Horticulture Pest Update - Spring Pests
submitted by Mary Jane Frogge, Extension Associate
Ash Sawfly (Early May):
A pale green larvae with a yellowish marking behind the head. Damaged ash trees have leaves stripped, typically near the tips of the branches on the new growth. Control is probably necessary only on small or newly planted ash trees that are heavily defoliated. The pests should easily be controlled with either acephate (Orthene 9.4EC) or carbaryl (Sevin 50WP)
Bagworm eggs are hatching now and young larvae will begin to feed on junipers, spruce and arborvitae in eastern Nebraska. Bagworms also occur on various deciduous trees such as flowering crabs, plums, linden, and cotoneaster. The large bags attached to the trees now are those left over from last year and are empty, except for the remaining egg masses that will finish hatching soon.
The larvae will be very tiny, probably 3/8 inch in length or less, and each contained inside a small protective sack or bag which they construct of silk and plant material. At this stage, the larvae are susceptible to insecticides but in another 6 weeks they will be more difficult to control.
Suggested materials are carbaryl (Sevin), permethrin (Eight) and various formulations of "BT" (Dipel, Thuricide). Follow label directions and be sure to spray trees and shrubs thoroughly to penetrate foliage. Good coverage is essential if control is to be effective.
Click on Images below
for larger view.
Kansas State Extension
Iris Borer (April):
Overwintering eggs hatch in April and young larvae start to cause damage by feeding on leaf surfaces causing scars. As the larvae grow, they begin to bore into the leaves and start mining downward toward the base of the leaf. Look for small pinholes in leaves, slits, or young leaves notched or with ragged edges. The larvae move toward the base of the plant resulting in a slimy appearance near ground level. Small piles of a sawdust looking substance or frass may appear near the base of the iris. This is also the time that the rhizomes are hollowed out by the maturing larvae. Larvae are about half-grown when they first enter the rhizomes. Mature larvae have whitish to pinkish bodies with dark brown heads and are about 2 inches long. Pupation starts in August and adults emerge in September and October.
The pupal stage normally lasts two to three weeks with the pupa found about 2 inches deep in the soil. The adults are seldom seen because they are nocturnal. Eggs are laid on brown, dried leaves. Damage by the iris borer is often associated with a disease known as bacterial rot. Wounded rhizomes are easily attacked by this bacterium which results in a foul-smelling decay of the rhizomes.
Recommendations: Removal of dead leaves in the fall will eliminate a number of the iris borer eggs. Larvae can also be killed by hand in June bye squeezing infested leaves in the vicinity of the injury. During division, rotted and heavily infested rhizomes should be discarded. Borers in lightly infested rhizomes can be killed by poking them with a piece of wire. Chemical control can also be effective. Start spraying when growth first starts in the spring. Normally, two applications are needed. Recommended insecticides include malathion and imidacloprid
Pine Sawfly (Early April):
The larvae are green with black heads and with two light stripes and one dark stripe on each side of the body. Full grown larvae feed vigorously on the needles of Scotch and Mugho pines. Use acephate (Orthene 9.4EC) or carbaryl (Sevin 50WP). Spot spraying is ok, but be sure to inspect your pines carefully so that groups or clusters of feeding larvae are not missed.
There is a good reason behind bindweed's name: the stems can grow to eight feet, intertwining in and among other plants. Bindweed is bad news for lawns and gardens. Bindweed is a perennial that quickly spreads by seed and runners. The roots may grow to 20 feet deep.
Two things will help rid the lawn and garden of this diligent plant, which is part of the morning glory family, old fashioned pulling and a 2,4-D product.
Pulling can help eliminate bindweed if it is pulled close to the ground and it is not seeding. Bindweed develops dark seeds usually July through September. It can, however, produce seed as early as June. If the plant is seeding, pulling it will further spread the seed.
Pulling is unlikely to get rid of all bindweed. If a chemical treatment is used, wait a day or two after pulling to spray with a 2,4-D product. This gives the weed a chance to resume growth and better take up the herbicide. Spray early in the season, in the morning when a sunny day is forecast. Keep children and pets away from sprayed weeds until there is no visible liquid on them. Once the spray is dry, there is little potential for harm. Reapplication of the herbicide will probably be necessary in two weeks. Always follow herbicide label directions.
