Cotoneaster Hedging in Alberta

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Cotoneaster Hedging in Alberta:

Q: My name is Terry Bedel and here I am at the Contoneaster hedge that separates my front yard from that of my neighbor. 2 years ago I noticed rust coloured spots and dying areas.  He cut it right back to the ground but never treated what was left. You can see it has sprouted again and there are a lot more rust spots on the old growth.  Will the hedge survive?  What can be done for it now?  I look forward to your help, Tam!

A:  Hello Terry, Thank you for your question on rejuvenating an old Cotoneaster hedge.  Yes, it will survive!  Here’s what can be done for it now:

Cotoneaster is the hardiest (zone 2) and best hedge for Alberta gardens. It grows quickly, and matures at 2 M, so does not get too tall, has lovely glossy green leaves and great red fall color.  Older mature hedges occasionally need to be rejuvenated, which can mean a severe cutting back. This has already been accomplished in this case. (How severely you cut it back really depends on you–and what you can withstand from a lack-of-privacy point-of-view.) The more you cut it back, the more vigorous it will become.

Growing Tips:

• Cut it Back: The rule of thumb for rejuvenation is to cut the hedge back in height at least by one-half—or if you feel like getting drastic, you could cut back to 30 to 45 cm (12-18”) from the ground.  This would remove most of the old wood and problematic dead stems.
• Water it: As the hedge is mature, it will have a large root system, which will serve it well.  You usually will not need to water it, except during extended periods of drought. Please consider using a soaker hose for several hours every couple of weeks.
• Feed it:  Spring is the best time to fertilize hedges in Alberta.  A healthy, vigorous hedge is less likely to succumb to diseases.  Use a well balanced granular (18-18-18) on the soil under it and coming out at least 45 cm from the centre line. It may be difficult to accomplish that on your neighbor’s side, but it really does need to be done there as well.  Excess nitrogen stimulates new growth, which is highly susceptible to fire blight, so do not use a high nitrogen lawn fertilizer.
• Trim it: – Formative pruning: Do not prune hedge plants so as to form a wall straight-up-and-down. Rather, prune hedges so that the base is wider than the top.  It should be 30 cm (12”) across at the top and 1 M (39”). This will allow sufficient sunlight to reach the growth at the bottom, keeping it healthy.
• When to Trim- Winter or fall: Formative pruning – just after planting, and for the first two years after planting, or after a severe cut back for rejuvenation. Shearing (maintenance pruning): as needed 2 or 3 times through the summer.

Here’s what these orange spots on the cotoneaster are about, and what to do about them:

Cotoneaster Troubleshooting

Coral Spot (orange spots on dead wood), cotoneaster

Nectria canker (coral spot) – Nectria canker (Coral Spot) is a fungal infection which causes orange dots on dead wood (nectria – necrosis – death). It is often seen on wood killed by cytospora canker, and makes it easy to identify dead wood which should be removed. It is often mis-diagnosed as fire-blight – as the spots are fiery red.  It is a secondary infection, and will not have any impact on the new growth.

• Cultural control – pruning out diseased wood is all that is necessary. If old, dead wood inside a hedge is removed and outside, healthy branches allowed to grow, it will rejuvenate it, but not prevent a recurrence as the inside wood again becomes an appropriate place for it to grow, and the fungus is in the sap.
• Chemical control – none

Cytospora Canker

Cytospora canker – Cytospora canker is often mis-diagnosed as fireblight, but the differences are quite obvious. It is a fungal infection which causes longitudinal cracks on branches, with the bark curled back, which often ooze sap in the spring. Because it invades the tissue, it prevents moisture from reaching beyond it, so young leaves develop, then wither and die during hot weather, whereas fireblight moves from the blossom end down the branch. Cytospora canker affects older branches of fruit-bearing trees and spruce, and also cotoneaster hedges. It multiplies in damp, dark places with poor air circulation – the inside of a hedge or spruce tree!

• Cultural control – pruning out diseased wood is all that is necessary. If old, dead wood inside a hedge is removed and outside, healthy branches allowed to grow, it will rejuvenate it but not prevent a recurrence as the inside wood again becomes an appropriate place for it to grow, and the fungus is in the sap.
• Chemical control – none

Fire Blight on Cotoneaster

Fireblight – Fire-blight is a bacterial infection of trees of the Rose family, mostly apples, crabapples, pear, and mountain ash. It is also seen frequently on Cotoneaster hedges. Blossoms appear water-soaked and turn brown. As it spreads to leaves, branch tips curl over like a shepherd’s crook and leaves turn brown, hang on the tree and don’t fall off. The leaves at the ends of the branches are so dark that they appear black, hence ‘scorched by fire’. Cankers are formed which are sunken and cracked, and exude bacterial ooze which contains the bacteria. Fruit rots and bacteria is attractive to insects, which can spread the infection. It can also be spread by birds, rain and tools.

• Cultural control – remove all infected wood well back to healthy wood, clean tools with a 10% bleach solution between cuts!
• Chemical control – copper spray can prevent infection from spreading in a tree or protect another tree if it is in the area, but only lasts 72 hours, so must be repeated often. If infection is caught early and infected branch pruned out, it may do well. If the bacteria infects other branches and is moving in the sap, the tree may not be able to be saved.