MNLA Pest Newsletter, April 2007, no: 1

http://www.entomology.umn.edu/cues

http://www.mnla.biz/

Soon to emerge, shades of Harmonia,
Asian lady beetle adults

Photo:  http://www.bba.de/mitteil/
presse/bilder/harmonia.jpg

Tulips in snow

Photo: Jerusalem Botanic Gardens

Hairy woodpecker finding insects

Photo: Andy's Northern Ontario Birds

Vera Krischik, Emily Tenczar, and Mary Rogers, Department of Entomology, University of Minnesota, contact us at krisc001@umn.edu

Landscape and Nursery

References:

Congressional report

National Academy of Sciences

Mid-Atlantic Apiculture

CNN The mysterious deaths of the honeybees:
Honeybee colony collapse drives price of honey higher and threatens fruit and vegetable production

Bees are dying. Three-quarters of the world's 250,000 flowering plants, including many fruits and vegetables, require pollination to reproduce.

Who is going to pollinate my crabapples and apples?: Honeybee Decline Concerns Congress

No bees, no crops. For many reasons, the U.S. honeybee population is declining. The phenomenon now called Colony Collapse Disorder (CCD) quickly spread across the nation and has now drawn the attention of the U.S. Congress. Agricultural crops pollinated by honeybees accounts for about one-third of the U.S. diet. The monetary value of honey bees as commercial pollinators in the United States is estimated at about $15 billion annually. Worldwide, three-quarters of all flowering plants require pollination to reproduce. Among food crops considered to be from 90-100 percent dependent on bee pollination are almonds, apples, avocados, blueberries, cranberries, cherries, kiwi fruit, macadamia nuts, asparagus, broccoli, carrots, cauliflower, celery, cucumbers, onions, legume seeds, pumpkins, squash, and sunflowers. Other important crops needing pollination, include many fruits and citrus fruits, peanuts, cotton and soybeans.

While honeybee declines have come and gone in the past, Colony Collapse Disorder is unsettlingly different. In it's March 26, 2007 report Recent Honeybee Colony Declines (link above), the Congressional Research Service found that current bee colony losses differ from past situations in that:

• colony losses are occurring mostly because bees are failing to return to the hive (a behavior uncharacteristic of bees),

• bee colony losses have been rapid,

• colony losses are occurring in large numbers, and

• the reason the losses are occurring remains largely unknown.

The reason for honey bee CCD may be a combination of multiple factors, such as disease, mite infestations in hives, insecticide use in hives, and insecticides in the foraging environment. One honey bee researcher in Florida are blaming the current bout of CCD on the use of imidacloprid (Merit). Imidacloprid affects bee behavior, orientation, grooming, and nest activities according to 100's of published studies.

Our research demonstrates that imidacloprid is translocated to nectar and kills foraging biocontrol agents, such as: green lacewings, parasitoids, and lady beetles.

Mossy rose gall
Diplolepis rosea

Spiny rose gall
Diplolepis bicolor

(Hymenoptera: Cynipidae)

References:

Pests of Roses (UMN Extension)

Rose stem borer
Agrilus aurichalceus
(Coleoptera: Buprestidae)

This pest was in the March 2006 newsletter, but you might also have rose stem borer; damage can look very much alike, so see the next entry!!

Time: May, June

Hosts: Roses

Mossy rose galls are caused by a cynipid gall wasp. They are becoming common on Rugosa cultivars. The presence of these insects is indicated by the formation of spherical, golf ball-size, spiny galls on the canes of host plants. The development of these galls is stimulated in the spring by newly hatched larvae. The galls encase the larvae until adult wasps emerge the following spring. The galls are unsightly and alter the plant's shape. They also stress the host plant, behaving like nutrient sinks, drawing nutrients away from the rest of the plant. Large numbers of galls can result in death of the plant. 

The most effective control is physical removal and disposal of galls in autumn after leaves have dropped and galls are visible. It is important to dispose of all galls since even a single missed gall can produce and reintroduce 30 to 40 mature wasps to the garden the following spring. Imidacloprid soil applications may be effective.

Another pest of rose canes is the stem dieback caused by the flatheaded borer, Agrilus aurichalceus. Rose canes are damaged when larvae tunnel in a spiral fashion beneath the bark, girdling and killing the canes (figures below). Their presence is indicated when a cane dies above the point of borer tunneling. Leaves on the infected cane turn brown as they die, creating a "flag" among healthy, green-leaved canes. On close observation, a swelling or gall on the infected cane can be seen below the dead tissue, indicating where the borer's tunneling occurred. The gall formation weakens canes and it is common to see infected canes broken off by wind. The quickest and most effective control is removal and disposal of infected canes in fall. Imidacloprid can be used in summer to kill borers.

