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Extension Entomology

Month: June 2016

Twospotted Spider Mites: “Hot and Ready”

— by Dr. Raymond Cloyd

The extreme heat we are experiencing throughout Kansas and the fact that plants are “stressed” due to a lack of moisture means you need to be on the look-out for the twospotted spider mite, Tetranychus urticae (Figures 1 and 2). Twospotted spider mite is a warm-weather mite because, in general, populations are active from late spring through early fall. Summer temperatures allow twospotted spider mites to reproduce rapidly, which helps them to overwhelm natural enemy populations. This article discusses the plant protection strategies that homeowners and professionals can implement in order to alleviate or avoid problems with twospotted spider mite populations.

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Fig 1: Twospotted spider mite adults and eggs (spherical shape objects).

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Fig 2: Twospotted spider mite feeding damage.

Twospotted spider mite management involves maintaining plant health, implementing sanitation practices, and/or using pesticides with miticidal activity (miticides/acaricides). First of all, avoid exposing plants to any type of “stress” by maintaining proper watering, fertilizer, and mulching practices so as to reduce potential problems with twospotted spider mite populations. For example, inadequate moisture or overfertilizing plants, particularly with nitrogen-based fertilizers, can enhance development and reproduction of twospotted spider mites. Also, be sure to monitor for twospotted spider mite populations regularly by shaking branches or twigs onto a white sheet of paper, and looking for the mites crawling around. You can crush the mites on the white sheet of paper to determine if they are a pest or not. For instance, plant-feeding spider mites typically leave a green streak when crushed whereas predatory mites leave a red streak. A quick method of dealing with 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 many 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 many options in regards to miticides. The only “true miticide” still available is hexakis or fenbutatin-oxide, however, this active ingredient cannot be purchased by itself as the active ingredient is usually formulated with acephate (Orthene). Always read the label and apply miticides before twospotted spider mite populations are extensive and causing aesthetic damage. Furthermore, be sure to rotate miticides with different modes of action in order to avoid twospotted spider mite populations developing resistance. If possible, try to 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 that 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.

 

LACE BUGS: NOTHING TO WORRY ABOUT?

–by Dr. Raymond Cloyd

Lace bugs are insects that are present throughout Kansas feeding on a variety of plant types; however, lace bugs are not really a major insect pest of garden and landscape plants because they typically do not inflict significant direct harm to plants. Nonetheless, abundant populations may reduce the aesthetic appearance of certain plant types. Lace bugs feed on a wide-range of trees and shrubs, including: azalea, basswood, cotoneaster, hawthorn, linden, oak, rhododendron, and sycamore. Herbaceous plants susceptible to lace bugs include: aster, chrysanthemum, and scabiosa. The major plant-feeding lace bug species include Stephanitis spp., and Corythucha spp. Stephanitis spp. are primarily pests of broad-leaved evergreens, whereas Corythucha spp., including the sycamore lace bug (Corythucha ciliata) are pests of deciduous trees and shrubs.

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Fig 1:  Lace bug damage on azalea plant. Note the stippled and/or bleached appearance of the leaves.

 

Lace bugs feed primarily on leaf undersides; using their piercing-sucking mouthparts to withdraw plant sap from individual leaf cells. Their feeding cause’s leaves to appear stippled and/or bleached (Figure 1). Lace bugs feed similar to the twospotted spider mite, Tetranychus urticae, with both withdrawing chlorophyll (green pigment) from plant cells. The damage associated with lace bugs is similar to that caused by spider mites and leafhoppers; however, lace bugs leave black, tar-spot-like droplets of

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Fig 2: Black, tar-spot-like droplets of lace bug excrement.

excrement (“Lace Bug Poop”) on leaf undersides (Figure 2). The presence of black excrement distinguishes lace bugs from spider mites and/or leafhoppers. Excessive lace bug populations and extensive feeding may reduce plant vigor; however, any direct plant effects are dependent on plant age and size (especially young or newly-transplanted trees and shrubs).

Adult lace bugs are very distinguishable and quite attractive. The adults possess lacy, clear, shiny wings that are held flat over the body (Figure 3).

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Fig 3:  Close-up of lace bug adult.

