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Ornamental Crops IPM E-newsletter, 2007

For Summer 2007

In this Issue:

  1. Thrips Biocontrol with Predatory Mites
  2. The Basics of Alternative Herbicides
  3. Canna Viruses
  4. Tour of Greenhouses in Canada – Register Now

Cornell IPM Team for Production Ornamentals

Thrips Biocontrol with Predatory Mites

Gary Couch, NYSIPM,

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The NYS IPM program has been evaluating the use of predatory mites for thrips control in bedding plants for over a decade. The results, both in production and retail settings, have been promising enough that we encourage other growers to utilize this approach.

The benefits of using biocontrol are numerous. The lack of an REI (re-entry interval) means they can be applied during normal working hours without disrupting other greenhouse tasks or incurring the added expense of overtime for late evening/night spray applications. No pesticide license is needed and applications are simple and straightforward. The applicator incurs none of the risks or general unpleasantness associated with mixing, handling and applying pesticides. Resistance is not an issue but use of the mites can prolong the usable life of other thrips insecticides by reducing our reliance on them.

While there are many positive benefits, we realize that a lack of confidence in the mite’s ability to successfully control thrips can be a strong barrier against adopting this practice. This is especially understandable if the grower has had the unfortunate experience of losing large numbers of plants to an outbreak of INSV, a virus that can be carried and spread by thrips.

How it works:

The predacious mite, Neoseiulus cucumeris, (often just called “Cucumeris” by greenhouse growers) feeds on young thrips and will also feed on spider mite eggs or even pollen. The idea is to flood the plants with these miniature “eating machines” so few, if any, thrips survive to reproduce.

How to implement:

The mites come in two formulations, sachet and loose. The sachets are essentially small paper bags that contain some predatory mites (approximately 300), bran, and bran mites. The predatory mites feed on the bran mites and breed. Once set out in the greenhouse a corner of the bag is removed and, as their numbers build, the predatory mites crawl out and spread over the crop. The sachets are set out at rate of 1 bag per 25 sq/ft. (approximate cost for a 2500 sq/ft house is $.03 per sq/ft per application). While they may continue to emerge for 12 weeks, most have emerged after about 6 weeks therefore it takes at least two “applications” to cover the bedding plant cycle. Alternatively you might go with a lower initial rate and set out additional, fresh, bags every two weeks. This method has worked reasonably well in our trials and only one spray application for thrips was needed all season (total cost of mites for a 2500 sq/ft house including shipping charges was $.05 per sq/ft. or $125. ).

A sachet used to release predatory mites. Photo by J. Sanderson

Bran particles visible on the leaf surface. Photo by B. Lamb

The second, loose, formulation has a high number of predators in a container with bran and enough bran mites to keep them alive during shipping. The bran and mites are sprinkled over the crop at a rate of 17-25 predators per sq/ft (40,000-60,000 for a 2500 sq/ft house (approximate cost $.01 per sq/ft per application). As the predators don’t reproduce to any great extent once released, weekly or bi-weekly repeat applications are recommended. Just as in a chemical control program, thrips levels should be monitored with yellow sticky cards.

Sprinkling mite/bran mix. Photo by G. Couch

Once the predators arrive they should be checked for viability, exposure to extreme cold or heat may have destroyed them during shipping. After gently shaking the container, place a small amount of the bran-mite mixture onto a piece of paper (dark colored paper works best). Examine the brownish-pink predators and white bran mites with a handlens for signs of movement. Don’t store the product, it’s advisable to get them into the houses within a day of arrival, two at most.