Cooley spruce gall adelgid
Adelges cooleyi

Eastern spruce gall adelgid
Adelges abietis

(Hemiptera: Adelgidae)

References:

IPM of Midwest Landscapes (UMN)

Cooley spruce gall adelgid

Eastern spruce gall adelgid
Photos: John Davidson

Time: May

Hosts: Spruce

Cooley spruce gall adelgid is a native pest. Galls can be found on Colorado blue spruce and Engelman fir. This aphid-like insect may use Douglas fir as an alternate host, but galls will not be found on this species.

Eastern spruce gall adelgid is an introduced pest that forms galls on Norway, white, red and black spruce.

Damage symptoms: Cone-shaped galls occur at the tips of the new growth of host plants. The galls turn brown in summer.

Monitoring and control of these two pests is the same.

Eggs hatch when common lilac blooms in the first two weeks of May (Herms). Use sticky traps in late summer to detect flying adults. Look in late winter at the base of needles for wax-covered nymphs overwintering. Look in spring for galls forming. Look for white covered Cooley spruce adelgid adults on Douglas-fir.

Physical control: Prune out green galls in spring or early summer and destroy them. For aesthetics, prune out remaining brown galls in summer.

Chemical control: carbaryl, chlorpyrifos (nursery only), deltamethrin. Sprays can be used to kill overwintering females in late fall. It is difficult for pesticides to penetrate waxy covering on females on Douglas-fir. Spray the underside of new branches.

Biological control: Lacewings, predatory bugs, and fungi.

Biorational insecticides: horticultural oil, insecticidal soap.

Birch leafminer sawfly
Fenusa pusilla
(Hymenoptera: Tenthridinidae)

References:

IPM of Midwest Landscapes (UMN)

Birch leafminer damage

Birch leafminer adult
Photos: Whitney Cranshaw
www.forestryimages.org

Time: April, May

Hosts: prefers gray and paper birch, but also feeds on black, European white, river and yellow birch

Damage symptoms: Larvae feeding singly on tissue between leaf surfaces cause small kidney-shaped mines. As larvae grow larger these areas coalesce to brown, irregular, wrinkled blotches. Heavy infestations can cause browning of all the leaves. Affected trees may be killed but are more commonly weakened, leading to attack by other insects.

Monitoring: Adults emerge when Eastern red bud and crabapple bloom in late April to early May (Herms). Look for adults on new leaves. Yellow sticky traps can be used to monitor adult populations for each generation. Look for the brown kidney-shaped marks that indicate larval mine formation.

Cultural control: Replace susceptible species with more resistant ones, such as Betula nigra, river birch.

Chemical control: Soil applied systemic insecticides, such as imidacloprid, should be applied to the soil in the fall to kill adult and larval birch leafminer the following spring. Soil applied systemic insecticides, such as disyston, should be applied to the soil in spring.

Biological control: The ichneumonid wasps Lathrolestes nigricolis and Grypocentrus albipes are considered the most important natural enemies. These were introduced into the Northeast from Europe, but have not spread to the Midwest (Guevremont and Quednau 1977). In addition, 17 parasitoids attacking native leafminers also attack this introduced pest (Cheng and LeRoux 1969).

Conventional pesticides: acephate, bifenthrin, carbaryl, chlorpyrifos (nursery only), cyfluthrin, deltamethrin, fluvalinate, imidacloprid, permethrin.

Bronze birch borer
Agrilus anxius
(Coleoptera: Buprestidae)

References:

IPM of Midwest Landscapes

Tunneling damage under bark of birch tree caused by bronze birch borer larvae

Bronze birch borer adult
Photo: David Laughlin

Time: May

Hosts: European and Asian species of birch

Damage symptoms: The bronze birch borer prefers exotic birches and stressed or injured trees. Repeat infestations kill trees. Larvae overwinter in galleries under birch bark.

Monitoring: Look in June for 3 mm long, D-shaped exit holes in bark. Adults emerge when black locust and multiflora rose bloom in late May to early June (Herms). Look for terminal dieback on susceptible birches.

