Most homeowners and gardeners pay the closest attention to the health of their plants and trees during the spring and summer growing season and ignore them during the rest of the year. But just because the leaves fall and the cold weather sets in doesn’t mean plant pests and diseases are no longer a concern.
“In fact, when the leaves drop you may notice an infection or other issues that weren’t apparent before,” said Heather Faubert, who manages the Plant Protection Clinic at the University of Rhode Island, where she diagnoses plant diseases, identifies pest insects and provides treatment suggestions.
“Now is also an especially good time to take a close look at your evergreens.”
According to Faubert, the big concern this winter is boxwood blight, a fungal disease native to Europe that affects boxwood shrubs and was discovered in Connecticut and North Carolina in 2011 and has now found its way to Rhode Island.
Boxwoods are extremely popular for their year-round greenery, their attractive use in Christmas decorations, and for the fact that deer won’t eat them. But the disease makes their leaves fall off and causes black lines to appear on their stems.
Not every unhealthy-looking boxwood is infected with boxwood blight, however.
“Boxwoods can also look bad as a result of drying out or from suffering winter injury,” Faubert said. “If the leaves turn orange or brown, that’s not boxwood blight. But if the only leaves left are on the tips of branches, that’s more likely to be boxwood blight.”
Those preparing holiday decorations from their holly bushes should be on the lookout for hollies whose berries are still green. Faubert said that’s a sign that a fly laid its eggs in the berry last spring and there is a growing maggot inside the berry.
“The maggot isn’t likely to emerge from the berry if you bring the cuttings inside your house, but I’d still pick off any green berries and get rid of them,” said Faubert.
And if you plan to cut boughs from spruce trees for your decorations, beware that many blue spruce and Norway spruce trees are affected by foliar diseases that cause their needles to drop. The diseases typically start at the bottom branches and work their way toward the tops of the trees, and they are caused by fungi infecting needles in the spring during times of too much humidity and not enough air circulation around the
“Pruning the lower branches will usually help, because humidity is greatest at the bottom of the tree and pruning will increase air circulation,” explained Faubert. “You could also use a fungicide spray.”
With the leaves now off the region’s deciduous trees, homeowners may begin to notice the appearance of scale insects on the trees. Soft scale insects are often about the size of a grain of rice and may look white and fluffy. They produce a sap-like substance on which black mold grows. Armored scale insects secrete a hard shell over their bodies to protect them from predators and may look like black bumps on branches and evergreen needles.
“Small numbers of them aren’t really a problem, but if they build up in number they can cause a tree to decline,” Faubert said. “The best bet is to hire a professional to treat the tree. The insects are often susceptible to horticultural sprays, but that’s best applied in April.”
Faubert also notes that winter is the season when houseplants tend to get the most attention, but that attention often means over-watering and over-fertilizing, both of which can kill plants.
“People tend to love their plants to death, especially in the winter,” she said. “Plants inside in the winter are more mellow, they’re not growing much, so they don’t need much fertilizer. And over-watering will lead to root rot issues.”
Those seeking diagnosis of plant diseases and pests may deliver or mail samples to the URI Plant Protection Clinic at the Extension Outreach Center, 3 East Alumni Ave., Kingston, RI 02881. Insects should be placed in a small container, like a prescription bottle, and wrapped to protect it from breakage in the mail. Fresh plant specimens should be placed in a plastic bag and mailed in a padded mailer. Various stages of a plant’s decline should be included (not just dead samples). A $10 fee per specimen must accompany all samples. For additional information call 874-2900.