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Extension Entomology

Category: Horticulture

New Extension Publications Associated with Horticultural Entomology Developed in 2019

–by Dr. Raymond Cloyd

 

Aphid Management in Greenhouse Production Systems (MF3442)

https://www.bookstore.ksre.ksu.edu/pubs/MF3442.pdf

 

Oak Leaf Itch Mite (MF2806)

https://www.bookstore.ksre.ksu.edu/pubs/MF2806.pdf

 

Bagworm: Insect Pest of Trees and Shrubs (MF3474)

https://www.bookstore.ksre.ksu.edu/Item.aspx?catId=524&pubId=22339

 

Grub Management in Turfgrass Using Insecticides (MF3439)

https://www.bookstore.ksre.ksu.edu/Item.aspx?catId=524&pubId=21619

 

Scale Insect Pests (MF3457)

https://www.bookstore.ksre.ksu.edu/pubs/MF3457.pdf

 

 

Dormant Oils

–by Dr. Raymond Cloyd

 

Dormant oils are applied during winter to kill insect and mite pests that survive the winter (overwinter) as eggs or mature females. Instead of waiting until spring to initiate management strategies, dormant oil applications can help reduce costs associated with pesticide inputs (in this case, insecticides and miticides) later in the growing season (spring through fall). The advantages of applying dormant oils include: 1) wide range of activity against the life stages of mite and scale pests—even the eggs; 2) less direct and indirect harmful effects to beneficial insects and predatory mites due to the timing of application; and 3) relatively low toxicity to humans and other mammals. The disadvantages of dormant oils include potential phytotoxicity (plant injury) and minimal residual activity or persistence.

Dormant oils are typically derived from paraffinic crude oil, and are the heaviest of the petroleum-based oil sprays with a low unsulfonated residue (Figure 1).  Picture not available!

The unsulfonated residue is an assessment of the phytotoxic compounds remaining after distillation and refining. An unsulfonated residue >92% indicates a highly refined product with less potential for phytotoxicity. Dormant oils generally have a unsulfonated residue value <92%.

Dormant oil applications are primarily directed at killing overwintering life stages of certain mites and scales (Figure 2),

Fig 2. Overwintering life stage (adult female) of scale (Auth-Raymond Cloyd, KSU)

before they become active in the spring and feed on plants. Applications are made during winter to minimize phytotoxicity to ornamental plants. A 2% to 4% application rate is generally recommended in early winter to early spring. Dormant oils have contact activity and either suffocate by blocking the breathing pores (spiracles), or directly penetrate and disrupt cell membranes. However, dormant oils have minimal residual activity once residues dissipate, so thorough coverage of all plant parts is important.

Since dormant oils are applied to all plant parts, the overwintering life stage of insect or mite pests must be located on the plant. However, not all insect and mite pests overwinter on plants. For example, dormant oil applications are not effective against the twospotted spider mite (Tetranychus urticae) because the mite overwinters as a female in plant debris, mulch, or other non-plant protected places. In contrast, the spruce spider mite (Oligonychus ununguis) overwinters as an egg on plants, primarily conifers, such as; arborvitae, hemlock, juniper, and pine. Therefore, the spruce spider mite is susceptible to dormant oil spray applications.

Dormant oils are effective in killing the overwintering stages of scales, especially first and second instars or nymphs (=crawlers). For example, euonymus scale (Unaspis euonymi) overwinters as second instar nymphs or mature females; both life stages are susceptible to dormant oil applications. However, certain scales that overwinter as eggs; such as, oystershell scale (Lepidosaphes ulmi) and pine needle scale (Chionaspis pinifoliae), are more tolerant of dormant oil applications because the eggs are generally stacked or piled on top of each other. Subsequently, dormant oils may not penetrate and contact the bottom layer. Consequently, supplemental insecticide applications are typically required after eggs hatch.

