In severe cases of venturia inaequalis fungal infection, the entire apple tree can die if the fungal scab is not treated. Fungal spores which have over wintered on apple plant debris such as fallen leaves and twigs, emerge. Venturia inaequalis fungal spores often over winter on fallen fruit which is known as a mummy, or mummies if there are more than one apple fruit. Fungal spores are also splashed from the cankerous scab lesions on the apple tree bark. Water splashes venturia inaequalis fungal spores from these over wintered portions of infected apple trees.
Wind can also spread venturia inaequalis fungal spores.
Those fungal spores which land on uninfected portions of healthy apple fruit trees, then begin to infect the healthy areas rapidly. As venturia inaequalis scab infection continues on previously uninfected leaves, twigs and apples the entire tree may quickly become reinfected and show signs of scab damage due to the spread of fungal spores which over wintered and spread each spring. This is why it is especially important to treat signs of venturia inaequalis scab as soon as they emerge and are evident as apple tree damage and not let the damage continue on to the following year s growing season. Once the characteristic olive or brownish velvety spots appear, you have no choice but to ride out the rest of the season. Apples which have spots but have not cracked open or split can be eaten if peeled.