Pesticides & Mites:

While the predators may keep your thrips levels low enough that you never need to spray for them (the lead grower that participated in the study has only made two applications for thrips in the past six growing seasons!), you may have to spray for other pests, such as aphids or spider mites, or for disease control. Since the predators are living creatures, it’s important to know what, if any, effects pesticides will have on them. In general, fungicides have not shown any adverse effects on the mites so disease control is usually not an issue. However, insecticides and miticides vary greatly both in their initial and residual effects. For example, the commonly used insecticide, Orthene, will kill the predators and its effect lasts up to 10 weeks so its use should be avoided if you wish to use predatory mites. Other insecticides may be harsh initially but have little or no residual effect so can be used just before a release. A few have no immediate or residual impact. A database of pesticides and their effects on predatory mites can be found at Koppert Biological Systems Side Effects Database.


It should be noted that the predators are not well suited to stopping a raging infestation. If you already have high thrips numbers prior to introducing the mites you should first knock them down with a compatible insecticide such as Conserve. The mites also have a more difficult time controlling thrips if you aren’t taking other thrips suppressive steps such as controlling weeds under the benches. With the great variation among different greenhouses and plant mixes the formulation and rates appropriate to your operation may need to be adjusted. If you are considering using the predators next season but have additional questions or would like assistance in trialing the predators please contact any member of the Ornamentals IPM Team.

The Basics of Alternative Herbicides

Betsy Lamb, NYS IPM

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There are a variety of herbicide products, based on naturally occurring compounds that are of interest as alternatives to synthetic herbicides. These products include corn gluten meal, vinegar, and various plant oils as the active ingredients. There are several soaps used as herbicides, which, while not naturally occurring, are often considered alternatives, as well. Although these herbicides are considered least-toxic alternatives, they require proper handling and can be skin, eye, or lung irritants. As with all herbicides, applicators must follow the application requirements on the label, including use of personal protective equipment.

The Alternative Ingredients: Corn gluten meal is a by-product of the corn milling industry. Acetic acid is the primary ingredient in vinegar with herbicidal activity. However,  the acetic acid levels in household vinegar are not high enough to use it as an herbicide. Eugenol is an oil extracted from plants, especially from clove, nutmeg, cinnamon, and bay leaf. Pelargonic acid is found in oil of pelargonium, among other plant sources. Soaps used as herbicides are potassium salts of fatty acids.

Corn gluten meal contains compounds that inhibit seed germination, so in certain settings it has some potential as a pre-emergence herbicide. However, part of its activity in weed control, particularly for turf, is as a nitrogen source, encouraging rapid grass growth to outcompete weeds. It has no activity on established weeds and will interfere with seed germination of desirable plants as well as weeds, so should be applied after desired plants have true leaves and are 2-3 inches tall.

Acetic acid and eugenol interfere with the action of the cell membrane, allowing cell contents to leak out and causing the death of the cell. Pelargonic acid and soaps remove the waxy cuticle of plant tissue, which allows the cells beneath to dry out and die.In both cases, herbicide application results in a burning of the leaves, which can be seen almost immediately. There is no movement of the active ingredients throughout the plant, so good coverage of the foliage is essential for weed control. Also, mature perennials and other plants that can regenerate from the root system will not be killed because the herbicide is not translocated to the root system. They are non-selective herbicides so will damage the foliage of any plant contacted. These products are most useful for control of young, actively growing, annual weeds in a situation where desirable plants are either not yet present or can be protected from the herbicide.

There are many different products available with these chemistries and the concentration of the active ingredient can vary dramatically. Users should check both the amount of active ingredient in the concentrate and the appropriate dilution ratio for the situation, as described on the label. Users also should be aware that in some cases the inert ingredients may also have herbicidal properties and be providing some of the control. Some products are available both as concentrates and as ready to use formulations. Cost per application can be high for some products, especially if reapplication is necessary for complete control. It should be noted that not all of the products described are labeled for certified organic food crop production. Users should check the OMRI list or other lists of products accepted under the National Organic Production (NOP) regulations. There is no equivalent list of products labeled for organic production of ornamentals.

Canna Viruses

Brian Eshenaur,

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Their bold foliage and bright flowers help make cannas a popular plant giving the tropical look to Northeast gardens. Unfortunately in the last couple of years two virus diseases: Canna Yellow Mottle Virus and Canna Mosaic Virus have impacted the production and sales of this popular plant. Symptoms include stunting and yellow and brown leaf flecks and yellow streaks along veins.

