Perennial Canker

Perennial canker, is characterized by oval or linear cankers which eventually become surrounded by a roll of callus at the margins.Cankers gradually enlarge until infected limbs are girdled and then die. Gummosis is usually associated with the cankers.

The canker fungi overwinter in active cankers in living wood or in dead wood.Infection occurs where the bark is damaged or injured.Infection following cold injury frequently occurs in the crotch angles of affected trees. Other ports of entry for these fungi include pruning wounds, mechanical damage, insect damage and leaf scars.Moisture is required for spore production,spore dissemination, and infection. The rate of canker development following infection depends on temperature and the species of fungus involved. When temperatures do not favor fungal activity, calluses form. Canker activity resumes when temperatures again favor the fungus. This back and forth battle between the tree and the fungus usually ends with the fungus winning.

Life Cycle: Cedar-quince rust is caused by a fungal pathogen called Gymnosporangium clavipes. This fungus occurs on a wide range of rose family plants, including mountain ash, hawthorn, quince, flowering quince, serviceberry, crabapple, and apple . In addition, eastern red cedars, common, prostrate, Rocky Mountain and savin junipers are possible evergreen hosts. In order to survive, the fungus must “move” from one type of host to another.

From the telial swellings on the evergreen host, basidiospores are released that infect deciduous hosts such as hawthorn. Seven to ten days after infection, spots or swellings develop, followed a few days later by the formation of tiny black dots within the spots.Four to seven weeks later, aecia are formed. Aeciospores, released from the aecia during rain or as morning humidity lowers,

become airborne and infect susceptible evergreen hosts during late summer and fall.The following spring (or one year later), swellings (consisting of both fungal and host plant tissues) develop on the evergreen host. When the swellings are mature, a few hours of wet, cool (74 and 78°F is optimal) spring weather is sufficient for repeated telial swelling and release basidiospores that infect the deciduous host. In contrast to cedar-apple rust galls, cedar-quince rust swellings may remain infectious for 4-6 years or more.

Damage: The fungi overwinter in active cankers or in dead wood that they have previously colonized. When conditions are cool and moist in the early spring, spores (conidia) are exuded in a sticky mass from fruiting structures (pycnidia) embedded in the wood. These are then spread by splashing and windblown rain to new infection sites, where the conidia germinate and the fungi begin to colonize under wet conditions. Both fungi are considered weak pathogens; that is, they are unable to invade healthy bark and must initially gain entry into the tree through injured, dying, or dead tissues.

The most common sites of entry are weak, winter-killed twigs in the center of the tree winter-injured wood on major limbs and trunks, short, dead pruning stubs, leaf scars and winter-killed buds on small twigs, and poorly healed pruning cuts especially common for L. persoonii. Broken limbs, injuries caused by farm equipment, and wounds caused by rodents, insects, and other disease organisms provide additional sites of entry.

Control: New plantings. Because perennial canker generally limits the profitability and longevity of northeastern peach orchards, new plantings should always be established with the idea of minimizing disease risk and delaying its introduction. Thus, it is important that new orchards not be established next to old cankered blocks of peaches.

experience shows that this is the best way to exclude the disease from new orchards. Similarly, any wild stone fruit trees with cankers should be removed from nearby hedgerows prior to planting. Choose planting sites with good air drainage and maximum protection against excessively cold temperatures, and plant only the hardier varieties recommended for local conditions.

Nursery stock should be canker free and not excessively large, i.e., no greater than 5/8-inch (16 mm) caliper. Trees should be protected against peach tree borer before planting and headed back once growth begins, to promote wide-angle branching. Heading cuts made on excessively large new trees (such as 2-year old nursery stock) or before new trees start active growth often fail to heal properly, providing a fatal entry point for the canker fungi. At the time of heading, small trees should be pruned to whips, or the retained side branches on larger trees should be pruned back to two or three nodes; do not leave pruning stubs, and remove any dead branches.

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