Floriculture Greenhouse Update

The hot, dry summer has resulted in outbreaks of western flower thrips, spider mites, potato leafhoppers,  and tarnished plant bugs have also been troublesome.  Smaller, black melon aphids also tend to be more prevalent in the summer and fall months.

ThripsThrips are pollen feeders, so as more plants are flowering, their populations tend to increase.  In the summer months, as grasses or nearby hay fields are mowed, thrips often enter greenhouses thru vents and open roofs. (It is often helpful to close the roofs if nearby areas are being mowed in the evening.)  They also may migrate to yellow flowering weeds such as galinsoga, so good weed control always helps.  

Here’s an example of how temperature speeds up their development:

Temperature:         Egg to Adult Development Times for Western Flower Thrips  (On chrysanthemum leaves, 45-55% Relative humidity, Robb 1989)59F            39 days 69F            26 days 77F            12.9 days 81F            10.2 days 80F            9.3 days 90F            10.7 days

With the increased development time, and emigration of thrips, it is very difficult to keep thrips levels at those maintained in the spring before plants bloom.  Sticky card counts vary depending upon the how attractive the plants are in the greenhouse to thrips, whether the plants are flowering, placement of cards, what stage of thrips is present, and migration of thrips into greenhouses.  Growers also need to relate sticky card counts to crop damage.  For example, high numbers of thrips may be present on the sticky cards in open roof greenhouses, but limited plant damage to garden mums may be observed.

Working grower action thresholds of 10 per card may be appropriate only during spring production.  Higher action thresholds may be more appropriate in the summer months for garden mum and poinsettias. (Woody plants such as roses and poinsettias are not hosts of impatiens necrotic spot virus).

If using chemical sprays, spray intervals need to be shortened to every 3-4 days.  For more information see, Thrips Management Plan andWestern Flower Thrips- Management on Greenhouse Grown Crops Nematode application frequency needs to be increased in hot summer weather conditions. It's also important to apply enough moisture with the nematodes.  Sprays may dry out too rapidly in the high, dry environment.  One grower says he is now applying 500 gallons instead of 200 gallons of spray solution  to the same sq footage.  As with any biological control measure, they are most effectively used preventively in conjunction with good cultural practices for thrips control (sanitation, rigorous weed controls, etc). For more information see the article:  Nematodes in Pest Management.

Fact Sheet: Field Grown Cut Flowers: Tarnished Plant Bugs

Leanne Pundt, University of Connecticut

Carefully inspect incoming poinsettia cuttings (by each batch, and variety) to insure that they are free of insects and diseases and are of the quality you expect.

Look for whitefly egg, nymphs and pupae on the underside of the leaves, especially the oldest bottom three leaves where most of the whitefly may be found. If possible, randomly inspect from 10 to 30% of the cuttings.  Inspect each shipment and cultivar separately.  Record which shipment or cultivar has whitefly and which stage is present.

Whitefly eggs and nymphs are very small, so a 10x  handlens or hands free optivisor is helpful. Patches of dried spray residue or dried latex might be confused with dusty appearance once sees near the whitefly eggs.

Don’t assume that if you don’t see whitefly adults emerging from the shipping containers, that you are free of whitefly. Adults are less likely to be observed compared to the more sedentary stages.

Record which shipments and varieties may need follow-up treatments.  For information on chemical control of whiteflies, including the highly resistant Q Biotype of the siverleaf whitefly see "The Best Guess" pesticide program for the Q whitefly on poinsettia. Scroll down to get to the recommendations and for links to more information.

If you are using biological control of whiteflies, see the pest message posted on Friday, June 25th.

In addition to whitefly, look for fungus gnat larvae and signs of their feeding damage (blunt root tips). Roots should be white and healthy with no signs of root rot disease.

Look for any angular leaf spots with a yellow halo, that may be indicate of a bacterial leaf disease. Bacterial leaf diseases spread rapidly under warm, wet conditions. See an example of a bacterial leaf spot disease on poinsettia.

Fact Sheets: Managing Whiteflies in Greenhouses University of ConnecticutManaging Fungus Gnats and Shoreflies in the Greenhouse University of Connecticut

Photo: Fungus gnat vs Shorefly adults on sticky card

Leanne Pundt, University of Connecticut and Tina Smith, University of Massachusetts

Damage from broad mites has been reported on peppers and New Guinea impatiens. Tarsononemid mites including cyclamen mite and broad mite can cause serious damage to a wide range of greenhouse crops such as New Guinea impatiens, garden impatiens, dahlias, gerbera, ivy, lantana, snapdragon, verbena, zinnia, peppers and other vegetable plants. Broad mites inject a toxin from their saliva as they feed. Their feeding causes twisted, hardened and distorted growth in the terminal of the plant and bronzed, rough, lower surfaces. Young terminal buds can be killed and leaves turn downward. Broad and cyclamen mites are too small to see without the aid of a microscope. Regular inspection of crops for their feeding damage is the best way to detect infestations. If characteristic symptoms are seen, send samples to the diagnostic laboratory where they can be inspected under a microscope.

Mites can be easily spread to healthy plants by workers' and infested hanging plants can infest plants below. During scouting and other tasks, enter mite-infested areas last. Clean the greenhouse thoroughly.

