Brown rot is one of the most destructive diseases of peach and nectarine in Virginia, and also occurs on other stone fruits such as apricot, cherry, and plum. When environmental conditions favor this disease, crop loss can be devastating.

The Virginia Pest Management Guide (PMG) series lists options for management of major pests: diseases, insects, nematodes, and weeds. These guides are produced by Virginia Cooperative Extension and each guide is revised annually. PMG recommendations are based on research conducted by the Research and Extension Division of Virginia Tech, in cooperation with other land-grant universities, the USDA, and the pest management industry.

This guide contains information on pesticides used in orchards, with a seasonal treatment of when and how these materials should be employed. Efficacy information toward major fruit pests as well as beneficial species is included.

In this publication, we describe apple blotch disease, also known as Marssonina leaf blotch, an emerging apple disease in the Eastern United States. This disease leads to severe apple tree crown defoliation that indirectly affects the apple fruit size, color, yield and twig development. The causal gent of this disease is a fungus Diplocarpon coronariae (also known as Marssonina coronaria).

Fungal species in the Colletotrichum genus are the causal agents of bitter rot on apples. In Virginia, six Colletotrichum species cause apple bitter rot: C. fructicola, C. chrysophilum, C. siamense and C. theobromicola from CGSC and C. fioriniae and C. nymphaeae from CASC. Over the past two decades, bitter rot infections have been increasing in the Mid-Atlantic region, where these pathogens are becoming more prevalent due to increasingly warm and wet weather conditions that favor Colletotrichum growth. The region produces approximately $500 million worth of a worth of apples every year. Losses to bitter range from 14% to 100% in commercial apple orchards. This publication describes causal pathogens, their biology and management approaches and has practical and scientific significance.

European canker, caused by the fungal pathogen Neonectria ditissima (Tul. & C. Tul.), is one of the most destructive diseases of apple (Malus domestica) that has been a significant issue in Canada, Europe and New Zealand. The disease leads to branch dieback, reduced yields, and significant orchard losses in regions with cool, wet climates. In Virginia and across the Mid-Atlantic, conditions can favor the establishment of this pathogen, especially in high-density orchards and at higher altitudes. Despite decades of study, N. ditissima remains challenging to manage due to its long latent infection period, ability to infect a wide range of wounds and hosts, and production of multiple spore types throughout the year.

Fire blight is one of the most damaging bacterial diseases that affects major pome fruit trees, causing high economic losses. It was first noticed in the Hudson Valley up-state New York in 1780 and has spread to the entire North American continent since then. It is endemic to Virginia consistently threatening apple and pear orchards across the state. The causal agent of this detrimental disease is a Gram-negative rod-shaped bacterium Erwinia amylovora. The most distinctive symptoms of the disease include wilting and blackening of flowers, shoots, twigs and foliage that appear as if it has been swept by fire, giving rise to the name ‘fire blight’. The principal pome fruits affected are from the Rosaceae family, such as apple (Malus x domestica), pear (Pyrus communis), Asian pear (P. pyrifolia), and quince (Cydonia oblonga). The fire blight pathogen overwinters primarily inside cankers on infected host plants, which are dead elliptical to irregular patches of bark on perennial wood of branches, central leader, trunk or rootstock. The bacteria spread from active symptoms on the plant or contaminated flowers through non-pollinating and pollinating insects, birds, wind and rain during the flowering and shoot growth periods. E. amylovora primarily enters host plants through nectarthodes (nectaries) of flowers, with mechanical openings like pruning wounds, breakage or abrasions serving as additional important infection pathway. Fire blight outbreaks significantly devalue the orchard, interrupts fruit production and/or reduces the crop yield and price, leading to severe economic losses. Several cultural and chemical management practices have been adopted to manage the pathogen. However, in the last 20 years, managing fire blight has been challenging due to frequently occurring favorable weather conditions during bloom and shoot growth, thus propelling multiple infection periods which are difficult to prevent.