In late summer, leafcutter bees arrive and oval holes with a very clean edge appear on the hackberry’s leaves. These solitary bees harvest the small circles of leaf to line their nests. There are several genera of leaf cutting bees but most of them are small to medium sized bees and carry pollen on the underside of their abdomen as opposed to on the hind legs. Within a burrow, several cells are constructed from leaf pieces. Each cell is stocked with nectar and pollen and an egg is deposited. The bee uses a few additional pieces of leaf to close each cell and finally, the opening of the burrow. The larvae fend for themselves, feeding on the supplies left by their mother. Leaf cutter bees are also attracted to my Florida elm and wild grape. Fortunately, plants seem to be able to tolerate the Swiss cheese leaves left by the leaf cutter bee. These non-aggressive bees are also important pollinators both in the wild and for some commercial crops. So I take no action to combat them and hope that they will also visit the vegetable garden.
Around the same time, the Asian wooly hackberry aphid (Shivaphis celti) makes its appearance. Accidentally introduced, this pest became noticeable about ten years ago in Florida. Members of the genus Celtis are it’s only host. These fluffy small creatures are concentrated on the bottom side of the leaves but may be seen flying around the tree, especially when disturbed. They produce honeydew when feeding which may attract the black fungus “sooty mold”. Supposedly, no long-term damage occurs but an infestation is unsightly. I have sprayed these insects off with water when I just couldn’t stand it anymore.
This year aliens landed on the poor beleaguered hackberry. Hexagonal, beige space ship like creatures had stuck themselves to small branches. These creatures turned out to be barnacle scale (Ceroplastes cirripediformis), sessile insects coated in a heavy layer of secreted wax and filled with orange eggs. After eggs hatch, mobile nymphs or crawlers move about the tree looking for a nice spot to settle in. Once well placed, they begin to secrete wax and transform in to their final form. There may be several generations per year. Like the aphids, wax scales injure plants by sucking plant sap. Leaf discoloration and leaf drop, death of small twigs can result. As with aphids, unsightly black sooty mold may form on the honeydew.
Natural predators are supposedly enough maintain scale populations below damaging levels. The lacewing larvae that feed off the scale seem quite happy but they need to eat more quickly. I sometimes need to spray the scale off with a hose. Summer weight horticultural oil might be another option if the infestation gets too heavy.
I have not yet seen the Hackberry Nipple Gall Psyllid (Pachypsylla celtidismamma) that is supposedly the most common pest of the hackberry. Nor have I seen any of the caterpillars of the several butterfly species that feed on hackberry. Their absence is probably a good thing. My hackberry limps into fall, looking tattered and torn. Still, the hackberry continues to grow. I am hoping that it will outgrow some of it’s bugginess and eventually make berries for the birds. Now I know that “tough” can sometimes translate to “survivies a ton of pests”.
(Editor's Note: this article wa soriginally published on September 14, 2007. Your comments are welcome, but please be aware that authors of previously published articles may not be able to respond to yoru questions.)