Vinca, also known as periwinkle or Catharanthus, is a hardy garden flower that produces pretty pink or white flowers. It is a perennial in hot climates but most gardeners grow it as an annual. Deer and rabbits do not like to eat vinca and the plant isn't bothered by too many insects or diseases, but there are a few pests gardeners should look out for when growing this flower.
Aphids are small, soft insects that are most often green or white but may also be brown, red or black. Aphids feed on the leaves of a vinca, but the insects are too small to produce visible holes in the leaf. Instead, look for leaves that are curled, warped or yellow. Aphids also leave behind a sticky residue that may look like black soot and may also transfer diseases to the plant which can damage the leaves or stunt growth. Beneficial insects such as lady beetles feed on aphids, and you can purchase lady beetles to release into your garden at some nurseries or through mail-order garden supply stores. For minor aphid infestations, you may be able to simply knock them off the vinca plants with a strong stream of water.
While scales are actually insects, to the naked human eye they just look like a small bump on a leaf or stem. Depending on the species, they may be either soft-bodied or protected by a hard shell called armor. Small numbers of scales don't do much damage to vinca plants, but a major infestation may weaken the plant and cause the leaves to wilt, turn yellow or fall off. Lady beetles, lacewings and parasitic wasps are all natural enemies of scales and encouraging their presence in your garden will help fight a scale infestation on your vinca.
Like aphids, whiteflies are small, white insects that feed on leaves and leave behind sticky residue. Unlike aphids, though, whiteflies can be difficult to manage. Removing whiteflies by hand or with a small vacuum will help, and beneficial lacewings will also eat whiteflies. Most insecticides are ineffective against whiteflies, but there are whiteflies traps which may lure the pests away from your vinca plants. Whiteflies often congregate on the undersides of leaves.
Spider mites are almost invisible and it takes a lot of them to inflict serious damage, but they can cause the leaves of vinca to discolor and drop off. Spider mites tend to gravitate toward drought-stressed plants, so keeping your vinca thoroughly watered will fight off spider mites.
Both adult and larvae weevils feed on the leaves of vinca plants. Adult weevils are brown or gray and have a distinct snout; larvae are green or white. The best way to control weevils is to simply pick them off the vinca plants and drop them in a jar of rubbing alcohol to kill them.