Damage caused by cyclamen mites has been observed on Delphinium. Symptoms are very characteristic and are sometimes mistaken for disease. Leaves cup or curl and are often blackened. Flower spikes are stunted and blackened. Aconitum, dahlia, chrysanthemum, verbena and viola are also hosts, although they do not exhibit so serious a reaction to the feeding.

Miticides labeled for broad mites and cyclamen mites on ornamentals include: products containing abamectin (Avid, Lucid, Minx and others), chlorfenapyr (Pylon), dicofol (Kelthane), fenpyroximate (Akari) and spiromesifen (Judo). Note that the effects of their feeding may persist long after the mites have been eradicated. The Judo (spiromesifen) label recommends not spraying impatiens spp. (including New Guineas). Follow label precautions for crop safety. It is an very effective spray against broad mites. For vegetable plants see labels of Pylon and Minx.

Fact Sheet: Managing Cyclamen Mites and Broad Mites in Greenhouses

Tina Smith, University of Massachusetts and Leanne Pundt, University of Connecticut

Watch for potato leafhoppers. Leafhoppers are found on many different out-door grown perennials, vegetables and sometimes garden mums. Of the many species of leafhoppers, the potato leafhopper and aster leafhopper are most likely pests on ornamentals in New England. Both adult species have slender bodies and wings that are held roof-like over their body. Leafhoppers jump or fly when disturbed and can quickly move sideways, backwards or forwards. The nymphs resemble adults but lack wings. They have piercing-sucking mouthparts and feed on plant sap, causing yellowing, stunting and loss of vigor.

The potato leafhopper feeds by inserting a needle-like beak into the plant and sucking out the sap. It also injects a toxin as it feeds so leaves may develop a v-shaped brown, edge burn at the tip known as "hopperburn". Photo: hopperburn on Astilbe. This injury may be confused with leaf scorch especially on drought-sensitive Astilbe. Plants may also be stunted with distorted new growth. Growers with retail customers should be aware that potato leafhoppers are building up in beans, potatoes and eggplants now. Damage is worse under drought conditions.

The aster leafhopper transmits the pathogen that causes aster yellows. Other species of leafhoppers may not inject a toxin or transmit diseases as they feed so control may not always be necessary.

Scouting: Brush the leaves of plants with your hand. Small light yellow-green potato leafhoppers dart around and fly up from foliage when disturbed. Tap the foliage over a yellow sticky card or briefly place a sticky card among the plants to catch adults. Potato leafhoppers (Empoasca fabae) adults are approximately 1/8 inch long, and light green with characteristic 6 white spots just behind their head. Once you see adults, look closely at several leaves for nymphs. Nymphs are small, narrow light green wedge shaped insects that move very fast sideways, front and back. Look on the underside of leaves along the leaf vein for the young nymphs especially on Alcea, Astilbe and Dahlia.

Management: The potato leafhopper does not overwinter in New England. It migrates into New England in late April or early May from the south. There may be from 3 to 4 generations per year. Potato leafhoppers also feed on woody plants such as birches, maples and apples. Field crops such as alfalfa, clover and sunflower are also hosts.

Systemic insecticides such as neonicotinoids may be applied to prevent feeding damage when leafhoppers first appear. There are many other pesticides labeled for leafhoppers including azadirachtin, (MOA Group 18) pyrethroids (MOA Group 3), and Beauvaria bassiana(MOA Group M). Pesticides with limited residual will need to be reapplied with good coverage on the undersides of leaves. See the New England Guide for specific pesticides.

Fact Sheet: Leafhopper Pests of Connecticut Nurseries and Landscapes

Leanne Pundt, University of ConnecticutTina Smith, University of Massachusetts

Lily leaf beetle adults and larvae are active, feeding on foliage of Asiatic lilies and Fritillaria in many areas. In other areas Eggs have been laid and are hatching.  Monitor for the bright red beetles and also for the eggs on the undersides of the foliage.  Inspect the leaves for fine tan-colored, irregular-shaped lines about one inch long.  On closer examination, these tan lines will be a row of eggs.  Just before hatching, these eggs turn a bright red color.  When eggs are found, they can be removed and destroyed.

Lily leaf beetle (Lilioceris lilii) is known to lay its eggs and develop only on true lilies, Lilium species (Turk's cap lilies, tiger lilies, Easter lilies, Asiatic and Oriental lilies) (not daylilies), and fritillaria (Fritillaria sp). Although lilies and fritillaria are the primary hosts, lily leaf beetle also feeds, sometimes just lightly, on a number of other plants, including lily of the valley (Convallaria majalis), soloman's seal (Polygonatum sp.), bittersweet (Solanum sp.), potato (Solanum tuberosum), hollyhock (Alcea) and various hosta species. It is however, a devastating pest to true lilies.

If your customers only have a few plants in their garden, hand-picking adults and eggs can be effective. Products containing neem (Bon-Neem, Azatin), a botanical insecticide, have been shown to kill very young larvae but must be applied every five to seven days after egg hatch. Products containing the systemic imidacloprid are providing effective control applied either as a foliage spray or soil drench depending on label instructions. Imidacloprid is the active ingredient in Marathon and Merit and one of the active ingredients in Bayer Advanced Rose and Flower Insect Killer for home gardeners. Products containing spinosad a microbial insecticide, are effective on larvae. Spinosad is sold as Conserve and Entrust for commercial growers and Monterey Garden Insect Spray, BULL’S-EYETM and others for home gardeners.