Henbit or Gound Ivy - How to Tell the Difference:
Infestations of henbit (Lamium amplexicaule) and ground ivy (Glechoma hederacea) can result in the patches of purple we see in the spring. These plants are not always welcome in our yards. Identification can sometimes be tricky. They both are members of the mint family (Lamiaceae) and have the characteristic square stems. However, they differ in their life cycles.
Henbit (above right) is a winter annual (completes it's life cycle in the spring), but ground ivy is a perennial (life cycle lasting more than one year). These plants can bloom as early as April and ground ivy can continue to bloom into June. The flowers are tiny, tubular, pink to purple, and can be found in the upper leaf axils of both plants.
Ground ivy's stems (right) generally lie along the ground, rooting at the nodes and the leaves are round to kidney shaped. However the reproductive stems are more ascending and can sometimes be confused for henbit. When looking at the reproductive stems, ground ivy leaves are bore on petioles. Whereas, the henbit has sessile (leaf is attached directly to the stem) leaves.
The rust fungi spend a portion of its life cycle on two hosts: apple or flowering crab apple and junipers or eastern red cedar. On juniper/eastern red cedar: In the spring, galls swell and produce orange, one-inch long, gelatinous tendrils. Trees with numerous galls are easily identified by their bright orange cast during rainy weather.
On apple/crab apple: In late spring or early summer, bright, yellow-orange spots approximately one forth inch in diameter form on the upper surface of leaves. These spots gradually enlarge and turn orange.
Infection of flowering crab and apples is favored by relatively cool temperatures (50 to 75 F) and prolonged leaf wetness (longer than 4 to 6 hours). Rust lesions begin to develop one to three weeks after infection. Leaf photo right: Kansas State Extension
Leaves with numerous spots drop during the summer. Premature defoliation can weaken trees and reduces fruit set and yield the following year.
On apple/crab apple: Fungicides can be applied to apple or flowering crab in the spring to prevent rust infection. Several chemicals, including Ferbam, triforine (Funginex, labeled for apples only), chlorothalonil (Daconil 2787, crabapple only), myclobutanil (Immunox, Eagle, Systhane, Rally) and triadimefon (Bayleton) are effective in controlling rust diseases.
On juniper/eastern red cedar: Although the presence of galls on twigs may be unsightly, rust diseases generally do not cause serious damage to junipers. Nevertheless, susceptible trees may be protected from infection by three to four fungicide applications sprayed at 10-day intervals, beginning in early July. Bordeaux mixture, Ferbam, and Bayleton are labeled for use on junipers.
Ash rust is not a serious disease.
The disease is often associated with wet weather during the spring. Leaves and petioles of ash become twisted and distorted; eventually birght orange powdery cups form on the leaves.
No control is needed.
Leaf photo right: Kansas State Extension
The most conspicuous symptom of the disease in early spring is death of twigs and new shoots. Small black fruiting structures of the fungus break through the dead bark of blighted, one-year-old shoots. Repeated killing of young twigs results in abnormal branching and gives the tree a ragged appearance. After bud break, sycamores show a scorching and wilting of new shoots and leaves. Later, fully expanded leaves develop elongated tan to brown lesions parallel with the midrib and veins. Infected leaves scorch and shed. In exceptionally cool, wet springs, sycamore trees leaf out and then can defoliate heavily.
The infection process is favored by relatively cool temperatures and prolonged periods of leaf wetness. Therefore, the disease tends to be more severe during wet, cool springs. After infection, the anthracnose fungus colonizes leaf tissue and begins to produce new fruiting structures and spores capable of reinfecting expanding leaf tissue. Disease development may continue throughout the spring into early summer if favorable weather persists. These diseases tend to be less of a problem during hot, dry summer weather. As temperatures increase, the disease becomes less active and the trees releaf.
University of Nebraska-Lincoln Extension in Lancaster County is your on-line yard and garden educational resource. The information on this Web site is valid for residents of southeastern Nebraska. It may or may not apply in your area. If you live outside southeastern Nebraska, visit your local Extension office