I share many horticultural ideologies with the Laidback Gardener. One of them is to avoid putting any effort into plants that grow poorly or are overtaken by insects or diseases. If a plant doesn’t grow well under my conditions, I get rid of it and plant something else.
That said, like any self-respecting passionate gardener, there are still a few plants that I love and for which I am ready to do ANYTHING! Even accept the worst! And that’s the case with rhododendrons (Rhododendron spp.).
A Passion for Rhododendrons
Rhododendrons form a large group of shrubs and in gardening circles, are usually subdivided into three categories. Small-leaf evergreen rhododendrons, large-leaf evergreen rhododendrons, and deciduous rhododendrons, the latter commonly known as azaleas.
It’s in this last group, the azaleas, that small green larvae appeared in my garden a few years ago. They quickly devour the leaves and then attack the flowers. In less than a week, an azalea plant can be completely defoliated. This voracious insect is the azalea sawfly.
The Azalea Sawfly: Two Pests In One
In truth, there are two species of azalea sawfly, Amauronematus azalea and Nematus lipovskyi, both native to North America. However, they are quite similar and cause the same damage.
You don’t need to be able to tell them apart, but, for the form, here are the differences. In Amauronematus, the circumference of the eye orbits, the base of the antennae, the neck and the legs are whitish, while its sister is more orange.
In both cases, the adult is a flying insect with an elongated body, long erect antennae, beige legs and wings longer than the body. It’s called a sawfly, because its ovipostor is like a small handsaw, with sharp-toothed edges, allowing it to make incisions in plant tissues to lay its eggs.
An Early Bird Insect
The adults emerge from the ground as the leaves begin to emerge, in April where I live, and the females immediately begin to lay eggs. They deposit their eggs in the midrib of young leaves. Seven to ten days later, the tiny larvae get to work and start chewing the leaves, usually leaving the midrib intact.
Since the caterpillarlike larvae are small (often less than ½ inches/1 cm long) and they are about the same color as the foliage, they are difficult to detect and it is often too late to act once you discover their presence.
Fighting With Soap and Water
The beginning of the attack coincides perfectly with the flowering of early azaleas. The first flower therefore sounds the alarm. That’s when I fill a bowl with soapy water. I mix bout 2 tsp (10 ml) of soft soap in 2 cups (500 ml) of water… although, I actually never measure! Then I go off … on a bug hunt!
Yes, you heard me. I treat ecology very seriously, so I don’t use insecticides. Not even those approved for organic farming. I don’t need them. If a plant is infested with insects, I toss it into the compost pile without even flinching.
However, for my beloved rhododendrons… well, it’s just not the same thing! So, I hand pick the larvae and drop them into my bowl of soapy water. When they feel threatened, the hind end of sawfly larvae rears up, while it continues to hold onto the plant with their mouth and legs, taking on the shape of a question mark. In 30 minutes I can make a careful round of all my deciduous rhododendrons (azleas) and harvest about one hundred. Then I go back two or three days later, because eggs hatch over about 2 to 3 weeks.
Any well-fed larvae that have escaped my hawk eye drop to the ground to metamorphose into pupae. This is how they will spend the winter. Luckily, there is only one generation per year.
Worthwhile Effort
This rigorous hunt is very essential in order to preserve a maximum of foliage. I have seen azaleas completely defoliated within a few weeks. And for rhododendrons and azaleas … well, let’s just say the foliage doesn’t regrow as quickly as it does in other shrubs, say willows or spireas. With azaleas, every leaf counts. The effort is therefore well worth it and the resulting bloom all the more spectacular.
Spring is my favorite season, and my spring would be nothing without my twenty azaleas covered with flowers… and leaves!