The University of Rhode Island (URI) Biological Control Lab is researching natural enemies of the lily leaf beetle. Small parasitic insects have been released throughout NewEngland and URI researchers hope that the insects will disperse naturally from these release sites, eventually reducing problems with the lily leaf beetle.

Lisa Tewksbury, URI is continuing to track these parasitic insects by collecting the large larvae covered with excrement (brown blobs) that are found on lilies. They will dissect the larvae to look for the parasitic insects. If you or customers you know have larvae, and wouldn’t mind sending them to URI please use the following instructions to send them to Lisa at the URI Department of Plant Sciences or contact her for more information. Instructions and more information

More information on LLB

Photos: Larvae Eggs Adult Beetle

Lily Leaf Beetle Fact Sheet, UMass

University of Rhode Island Bio Control Lab (includes photos of parasitic wasp) Evaluation of resistance to Lily Leaf Beetle in Lilium spp. Cultivars

Tina Smith, University of MassachusettsLeanne Pundt, University of Connecticut

Viburnum leaf beetles are becoming active in nurseries and retail garden centers. See information and photos: Viburnum Leaf Beetle UMass and Cornell

High temperature is one of the most important factors to control in the retail yard. Shading and air movement are ways to help keep temperatures cooler for plants in the retail setting. The use of 50% shade of the midday sunlight will reduce light to appropriate levels. See the fact sheet Caring for plants in retail settings: 

Two-spotted spider mites are showing up on Ipomoea. See message and photos on managing mites.

Spittlebugs: The white foam from spittlebugs can be seen now on many perennials as the spittlebugs move in from grassy areas. Most of the damage is cosmetic only and does not harm the plant. If the infestation is small, either handpick the spittle masses with a gloved hand or use a forceful jet of water to dislodge the nymphs. For more information and photo see this previous message.

Plant nutrition: Bedding plants in retail yards may be showing signs of lack of feed. With the recent prolonged high temperatures and frequent watering, fertilizer may have leached out. If new growth is yellowing and roots are healthy, fertilize with 200 ppm of a complete fertilizer such as 20-10-20 at every watering. Bedding plants usually recover easily because they are quickly purchased, and are planted out in the garden, fertilized and have room to grow.

Hanging baskets and patio pots are a different story. Plants in hanging baskets and planters will stay in those containers throughout the summer. The small volume of soil in a container is the only available source of nutrients for the plant compared to the much larger volume of soil available to the plants in a garden. Frequent watering causes much of the fertilizer to be leached out. If hanging baskets and planters are not fertilized in the retail sales area, or if controlled-release fertilizer was not used, all the fertilizer will leach out by the time the consumer buys the plants. The plants will quickly decline in quality once the customer takes the basket home. There are solutions. One is to fertilize baskets and planters in the retail sales area, on a weekly basis, using 400 ppm N, or using 200 ppm N at every watering. Another solution is to top-dress the basket or planter with a controlled- release fertilizer using 3-5 grams of N of a shorter term, 4-6 month material or use tablets according to directions. Retailers should communicate with their wholesale growers to make sure controlled-release fertilizer has not already been applied prior to shipping before fertilizing plants.

Tomato plants: Monitor for late blight and bacterial canker. See message.

Garden Mums should be planted as soon as possible upon arrival. See the message  about early season care including fertilizing and crown buds.

Tina Smith, University of MassachusettsLeanne Pundt, University of ConnecticutPaul Lopes, University of Massachusetts

Weather related problems were observed over this past week. Paper thin brown spots - sunscald (many crops) caused by sun and wind, wilted new growth (basil) caused by chilling injury and silver color foliage (bacopa) were just a few of the symptoms observed. Shade perennials placed in full sun in both retail and grower locations resulted in sunburned foliage. Continue to watch weather reports over the next week. Cover plants at night, protect plants from the wind. Gradually expose plants grown in the greenhouse to cool temperatures.

Late season thrips and Impatiens necrotic spot virus were observed on plants this week.

Many growers used biological control for aphids and other pests this season. There has been confusion over identification of aphid mummies versus healthy aphids at retail locations. See photos of black aphid mummies and brown aphid mummies, many on a leaf.

Monitor for Rhizoctonia web blight on impatiens, herbs and other plants encouraged by dense canopies, closely spaced plants and humid conditions. Rhizoctonia is more commonly known as a fungus that causes root rot diseases.  It may grow up from the media causing web blight during favorable environmental conditions. Stems and leaves collapse, with fine, web-like mycelium present. If you look closely, you can see the fine strands of the fungus.  If there are certain houses or locations where you have seen outbreaks of Rhizoctonia web blight, consider growing crops that form a less dense canopy in those locations.  Web blight can occur in the some locations and on the same crops year after year.   Many of the fungicides labeled for Rhizoctonia root rot may also be helpful in limiting web blight. Rhizoctonia is a natural inhabitant of the soil and can survive there indefinitely.

