Begonia plants (April) in greenhouse, thought to have been eaten by voles.
Insects and Mites
The tarnished plant bug is a very general feeder, attacking many kinds of trees and herbaceous plants. It feeds on many flowers including dahlia, aster, calendula, chrysanthemum, cosmos, gladiolus, poppy, salvia, daisy, sunflower, verbena, zinnia, and others. It has piercing-sucking mouth parts as do all the true bugs. The long sucking mouthpart is inserted into the plant tissues and introduces toxic saliva into the plant as it feeds.
Flea beetles (Red Headed Flea Beetles) can be an occasional pest on chrysanthemums and herbaceous perennials. Shiny black beetles (about 3/16 -1/4” long) with a reddish head (in good light) feed primarily on young foliage, chewing holes and causing leaf spot damage. Symptoms are similar to four-lined plant bug injury, but the flea beetle spots are more irregular in shape.
Tobacco budworm feeds on buds and petals of geranium, calibrachoa and petunia. Tobacco budworms are generally a pest of home gardens and landscapes. However, adult moths can enter greenhouses with rollup sides, and lay their eggs on geranium or petunia buds. Caterpillars feed at night on flower buds, so that flowers fail to open. Petals may also be chewed. Fecal droppings may also be evident.
Potato aphids are common on ornamental plants. The potato aphid is pink or green (in this photo), with a darker stripe down its back (seen in related photo). Antennae are longer than their bodies, with long, black tipped cylindrical cornicles. This photo shows potato nymphs, shed skins and parasitized aphids. As aphids increase in size they shed their exoskeletons (cast skins) which are white and light weight. These white cast skins are often mistaken for whiteflies. The parasitized aphids (aphid mummies) appear as small brown swollen aphids.
Feeding damage appears as spotting on the upper leaf surface. The adult is greenish yellow with 4 black lines running down the back and about 3/16 in long. The immature stage is bright red or orange with black spots on the segment behind the head. As they mature, a yellow stripe appears on each side of the wing pads. They feed for about 6 weeks. Plant bugs move rapidly and try to hide out of sight when disturbed. Depending on the plant, the spotting on leaves may be dark or light to dark tan and may coalesce to damage entire leaves.
Western flower thrips cause direct damage by feeding on plant leaves and flowers as seen in this photo. Note the long, narrow shaped body of the thrips feeding on this leaf. Western flower thrips possess piercing-sucking mouthparts, and tend to feed on the mesophyll and epidermal cells of leaf tissues. Symptoms of feeding include leaf scarring, distorted growth, sunken tissues on leaf undersides. Flowers and leaves have a characteristic “silvery” appearance.
Shore flies, Scatella stagnalis occur in greenhouses, especially in propagation areas and around slow growing plants, where algae is present. Adult shore flies have a robust body (similar to a housefly, but smaller) and short antennae.
The caterpillar of the sunflower moth, Homoeosoma electellum, damages the flowers of echinacea, sunflower, marigolds cosmos, coreopsis and other composites (Asteraceae). Newly hatched larvae are pale yellow, but darken to shades of brown or purple with longitudinal white stripes. Look for premature browing of petal and mats of webbing on the face of flowers for signs of larval feeding. The injury caused by larval feeding can lead to Rhizopus head rot.
Striped cucumber beetles over-winter in plant debris outdoors, and migrate into greenhouses to feed on cucurbits. Adult feeding on cotyledons and young leaves can delayed plant growth. The striped cucumber beetle vectors (Erwinia tracheiphila), the causal agent of bacterial wilt, and this can be more damaging than direct feeding injury. Cucurbit plants at the cotyledon and first 1-4 leaf stage are more susceptible to infection with bacterial wilt than older plants.