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Garden Q&A: When is best time to trim plants that show signs of fire blight?

Q: This past year, my flowering quince shrub suffered some dieback from what I was told was fire blight. When can I prune them to clean them up a bit?

A: Winter is the best time to trim off branches infected with fire blight. This is because the infection is dormant in the winter, so the removal of contaminated wood is least likely to spread the disease at that point. Granted, winter pruning of a spring-blooming shrub removes flower buds, but since you’re taking out mostly dead wood anyway in this case, you’re not going to be missing much. Plus, temporarily reducing bloom abundance is a small price to pay for discouraging recurring disease. You can learn more about disease management approaches on our Fire Blight Disease page.

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Classic symptom of fire blight, with burnt-looking foliage clinging to a crook-tipped stem.

The bacterium that causes fire blight can infect a wide range of host plants belonging to the rose family, a group so large and diverse that many of its species are found in gardens. Frequently grown host plants include pear, apple, chokeberry, serviceberry, hawthorn, cotoneaster, and quince (both the large-fruited tree species and the decorative-blooming shrubby species). Learn to identify the particular crook-tipped stem appearance of symptomatic branches so you can remove all traces of infection during winter.

Q: I just noticed odd dots on our cut white-pine Christmas tree’s needles. They’re glossy black rice-shaped things glued to the needle, all in a row. I’ve found the occasional praying mantis egg case before, but not this. Any guesses?

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A: These are the eggs of the white pine aphid. Gardeners are accustomed to aphids giving live birth rather than laying eggs — one reason a population booms so quickly — but they can use both approaches to reproduction at different times of the year. The other reason this can be tricky to identify at first glance is that these eggs are huge for an aphid, bigger than most aphid species themselves. That’s because this species of aphid is pretty large — as an adult, about 6 to 7 millimeters. The group they belong to are called giant conifer aphids. (It’s akin to a swan’s egg being about the size of an adult wren or chickadee … same type of animal, drastic difference in size.)

These are host-specific aphids, so even if they were to hatch in the warmth of the house, they won’t infest any indoor plants. My guess is they won’t hatch to become a nuisance, especially if they haven’t thus far and you are going to be taking the tree down soon. If you leave it up well into the winter, be on the lookout for spidery legged black aphids roaming around, just in case. Don’t squish them since they might stain objects purple in the process.

These aphids overwinter as eggs, but don’t worry about introducing them to your landscape if you compost the tree yourself or use the brush to shield pansies from the brunt of winter’s weather. They are a native species, and only excessively high populations would pose a health risk to young white pine trees. Plenty of predatory insects and even insect-infecting fungi attack aphids and keep their populations in check.

University of Maryland Extension’s Home and Garden Information Center offers free gardening and pest information at extension.umd.edu/hgic. Click “Ask Extension” to send questions and photos.


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