Leanne Pundt, University of ConnecticutTina Smith, University of Massachusetts

It is not unusual to discover outbreaks of pests such as spider mites, thrips, whiteflies and aphids in greenhouses full of flowering bedding plants scheduled to be sold in the next week or two. If you discover an insect problem now, we suggest using a safe, effective contact spray that will knock down the infestation to provide good protection for a couple weeks. If infestations are localized, spot treating may be best. Once plants are planted outdoors in a garden, aphids, mites, whiteflies and thrips are not usually a problem. Some good choices for out-the-door treatments are:

• Thrips, aphids, whiteflies: abamectin (Avid), imadacloprid (Marathon II), dinotefuran (Safari), pyridaben (Sanmite), acetamiprid (Tristar), thiamethoxam (Flagship), and bifenthrin (Talstar).
• Aphids and whiteflies: pymetrozine (Endeavor)
• Mites: abamectin (Avid), bifenazate (Floramite), hexythiazox (Hexygon), pyridaben (Sanmite).

You will want to use the safest products available with everything in bloom. None of the products listed above are known to cause a phytotoxicity problem when used at the rate on the label. Usually wettable powder and flowable formulations are the least likely to be phytotoxic. However, wettable powders may cause visible residue. Make sure wettable powders are completely dissolved in the spray tank and the tank is agitated. This will prevent slurry from forming at the bottom of the spray tank, which could be phytotoxic if sprayed on plants. The re-entry time-period following application of the products listed above is 12 hours with the exceptions of Tristar (24 hours). Note that Endeavor works by interfering with the insect’s ability to feed and may take 5 – 10 days or longer to see results.

Tina Smith, University of MassachusettsLeanne Pundt, University of Connecticut

Monitor for Downy Mildew. See previously posted message on Downy Mildew.

Thrips populations are increasing with the warmer temperatures. Monitor for thrips using yellow sticky cards and monitor plants for Impatiens necrotic spot virus. See the message Thrips and Tospoviruses

Iron deficiency symptoms are showing up on crops. Symptoms appear as an interveinal chlorosis, normally starting at the shoot tips, but often they occur throughout the entire plant. Sometimes the leaves of iron deficient plants turn almost white. Bacopa, calibrachoa, scaevola, snapdragons, and petunia are crops susceptible to iron deficiency. Preventing iron deficiency can be accomplished by controlling pH and using an iron chelate fertilizer. Before applying iron, check the plants roots to be sure they are healthy. Unhealthy roots will result in yellow, stunted plants that may be confused with iron deficiency. See Preventing Iron Deficiency and Selecting which iron chelate to use.

Late Blight reminder to retailers: Buy and sell only tomato plants that have been started and grown here in the northeast. Tomato growers and home gardeners will be very appreciative if you do not bring late blight into New England. Late blight is a very destructive and very infectious disease that killed tomato and potato plants in gardens and on commercial farms throughout the eastern U.S. during 2009. Please do your part to prevent this disease! For information and photos on late blight, see the message: Garden Retailers and Late Blight

Tina Smith, University of MassachusettsLeanne Pundt, University of Connecticut

Plants at many greenhouses appear to be a little ahead. If you are thinking about holding plants using growth regulators, review the message: Using Plant Growth Regulators to Hold Finished Plants. A proper hold rate using growth regulators should give enough control to hold a mature plant under hot weather for 2-3 weeks but low enough that the plant will recover and grow for the consumer. Spray treatments carry less of a risk of overdose than drench treatment, especially when the root-active PGRs are used.Monitor for powdery mildew on gerberas. A good short video on the subject is available from Floricast by Margery Daughtery, Cornell University.Spider mites continue to be a problem on crops such as ivy geraniums and mandevilla and on perennials such as salvia, monarda, nepeta and perovskia. Spider mite injury on ivy geraniums looks like oedema, so be sure to monitor carefully with a hand-lens. See photos of oedema vs spider mite damage.

See message: Managing Two-spotted spider mites  Spider mites are very successful at surviving over the winter in their resting stage. The can hibernate in any crevices in the greenhouse so growers having problems last year are likely to have problems this year.Finally, when sunshine turns to clouds and rain, avoid wet foliage, reduce humidity by heating and venting and monitor for Botrytis. See messages: Heating and Venting and Botrytis

Leanne Pundt, University of ConnecticutTina Smith, University of Massachusetts

When scouting, it’s important to be able to tell the difference between pest mite species and beneficial mite species.  In general, beneficial predatory mites are very active, fast moving pear-shaped mites. One of the most commonly released predatory mites in greenhouse production is Phytoseiulus persimilis.  This beneficial, predatory mite is bright orangish-red, pear-shaped mite is very fast moving compared to the more sedentary, pest species, two-spotted spider mite. The female P. persimilis is about 0.6 mm in length and the male is slightly smaller.   

With decreasing day length in the fall, as well as falling temperatures and less available food, female spider mites enter diapause.  Females entering diapause become an orange-red color within a few days of becoming an adult. They may overwinter in hoop houses and cooler greenhouses in a dormant stage. During this time, they do not eat, or lay eggs and are less susceptible to pesticides.  They are also more difficult for predatory mites to find.  By looking at the body shape (which is NOT pear shaped), you can tell the difference between diapausing spider mites compared to P. persimilis mites.

