Over the years of writing this column, some readers will remember me periodically bemoaning the state of our two beautiful azaleas as you walk towards the side gate entrance to John鈥檚 garden. It all started in early spring of 2016 when the azalea sawfly (Nematus lipovskyi) females found our shrubs and laid their eggs along the midribs on the underside of the leaves.
No idea where these flies came from. We had not introduced any new azaleas into our garden prior to 2016 and the only other azalea in the back garden remained unscathed. But it quickly developed into a full scale problem as soon as the eggs hatched in late April. Hordes of ravenous larvae devoured entire leaves all over the shrubs, leaving only a fan of thin midribs as a reminder there had been a flush of green at the tip of each branch mere days before.
Aesthetics were helped鈥omewhat鈥hen the flower buds burst open, covering some of the dastardly larval damage. But as soon as the flowers dropped the horror was revealed once again.
For years, I valiantly tried to control the larval infestation, engaging in hand-to-hand combat. (Good thing I am not squeamish!) I even tried making sticky traps using white cardstock one year as I had read somewhere that white attracted the sawfly females. Caught other flies but none of the sawfly genus so that was a bust.
We started throwing buckets of soapy dishwater around the roots of those azaleas every couple of weeks, or so, from June through to April. Our theory was to regularly douse the pupating larvae in the soil until we could expect the adults to emerge in the hope that we could decrease their numbers鈥f not completely eradicate the pest.
Well鈥t has taken nine years but I am optimistic we have finally won the battle with the azalea sawfly. (I say this quietly under my breath, with all fingers crossed!) This spring, for the first time since 2016, we have not found any larval chewing damage on either shrub.
So, after such a botanical high, you can imagine my chagrin at discovering masses of destroyed leaves on my aquilegia (columbine) plants. Yup, you might have guessed. Another sawfly species (Pristiphora rufipes) but this one is specific to aquilegia plants.
Truthfully, these sawflies have been around in my garden for a while. But somehow, the damage to the columbines did not seem as dire compared to the scope of what was done to the azaleas. (The damage may also have been overlooked as I had been letting my golden-leaved Aquilegia vulgaris 鈥榃oodside Gold鈥� go to seed in order to develop a nice clump in my island bed.)
Thankfully, my columbines had not been completely defoliated. It was mostly just the leaves closer to the ground which the newly emerged larvae could easily reach as they crawled out of the soil. But, as each of the larvae grew bigger, they were definitely making their way up the plant.
There is good news though. Most plant experts aver columbines do manage to recover from complete sawfly larvae defoliation. However, I also found a few experts who hedged their bets on columbine defoliation survival in my research about this pest. Thankfully, all my columbines are in the 鈥渟urvival鈥� group.
So, imagine my surprise when I read that 鈥渟awflies are a part (of) the biodiversity a healthy garden supports鈥� according to the Royal Horticultural Society鈥檚 website.
Indeed, they do attract predator species such as wasps, hornets and ground beetles. But in my experience with the azalea shrubs, the predator numbers alone could not keep the sawflies under control without some assistance from the gardener.
