Symptoms are first noticeable in mid to late July. A broken limb or twig will serve as an overwintering site. The organism overwinters in decayed fruit and in cracks on the old bark. With age the spots become almost black and have a saucer-shaped depression. Infected fruit are characterized by a firm rot which forms a circular light brown spot. Fungicides should be applied at full leaf development and continued at two week intervals for four sprays.īitter Rot (fungus – Glomerella cingulata): The fungus attacks apples and pears and enters the fruit through uninjured skin. Secondary infection can occur during the spring and summer when the temperature is near 75oF. After infection there is a period of one week before symptoms are observed. In the spring, twig lesions produce spores which are washed by rainfall to leaves. Lesions also occur on twigs and are the overwintering inoculum. They sometimes coalesce to cover a large portion of the fruit surface. Fruit spots are one-fourth inch in diameter, black, and slightly depressed. As the spots get older, they develop purple margins with brown centers. Leaf Blight and Fruit Spot (fungus – Entomosporium maculatum): Leaf spots first appear as small purple spots which enlarge. Reapply a bactericidal spray to an orchard if it is damaged by hail or receives a heavy rain immediately after an application.Apply bactericides on 5 day intervals between early bloom and late blooms. Make pruning cuts 8 to 12 inches below visible sign of disease. Remove overwintering bacteria cankers by pruning.Summer pruning may encourage tender succulent growth which is more susceptible to disease. Plant resistant or tolerant varieties: Kieffer, Orient, Garber, or Douglas.The control of fire blight is based on several steps: Fire blight is favored by a mean temperature of 60oF or above. During periods of high humidity, the bacteria can enter into young leaves. Ooze is continually being produced which can add to secondary infection. After blossom infection, bacteria spread into the fruit peduncle and finally into the twig. Spread by honey bees is increased during periods of warm temperature, sunshine, and still air. Bacteria continues to be spread further by insects visiting the blighted blossom and carrying the bacteria to adjoining blossoms. Once bacteria enter a blossom, the blossoms are blighted within 7-10 days after infection. Splashing rain can also spread the bacterium. Insects are attracted to the ooze and it is carried to the open blossoms. As the bacterium increases, an ooze is formed at the margin of the canker. In the spring the bacteria begin to multiply at the same time growth starts. Active bacteria are in the healthy tissue next to the canker rather than in the canker. Fire Blight (bacterium – Erwinia amylovora): The bacterium causing fire blight overwinters at the margins of the cankers formed on twigs and branches in the previous season.
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