To evaluate whether predatory mites are working, look for shriveled, dried up spider mites plus the presence of predatory mites and their eggs. P. persimilis eggs are oval or “football shaped” and roughly twice the size of spider mite eggs.  Eggs are laid close to a food source. When first laid, they are a transparent light pink shade and later turn darker.  You may start to see the eggs about two weeks after releasing the beneficial (depending upon temperature).

Spider mite eggs are round or barrel shaped and are often found along the midvein on the underside of leaves. When spider mite eggs are first laid, they are transparent.  They turn straw colored near the time of hatching.  Eggs hatch into larvae and then two nymphal stages before becoming adults. Larvae are at first colorless and develop color as they feed. Their characteristic body spots are more distinct in the nymphal stage.  Spider mite adults are easily recognized by their two dark spots on either side of their body.  Eggs, nymphs and adults can be found on the underside of the leaves.

Leanne Pundt, University of Connecticut

Just like you need to inspect incoming plants to assess their quality, it’s also important to inspect biological control agents as you receive them.  Here are some tips for assessing the quality of the various types of natural enemies.  Also, ask your biological control supplier on how to best evaluate any incoming shipments.

* Check number of shipment days and how cold or warm the ice packs are. * Keep the package out of extremes of sun, heat or cold. Release as soon as possible. * Predators and parasitoids that are shipped as mobile stages (predatory mites, some wasps) should be inspected upon arrival to determine if they are actively moving.

As an example, to assess the quality of predatory Mites such as Neoseiulus cucumeris or P. persimilis, spread a small sample of the mites on a white sheet of paper. Check with a 10 to 16x hand lens to make sure the predatory mites are active and moving rapidly. You should also check the rim of the container in which the predatory mites are shipped for the presence of live individuals.  Shipments of N. cucumeris may also contain grain mites which serve as a food source. Grain mites are white, have long protruding hairs on their back and are generally less mobile than the tan-colored N. cucumeris.

Biological control agents shipped as eggs or pupae should be checked for viability by placing a small sample in a clear, airtight, dry container. Keep the container in a shaded, unsprayed area for two or three days, and carefully looking for the active larvae or adults.

Storage Most natural enemies have a very short shelf-life, especially those that are shipped without a food source, and thus should be applied immediately. Natural enemies that are supplied with a food source can be stored for a few days before use; however, it is strongly recommended to use natural enemies immediately upon arrival. Storage time depends on the particular natural enemy and environmental conditions. If natural enemies must be stored, maintain them at 50-60ºF  and 50-70% relative humidity. Do not place parasitoids or predators into refrigerators or in direct sunlight since refrigerator temperatures (35-45ºF) and exposure to sunlight are detrimental to both natural enemy types. In general, the longer that natural enemies are stored, the lower the survivability of the individuals. One common cause of natural enemy mortality during storage is desiccation, which may be avoided by placing containers of natural enemies in a plastic bag along with a moist sponge, and then securely sealing the bag. From: New England Greenhouse Floriculture Recommendation Guide For more information:  Greenhouse IPM with an Emphasis on Biocontrol by Penn State University - Appendix D: Quick Methods for Evaluation Biocontrol Shipments. This is a overview chart of how to determine viability, and to determine establishment and reproductive success in the greenhouse for a number of biological control agents.   Also, check with your supplier for additional information.

Leanne Pundt, University of Connecticut

Thrips are active in many greenhouses now. If you use pesticides to manage thrips then plan to treat in the early evening. Thrips have two mass flights per day, so sprays in the early evening may contact more thrips.  Treating before you see a peak in adult numbers on yellow sticky cards is critical. Adult thrips numbers on cards tend to peak every two to three weeks. Apply insecticides before this peak, so adults will be killed before they lay eggs. Small droplets of pesticide sprays are most effective for coverage.

To manage thrips, make two to three pesticide applications about 5 days apart and rotate pesticides with different modes of action. Two materials that some growers are successfully using are pyridalyl (Overture) and chlorfenapyr (Pylon).  It appears that pyridalyl (Overture) is more toxic to second instar nymphs than adults. Also, Overture takes at least seven days to kill a majority of WFT, so don’t expect an immediate reduction in populations when using this insecticide. Read the label for plant safety. Both products have precautions. Both of these products also have translaminar activity. Remember that translaminar insecticides penetrate leaf tissues and form a reservoir of active ingredient within the leaf, providing residual activity. Insecticides with contact or translaminar activity are generally better than pesticides that are systemic because systemic insecticides typically don’t move into flower parts (petals and sepals) where WFT adults normally feed. Azadirachtin (Molt X, Aza-Direct, Azatin, Ornazin, Neemix) is an insect growth regulator (IGR) and "stressor" so may be helpful in some tank mixes. For example, if thrips populations are low and plants are not yet in flower, Beauveria bassiana (Botanigard, Mycotrol) and azadirachtin may be an option. Abamectin (Avid) (translaminar activity) with azadirachtin has also been working well for some growers.

