significant sign confirming the spread of a bacterial burn in a pear garden is the nature of the damage to the leaves and shoots: the blackened leaves do not fall off, but remain on the branches;shoots with leaves have the appearance of scorched fire, hence the name - a burn.
Necrosis of the cortex occurs with extensive spots with a clearly defined area of extinction. Lots of extinction are accompanied by cracks, the crust in these places shrinks.
Infected shoots often form a "shepherd's hook" on their tips.
Bacterial pear burn - “shepherd's hook” The extent of the spread of a bacterial burn depends on the variety of plants affected. Trees unstable varieties die. Partially resistant varieties tolerate the disease in a more or less severe form. The remaining plants in the third or fourth year after infection can restore productivity.
A distinctive feature of a garden with a bacterial burn patient with pear plants was a large number of wasps. It can be assumed that in the first half of the growing season, before the appearance of the fruits, one of the essential elements in the diet of the wasps was exudate( mucous fluid) secreted by plants during a bacterial burn.
Bacterial burn can also spread in the root zone, which leads to the death of trees. Rhizome does not show the typical symptoms of a bacterial burn. They are sometimes mistaken for root rot.
The affected parts of the plant( flowers, fruits, branches, shoots) often have droplets of a milky 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 can be covered with bacteria. Rain, wind, and fog can also transmit bacteria from diseased to healthy parts of plants.
Of course, for a rigorous definition of a disease, it is necessary to conduct more detailed and systematic observations of the development of the disease in the next season from the time of flowering. Experimental confirmation of the infectious onset of a bacterial burn, isolation and accumulation of the pathogen, its microbiological research, microscopy and serodiagnosis are also necessary.
However, we can already recommend some measures 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 15-20 cm below the point of infection. Cut-off sites, cutting tools( pruners, saws) are treated with disinfectors. Cut branches are burned without fail.
In addition, with the beginning of the growing season, multiple Bordeaux liquid treatments( up to nine sprays) are carried out. The most effective treatment performed in phenophases: the extension of the inflorescences, pink bud, flowering and the end of flowering. Also carry out the eradicating treatment with insecticides to kill insect vectors - wasps, flies, aphids.
Not only old trees, but no less young trees, are dying from a bacterial burn. Pears are mainly susceptible to this disease, but bacteria can also infect apples, hawthorn, quince, ashberry, raspberry.
