Eutypa dieback—Eutypa lata
Brown rot—Monilinia spp.
Blossoms on plants infected with brown rot fungus turn brown and wither. Dead blossoms often cling to twigs for a long time. Sunken, brown areas may develop around twigs at the base of infected flowers, causing leaves at the tips of twigs to shrivel up. Brown, sticky droplets of gum may exude from the base of dead flowers and the bark of infected twigs. Velvety gray or tan tufts of spores are formed on diseased blossoms or twig cankers. Brown or tan spots spread rapidly over the fruit surface and produce spores.
Seasonal development and life cycle—Brown rot
If you have had problems in the past, applications of copper-containing or synthetic fungicides such as myclobutanil at pink bud stage can help avoid serious losses. Additional applications when fruit starts to color may be needed if rainy weather persists. Do not apply copper compounds after bloom.
Shot hole disease (Coryneum blight)—Wilsonomyces carpophilus
Shot hole, or Coryneum blight, is a serious fungal disease of almonds, apricots, nectarines, peaches, and other Prunus species in California. Reddish or purplish brown spots about 0.10 inch in diameter occur on new leaves and shoots. The spots expand and their centers turn brown. Tiny, dark specks sometimes form in the center of lesions, especially on leaves. Spots on young leaves have a narrow, light green or yellow margin and their centers often fall out as leaves expand, leaving "shot holes." Buds of peach, nectarine, and sometimes apricot are killed in the winter. Fruit may become rough and corky. Spotting occurs on the upper surface. Concentric lesions may develop on branches.
Prune and dispose of infected tissue as soon as it appears. After leaf drop, inspect plants carefully and prune infected buds and twigs with lesions. Diligent sanitation and water management can provide adequate control where the incidence of shot hole is low. Avoid overhead sprinklers or use a low angle to avoid wetting foliage. Also, some varieties may be less susceptible. Where disease incidence is high, fungicides such as Bordeaux mixtures or fixed coppers may be applied. On peaches and nectarines, a dormant spray of copper in late fall will work well.
Peach twig borer—Anarsia lineatella
Peach twig borer is a pest of apricots as well as peaches, nectarines and other stone fruit. Peach twig borer larvae are dirty white or light brown with a black head when they first hatch. The body turns chocolate brown as it grows and the white portions between each body segment give the appearance of bands. Mature larvae grow to about 0.5 inch.
Identification of species
Read about other pests and diseases of apricots.