Pesticide rotation options for management suggested by Dr. Raymond Cloyd, Kansas State University are: * Spinosad (Conserve), Chlorfenapyr (Pylon), Abamectin (Avid), Methiocarb (Mesurol) * Novaluron (Pedestal), Pyridalyl (Overture), Chlorfenapyr (Pylon), Spinosad (Conserve) * Beauveria bassiana (BotaniGard/Naturalis), Acephate (Orthene), Spinosad (Conserve) * Abamectin (Avid), Pyridalyl (Overture), Chlorfenapyr (Pylon), Spinosad (Conserve) * Chlorpyrifos (DuraGuard), Novaluron (Pedestal), Abamectin (Avid), Bifenthrin (Talstar)

Horticultural oil (Pure Spray Green, Saf-T-Side, or Ultra fine oil) may also be an option provided label cautions regarding plant safety are followed. Note that Mesurol has a 24 hour REI plus it may leave an unsightly residue, so it may be best early in the growing season. Pedestal is an insect growth regulator (IGR) labeled for immature stages. TriStar (acetamiprid - group 4A) or Aria (flonicamid - Group 9C) may also help suppress thrips.

Articles: Western Flower Thrips Management: Have We Reached an Impasse?by Raymond Cloyd

2010 Thrips Management Plan

Tina Smith, University of Massachusetts Leanne Pundt, University of Connecticut 

Questions have been asked about using pheromone lures to detect Western flower thrips and the effectiveness of using sugar in the spray mix to enhance spray efficacy.

Phermone Lures

A new item for WFT is a sex aggregation pheromone lure for early detection of low level populations. It is reportedly best used very early in the crop cycle. A number of companies sell or distribute lures that are suppose to increase the number of WFT thrips adults captured on sticky cards or attract WFT out of hiding places such as flowers or buds, increasing their exposure to insecticide spray applications and achieving higher mortality. Note that a pheromone lure is not a “control” device. Some growers are concerned about attracting WFT to un-infested areas, especially if used this late in the growing season with active thrips infestations. Also there are questions about the longevity of the scent within a greenhouse and how effective the pheromone lure is when many different plant types are in flower.

Using Sugar in Spray Solution

Growers for years have suggested that mixing white or brown sugar with a contact insecticide in the spray solution enhances efficacy of the spray application against western flower thrips. Research by Dr. Raymond Cloyd, Kansas State University showed that the addition of sugar and other sweeteners to lure thrips from hiding does not work and in some cases can cause the growth of black sooty mold.

Information on thrips management by Dr. Raymond Cloyd: Western Flower Thrips Management: Have We Reached and Impasse?

Does Dew Do It?

Tina Smith, University of Massachusetts

 

Inspect incoming plants carefully for signs of insects, diseases, weeds and cultural problems. Inspect the entire plant - leaves, stems and roots for signs of pest activity and for general health. Look for any distorted new growth on incoming plugs and transplants that might be caused by thrips. Blackened, firm stems and leaf spots on garden impatiens and New Guinea impatiens are signs of Impatiens necrotic spot virus (INSV). INSV test kits are useful for quick tests of suspicious looking plants.

Look on the undersides of leaves for spider mites. They are often found along the mid-vein of ivy geraniums, ipomea, thunbergia and other susceptible plants. On ivy geraniums, spider mite damage is similar to damage caused by thrips and oedema. Inspect root health also. Roots should be white with vigorous growth. Roots that are brown or decayed are evidence of root rot disease or may be caused by overwatering or high soluble salts.

When handling and cleaning incoming plants, work in blocks and wash hands thoroughly between blocks of plants. If disposable gloves are worn, change or clean them between blocks. This will prevent spreading infectious diseases that are transmitted mechanically, such Bacterial leaf spot on geraniums and Tobacco Mosaic Virus on petunias and related crops.   If at all possible, do not accept plant shipments with serious insects or diseases with wide host ranges, and are difficult to treat. Do not accept plant material infected with incurable diseases, such as root rots, viruses, bacterial leaf spot diseases, or foliar nematodes. If you need confirmation, isolate a few plants showing symptoms and send them to a diagnostic laboratory. If you find isolated evidence of some insect activity, for example, aphids, and decide to keep the shipment, identify an isolated, quarantine area in which to keep the plants. Treat immediately and hold the plants in this area until you are sure that they are healthy, salable and free of pest problems. Only enter this quarantine area at the end of the day to avoid moving pest problems throughout your operation.

Tina Smith, University of Massachusetts

Hunter flies are becoming more common on sticky cards in greenhouses. The Hunter fly (Coenosia attenuata) is a greyish, predatory fly in the same family as the housefly and similar in appearance, but smaller than the common housefly. Some growers confuse them with shore flies. Adult shoreflies also resemble small houseflies, with their short robust bodies, short legs and short antennae, but are smaller than the hunter fly, darker in color and have characteristic five clear spots on the wings.

The adult hunter fly preys on other flying insects, catching them in flight. It feeds on fungus gnats and shoreflies, but also on other flying insects such as leafminer and, to a lesser extent, whiteflies. The larvae live in the soil and are generalist predators on soil-dwelling organisms such as fungus gnat and shorefly larvae.

