Dieback and canker diseases threaten productivity by reducing the lifespan of trees. Dieback symptoms are often observed in spring when buds fail to sprout, foliage appears stunted and cankers and gummosis are evident (Heynes 1960) and summer when dead limbs become apparent following heat or water stress. Symptoms include branch and main scaffold dieback as well as cankers and vascular necrosis. Canker diseases cause necrosis of vascular tissues, which restrict water movement and result in dieback symptoms (Agrios 2005).

In the Pacific Northwest, dieback in cherry is most commonly caused by bacterial canker (Pseudomonas syringae) and the fungal canker Leucostoma canker (Leucostoma persoonia, Leucostoma cinctum, Cytospora leucostoma, and Cytospora cincta) (Regner et al. 1990). In California Calospheria canker is also common and Eutypa canker has been found in stone fruit (Trouillas 2012).

Leucostoma canker of stone fruits (Cytospora)

Leucostoma canker, is also called perennial canker, Cytospora canker, and Valsa canker.

Symptoms

• ‘Flagging’ of dead scaffold limbs (Biggs and Grove 2005).
• Sunken elliptical lesions (Abramians 2013).
• Branches girdled by cankers wilt, defoliate and dieback (Biggs and Grove 2005).
• Gummosis.
• Often pimple-like spore producing structures on canker surfaces.

Figure 2. Canker margins are generally distinct compared to those of Bacterial canker which often have unclear margins.

Figure 3. When bark is removed pinhead size structures called pycnidia may be present.

Pathogen

Leucostoma persoonii and Leucostoma cinctum (teleomorphs) Cytospora leucostoma and Cytospora cincta (anamorphs) (Syn. Valsa leucostoma, Valsa cincta) (Biggs and Grove 2005).

Hosts

Cultivated peach, plum, prune and cherry (Prunus spp.), other wild Prunus species, also encountered occasionally on apple (Malus domestica).

Disease cycle

Leucostoma pathogens invade the host through wounds (sunburn, winter-injury, pruning wounds, shot hole borer, frozen buds) or dead tissue (Ogawa et al. 1995). From late winter to early spring, these fungi produce an abundance of pimple-like pinhead size structures called pycnidia, which appear as small raised dots on the branch (Abramians 2013). The conidial spores, which cause infection, develop throughout the year, but are greatestin number in spring and summer (Grove and Biggs 2006). Spores are moved by splash from rain and over and under-tree irrigation (Grove and Biggs 2006) and can travel up to 7.6 m. Under humid conditions cream to orange colored spore tentrils called cirrhi exude from mature pycnidia and contribute to the disease spread (Abramians 2013). Cankers grow rapidly in the spring. When the tree grows rapidly through the summer the tree resists further growth of the fungus into healthy tissue and may form a callus ring around the canker. Often in the fall or early spring the canker continues to expand and can cause concentric rings (Biggs and Grove 2005).

Management

• Management which reduces injury from sunburn and winter injury is critical (Ogawa et al. 1995). Avoid excessive and late season nitrogen fertilization to limit low-temperature injury and use leaf analysis to determine nutrient needs.
• Remove dead and diseased, weak limbs.
• Remove infected limbs at least one foot below sign of disease. Infected material should be removed from the orchard and burned if possible.
• Infection at pruning is less frequent when pruning is delayed until late in the spring when wounds heal more rapidly and conditions are dry (Biggs and Grove 2005).
• When summer pruning delaying irrigation until wounds heal (14-21 days) can reduce infections (Grove and Biggs 2006).
• Severity of infection declines beginning about three days after wounding (Biggs 1989).
• White trunk paint on newly planted trees can reduce incidence of cankers (Spotts et al. 1990). Winter injured tissue can be a significant location of infection.
• Avoid under-tree impact sprinkler irrigation systems – they are extremely efficient at disseminating the canker pathogens (Biggs and Grove 2005).

Table 2. Efficacy of Fungicide treatments

Eutypa dieback

Symptoms and Signs

• Limb and twig dieback and wilt suddenly occurring in spring and summer.
• Dark discoloration of bark with sunken cankers (Munkvold 1994).
• Amber gumming (Munkvold 1994).
• Can cause V shaped discoloration in cross section of branch. Other canker pathogens such as Botraspheria can cause similar v shaped discoloration (Abramians 2013).
• When bark is scraped back black perithecia of lata are embedded in black stromata consisting of a mix of fungal and host tissue (Abramians 2013).

Pathogen

Eutypa lata common as a dieback pathogen of grapes is known to infect sweet cherry in California (Munkvold 1994).

Disease Cycle and Infection

The pathogen infects wounds (eg pruning) when wet from rain or irrigation (Adaskaveg and Caprile 2015). A spore called an ascospore infects the plant (Pearson, 1980).

Host range

Often considered a pathogen of grapevines, occurs on at least 88 species with pathogenicity confirmed for grapevine, apricot, sour cherry, chokecherry, apple, pear, walnut, olive, and sweet cherry (Grinbergs D et al. 2021;  Munkvold 1994) (Carter 1991).

Management

• Remove infected limbs at least one foot below sign of disease (Adaskaveg and Caprile 2015).
• Removal of diseased limbs is best when it is dry (July, August). If pruning outside of dry periods, protect pruning wounds with a fungicide (Adaskaveg and Caprile 2015).
• Susceptibility of pruning wounds decreases over time (Abramians 2013). Perform horticultural pruning in time periods with four plus weeks of dry weather.

Table 2. Efficacy of Fungicide treatments

Contact

Tianna DuPont
Regional Extension Specialist, Tree Fruit
509-293-8758
Cell 509-713-5346
tianna.dupont@wsu.edu

Gary Grove
grove@wsu.edu

August, 2023.

Source: Washington State University