An issue when using dormant oils is the potential for phytotoxicity. Some plants, such as arborvitae, beech, redbud, and certain maples (Japanese, red, sugar, and amur), may be harmed by dormant oil sprays. Furthermore, the needles of Colorado blue spruce (Picea pungens) may be discolored or change from blue to green as a result of a dormant oil application. Phytotoxicity may be a problem when >4% application rates are used and/or when applications are conducted in early fall before dormancy or in late spring at bud-break. Problems associated with phytotoxicity are less likely to occur when applications are made in late November through February, which is when most plants are completely dormant. To avoid phytotoxicity, always ensure the spray solution is continually agitated.

Never apply dormant oils when ambient air temperatures are ≤40ºF (≤4.4°C). Dormant oils should be applied to deciduous plants (trees and shrubs) when the ambient air temperature remains above 40°F (4.4°C) for at least 24 hours. Conifers, in general, are more susceptible to damage than deciduous plants, so it is best to apply dormant oils when temperatures remain above 40ºF (4.4°C) over a 24-hour period although there is no quantitative evidence suggesting that applications made at ≤40°F (≤4.4°C) will damage dormant fruit trees. In addition, dormant oils should never be applied to plants that are stressed since stressed plants are more susceptible to phytotoxicity. For example, lack of moisture, extreme temperatures, sudden drastic changes in the ambient air temperatures after spraying, prolonged windy conditions, and disease or insect infestations may predispose plants to phytotoxicity. However, there is no direct evidence indicating that dormant oils are harmful to stressed trees.

There is a general misconception that insect and mite pest populations are unable to develop resistance to dormant oils. However, this is not true. For instance, a Christmas tree plantation of Scots pine (Pinus sylvestris) trees was sprayed with dormant oils for more than 10 years in succession to “control” pine needle scale. Eventually, the scale population became more and more difficult to “control.” Why? Well, what was discovered was that the scale covers actually increased in thickness; making it difficult for the dormant oil to penetrate the outer covering and kill the eggs.

Dormant oil applications can alleviate dealing with insect and/or mite pest populations during the growing season. Therefore, inputs from insecticide and/or miticide applications can be reduced, thus preserving the natural enemies of mites and scales, including; predators and parasitoids that may naturally regulate populations of these pests.

 

 

 

 

Green June Beetle Larvae

–by Dr. Raymond Cloyd

We have received numerous inquiries regarding large grubs (larvae) crawling on their backs across pavements or other hard surfaces. Well, these are the larval stage of the green June beetle, Cotinis nitida. Larvae are 3/8 (early instars) to 1-1/2 (later instars) inches long, and exhibit a strange behavioral trait—they crawl on their back (Figures 1 and 2)—likely due to having a constant itch J. This behavior of crawling on their back is unique among turfgrass-infesting larvae.

 

 

Fig 1. Green June Beetle Larva (Grub) Crawling On Pavement Surface (Auth–Raymond Cloyd, KSU)

Photo for Fig. 2 not available

 

The larvae are abundant now due to the excessive moisture (rain) we have received. Young larvae are generally located at the interface between the soil and thatch layer feeding primarily on organic matter including thatch and grass-clippings; preferring material with a high moisture content. The larvae can be found in swimming pools, garages, and basements. Green June beetle larvae can tunnel 18 inches into the soil; and even deeper in sandy soils.

 

 

 

 

 

 

Scolia dubia: Parasitoid of the Green June Beetle

–by Dr. Raymond Cloyd

 

We continue to see large “wasps” (not cicada killer wasps) feeding on flowering plants such as goldenrod (Solidago spp.) and wild onion (Allium spp.). This is Scolia dubia, which is a parasitoid of green June beetle (Cotinis nitida) larvae or grubs located in the soil. Since there were so many green June beetle adults flying around this year, there is likely to be high populations of grubs/larvae for the parasitoids to attack.

The parasitoids are approximately 3/4-inches long with purple to black wings. The abdomen has red-brown markings with two conspicuous yellow spots on both sides of the third abdominal segment (Figure 1).

