What do you do about leaf-rollers on Cannas, Vinca Minor and Vinca Major?
Systemic insecticides are a special group of insecticides that are taken up into the plant through its leaves or through its roots. Unlike most insecticides that remain on the foliage, systemic insecticides make the plant sap poisonous to feeding insects.
Damaged canna blades become notched and ragged. When they mature and open, they look like someone has shot them with a B B gun. One finds robust caterpillars hidden inside leaf rolls. Canna leaf-roller caterpillars are clear white at first. They become semi-pale green with age. Lesser canna leaf-roller caterpillars are smaller and yellow. Large ornate butterflies lay eggs from which they hatch. The caterpillars spin silk thread used to pull leaf edges together. They hide inside the protective tube, presumably to avoid predators.
Leaf rollers in late summer are devastating to foliage of vinca major and to some lesser degree to vinca minor and should be prevented with systemic insecticide before they begin. Apply a systemic insecticide 2 to 3 weeks before you traditionally would see their damage start to occur. If the damage has been done, you will may want to cut the marred foliage back and allow new growth to cover the area.
Control canna, vinca minor and vinca major leaf rollers with BT insecticides, Orthene or Sevin. BT insecticides contain a bacterium (Bacillus thuringiensis). They are sold under trade names such as Dipel. Caterpillars ingest the bacterium and die shortly thereafter. Orthene and Sevin are chemicals that may give a quicker kill of established populations. BT-type insecticides have worked.
Researched by Parker County Master Gardener La Donna Stockstill