Cultural control: Planting resistant birch species is a way to minimize damage by bronze birch borer. Betula pendula (European white birch) is highly susceptible. Betula alleghaniensis (yellow birch), B. lenta (cherry birch), B. papyrifera (paper birch), and B. populafolia (gray birch) are moderately resistant. Betula nigra (river birch) and its cultivar Heritage birch, are the most resistant. Improve tree vitality by watering and mulching roots. Grow herbaceous plants over the shallow roots to reduce heat stress. Do not plant birches in the full sun.

Chemical control: Spray bark within week of first adult emergence. Imidacloprid can be applied to the soil or injected in early spring to kill bronze birch borer larvae. Mauget with bidrin is also effective.

Conventional pesticides: bidrin, chlorpyrifos (nursery only), imidacloprid, permethrin.

Biological control: Egg parasitism by Thysanus and Coccidencyrtus spp. was reported to be 50% in New Jersey (Barter 1957). It was lower (7%) in Pennsylvania on European white birches that were planted to reforest strip mines, and the parasitoids that were responsible were mostly the encyrtids Avertianella sp. and Ooencyrtus sp. (Loerch and Cameron 1983). Larval parasitism rates reached about 18% in New Jersey and Pennsylvania (Barter 1957). Important larval parasitoids in New Jersey include the chalcidid Phasganophora sulcata, the braconid Atanycolus charus, and the eulophid, Tetrastichus sp. in Pennsylvania.

White pine weevil
Pissodes strobi
(Coleoptera: Curculionidae)

References:

IPM of Midwest Landscapes (UMN)

Leader damage

Time: May

Hosts: White pine, Colorado spruce, white spruce, Douglas-fir, true firs, Scotch pine, Swiss stone pine, and Mugo pine

Life history: Native pest. When you get several days that are sunny and the temperatures reach the mid-60 F, females emerge from litter under trees and crawl to the upper parts of their host trees. The female weevil chews new holes at the leader tip to insert her eggs just under the bark. New adults emerge from July to September feed on branches in late summer and fall. They often make holes by the base of the trees and cause sap flow.

Insecticide timing: Nursery and landscape: Astro (a long lasting permethrin, pyrethroid formulation) or Onyx (long lasting bifenthrin, pyrethroid) can be applied to the top leader of trees that are likely to be attacked. Retreatment is needed every 14 to 20 days until June.

Christmas trees: Metasystox-R or dimethoate two times, once in early to May and again about three weeks later! While MSR can still be used by professional applicators and dimethoate is only registered for tree plantations (including), this leaves much to be desired for protecting residential trees.

Adult white pine weevil

Pine root collar weevil
Hylobius radicis
(Coleoptera: Curculionidae)

References:

IPM of Midwest Landscapes (UMN)

MN DNR Forest Disease Newsletter

Ohio State University Fact Sheet

Pitch encrusted soil and damage caused by root collar weevil feeding

Time: May to September

Host: Scotch, Austrian, red, and occasionally eastern white pine

Life history: Native pest. Adults feed on bark near the ground in early spring and begin egg laying. They later move to and feed in the upper crown branches. Eggs are deposited throughout the summer. Development may take more than one year. Larvae feed just below the soil surface on the inner bark and sapwood of stems and large roots. This feeding girdles the bark and restricts the transport of nutrients, thus weakening the tree and retarding growth. Eventually the tree's needles yellow and turn a deep reddish brown. A swollen trunk at ground line and darkened, pitch-infiltrated soil around the root collar indicate an infestation. Chronically damaged trees are easily blown over.

Monitoring: Carefully monitor small trees (2.5 to 10 cm in diameter) and trees growing in poor soil, as these are usually most severely damaged. Look for white pitch flow on bark and into the soil around the root collar during the growing season. Search debris under trees to look for adults. Cut into the bark of infested root crowns to detect larvae.

Physical control: Prune away lower branches and expose soil to sun at the base of the tree.

Insecticide timing: Use a persistent registered insecticide to drench the root collar of infested trees, such as Onyx (bifenthrin), chlorpyrifos, permethrin. Research indicates that this will control parent adults hiding at the base of the tree, and newly emerging adults. Apply cover sprays in mid-May (about 300 to 350 degree days [base 50]) and again in mid-August (1200 to 1400 degree days [base 50]) to control adult weevils feeding on shoots.

