Agriculture Reference
In-Depth Information
Diseases of Both Pome and Stone Fruits
Some diseases have wide host ranges and attack both pome and stone fruits.
Powdery mildew and root diseases are especially common, and some viruses
can be troublesome for orchardists.
Powdery Mildew
Powdery mildew is caused by many different fungi and attacks the shoots,
leaves, and fruits of many plants. In stone fruits,
Podosphaera pannosa
and
Podosphaera clandestine
cause powdery mildew. In pome fruits,
Podosphaera leucotricha
causes powdery mildew and appears to cause rusty
spot disease on peaches and nectarines.
Symptoms.
Signs of infection are similar in all crops. Leaves and new shoots
become covered with powdery, grayish-white spores, often becoming distor-
ted and developing brown necrotic areas. Infected new shoots often die back,
and new twigs can grow deformed.
Infected fruits first become covered with white mold and gradually turn
russetted and scabby. Rusty spot symptoms appear as small, round orange to
tan spots that enlarge as the fruits grow. On pome fruits, infected fruits de-
velop a network of roughened lines on the skins. Peach and nectarine fruits
are susceptible to infection until the pits harden. Powdery mildew weakens
the trees and reduces the fruit's marketability.
Management.
Remove and destroy diseased wood and fruits while pruning
and thinning. Unlike many fungal diseases, powdery mildew does not need
free moisture (water droplets or films) in order to infect plants. Reducing hu-
midity levels, however, can help combat the disease, so maintain open canop-
ies and good air movement. Shading increases powdery mildew problems, so
keep your fruit crops in full sun. Remove roses and wild and escaped stone
and pome fruits from in and around your orchard.
