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PESTS OF LANDSCAPE PLANTS

The environment in urban areas of Arizona can increase the potential for insect problems in shrubs and trees for the following reasons:

• Many more types of trees and shrubs are being grown, and a significant number are not adapted to our harsh climate.
• The temperature extremes, salty water and heavy soils all stress plants native to more favorable climates.
• Care and maintenance is often inadequate or does not fit the growing conditions. For example, plants that prefer shade are planted in the sun and vice versa. Trees are often planted too close to structures. Plants are often under or over-watered.
• Pruning shrubs and trees into exotic shapes or improper pruning may cause unnecessary wounds and further stress the plants.

Keep in mind that shrubs and trees that are in poor condition often are more attractive to insect pests, and are more susceptible to damage when they are attacked.

DIAGNOSIS OF INSECT PROBLEMS

1. Examine the plant for signs of insect feeding.

• Foliage: holes, ragged edges, "skeletonized" leaves
• Sap: wilting, change in color of foliage, abnormal growth
• Trunk and/or limbs: holes, leaking sap, dead spot in bark
• Roots: stunted growth, wilting, sudden die back

2. Identify the insect

• Chewed foliage: caterpillars, beetles, grasshoppers, leafcutter bees
• Sucking sap: aphids, mites, true bugs, scales, thrips, whiteflies
• Trunk and/or limbs: borers; beetles and some moth larvae
• Root feeding: beetle larvae (grubs)

3. Recommend protective action, if needed.

• Evaluate the damage to the plant. Can it survive the insect attack? How much is "how it looks" worth? For example, whiteflies will sit on many plants, and breed on quite a few, but only a handful of susceptible species such as lantana and hibiscus are potentially killed. Also, how valuable is the plant?
• Evaluate the environment. If a tree or shrub is planted in an inappropriate location it will always show signs of stress, no matter how successfully insects are controlled.
• Evaluate care and maintenance practices. How have the watering and fertilization practices been conducted? Has it been pruned correctly? Improving the growing conditions may eliminate further insect problems.
• Consider control procedures. Examine possible mechanical or biological control methods for usefulness. As a last resort, consider the application of an insecticide. Depending on the feeding site and biology of the pest:
  
  

  Foliage Feeders:	-liquid sprays -dusts -systemics (trunk implants)
  Sap Feeders:	-liquid sprays -dusts -systemics (trunk implants)
  Trunk and Limb Feeders:	-liquids -implants (if properly timed)
  Root Feeders:	-granules -liquids

SOME COMMON PESTS OF SHRUBS AND ORNAMENTALS

(Note: This section contains pests of landscape plants only. Pests of citrus, deciduous fruits, and gardens and annual plants will be covered in further sections.)

FOLIAGE FEEDERS

Coleoptera

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.

Lepidoptera

Bagworm
Bagworms get their name from the fact that the larvae carry around a spindle-shaped bag-like 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.

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.

Hymenoptera

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.

Orthoptera

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.