Hunter flies are originally from Europe. They were first found in the United States in October of 1999 at a commercial greenhouse in upstate New York. Adult females lay eggs in the soil that hatch in about 5 days. The hunter fly larvae seek other soil dwelling insects such as fungus gnat larvae as prey. Larvae grow for about two weeks and then pupate in the soil for two weeks.

Photos: Hunter fly adult, Hunter flies on sticky cards, Fungus gnat and shorefly on sticky card, Shoreflies and others on sticky cards

More Photos: Fact sheet on fungus gnats and shoreflies including photos of hunter flies, shore flies, fungus gnats and common parasitic wasps found on sticky cards.   Need to scroll to figures 11-14

Leanne Pundt, University of Connecticut Tina Smith, University of Massachusetts

Nematodes are small, colorless, cylindrical round worms that occur naturally in soils throughout the world. Different species work best against different target pests. Steinernema feltiae is primarily used against fungus gnat larvae and thrips pupae in the soil. Fungus gnat larvae may be parasitized in any larval stage.  Nematodes have traditionally been used against soil dwelling pests because they are sensitive to ultra violet light.

The nematodes enter the insect host through body openings. They multiply within the host and release a symbiotic bacterium whose toxin kills the fungus gnats. The larvae are killed in one to two days by blood poisoning.  More than one generation of nematodes may develop in dead host insect in the media. The infective juveniles then exit the dead body and search for new hosts to infect

The nematode S. feltiae is sold under the trade names of NemaShield and Nemasys. Both of these products are labeled as a soil drench treatment against fungus gnat larvae. Preventative applications to moist soils work best.  Apply nematodes with a sprayer (remove screens and filters), injector, hose end sprayer or even a watering can. If using an injector, set the dilution to 1:100. Remove all filters or screens on the intake tube. Remove pump filters. Use a small battery powered submersible pump to keep the solution agitated.

Unlike many traditional pesticides there is no REI (an added bonus in propagation houses), nor possibility that the target pest will develop resistance. No adverse effects have been shown against non-target organisms in many different field studies. But, beneficial nematodes are living organisms, so there are a number of precautions you need to follow for their successful use.

Check viability before application. To do this, place a small amount of the product in a small container or petri dish. Add 1 or 2 drops of room temperature water; wait a few minutes and look for actively moving or swimming nematodes. Use a dark black background and a hand lens or field microscope to see the small (0.6 mm or 0.02 inches in length) nematodes. Apply in the evening or at dusk or on a cloudy, overcast day. (Nematodes are very sensitive to UV light and desiccation).

Nematodes are compatible with a number of different pesticides. However, they are generally not compatible with organophosphates, carbamates, and nematicides.   However, do not mix nematodes with your fertilizer solution!  

For more detailed information on pesticide compatibility: consult with your supplier or with the following resources on the Internet:

- Pesticide Side Effects Database – www.koppert.com

- Pesticide Side Effects Database - www.biobest.be/

Apply immediately after receiving them, if possible.  If you must store the nematodes, store in a refrigerator (38-42°F). Avoid placing in a small refrigerator where they may freeze. Check expiration date on the package for how long you can store them.

Specific Tips for Use Against Fungus Gnat Larvae. 

• Treat as soon as possible (2 to 3 days) after sticking cuttings, planting plugs or starting seeds. 
• Apply as a media drench to target the fungus gnat larvae.
• Media temperatures should be above 50° F but avoid applying when soil temperatures are above 80°F. Optimum media temperatures are between 60-70°F. (Use a soil thermometer to monitor temperatures).
• Water the growing media before and after application. (Nematodes need moisture for movement). But, avoid over watering, so they aren’t washed out of the container.
• Apply in the evening or at dusk or on a cloudy, overcast day. (Nematodes are very sensitive to UV light and desiccation).
• Repeated applications are often needed. Reapply in 2 to 4 weeks under moderate to heavy infestations. For longer term crops, apply at the beginning and at mid crop.

The symbiotic bacteria breaks down the host insect’s cuticle. The infected larvae rapidly disappears, so may be difficult to locate. Infected fungus gnat larvae are often opaque-white to light yellow in color.

In addition, the product Nemasys is also labeled for use against western flower thrips. Specific tips for use against western flower thrips (from the Nemasys label).

• Nematodes require moist conditions to enhance effectiveness.
• If plants are dry, provide light overhead irrigation prior to nematode application.
• Ensure good foliar coverage of spray mix to enhance contact with the target pest.
• Use of a wetting agent or surfactant will enhance wettability of the spray mix and encourage nematode movement.
• Following application, ensure that the crop remains wet for at least two hours.
• Do not apply in direct sunlight.

Note: the nematodes will dessicate after about one day.  Growers who have had success with this application method, apply the nematodes on a weekly basis, and target the young growing point where thrips tend to hide.