Fig 1. Scolia dubia adult feeding on flower (Auth–Raymond Cloyd, KSU)

The parasitoids can be observed flying in a figure-eight pattern several inches above turfgrass infested with green June beetle larvae. A female enters the burrow of a green June beetle larva, uses her ovipositor (egg-laying device) to paralyze the larva, and then she attaches an egg to the underside of the larva. The larva hatches from an egg and consumes the paralyzed green June beetle larva. The larva overwinters in a cocoon at the bottom of the burrow and then pupates in the spring. Adult parasitoids typically emerge from August through September, and feed on flower nectar. They are likely emerging and present later than usual due to the weather conditions we have experienced this year (lots of rain and cool temperatures). Scolia dubia adults, unlike cicada killer males, are not aggressive and females will only sting when handled.

 

 

New Extension Publication – Oak Leaf Itch Mite

–by Dr. Raymond Cloyd

 

We have a new extension publication available entitled, Oak Leaf Itch Mite

This new extension publication, which is actually an update of a previous extension publication, provides up-to-date information on the biology, bites and symptoms, and prevention associated with the oak leaf itch mite (Pyemotes herfsi). The extension publication is available from the following website:

https://www.bookstore.ksre.ksu.edu/pubs/MF2806.pdf

 

Wheel Bug…A Cool-Looking “Bug!”

–by Dr. Raymond Cloyd

If you have spent any time outdoors lately, you may have noticed a very distinct, grotesque looking insect on trees, shrubs, or near homes. This insect is the wheel bug (Arilus cristatus), which is common, and widely-distributed throughout Kansas and the USA. Wheel bugs, also called assassin bugs, are predators that prey on insect pests. However, the nymphs and adult can inflict a painful bite when handled by humans.

Adult wheel bugs are 1.0 to 1.25 inches long, robust with long legs and antennae, and have a stout beak and large eyes on a narrow head (Figure 1).

Fig 1: Wheel Bug Adults Mating. Male is on top of Female (Auth: Raymond Cloyd, KSU)

They are dark-brown to gray and possess a wheel or crest with 8 to 12 protruding teeth-like structures (tubercles) on the thorax that looks like a cogwheel—similar to the dinosaur—Stegosaurus (Figure 2).

Fig 2: Wheel Bug Adult (Auth: Raymond Cloyd, KSU)

Wheel bugs have two long, slender antennae that are constantly moving or weaving around. Females are typically larger than males. Females lay eggs that resemble miniature brown bottles with white stoppers (Figure 3).

Fig 3: Wheel Bug Eggs on Leaf Underside (Auth: Raymond Cloyd, KSU)

The eggs are laid in clusters of 40 to 200, and are glued together and covered with gummy cement that protects eggs from weather extremes and natural enemies (e.g. parasitoids and predators). The egg clusters are located on leaves, or the trunk or branches of trees or shrubs. The nymphs hatch (eclose) from eggs and are bright red in color with black markings. The nymphs do not have the wheel or crest. The life cycle, from egg to adult, can take 3 to 4 months to complete. Wheel bugs are active day and night, and are very shy, tending to hide on the underside of leaves. The wheel bug has one generation per year and overwinters as eggs.

Wheel bugs are voracious predators feeding on a wide-variety of insects, including caterpillars (Figure 4)

Fig 4: Wheel Bug Adult Preparing to Attach a Caterpillar (Auth: Raymond Cloyd, KSU)

beetles, true bugs, sawflies, and aphids. Unfortunately, wheel bugs will feed on beneficial insects such as ladybird beetles and honey bees. The mouthparts are red-brown in color and resemble a tube or straw that is located underneath the head. The mouthparts extend out when wheel bugs are ready to “stab” prey. Wheel bugs paralyze prey with their saliva, which contains a toxic substance that immobilizes prey within 30 seconds. In addition to feeding on insects, wheel bugs are cannibalistic, and will feed on each other…AWESOME J.

