Q: I have a large sugar maple in the front yard, and I’m alarmed because many of the leaves have fallen to the ground. What could be causing this, and what should I do?
A: The maple petiole borer is a small wasp that causes maple leaves to fall early in the summer.
In the spring, female petiole borer wasps lay their eggs in the petiole or leaf stem. The eggs hatch, and the developing larvae eat the tissue inside the petiole. Several weeks later, the petiole begins to darken, then it weakens and breaks.
The leaf blade and severed petiole fall to the ground, while the larva remains in the other portion of the petiole still attached to the tree. About 10 days later, the smaller portion of the petiole drops to the ground. The larva emerges and tunnels into the ground, where it continues its development as a pupa until the following spring, when the adult wasp emerges.
Outbreaks of maple petiole borer are sporadic and unpredictable. Additionally, although the tree can lose 25 percent of its leaves to this pest, this loss of leaves is not significant enough to damage the tree. Because of these factors, no control methods are recommended. Just break out the rake and compost the leaves.
Q: I’ve moved into a new house, and some of my beds are infested with Canada thistle. The previous owner said she sprayed with Roundup, but it didn’t kill the thistle. Is Canada thistle resistant to Roundup? What should I do?
A: Canada thistle is one of the worst perennial weeds to deal with in landscape beds, right up there with quack grass.
What makes these two weeds so difficult to manage is the fact that they spread by underground stems called rhizomes. These rhizomes make the weed function as one huge colony, so that instead of dealing with an individual plant everywhere you see a sprout, you’re actually dealing with an underground monster.
One spray of glyphosate, the active ingredient in Round-up, will have little effect on a large Canada thistle colony. The weed isn’t resistant, but the plant has mammoth reserves and can continue to sprout.
With persistent application, however, glyphosate can effectively take out Canada thistle. This will likely take several applications and several months.
If the Canada thistle is growing right in among desirable plants, your job is much more challenging. Drift or overspray of the herbicide will kill any desirable plants, so great care must be taken to protect surrounding plants.
One effective method used by gardeners and professionals is to use a chemical-resistant glove, available at hardware stores, covered by a cotton garden glove. Carefully apply the herbicide to the cotton glove, then rub the herbicide on to the weeds. Wait a few weeks to see where new sprouts emerge, then repeat this procedure until all weeds have been killed.
Other options are available to control Canada thistle, but pulling is not one of them. Pulling Canada thistle is like harvesting broccoli; everywhere you cut a piece off, small new sprouts will emerge.
Large areas can be covered with plastic, thick newspaper or landscape fabric to smother the weed. This may take some time and persistence as new sprouts may emerge in different locations.
Learn what small weeds seedlings look like, so that you’re sure to rouge Canada thistle from the garden as soon as it’s seen. This will hopefully prevent any future weed nightmares. Visit Ohio State University’s Weed Workshop website for images of dozens of weeds in all stages: (www.oardc.ohio-state.edu/weedworkshop/). Once on the site, click on weed workshop, then select Ohio Perennial and Biennial Weed Guide to view weed images.
Denise Ellsworth directs the honeybee and native pollinator education program for the Ohio State University. If you have questions about caring for your garden, contact her at 330-263-3700 or click on the Ask Denise link on her blog at www.osugarden.com.