I’ve told students who are learning to identify plants to remember that hollyhock is the one with all the holes in the leaves. Bugs just love it, yet it’s tough enough to strike up a ragged coexistence, permitting the plant to thrive even though its leaves occasionally look like Swiss cheese.
The larval form of hollyhock sawfly is a holey terror.
Photo Credit: Gerald L. Klingaman
Hollyhock isn’t for the fastidious gardener who agonizes over every calamity that may befall a plant. This old-timer seems to live under its own cloud, because some affliction is always waiting in the wings to attack it. Of these, the hollyhock sawfly is probably its most common insect pest.
The larval form of the hollyhock sawfly (Neoptilia malvacearum) is a leaf skeletonizer that munches its way through hollyhock foliage, leaving behind see-through leaves consisting of patches of leaf tissue and the main leaf veins. The translucent green worms are up to ½ an inch long and club-shaped, with a black spot on their head and on the spine of each body segment. They seem to get lonely, because it’s not uncommon to see them grazing side by side on the leaves like a heard of cattle in a lush pasture.
As the larva matures, it spins a dirty silken web over itself – usually near the base of the plant – and then it pupates. As an adult, the insect is a black fly with an orange thorax. It has split antennae divided almost to the base, making the pest look like it has four instead of the customary pair. The adults lay their eggs singly in the leaf tissue; in the South there can be as many as six generations per year.
Control is not especially difficult, but it should be initiated as soon as the first holes are seen on the plant’s lower leaves. Sevin or Bacillus thuringiensis (Bt) should prove effective. If you decide to forego control, your hollyhocks will survive – they may just be a little tattered.
