Pear rust: identification and control

Pear trees are planted in the landscape for their ornamental spring flowers or edible fruit. They tolerate most soils and easily adapt to many regions. However, pear trees are susceptible to a disease called pear rust which causes leaf spots and fruit destruction. The disease can cause premature leaf drop and total crop loss.


Summary Guide

  • Agent: mushroom
  • name: pear rust (Gymnosporangium sabinae).
  • affected plants Pyrus spp. (pears) and junipers spp. (Junipers).
  • Main symptoms: bright orange spots on the leaves.
  • Calendar: The first leaf spots on pear trees appear in mid-spring, throughout summer, and early fall in warm climates.

Visual symptoms of pear rust

  • Yellow or orange spots of small size (0.5-3 mm) and oval shape, located on the upper side of the leaves of the pear tree.
  • Over time, they enlarge and darken to more orange tones with coppery edges, in some cases with a yellowish border and small dark colored pustules located in the central part.
  • As pear rust progresses, a series of reddish-brown bumps with whitish filaments appear on the underside.
  • Although the disease affects the leaves more, these symptoms can also appear on the fruits, with dark spots and deformations.
  • At an advanced stage, the leaves of the pear tree fall precociously and lesions can form on the branches in the form of cankers.

Usually, bright orange spots appear on the upper side of the leaf. As summer progresses, brown gall-like growths develop on the underside of the corresponding leaf. Fruit can be affected, but it is much less common. In continental Europe, the fungus can also cause persistent cankers (bark lesions) on branches, which can be detrimental especially to young trees.

The leaves can be infected when they emerge from the shoots. If a leaf is infected when it is very young, the degree of mottling and tissue distortion can be severe. If the leaves are larger when infected, the spots will be more spread out on the leaf

These points will grow in the coming months and may merge. Young leaves, flowers and fruits are susceptible to infection. In late spring, tube-like projections are visible on the fruits or on the underside of the leaves.

read more: pear treatment guide

Life cycle of rust on pear

Pear rust (Pyrus spp.) is caused by various fungi of the genus gymnosporangium. Rust fungi of this genus have complicated life cycles that alternate between two different hosts.

The fungus overwinters on the galls of pear and conifer hosts. From late February to early May, these fungal galls produce conspicuous orange gelatinous structures that contain spores.

different species of gymnosporangium cause different symptoms and signs on cedar trees, including orange sticky galls (cedar-hawthorn rust, G. globosum), orange swollen branch galls (cedar quince rust, G. clavipes) and needle rust (cedar Asian pear tree), G. Asian).

Conditions for the development of pear rust

  • Pear rust requires alternation between 2 hosts to cover its full cycle (it is a heteroecious fungus), so it relies on other species of the genus juniperslike junipers and junipers as hosts for winter and pear trees, for spring and summer.
  • From early spring, pear rust becomes active in species juniperscarrying the developed spores (basidiospores of teliospores) by the wind, even up to several kilometers, infecting the newly germinated leaves of the pear tree.
  • The first symptoms of the disease appear from mid-spring or, in later climates, early summer.
  • The optimum conditions for rust are mild temperatures (15-20 ºC) and high relative humidity, often due to rainy periods lasting several days, without wind.
  • Practically all pear varieties are susceptible to attacks, with a particular incidence on the Conference, Blanquilla, Cañella, Limonera, Passa Crassana and Castell varieties.
  • In late summer, pear rust spores (eciospores) infect junipers to repeat the cycle.

rust control

In growing areas where pear rust has been a problem in previous seasons, preventative applications of fungicides to pear trees are recommended.

Some active questions updated to August 2022 are:


Dose of 0.02% (0.2 ml/L or 0.2 L/1000L). Make a maximum of 4 applications per campaign with an interval of 10 days outside pear bud swelling, until the fruit reaches 1 cm in diameter, or every 12-18 days in later stages. Broth volume of 1500 L/ha without exceeding a cost of 0.3 L/ha.

Preventing rust on pear trees

Cultural practices are an important conditioning factor in the development of pear rust. Here are some practical tips to significantly reduce the onset and progression of the disease:

  • Maintenance pruning to eliminate stem rust infections or simply removing entire plants near pear trees will reduce the risk of infection. In general, proceed with a pruning that facilitates aeration.
  • Avoid excessive nitrogen fertilization causing excessive germination.
  • Destruction of pruning and remnants of infected leaves and branches from the previous year.
  • Removing leaves from heavily infected pear trees may do more harm than good.
  • Prune branch cankers seen on pear trees if they are not all over the plant and the pear tree is not badly affected.
  • In new plantations, avoid planting pear trees close to junipers
  • Use of varieties less susceptible to the disease.
  • Avoid planting frames that are too dense.
  • Drip irrigation instead of sprinkling.

For gardening, you can use small containers large enough to carry out 1 or more applications with a 15 L backpack.

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