Pests of Landscape Plants

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Lora Hill
5 years ago
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1 N. 4th St. P. O. Box 3858 Flagstaff, AZ Pests of Landscape Plants Agave Weevil Adults are dusty black weevils about one inch long, with a long snout. Adult agave weevils don't have wings, so they move from plant to plant by walking on the ground. Larvae are similar to white grubs except they are legless. The adults chew into the leaves and introduce a bacterial rot that appears to be necessary for larval development. They lay eggs into the holes and the larvae burrow into the plant. Infested plants exhibit wilting and wrinkled leaves, and quickly decline due to the bacteria. Remove and destroy plants as soon as damage is evident. Remove larvae and adults from soil around where the plant was removed Bruchid Seed Beetles Bruchids are oval beetles often less than 2/5 inch long with shortened fore wings. Their head tapers forward into a short, broad snout. They are generally brown or black with a fine covering of white hairs over the wings and body. They do not consume foliage, but several species lay eggs on the seed pods of honey mesquite and other mesquites. The larvae bore into and feed on parts of the seed within the pod. The adults exit through holes chewed in the seed pod, a telltale sign of infestation. Cactus Longhorn Beetle Adults are shiny black beetles with antennae as long as their body. They feed on chollas, prickly pears, and barrel cactus. Immatures are grubs that burrow into the cactus and feed. This feeding may kill species of cactus that are susceptible, or stunt growth. Chemical controls are not effective. Search for adults in early summer and destroy them. They seem to be most active early in the morning and late in the afternoon. Elm Leaf Beetle The adult beetle is about 1/4 inch long with black and yellow stripes on wing covers of the adults. The young larvae are nearly black. In contrast, full grown larvae are up to 1/2 inch long, dull yellow in color with two black stripes. Both larvae and adults feed on elm leaves. There are several generations from April to August. Trees can withstand defoliation one year, but may die if defoliated for a number of years in a row. Bagworm Bagworms get their name from the fact that the larvae carry around a spindle-shaped baglike covering, which they retreat into when threatened. They cover the bags with plant debris so they are camouflaged. Adult females are unusual for moths, because they lack wings and only have minute legs. They are white in color, and remain in the bag they developed for their entire life. The male moths are dark, almost black and do have wings. They are common on arborvitae and juniper in the higher elevations. Hand-picking is often the simplest, most effective control.

2 Gulf Fritillary Adults are orangish-brown butterflies with black spots on the fore wings and a row of open black circles along the margin of the hind wing, with silvery spots on the underside of the wings. The larvae are over one inch long when full grown, and are reddish orange with black spots and dark spines. The larvae are commonly found feeding on passion vine here in Arizona. Palo Verde Webworm Adults are tan moths approximately 1/4 inch long. Caterpillars are no more than 1/2 inch long, and hide in silken tubes of webbing when they are not feeding on the leaves of the foothills palo verde. They appear in the spring. Control is generally not necessary, because the palo verde is resilient. Birds and lizards feed on the caterpillars. Tent Caterpillars The adults are pale yellow moths. The larvae are hairy caterpillars with a black body, a blue-gray head, and pale blue and orange stripes running down their backs. The larvae construct and hide in silken "tents" in the crotches of tree branches. They feed on ash, plum, cherry, aspen, cottonwood, manzanita, oak, willow, etc. The larvae may completely defoliate a tree. Remove nests with a pole or brush, and destroy all caterpillars seen. Western Grape Skeletonizer Adult moth is blue-black and about 1/2 inch long. Larvae have black and yellow bands and are up to 1/2 inch long. The caterpillars line up and feed in groups. They feed behind the veins in the leaf, creating a net-like appearance. The adults produce masses of yellow eggs. Look for the adults and eggs in early May, and destroy any you see. Leafcutter Bees Adults are fuzzy gray to brown bees about 1/2 to 3/4 inch in length. They cut neatly rounded pieces from edges of leaves from many different plants, particularly roses. The adult female stuffs the pieces of leaf into a tunnel or burrow to create a safe chamber for her larvae. She then gathers pollen to serve as food for her offspring. Chemical controls are of little use because bees will just move on to other plants that are not treated. In general, damage is unsightly but causes minimal harm to the plant. Leafcutter bees are important pollinators of crops and should be left alone if possible.

3 Grasshoppers Many species of grasshoppers feed on foliage in Arizona. They have chewing mouthparts and leave holes in leaves or consume leaves entirely. One common species is the vagrant grasshopper. The adult is grayish or brownish with a pale stripe down the back of the head and thorax. The hind legs have alternating light and dark bands. The adult female lays her eggs in the soil. One or a few grasshoppers may be captured and removed by hand, particularly on cool mornings when they are slow. Cactus Bug Cactus bugs are true bugs with sucking mouthparts. They are light yellow with a dark brown head, with a wide yellow stripe down the back of their head, and a darker triangle in the middle of the back. Females attach their eggs to the underside of cactus spines. Cactus bugs are introduced pests of Opuntia cactus. Their feeding causes yellowing of the pads and sometimes death of the plant Lacebugs Lacebugs are flattened insects, roughly rectangular in shape when viewed from above. They take their name from the lace-like expansions projecting from the thorax and front wings. Several species are found in Arizona. Adult females lay eggs near the leaf veins on the underside of leaves. Nymphs and adults suck sap from the underside of leaves of plants such as basswood, sycamore and lantana. They are also destructive to composites and annual flowers. The feeding damage looks similar to spider mites, except lacebugs often leave dark spots of excrement as well as causing yellow stippling. Aphids Aphids vary in color depending on the species and their host. Numbers can build up quickly because the adults are capable of producing live offspring without mating. They feed in groups, often on the growing tips of a plant. Aphids suck the juices from a plant, and the excess they excrete as a sticky material called honeydew. A black fungus known as sooty mold often grows in the honeydew, and if there is enough covering the leaves it may interfere with photosynthesis. The arborvitae aphid is a brown species that infests arborvitae, Italian cypress and false cypress. The cotton or melon aphid is dark green to black in color, and feeds on cotton, oranges, melons, poppy, chrysanthemum, cucumber, dogwood, begonia, milkweed, spinach, beets and many others. The oleander aphid is a yellow-orange aphid with black cornicles found on oleander during the spring and on desert milkweed at other times. They rarely cause significant damage to either plant, and may actually be beneficial because they serve as food for biological control agents. The rose aphid is a relatively large species which is either green or pinkish in color. It is commonly found on the unopened flower buds. The rusty plum aphid is a rusty brown species found feeding on plum, corn, grasses and many wild flowers. Aphids may be washed off with a garden hose, but be careful when temperatures are high because the water may cause leaf burn. If aphids persist, try spraying with a solution of up to two tablespoons of liquid detergent per gallon of water. Test a small number of leaves first, because some plants will be sensitive to soaps.