Adult pine root collar weevil; looks like white pine weevil, but damage is different

Twospotted spider mite
Tetranychus urticae
(Acari: Tetranychidae)

References:

Interiorscape Website (CUES)

Twospotted spider mite and eggs
Photo: University of Wisconsin Urban Horticulture

Twospotted spider mite damage
Photo: Clemson University

Twospotted spider mite damage
Photo: http://www.inra.fr/hyppz/RAVAGEUR/6teturt.htm

Time: All times of the year, but particularly during winter and early spring when greenhouses are drier

Hosts: over 300 woody and herbaceous species

Twospotted spider mites can occur at any time of the year in the greenhouse; however, populations are more severe in dry conditions, particularly in winter and early spring. They attack over 300 host plants; both woody and herbaceous plants are at risk.

Adults are 0.4 mm long and have eight legs. They are easily recognized by the two to four black spots on the semi-transparent body. Eggs are round and transparent. Larvae have six legs, and nymphs have eight.

Twospotted spider mites damage plants by inserting their chelicerae into plant tissue and sucking the contents of leaf cells. This causes characteristic stippling on the leaves. In heavy infestations, the mites produce extensive webbing over plants and can cause leaf drop. Monitor for mites by looking for damage and examining the undersides of leaves for mites and eggs. Beat plants with a stick and collect mites and eggs over a white cloth. Mites mature in 5 to 20 days depending on temperature and females lay over 100 eggs during their lives.

Management: Small populations of twospotted spider mites can be managed with oils, soaps, or biological control agents. Washing leaves with water may dislodge some of the mites, and increasing the humidity in the greenhouse will make a less favorable habitat. In heavy infestations, miticides should be used. Rotate between classes of miticides to prevent spider mites from becoming resistant to the miticides.

Darkwinged fungas gnat
Lycoriella and Bradysia spp.
(Diptera: Sciaridae)

References:

Interiorscape Website (CUES)

Darkwinged fungus gnat adult
Photo: Richard Leung, www.bugguide.net

Darkwinged fungus gnat larvae
Photo: Jim Kalisch, UNL Entomology

Time: All times of the year, but particularly during winter and early spring when greenhouses are drier

Hosts: Alfalfa, carnations, clover, corn, cucumbers, Easter lilies, geraniums, lettuce, nasturtium, peppers, rape, poinsettias, potatoes, soybeans, wheat, and others

Darkwinged fungus gnats are small flies that commonly occur in the greenhouse. Larvae feed on roots of plants and mature in two weeks. They are white with black head capsules and reach 5.5 mm in length. Adults are small (2.5 mm long), dark gray to black, with long legs and long, filiform antennae. They live for one week and females can lay up to 150 eggs on the soil surface during that time. Adults are weak fliers and do not feed.

Fungus gnats are usually considered nuisance pests, but larvae sometimes vector root rot pathogens to plants. Monitor for larvae by placing potato slices on the surface of the soil, and monitor for adults with yellow sticky cards. Wilted plants may indicate the presence of fungus gnat larvae and root rot.

Management: Avoid overwatering and, when practical, use potting mixes that contain bark as opposed to peat moss. Be sure potted plants have proper drainage.

Western flower thrips
Frankliniella occidentalis
(Thysanoptera: Thripidae)

References:

Western Flower Thrips in Commercial Greenhouses (UMN Extension)

Western Flower Thrips Feeding Scars and Tospovirus Lesions on Petunia Indicator Plants

Agdia DAS ELISA and ImmunoStrip test

Interiorscape Website (CUES)

Thrips damage
Photo: University of Florida

Time: All year in greenhouse

Hosts: Many flowering plants

Thrips feeds on the flowers and foliage by inserting its modified left mandible into the tissue, and sucking the fluids from cells. Oviposition and feeding scars reduce the aesthetic quality and marketability of ornamental plants. These thrips spread tomato spotted wilt (TSWV) and impatiens necrotic spot viruses (INSV).

Females lay eggs in tender plant tissue. The eggs hatch in 2 to 14 days, depending on temperature. Larvae are found in the protection of perianth of the flower or within developing terminal foliage. Late in the second instar they stop feeding and move down the plant to pupate. Thrips develop through two quiescent, non-feeding pupal stages in the soil, plant litter or in a protected area on the plant. Adults emerge and resume feeding on flowers, buds, and terminal foliage. The entire life cycle from oviposition to adult emergence can take 12 days in hot weather to 44 days in cool weather.

Management: Rotate classes of insecticides to prevent resistance. Use blue or yellow sticky cards to monitor for adults.

