News release: Fireblight, Part II

Tim Baker, MU Extension Horticulture Specialist
102 N. Main, Suite 1, Gallatin, MO 64640
660-663-3232, bakert@missouri.edu

Release Date: August 7, 2014

Headline: Fireblight, Part II

In my last column, I discussed a serious bacterial disease of apples, pears, and related species.  This week, I would like to give you a few ideas on how to approach the problem.

Control of fireblight is not easy, once the plant is infected.  There are some chemical means of control, using streptomycin sprays, but this is sometimes not practical for homeowners due to its cost and the difficulty of treating large trees.  If your tree is particularly valuable, you may want to use these sprays anyway.  They will require up to five applications to effectively control the disease.

In addition to sprays, removal of infected plant parts by pruning is necessary.  The best time to prune is late winter, before the disease starts to spread.  Unfortunately, the cankers where the bacteria overwinter may not be as visible compared to during the growing season.  Pruning should not be attempted during the spring or early summer, since it is easy to spread the disease into healthy parts of the tree at this time.  You may prune lightly during late summer after all leaf growth has stopped.  Be sure to cut at least 12 to 18 inches into symptom-free wood to be sure you are getting the entire diseased portion.  Larger limbs should only be removed in late winter.

Be careful in applying fertilizer.  An excess of nitrogen will encourage vigorous shoot growth, which provides optimal conditions for fireblight infection.  If the tree is susceptible to fireblight, it is best not to add fertilizer unless the tree definitely needs it.  By encouraging slower growth, this will give you more time to control the disease.

The best way to control fireblight is by choosing resistant varieties to plant.  This is especially true for pears, which are highly susceptible to the disease.  If you are considering planting apples, you may want to request a guide sheet that we have on disease-resistant apple cultivars.

As I mentioned last time, an excellent video about fireblight has been produced by another MU Extension Horticulture Specialist. You can find it on the web at: http://vimeo.com/98732725