Powdery Mildew

Powdery mildew can be a persistent disease of susceptible apple cultivars throughout the United States. It is one of the most predominant diseases in the more arid apple growing areas. It is the only fungal apple disease that is capable of causing infection without wetting from rain or dew.

Powdery mildew causes whitish lesions on curled or longitudinally folded leaves, stunted whitish-gray twig growth evident on dormant shoots, and fruit russeting. Economic damage occurs in the form of aborted blossoms, …

Fire blight

Fire blight is a destructive bacterial disease of apples and pears that kills blossoms, shoots, limbs, and, sometimes, entire trees. The disease is generally common in most apple-growing regions of the US; although, outbreaks are typically very erratic, causing severe losses in some orchards in some years and little or no significant damage in others. This erratic occurrence is attributed to differences in the availability of overwintering inoculum, the specific requirements governing infection, variations in specific local weather conditions, and …

Disease Management in Apple Trees and Fruit

Southern Blight in Apple Trees

Southern blight is a fungus disease caused by Sclerotium rolfsii. The disease is a problem primarily in the Piedmont apple growing region in the southeastern United States. S. rolfsii is a widespread pathogen that affects several hundred plant species. The fungus affects the lower stems and roots of apple trees, killing the bark and girdling the trees. The disease is characterized by the presence of a white, weblike mycelium, which often forms at the bases and on the lower stems …

Apple Scab

Apple Scab

Apple scab is a fungus disease caused by Venturia inaequalis. It is of major economic importance and, if not controlled, can cause extensive losses (70% or greater) where humid, cool weather occurs during the spring months. Losses result directly from fruit or pedicel infections or indirectly from repeated defoliation, which can reduce tree growth and yield.

Symptoms

Apple scab lesions occur on leaves, petioles, blossoms, sepals, fruit, pedicels, and less frequently, on young shoots and bud scales. The first lesions …

What apple cultivars are resistant or susceptible to bitter rot?

Bitter rot is a fungus disease that causes fruit rot during the summer and preharvest period. The bitter rot fungi are almost worldwide in distribution and cause an especially important disease in the southern areas of the United States. Outbreaks can occur rapidly, and losses can be severe, especially under prolonged warm, wet weather. Several host species can be affected. On peach and nectarine, the same fungus causes a disease known as anthracnose, and on grape it causes ripe rot. …

What is thread blight, and how do I identify and manage the disease on apple trees?

Thread blight is a fungus disease caused by Corticium stevensii. The disease is primarily a problem in poorly managed orchards in the southeastern United States. Thread blight symptoms are readily noticed in early summer. Leaves wilt and turn brown, usually in the interior or shaded portions of the tree. Dead, curled leaves cling to blighted branches, frequently in mid-branch, with unaffected leaves still appearing on both sides of the diseased area. In well-managed orchards, the disease is usually not …

What is white rot, and how do I identify and manage the disease on apple trees?

White rot is often referred to as Botryosphaeria rot or Bot rot and is caused by Botryosphaeria dothidea, a serious fungal pathogen of apple fruit and wood. The fungus causing white rot is ubiquitous in nature, occurring on a wide variety of woody plants including birch, chestnut, peach, and blueberry. Fruit rot infection is most common in areas of the southeastern United States where losses of up to 50% have been reported. The canker phase of the pathogen can …

What are wood rots in apple trees?

Wood-rotting fungi cause losses over longer periods of time than most other diseases. Losses are caused mainly by breakage of branches and trunks due to a decline in the structural integrity of the wood. Structural integrity of the wood is altered by the enzymatic digestion of wood cell-wall components by the fungal pathogen or pathogens that have colonized the wood. Some of the same fungi that cause wood rot can also cause dieback. Learn more and see images in this …