Pear Rust


How to prevent pear rust from happening each year? Is there chemical spray can be use before it starts. If so, when can I spray?
Also how to prevent decease on leaves of plum trees that make leaves curled with millions of very tiny white insects?
Thank you very much.



Unfortunately, pear rust is now a very common disease in southern Ontario. It appeared about 10 years ago and over the years Toronto Master Gardeners have fielded numerous questions on this topic.

Please visit our website at  for information. On the right side of the screen under Find it Here there is a search box. Type in pear rust and press enter. A wealth of information will appear in the form of articles on this topic for you to read.

Small white insects found inside the curled leaves of your plum tree is most likely Leaf Curl Plum Aphid. These aphids cause the leaves to curl as they suck on the tree’s fluids. This insect produces a high volume of honeydew, which is the excretion of the aphid. This in turn attracts ants that feed on the sweet liquid and causes a fungus to form that produces a sooty mold. The eggs of the aphids overwinter on trees thus making it very hard to control. These insects can cause considerable damage to fruit trees and reduce fruit production. Unfortunately, populations of these aphids can quickly get out of hand.

With regard to using chemical sprays, homeowners have to abide by the Ontario Pesticides bylaw. One can buy only what has been approved for home gardens. [See: <>]. As it happens, there is no registered pesticide in Ontario for control of the rust. This means chemicals are not available to us for combatting diseases such as Pear Rust and Leaf Curl Plum Aphid.

You can apply cultural (natural) methods to control both these problems but they have limited success and require a lot of patience. Continued vigilance is necessary over several years.  Ensure your pear trees are a good distance away from any junipers (the winter host). Good sanitation practices are crucial. Prune out and dispose of  infected branches. make sure you clear everything from under trees. Continually rake up infected leaves and dispose of as they can harbor pests and diseases. Make sure you do not place them in any compost you are producing.  You can try using quick blasts of water from a hose to rinse off the aphids on the plum tree. Limit use of nitrogen fertilizers, which encourages the formation of tip growth, a favourite of aphids. Natural predators such as Lady Beetles are another way to control plum aphids. These can be purchased from reputable garden centres. Other possible treatments include: horticultural oil, neem oil, pyrethrins or non-toxic insecticidal soap. See article below for more information.


Diseased Plum Tree