4 Cochineal Scale Cochineal scales may be mistaken for mealybugs. The females are red in color with white waxy plates, which gives them a cottony appearance. The species in Arizona feeds on Opuntia (prickly pear) cactus. The insects may be brushed from the cacti, dried and their red color used as a dye. Several insect predators control this scale, including several species of lady beetles, syrphid flies and lacewing larvae. Leafhoppers Leafhoppers are wedge-shaped insects, about 1/8 inch long with jumping legs. They are capable of strong flight. Some species may be serious pests. They suck the juices from the plant and excrete excess fluids in the form of honeydew. As with aphids, this sugary substance may support the growth of sooty molds. Because they are so mobile, leafhoppers may be difficult to control. Floating row covers may be used to prevent leafhoppers from damaging gardens. Whiteflies Adults are less than 1/16 inch long and have a pale yellow body covered with a white waxy material. The sedentary, scale-like immatures suck sap from the under side of leaves. The species of whitefly that is currently the most significant pest becomes abundant in late summer and early fall. However, other species of whiteflies are found here, including greenhouse whiteflies, ash whiteflies and banded-wing whiteflies. These species may be abundant at different times of the year and require different control measures. Control whiteflies by spraying the underside of leaves with a mixture of one teaspoon to two tablespoons of dish detergent per gallon of water. Test for toxicity to plants by starting at the lowest dose and gradually increasing the amount of dish detergent added. Spray every three to four days or as needed. Spider Mites Spider mites are tiny creatures, some less than 1/50 of an inch. Most are so small they can not be seen without the aid of a microscope. Mites are usually oval or rounded in shape, and may be yellow, red, greenish, or brownish in color. Spider mites get their name from the fact that they produce a fine webbing between leaves, a sign of infestation. They suck sap from leaves and fruit, which causes yellow spots or ÒstipplingÓ on the leaves. Their feeding may cause deformations such as twisting and stunting of leaves, as well. Other types of mites cause galls. A mix of soap and water may be used to wash plant mites off leaves, as with whiteflies. Several biological control agents are also available for the control of spider mites

5 TRUNK AND/OR LIMB FEEDERS Flatheaded Borers Adult flatheaded borers are 1/2 to 3/4 inch long, often olive-gray to brown with a metallic gold, bronze or green cast to the fore wings. Some may be brightly colored. The larvae are cream-colored, legless grubs up to 1 1/2 inch long. The segment behind the head is greatly widened. Larvae burrow beneath the bark of shrubs and trees such as apple, ash, box elder, cherry, peach, pear, pecan, raspberry, and roses. They are usually host specific. Flatheaded borers invade most commonly where the trunk of trees or bark of shrubs has been sunburned or otherwise damaged. The best way to avoid infestations is to protect young plants from sunburn and keep older trees sound. Prune out infested material and destroy it. Insects that are hidden within the wood are not accessible to chemical sprays. Ocotillo Borer Related to the flatheaded borers that attack roses and apples, the ocotillo borer is a species that attacks only ocotillos. The adults lay eggs into the bark, and the legless larvae mine into the cambium, causing rapid decline of the plant. They seem to prefer plants which are stressed, particularly newly planted ocotillos. Avoid planting new ocotillos during the summer, when adults are active. Cut any branches that do not leaf out below the leafless area and dispose of immediately (the beetles can survive in cut portions). If the plant does not leaf out in the spring, inspect for grubs and if present, dig it up and dispose of immediately. Round-headed Borers The adults are called long-horned beetles because their antennae are often as long as or longer than their body. Some may reach lengths of four or five inches. One common species is the locust borer, which is black with yellow stripes, and mimics a wasp. The larvae bore in solid wood of plants such as apple, hickory, locust, mesquite and poplar. They are legless cream or white grubs which are uniform in width (the segment behind the head is not enlarged). Borers generally attack weakened trees and shrubs. They may be prevented by keeping trees and shrubs in their best condition. An exception is the mesquite twig girdler, which girdles and kills small twigs of mesquite trees. The female beetle then lays an egg in the section that is killed and the immature develops within the wood. ROOT FEEDERS Palo Verde Beetle Immatures (grubs) feed on the roots of Mexican palo verde and other non-native trees, and are six inches long when mature. They spend up to three years underground. Adult beetles are four to six inches long with long antennae and a "collar" of spines on the thorax. They are active in July. Currently there is little that can be done to control these beetles. They attack stressed trees, so the best prevention is to keep trees as healthy as possible.

Tree and Shrub Insects

Tree and Shrub Insects Aphids Aphids are small soft-bodied insects that suck plant juices. High aphid populations can cause leaves to yellow, curl, or drop early. The most bothersome aspect of aphids is the honeydew they produce.