For more information on Steinernema feltiae:

NemaShield- BioWorks Nemasys - BeckerUnderwood Searchable Database on Insect Parasitic Nematodes: Ohio State University

Leanne Pundt, University of Connecticut

It is time to plan aphid management if you will be using biological control agents. See the message posted January 29, 2009 for more details. Ornamental plants are susceptible to many aphid species such as green peach, melon, potato and foxglove. Managing aphids using biological control agents is a bit complicated because parasitic wasps are not general feeders and they parasitize specific aphid species. Some suppliers primarily recommend several parasitic wasps, banker plants and a predatory midge to manage the various aphid species. Other suppliers also recommend using predatory lacewings. Place orders for banker plants about 6 weeks prior to expected aphid infestations. Banker plants with Aphidius colemanii should be started 3 weeks prior to seeding or sticking cuttings in propagation houses as a preventative measure for green peach and black melon aphids. Since cereal aphids used in this banker-system attack monocots, they should not be used in greenhouses containing lilies or grasses. The first Aphidius colemanii banker plants containing the grass feeding aphid species need to be transplanted into larger pots (10”) upon arrival. A week later, the parasitic wasps, Aphidius colemani should be ordered and immediately released on the banker plants. If aphids are observed in the crops, they should be identified and additional biological control agents selected for that species. If aphid populations increase and more control is needed, Aphidoletes aphidimyza can be introduced weekly for 3 weeks in hot spots to supplement the parasites. Aphidoletes aphidimyza is a generalist predator that feeds on many different species of aphids. They arrive as midges and adults and adults fly out of the tubes upon opening. The midges and other stages are evenly sprinkled upon the leaves of the crop. If using predatory midges, placing the pots in trays with moist sand will help provide pupation sites for them. (The predatory midges pupate in the soil).The parasitic wasps Aphelinus abdominalis and Aphidus ervi are used for potato and foxglove aphids They are released weekly for at least 3 weeks or until aphids are controlled. Yellow sticky cards should continue to be used to monitor aphid predators and new growth should be inspected for aphid populations.

Work with your supplier for rates. Guidelines are available in the 2009-2010 New England Greenhouse Floriculture Guide (ordering info)

Photos: Banker plants with aphids, Close up, Starter cage 

More information: Biobest - biological control, Propagation of ornamental crops

Two good articles in "Greenhouse IPM Bi-Weekly Report" by Stanton Gill, University of Maryland on experiences using banker plants:  Aphid Control -Results in Maryland and Banking and Investing on Aphid Control in Greenhouses 

Tina Smith, University of Massachusetts Leanne Pundt, University of Connecticut

Planning ahead is essential for success if you are considering using biological control for pest management. Growers that successfully use biological control for spring crops start in propagation greenhouses at the very beginning of the crop cycle. Biological control should never be started in the middle of a crop cycle. For growers purchasing plant material from other growers, request information on what specific pesticides were applied to the plant material to ensure that no long lasting pesticide residues adversely impact the biological control agents. For example, many organophosphate and pyrethroid pesticide residues may impact biological control agents for 3 to 4 months. See message posted October 9th for more details on preparing your greenhouse.   Growers starting their own seeds or cuttings, begin by using beneficial nematodes (Steinernema feltiae) as a preventative measure for fungus gnats, but also thrips larvae suppression. The nematodes are mixed with water and applied during the first or second watering as a soil drench with a repeat application when repotting or transplanting. As a guide, 2 applications spaced 2 weeks apart usually provide 6 weeks of protection. Nematodes do not control shore flies.  Beneficial nematodes can also be applied with Trichoderma (RootShield) which also needs to be applied preventatively. Hydrogen dioxide (XeroTol) and fertilizer solutions are not compatible with the beneficial nematodes and need to be applied separately.   For shore flies (and also fungus gnats), Atheta coriaria (Rove Beetle) is commonly used, applied one time during seeding or sticking cuttings. Atheta are nocturnal and are easily established in greenhouses. They come in a tube of peat-vermiculite mix with all three stages of the insect present (egg, larva and adult). Open the container where you will release them and sprinkle them evenly across the area to be treated. Reapply when transplanting or repotting. The predatory mite, Stratiolaelaps scimitus  (formerly known as Hypoaspis miles) is also included for fungus gnats during propagation. It is applied once during seeding or sticking. Hypoaspis are very mobile and will colonize the surface of the growing media. They also come in a tube of vermiculite/peat which should be evenly distributed by sprinkling across the area to be treated and should be reapplied when transplanting or repotting. Growers are also including the predatory mite Amblyseius cucumeris as a preventative for thrips in their propagation areas. Amblyseius come in a tube of bran. A small pile of bran is placed on each seedling tray which acts a breeder pile for mites. Adult mites emerge from the pile and attack early larval stages of thrips development and sometimes eat spider mites and their eggs. The pile needs to be kept intact for breeding to continue and mites to emerge. Amblyseius should be reapplied when transplanting or repotting. Use yellow sticky cards to monitor for shore flies and fungus gnat adults and use potato wedges to monitor fungus gnat larvae. For information on rates, contact your supplier. Also see: 2009-2010 New England Greenhouse Floriculture Guide (ordering info)

Becker Underwood: Chemical Compatibility Chart for Beneficial Nematodes

Biobest, Crop Info-Sheet: Propagation of Ornamental Crops  (Biocontrol)

Biobest, Crop Info-Sheet: (Biocontrol) Spring Crops (Bedding Plants and Hanging Baskets)

Technical Bulletin: Propagation of Ornamental Crops Using Biological Control Agents for Pest Protection

Sometimes rates are in metric. For metric conversion see: www.metric-conversions.org 

Tina Smith, University of Massachusetts Leanne Pundt, University of Connecticut