 

They are 1/8 to 1/4 inch (3 to 8 mm) in length, and move sideways when disturbed. Female lace bugs lay between 20 to 50 eggs during their lifespan underneath leaves. The eggs are usually positioned alongside leaf veins and are black and shaped like a wine flask. Shiny, black nymphs with spines around the periphery of the body emerge from the eggs (Figure 4).

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Fig 4: Lace bug nymphs on leaf underside.

Nymphs undergo five instar stages before reaching adulthood. Shed skins on leaf undersides are evidence of nymphs that have transformed into adults. The life cycle (egg to adult) generally takes about 30 days to complete. There may be up to three generations per year although development is contingent on temperature. Stephanitis spp. overwinters as eggs that are cemented onto leaves and Corythucha spp. overwinters as adults in bark crevices and branch crotches. Adult activity commences in the spring when leaves unfold.

Lace bugs are more abundant on plants such as rhododendron and azalea that are exposed to full sun rather than on plants in shady locations. The management of lace bugs is generally not warranted because lace bugs are susceptible to many natural enemies including predators; such as, green lacewings, plant bugs, assassin bugs, minute pirate bugs, and spiders. A forceful water spray may be effective in quickly dislodging lace bugs from plants. However, if necessary, a number of contact insecticides registered for use against lace bugs can be applied. Be sure to read the label to make sure lace bugs are listed. Be sure to thoroughly cover leaf undersides to maximize the effectiveness of spray applications because the leaf undersides are where all the life stages (eggs, nymphs, and adults) of lace bugs are located.

If you have any questions regarding the management of lace bugs contact your county horticultural agent, or university-based or state extension entomologist.

 

 

 

 

Corn Update

–Dr. Jeff Whitworth and Dr. Holly Schwarting

The first western corn rootworm adults were collected on 17 June from a corn field in north central Kansas.  Development is being completed very quickly, which should be expected based upon the temperatures we have been experiencing.  However, there are still some larvae feeding on roots.

CRW adult 2016

CRW larva mass in root

None of the plants sampled have started tasseling and therefore adults are feeding on leaves.  This typical leaf feeding by adults will not impact yield.

WCRW adult leaf feeding

Adults will probably start feeding on emerging tassels and then shift to silk feeding when silks start emerging.  Remember, corn plants are very efficient pollinators, so as long as a little silk is showing above the husk, the pollen will be successful.  There are still many adult tarnished plant bugs in the corn fields and these are quite commonly confused with adult western corn rootworms.  However, they will NOT clip silks.

tarnished plant bug adult

 

Some leaf feeding is also evident by corn earworms and fall armyworms.  Again, these leaves can look ragged, thus the name ragworm, but will not impact yield.

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Corn and Sorghum Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

As wheat senesces, or matures, the chinch bugs are migrating to adjacent corn and/or sorghum fields.  V6+ stage corn can withstand considerable chinch bug feeding but younger plants may be stressed, especially dryland corn.

Chinch bug nymph

chinch bug adults

Seedling sorghum adjacent to wheat will be somewhat protected by insecticide seed treatments if chinch bug populations aren’t overwhelming as they migrate from the wheat, but only for about 28 days, maximum.  Waiting about 2 weeks after wheat harvest to plant sorghum will mitigate chinch bug nymph infestation problems. For more information on chinch bug biology and management, please visit: https://www.bookstore.ksre.ksu.edu/pubs/MF3107.pdf

Soybean Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Soybeans are germinating and thus attracting the usual defoliators.  Fairly neat, oval shaped holes indicate adult bean leaf beetle feeding.  Ragged holes generally indicate green cloverworms, which are starting to reach larval maturity in alfalfa and may therefore move into young soybeans, after pupation, and start ovipositing eggs.

BLB feeding

BLB

Cloverworm

There are also numerous young grasshopper nymphs in both alfalfa and soybeans, still around the outside edges of fields.  The next couple of weeks will be an ideal time to spray borders, weedy patches, grassy waterways, etc. for grasshopper control.

grasshopper nymph

For more information on pest management in soybeans, please visit the Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf

Alfalfa Update

–Dr. Jeff Whitworth and Dr. Holly Schwarting

Potato leafhopper populations are very active throughout north central Kansas.  There are small nymphs, many adults, and the adults seem to still be migrating into the fields.

