Stone Fruit Disease - Brown Rot

The disease can also infect apple fruit late in the season, especially if the orchard is in proximity to stone fruit with a high incidence of brown rot. It is one of the major stone fruit diseases in Pennsylvania.

Symptoms

Brown rot first affects blossoms, which wilt and turn brown. Blossom infections may also extend into twigs, causing necrosis and eventual girdling. The infected blossom parts serve as a source of fungus spores for future fruit infections. Fruit decay occurs as the fruit ripens. The infections begin as small brown spots, and the entire fruit can rot within a few hours under favorable conditions. Under wet and humid conditions, ash-gray to brown tufts of fungus develop over the surface of the infected area. If favorable weather conditions persist, the infection can spread from the fruit into small twigs and cause a canker. The canker may girdle the twig, causing it to die. Rotted fruits dry out and become mummified.

Disease cycle

The fungus overwinters in mummies and cankers formed the previous season. The mummies persist in the trees or on the ground over winter. The first fungus spores are formed about the time the blossoms begin to open. Upon wetting, the spores are forcibly ejected into the air to be blown by the wind to blossoms. Infected blossoms serve as a source of the fungus for future fruit infections; however, infected blossoms do not need to occur for fruit infections later in the season. Environmental conditions are important for the development of the disease. Warm, wet, or humid weather is very favorable for the development of the disease. The severity of brown rot increases as the fruit ripens. Wounded fruit is more susceptible to infection. Mature fruit can completely decay in two days from the time of infection under favorable weather conditions.

Disease management

Removing all rotted fruit after harvest helps to reduce the amount of fungus overwintering in orchards. In addition, remove dead or cankered wood when pruning. Summer pruning will increase air circulation, allowing faster drying and fewer fruit infections. Insects can be important vectors of the fungal spores during fruit ripening by carrying spores to injury sites produced by oriental fruit moth, Japanese beetle, green June beetle, and other insects that can injure fruit. Wounded fruit are much more susceptible to brown rot than unwounded fruit. It's critical to be on top of insect management. Under the right conditions, "healthy" fruit harvested can be contaminated and may decay later during storage. Apply fungicide sprays during bloom and at 18 days, 9 days, and 1 day before peach harvest to limit rots pre- and postharvest. Captan used as a cover spray has been shown to decrease the available spore load leading to harvest. To reduce the risk of resistance, alternate fungicides by FRAC Group. The key for growers who farm organically or prefer using alternative products is to spray as often as possible as disease conditions persist, manage insects, scout often, and prompt removal of infected fruit as soon as you see it. Spraying often ensures you have continuous protection; removing infected fruit from the trees ensures you are decreasing the amount of spores available to cause disease and hopefully minimizing an epidemic. This may translate to spraying every few days, especially if rain washes off products. Some organic options labeled for brown rot control are sulfur, Serenade ASO, Double Nickel, and Oso.