Alison Arnold: Common Concerns In the Landscape Garden

Jun 8, 2016

In her commentary this week, WCQS gardening expert Alison Arnold takes us through some of the common problems we see in our gardens this time of year. 

Q (Jeremy): It’s June and while it’s still early in the growing season many landscape plants have grown enough for us to know whether they are healthy or not.. what type of problems are you seeing or commonly see in the garden at this time?

A (Alison): I think the most obvious thing this time of year is falling leaves.. on large trees we often don't know something is wrong until the leaves start falling and when this happens in June it can be quite alarming.

Q: Are there specific trees this happening too?

A: Tulip trees often called yellow poplars are once again being invaded by the Yellow poplar weevil. It’s a small black weevil looking insect with a long snout that feeds on the foliage causing small pits which later turn into holes. They over winter in the lead litter below the tree and typically hatch out as the new leaves emerge. They mate and then the female lays eggs in the leaf. As the eggs hatch the small larvae or grubs feed within the leaf tissue causing large brown blotches. These mature into adults, continue to feed on the leaves and later seek out their place over winter. All of this causes the damaged leaves to drop to the ground well before fall color season

Q: Does this only happen on tulip poplars? And is there anything to do about it?

A: Yellow poplar weevil also feeds sassafras and magnolias. On the large trees we commonly have around here it’s best to rely on native wasps and other natural predators to do their work .The affect is aesthetic and should not affect the overall health of the plant. The best strategy is to maintain good tree health.

Q: What else might we be on the look out for?

A: We’ve been in a good window to look for signs of stem borers on rhododendrons, azaleas, mountain laurel, and blueberries. The adult is a slender long-horned beetle that emerges from hibernation in the soil, climbs up the stems, and lay eggs under the bark. As they hatch, the young larvae bore in and down the stem.

Q: What type of symptoms do you look for?

A: The most obvious symptom can be individual stem with drooping leaves. Also look for a small hole in the stem often with fine sawdust coming out that can also be on stems, leaves, or underneath the shrub. If you see this then the best thing to do is simply prune and remove the branch entirely to below where the borer is feeding - basically to the point where the stem is solid and doesn't have a hole in the middle. Dispose of the cut stem and hopefully the borer inside.

Q: It sounds like a good idea to regularly look at your plants so you can to stay on top of things like this

A: Observation is key! I like to encourage people to get to know their plants, not only read about them but observe them and how they look. It’s really good to check them out regularly so when there is a change in leaf color for instance or an insect or disease appears you can maybe catch it early, watch it to see if it progresses and maybe do something about it you need to.