Normally diseases show up in a spotty or clustered pattern in a greenhouse crop. Rarely are all plants infected. However when the stock material arrives infected this can be the case. This spring an alert greenhouse grower in NY noticed that all his cannas of one variety ‘Rosemond Cole’ seemed stunted and had some foliage discoloration. Working with his extension educator he had the plants tested and they were found to have both Canna Yellow Mottle Virus and Canna Mosaic Virus. He was not alone as these viruses diseases were widespread this year.

Spread of these viruses can occur by propagating from infected stock plants.  Aphids can transmit Canna Mosaic Virus (also known as Bean Yellow Mosaic Virus) to certain other plant species including gladiolus and lupine but insects have not been found to transmit Canna Yellow Mottle Virus, which only affects canna.

Plant virus diseases infections are systemic in the plant and the only treatment is to remove and destroy infected plants. It is very important to use only virus free rhizomes or plants for production. Ask your supplier if the plants you are considering purchasing have been tested to confirm they are virus-free.

Canna Virus Testing

This type of virus testing on cannas and hostas is a still a specialized area and researchers at the University of Minnesota are the experts. They allow for samples to be submitted from out of state.

The typical price at the University of Minnesota’s lab is $25.00 for the first sample and $7.00 for each additional. Make checks payable to the University of Minnesota.
Specify that you want them tested for canna virus. (Call ahead to confirm.)

They request that a lab form be completed and sent with the sample. It can be found at the University of Minnesota Plant Disease Clinic website under how to submit a sample.

Univ of Minnesota Plant Clinic
Plant Disease Clinic
495 Borlaug Hall
1991 Upper Buford Circle
University of Minnesota
St. Paul, MN 55108-6030
(612) 625-1275

Tour of Greenhouses in Canada –Register Now

Betsy Lamb

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Learn from Growers in Canada about Greenhouse Biological Control

There’s still time to sign up for the biocontrol tour – August 14-16!

If you or any growers are still wavering about whether to attend the tour, the deadline for signing up for lodging and for registering have both been extended until August 3rd.Registering for the hotel before the deadline saves you $44 Canadian per night!

The itinerary and farm details are below so you can see all the specifics. Don't forget the 5.25 pesticide recertification credits! And the price is right – only $50 plus your lodging!

Even growers who are not interested in biocontrol can learn something from other New York and Canadian growers and get a chance to see a diversity of other greenhouses.

All educators are warmly welcomed with or without a local grower!

Let me know if you have any questions.

Greenhouse Biological Control – Tour in Canada


Tuesday August 14, 2007

8:00amRegistration in Ithaca at Baker’s Acres,

1104 Auburn Rd.Groton, NY 13073

Coffee and pastries.


From Auburn: Take Rt. 34 south out of Auburn for approximately 22 miles to Bakers' Acres. We are located on the right hand side of the road. A marker to watch for is the intersection of Rt. 90. We are located approx. 5 miles south of that intersection.

From Ithaca: Take Route 13 to Triphammer Rd. exit for the malls. Turn left onto Triphammer Rd. Travel approx. 4 miles to the end of Triphammer Rd. At the stop light go straight past Crossroads restaurant. At stop sign turn right onto Rt. 34. Bakers' is approximately 5 miles north on Rt. 34. It will be on your left. (You'll pass The Rose Inn on the right about 1 l/2 miles before you come to us.)

8:30 am Leave Ithaca

12:00 pm Arrive in Buffalo at Shanghai Red’s Restaurant

Meet with additional participants from Buffalo area


From Route 90.

