. Minnesota plant diseases. Plant diseases. Fic. 194.—Black rot of apple. After Clinton. fruit, when attacked, turns at first a reddish brown but later be- comes blaclf. On attacked portions of the tree the fungus pro- duces its spores. It is an "imperfect" fungus and produces spores in small capsules, which appear on the leaf, twig or fruit spots as tiny black warts. These open to the exterior by minute pores through which the spores, which are cut off of threads lin- ing the interior of the capsule, are thrown out. The treatment which is used against the apple scab is usually recom
. Minnesota plant diseases. Plant diseases. Fic. 194.—Black rot of apple. After Clinton. fruit, when attacked, turns at first a reddish brown but later be- comes blaclf. On attacked portions of the tree the fungus pro- duces its spores. It is an "imperfect" fungus and produces spores in small capsules, which appear on the leaf, twig or fruit spots as tiny black warts. These open to the exterior by minute pores through which the spores, which are cut off of threads lin- ing the interior of the capsule, are thrown out. The treatment which is used against the apple scab is usually recommended in treat- ing black rot. In addition, the dead twigs and limbs should be pruned to prevent the win- tering of the fungus in the twig spots. Rotted fruit should be removed and destroyed. Win- ter spraying has also been recommended. Apple and pear blight [Bacillus amylovorus (Burr.) DeToni.]. This disease is also known as fire blight. Its cause is a bacte- rium. The bacteria gain entrance to the twigs of the apple through wounds or through the flowers. They are carried by insects to the stigma of the flower and from this point work their way into the branches. On the branches they form first small, dead spots, which later enlarge to canker- / like sores, from which a dark mucil- / aginous fluid oozes. In this fluid one finds millions of bacteria. In the canker growth butyric acid, carbonic acid gas, and alcohol are formed. The branch above the canker is killed, often suddenly, and the leaves turn brown as though scorched by fire, hence the common name of fire blight. No successful remedy for diseased branches is known. Pruning back is the only successful method of combating the Fig. 195.—Fire blight of apples. Bacteria which cause the dis- ease. Highly magnified. Aft- er B. M. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations ma
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