CANKER (NEONECTRIA GALLIGENA)
Apple Canker is a disease caused by a fungus, Neonectria Galligena which does damage by attacking the bark of apples and some other trees causing huge losses through girdling of branches, resulting in death of the plants. If it is not checked in time, it can affect every branches and sections of trees. It is common where trees are suffering stress as a result of drought or water logging. Canker is also a result of improper pruning techniques and undressing of large wounds with paste. Canker infections are seen more in lower altitudes below 5000 feet above sea level and where chilling hours requirement is not met with completely.
In spring canker causes reddish brown scars on small branches. These scars elongate into cankers which causes die-back of shoots. The infection may damage the stem and kill it in a single season. It infects young twigs in the spring and cross infect to older wood, it can infect the trunk and can kill a tree. On the positive side older trees badly infected will often fruit well, as the tree is put under pressure where the sap flow is constricted, it can infect fruit and effect storage qualities.
Spores from new cankers are spread by rain or overhead irrigation during the late summer and leaf fall, and initiate new infections that appear as cankers during April through July of the following year. Cankers that are allowed to overwinter produce airborne spores during the following spring and summer that can initiate new infections at a distance from the source. The airborne spores function mainly to initiate new infections, while the water-borne spores serve to intensify the disease in trees that are already infected. Small bodies appear on dead wood and begin to produce spores once temperatures are above freezing. Infections does not occur when trees are growing vigorously, mainly it occurs during early spring, fall, and winter. Most important sites of infection are pruned wounds and injured wood caused by mechanical injury.
Completely cut all affected smaller branches and in large branches try to cut all infected material. Paint immediately with a protective wound paint such as Chaubatia paste or Bordo paste to prevent the wounds becoming reinfected. Collect the infected wood and burn it. The fungus can still infect other plant life through wind transfer of the fungus.
The best way is to spray with copper containing fungicides like bordeaux mixture, copper oxychloride or copper hydroxide. BORDEAUX MIXTURE can be prepared by mixing hydrated lime solution with copper sulphate solution. Dress the wounds by chaubatia paste comprising of copper carbonate, lead oxide and linseed oil in ratio 0.8:0.8:1 respectively. Best time to spray is after pruning and after fruit harvest.