PLH adult2

Leafhopper nymph (2)

PLH burn

Could not find significant populations in fields swathed within the last 7-10 days but as regrowth occurs and immigration continues, these fields need to be monitored.  Fields not yet cut are already showing signs of “hopper burn” and should be swathed ASAP or an insecticide application may be justified.  Potato leafhoppers have few, if any, natural enemies.  Thus, these populations probably will not diminish without management, i.e. either swathing (my preference) or insecticide application.  For more information on potato leafhopper management, please visit the Alfalfa Insect Management Guide: http://www.bookstore.ksre.ksu.edu/pubs/mf809.pdf

 

Bagworms Are Back

–by Dr Raymond Cloyd

It is the time of year you have all been waiting for, that is, dealing with that

“infamous” of insect pests known as the bagworm (Thyridopteryx ephemeraeformis). Throughout Kansas, bagworm eggs have hatched and the young caterpillars (“munching machines”) are out-and-about feeding on both broadleaf and evergreen trees and shrubs. Bagworms were first considered a pest of conifers but over the years they have expanded their host range to include a number of broadleaf plants, including: rose, honeylocust, and flowering plum. So, what is the best way to deal with bagworm caterpillars and thus prevent them from causing damage? Hand-picking any small caterpillars (along with their accompanying bag) and placing them into a container of soapy water will kill them directly. This practice, if feasible, will quickly remove populations before they can cause substantial plant damage. I recommend that everyone should consider having a weekend “bagworm hand-picking party” with prizes awarded to those individuals that collect the most bags J. These “bagworm hand-picking parties” will be a way to enhance family quality time J.

For those less interested in hand-picking, there are a number of insecticides labeled for use against bagworms including those with the following active ingredients (trade name in parentheses): acephate (Orthene), Bacillus thuringiensis subsp. kurstaki (Dipel/Thuricide), cyfluthrin (Tempo), lambda-cyhalothrin (Scimitar), trichlorfon (Dylox), indoxacarb (Provaunt), chlorantraniliprole (Acelepryn), and spinosad (Conserve). Many of these active ingredients are commercially available and sold under different trade names or as generic products. However, several insecticides may not be directly available to homeowners. The key to dealing with bagworms when using insecticides is to apply early and frequently enough in order to kill the highly susceptible young caterpillars that are feeding aggressively on plant foliage (Figure 1).

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Figure 1

Older caterpillars that develop later in the season, in the bags (Figure 2), are typically more difficult to kill with insecticides. In addition, females feed less as they prepare for reproduction; thus, reducing their susceptibility to spray applications and any residues. The bacterium Bacillus thuringiensis subsp. kurstaki is active on young caterpillars; however, the active ingredient must be consumed to be effective, so thorough coverage of all plant parts and frequent applications are required to avoid having to deal with later life stages.

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Figure 2

This compound is sensitive to ultra-violet light degradation and rainfall, which reduces residual activity. Spinosad is the active ingredient in a number of homeowner products, including: Borer, Bagworm, Tent Caterpillar & Leafminer Spray; Captain Jack’s DeadBug Brew; and Monterey Garden Insect Spray. These products work by contact and ingestion (stomach poison) although they are most effective when ingested and can be used against older or larger bagworm caterpillars (Figure 3).

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Figure 3

Cyfluthrin, lambda-cyhalothrin, trichlorfon, chlorantraniliprole, and indoxacarb may be used against both the young and the older caterpillars. However, thorough coverage of all plant parts, especially the tops of trees and shrubs, where bagworms commonly start feeding, and frequent applications are required. The reason why multiple applications will be needed when bagworms are first detected is because bagworms “blow in” (called ‘ballooning’) from neighboring plants. If left unchecked, bagworms can cause significant damage, thus ruining the aesthetic quality of plants. In addition, they may actually kill plants, especially evergreens since they do not usually produce another flush of growth, and newly transplanted small plants.

If you have any questions regarding the management bagworms contact your county horticultural agent, or university-based or state extension entomologist.

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