Dwarf Alberta spruce notoriously trouble plagued
Q uestion: I have a dwarf Alberta spruce in front of my house, next to the walkway. Last season, I noticed that some of the needles were turning brown and falling off the plant. At first it was just from the inside of the plant, but now it appears that the whole plant is losing needles. It’s about 10 years old so I’d like to try to keep it alive if possible. Do you know what’s going on with my dwarf Alberta spruce?
Answer: Dwarf Alberta spruce (Picea glauca ‘Conica’) are notoriously trouble-plagued plants, prone to a number of maladies. Though they remain fairly popular among homeowners, there are many trouble-free alternatives that make a far better choice for homeowners who don’t want the fuss. Good alternatives include weeping blue spruce (Picea pungens ‘The Blues’), dwarf Hinoki cypress (Chamaecyparis obtusa nana gracilis), Blue Wonder spruce (Picea glauca ‘Blue Wonder’) and boxwoods.
If you’d like to get to the bottom of what’s wrong with your plant, here are a few common problems with this variety of spruce.
First, dwarf Alberta spruce are not tolerant of salt spray. If you use rock salt or another ice melter on your front walk, salt build-up or salt splash could be causing your needle drop. Discontinue using these products and add compost to the soil in spring to help process some of the salts out of the soil.
Dwarf Alberta spruce also much prefer drier conditions to humid ones, so if the planting site is very sheltered with limited air circulation, the plant can suffer and be more prone to the following two afflictions.
Most commonly, dwarf Alberta spruce fall victim to spruce spider mites. These tiny yet extremely destructive relatives of spiders can quickly kill a tree. Since they’re so tiny, mites are almost impossible to see. To check for an infestation, come spring, head out to the plant with a piece of white paper. Hold the paper out flat an inch or two beneath a branch. Shake or tap the branch and then check the paper, carefully inspecting it for miniscule moving spots. If they’re present, mites are to blame for your problem.
Controlling mites is extremely challenging. They’re resistant to many chemical pesticides (some even enhance their reproductive capabilities!). Sprays of horticultural oils can be effective, though they also kill the beneficial mite species that help keep spruce mites under control naturally. Spruce mites are most active during cooler temperatures, when they feed by sucking the juices out of the needles. They also leave very fine webbing behind.
Generally, when mite populations build up enough to cause significant needle drop, there’s little that can be done. At that point, it’s best to find a replacement.
Another possibility is a fungal canker known as cytospora canker that can also cause needle browning and drop. This pathogen is most common on older Alberta spruce. In addition to needle drop, when this pathogen strikes, you’ll also see patches of a white, dried sap-like substance on the innermost branches and trunk. This fungus loves wet weather like the conditions we had last summer. There is little to be done once cytospora canker is confirmed. It easily spreads from plant to plant on pruning equipment and clothing. Again, it’s best to replace the plant with a trouble-free choice if this fungal disease strikes.
Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio with Doug Oster. She is the author of several gardening books, including “Attracting Beneficial Bugs to Your Garden,” “Good Bug, Bad Bug,” and her newest title, “Container Gardening Complete.” Her website is jessicawalliser.com. Send your gardening or landscaping questions to email@example.com or The Good Earth, 622 Cabin Hill Drive, Greensburg, PA 15601.