 

Euonymus Scale

–by Dr. Raymond Cloyd

This is the time of year when euonymus scale (Unaspis euonymi) becomes noticeable in landscapes on evergreen euonymus (Euonymus japonica) and Japanese pachysandra (Pachysandra terminalis). Euonymus scale overwinters as a mated female on plant stems. Eggs develop and mature underneath the scale, and then nymphs hatch from eggs over a two to three week period. The newly hatched nymphs (crawlers) migrate along the stem and start feeding near the base of host plants. Nymphs can also infect adjacent plants by being blown around on air currents, resulting in infestations often not being detected until populations are extensive and damage is noticeable—like right now. Leaves eventually become spotted yellow or white. Plants located near structures such as foundations (Figure 1),

Fig 1: Euonymus Scale Infestation on Euonymus Plants Located Near Building (Auth: Raymond Cloyd, KSU

walls or in parking areas are more susceptible to euonymus scale than plants growing in open areas that receive sunlight and air movement. Moreover, the variegated forms of euonymus are more susceptible to euonymus scale than the green forms.

Heavy infestations of euonymus scale can ruin the aesthetic appearance of plants, causing complete defoliation or even plant death. Females are dark brown, flattened, and resemble an oystershell. Males, however, are elongated, ridged, and white in color (Figure 2).

Fig 2: Male & Female Euonymus Scale on Leaf (Auth: Raymond Cloyd, KSU)

Males tend to be located on leaves along leaf veins whereas females reside on the stems. There may be up to three generations per year.

 

Cultural practices such as pruning out heavily infested branches—without ruining the aesthetic quality of the plant—are effective in quickly reducing euonymus scale populations; especially this time of year. Be sure to immediately discard pruned branches away from the area. If feasible, avoid planting Euonymus japonica in landscapes since this species is highly susceptible to euonymus scale. Winged euonymus (Euonymus alata) is less susceptible to euonymus scale, even when adjacent plants are infested. Insecticide applications in May through June (now is too late!), which is when the nymphs are most active, will help alleviate problems with euonymus scale later in the season (like right now!). Insecticides recommended for suppression of euonymus scale populations, primarily targeting the nymphs, include acephate (Orthene); pyrethroid-based insecticides such as bifenthrin (Talstar), cyfluthrin (Tempo), and lambda-cyhalothrin (Scimitar); potassium salts of fatty acids (insecticidal soap); and horticultural (petroleum or mineral-based) and neem (clarified hydrophobic extract of neem oil) oils. Always check plants regularly for the presence of nymphs, which will help time insecticide applications. Three to four applications performed at seven to 10-day intervals may be required; however, this is dependent on the level of the infestation. Euonymus scale is a hard or armored scale, so, in most cases, soil or drench applications of systemic insecticides such as imidacloprid (Merit) are not effective in suppressing euonymus scale populations; however, the systemic insecticide dinotefuran (Safari/Zylam), due to its high-water solubility (39,000 ppm), may provide suppression of euonymus scale populations when applied as a drench to the soil. Dormant oil applications can be conducted in winter to kill the overwintering mated females on stems. However, thorough coverage of all plant parts is important to obtain sufficient mortality.

 

Euonymus scale is susceptible to a multitude of natural enemies (e.g. parasitoids and predators), including: braconid and ichneumonid wasps, ladybird beetles, green lacewings, and minute pirate bugs. However, natural enemies may fail to provide enough mortality (‘killing power’) to significantly impact extensive populations of euonymus scale. Furthermore, insecticides such as acephate (Orthene), and many of the pyrethroid-based insecticides, including bifenthrin (Talstar), cyfluthrin (Tempo), and lambda-cyhalothrin (Scimitar) are very harmful to most natural enemies, so applications of these materials may disrupt any natural regulation or suppression.

 

 

Twospotted Spider Mites

–by Dr. Raymond Cloyd

The recent hot weather we are experiencing throughout Kansas is conducive to the development of the twospotted spider mite, Tetranychus urticae (Figure 1), resulting in extensive feeding damage to the leaves of horticultural plants in gardens and landscapes (Figures 2 and 3). Twospotted spider mite is a warm-weather mite with populations commonly active from late spring through early fall. Summer temperatures allow twospotted spider mite females to reproduce rapidly, which helps to overwhelm natural enemy (e.g. predators) populations by producing multiple generations throughout the season.