Greenhouse thrips
Heliothrips haemorrhoidalis
(Thysanoptera: Thripidae)

References: Interiorscape Website (CUES)

Time: All year in greenhouse

Hosts: Many flowering plants

Thrips feeds on the flowers and foliage by inserting its modified left mandible into the tissue, and sucking the fluids from cells. Oviposition and feeding scars reduce the aesthetic quality and marketability of ornamental plants. Greenhouse thrips move relatively slowly and rarely fly. They prefer a cool, shady, and fairly moist atmosphere. Reproduction is usually by parthenogenesis (laying unfertilized eggs). Under optimum conditions the time for development is 17 to 20 days for the eggs, about 13 days for the two larval instars, and about 5 days for the prepupal and pupal stages. The adults can live 7 weeks on plants growing in the greenhouse. Dark spots of excrement are often noticeable on the leaves and fruit. Pupae are found on leaves.

Management: See western flower thrips.

Black cutworm
Agrotis ipsilon

Bronzed cutworm
Nephelodes minians

Variegated cutworm
Peridroma saucia

(Lepidoptera: Noctuidae)

References:

IPM of Midwest Landscapes (UMN)

Bronzed cutworm

Black cutworm

Variegated cutworm

Time: May to October

Hosts: Turfgrasses, blade feeding larvae; adults do not feed

Life history: Native pests. Full-grown cutworm larvae are about 1-1/2 inches long When disturbed, cutworms roll into a ball. Black and variegated cutworms are the most common pests on home lawns. Black cutworm (three generations per year) does not overwinter in the upper Midwest. Moths migrate northward from southern states in early spring and deposit clusters of 10 to 20 eggs on grasses and weeds. Bronzed cutworms (one generation per year) overwinter as eggs that hatch in early spring. Fully-grown larvae are present by late April and pupation occurs during mid-August. Variegated cutworms (one generation per year) overwinter as partially grown larvae and resume feeding as grasses start to green. Cutworms feed at night leaving trails that can be seen in the dew. Cutworms hide during the day in aeration holes or in the thatch.

The black cutworm is dark gray to black with a pale stripe down the back, but with few other distinguishing markings he variegated cutworm is grey to brown with an orange lateral stripe and a series of darker lateral markings with a row of yellow or white dots runs down the middle of the back. Black cutworms are common on golf courses. Light traps and pheromone traps can be used to monitor adult activity. Bronzed cutworms are dark brown to black on the upper side of the body and paler on the underside. The upper surface has three narrow yellow stripes and a broad white-yellow stripe running down each side. The entire body has a distinctive bronze sheen. Bronzed cutworms are spring and early summer pests. During the day they hide in the soil or under debris.

Insecticide timing: Best efficacy is achieved by spraying late in the day and not irrigating, but follow label directions. Aeration holes in greens are often utilized by cutworms as burrows. However, the presence of these aeration holes does not increase the beta-cyfluthrin, bifenthrin, carbaryl, chlorpyrifos (golf course and nursery only), cyfluthrin, deltamethrin, lambda-cyhalothrin, trichlorfon.

Biorational insecticides include halofenozide, nematodes (Heterohabditis bacteriophora, Steinernema carpocapsae), and spinosad.

When disturbed, cutworms roll into a ball

Sod webworm
Crambus and Parapediasia spp.
(Lepidoptera: Pyralidae)

References:

IPM of Midwest Landscapes (UMN)

Sod webworm adult

Sod webworm larva

Time: May, June, July

Hosts: Grubs on grass roots; adults on foliage

Life history: The adults of sod webworms are called lawn moths. They are light-colored moths, which make short, erratic, darting flights above the turf and are attracted to lights at night. When resting they fold their wings back closely against their bodies, which gives them a very narrow appearance. Also, their heads appear to have a long snout.

The moths lay their eggs in the lawn. The older larvae are a dirty white to light brown with darker spots and are about 3/4 inch long with a black head. The larvae feed at night on grass blades. During the day the larvae hide in silk-lined tunnels or burrows at or slightly into the soil surface. Some species damage plant crowns or roots as well as blades.

Two or more generations can occur in Minnesota. Although webworm adults are commonly seen, larval damage is uncommon in Minnesota.

Insecticide timing: Look for dew sparkling on the webs in the early morning or at dusk. Beta-cyfluthrin, bifenthrin, carbaryl, chlorpyrifos (golf course and nursery only), cyfluthrin, deltamethrin, lambda-cyhalothrin, trichlorfon, permethrin.

Biorational insecticides include halofenozide, nematodes (Heterohabditis bacteriophora, Steinernema carpocapsae), spinosad.