Take exit 53 to merge onto I-190 N/New York State Thruway toward Downtown Buffalo/Niagara Falls (5.5mi). Take exit 7 to merge onto Broadcast Plaza/Church St. Continue to follow Church St (0.2mi). Turn right at Lower Terrace St (0.2mi). Turn right at Erie St (0.3mi)

12:15 pm-1:00 Lunch at Shanghai Red’s

1:00-2:00 Visit Erie Basin Marina Field Trials

2:15 pm Leave Buffalo for Canada

3:30 pm Arrive at Vineland Station, Ontario

Sodas and snack.

Meet with Graeme Murphy, Greenhouse Floriculture IPM Specialist, Ontario Ministry of Agriculture and Biological Control Suppliers.

History of Biological Control in Canada

Technical support to growers from suppliers.

5:30 pm Leave Vineland Station

5:45 pm Arrive at the Casablanca Winery Inn

7:00 pm Social in hotel lounge. Cash bar

7:30 pm Dinner in the Lakeside Ballroom.

Wednesday August 15, 2007

7:00 am Breakfast in Bogey’s Grill House at the Inn.

7:45 am Leave Inn

8:30 am Jeffrey’s Greenhouse

Details: Bedding plant and potted plant (cyclamen, poinsettia) grower working increasingly with biocontrols over the past few years. Primary pests and biocontrol targets: thrips, aphids and whitefly on poinsettia.

9:45 am Boekestyn Greenhouses

Details: Potted plant grower (mums, kalanchoe, Easter lilies, poinsettia) and some spring crops (geranium). Over the past 2-3 years has developed innovative biocontrol programs for spider mites and thrips.

11:15 am GroMax Greenhouses

Cucumber grower using biocontrol

Lunch En route.

1:00 pm Waldan Gardens

Potted plant grower (cyclamen, kalanchoe, poinsettia, mums), spring baskets. Working with an IPM consultant to develop biocontrol programs. Have developed their own rearing system for aphid parasitoids.

2:30 pm Ravensbergen & Sons Greenhouses

Potted plants (mums, begonia, poinsettia, hibiscus) and spring plants (bedding, geraniums, baskets). Working with an IPM consultant to develop IPM and biocontrol programs for aphids, mites, thrips and whitefly (poinsettia)

4:00 pm Orchardcreek Greenhouses

Grower of cut gerbera. Has been working with biocontrol of whitefly (primary pest), mites, aphids, thrips for a number of years. Has worked with many different natural enemies to develop programs that work for him.

5:30 pm Return to Inn

6:30 pm Social hour sponsored by BioBest. There will a short presentation and discussion with a representative.

7:30 pm Dinner

Thursday August 16, 2007

7:00 am Breakfast in Bogey’s Grill House at the Inn.

8:30 am Leave hotel

10:00 am Mischler’s Greenhouse, Williamsville, NY

Eggplant trap crops and other methods of biocontrol in a greenhouse with a diversity of ornamental crops.

11:30 am Return to Shanghai Red’s to drop-off Buffalo participants.

Lunch on the bus.

4:00 pm Return to Ithaca

** Water and light snacks will be available on the bus.


Betsy Lamb
Office phone 607-254-8800 (use prior to the event)
Cell Phone 607-342-8983 (use during the event)

Karen Hall, NYSFI
Office phone 716-941-3502 (use prior to the event)
Cell phone 716-492-4562

Cornell IPM Team for Production Ornamentals
Betsy Lamb
State Coordinator for Ornamental Crops IPM
Ithaca, NY,
Gary Couch
Eastern New York Specialist
Brian Eshenaur
Western New York Specialist
Rochester NY
Disclaimer: Pesticide recommendations are for informational purposes only and manufacturers' recommendations change. Read the manufacturers' instructions carefully before use. Cornell Cooperative Extension and Cornell University assume no responsibility for the use of any pesticide or chemicals.
Some of the links provided are not maintained by Cornell Cooperative Extension and Cornell University. Cornell Cooperative Extension and Cornell University are not responsible for information on these websites. They are included for information purposes only and no endorsement by Cornell Cooperative Extension or Cornell University is implied.
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