Fig 1. Close-up of twospotted spider mite adults.

Fig 2. Twospotted spider mite feeding damage on euonymus bush leaves (Auth–Raymond Cloyd, KSU)

Fig 3. Twospotted spider mite feeding damage on tomato leaves (Auth–Raymond Cloyd, KSU)

The management of twospotted spider mite populations involves maintaining plant health by avoiding ‘stress,’ implementing sanitation practices, and/or using pesticides with miticidal activity (miticides/acaricides). First, prevent plants from experiencing moisture ‘stress’ by maintaining proper watering and mulching practices, which will be helpful in minimizing potential problems with twospotted spider mite populations. For instance, inadequate moisture or over fertilizing plants, especially with water-soluble nitrogen-based fertilizers, can enhance development and reproduction of twospotted spider mites.

It is important to monitor for twospotted spider mite populations regularly by shaking plant parts (e.g. leaves, branches, or twigs) onto a clipboard with a white sheet of paper, and then look for the mites crawling around (you can actually see the mites). You can crush the mites on the white sheet of paper to determine if they are a pest or not. For example, plant-feeding spider mites typically leave a green streak when crushed whereas predatory mites leave a red streak.

A quick and effective method of managing twospotted spider mite populations is applying a forceful water spray throughout the plant canopy at least twice per week during the season. Forceful water sprays will dislodge eggs and the motile life stages (larvae, nymphs, and adults). Be sure to direct forceful water sprays toward the leaf undersides where all life stages (eggs, nymphs, larvae, and adults) of the twospotted spider mite are located. The removal of plant debris and weeds eliminates alternative hosts and overwintering sites.

There are a number of pesticides with miticidal activity available to professionals for suppression of twospotted spider mite populations outdoors, including: abamectin (Avid), acequinocyl (Shuttle), bifenazate (Floramite), etoxazole (TetraSan), hexythiazox (Hexygon), potassium salts of fatty acids (M-Pede), and horticultural oils (petroleum, mineral, or neem-based). Homeowners do not have as many options. In fact, the only “true miticide” still available is hexakis or fenbutatin-oxide, however, this active ingredient cannot be purchased alone as the active ingredient is typically formulated with another pesticide (insecticide) such as acephate (Orthene). However, homeowners can apply commercially available insecticidal soaps (potassium salts of fatty acids) or horticultural oils. Always read the label and apply miticides before twospotted spider mite populations are extensive and causing damage. Moreover, be sure to rotate miticides with different modes of action to avoid twospotted spider mite populations developing resistance. If possible, target ‘hot spots’ or localized infestations of twospotted spider mites, which will reduce the potential for resistance developing. Be sure to thoroughly cover all plant parts with spray applications; especially when using pesticides with contact activity. Some miticides such as abamectin (Avid) and etoxazole (TetraSan) have translaminar activity, which means the material penetrates into leaf tissues and forms a reservoir of active ingredient within the leaf. This provides residual activity even after spray residues have dried. Mites that feed on leaves will ingest a lethal concentration of the active ingredient and be killed.

It is important to note that many pesticides used to suppress other insect pests encountered on plants in landscapes and gardens may be harmful to the natural enemies of twospotted spider mite; consequently, resulting in an inadvertent increase in twospotted spider mite populations or secondary pest outbreaks.

 

 

 

“Bugs” To Be On The Look-Out For

–by Dr. Raymond Cloyd

 

Green June Beetles: lots still flying around. This has been one of the best…or worst years…depending on your perspective.

Japanese Beetle Adults: many are feeding on fruit trees and roses.

Bagworms: time is running-out in regards to applying insecticides…you have about two to three more weeks…and then it is too late.

Mosquitoes: with all the rain and moist conditions, mosquitoes (adults) are very prevalent.

Milkweed Aphids: many milkweed plants are literally covered with the milkweed aphid. Simply use a forceful water spray to dislodge them from plants.

Squash Bugs: eggs have hatched and nymphs are looking for suitable feeding sites…on the leaf underside.

 

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