Deer can be picky. A Maryland cut flower grower has learned deer can be as picky as humans when it comes to which plants they prefer. With hydrangeas, ‘Endless Summer’ and ‘Limelight’ are the varieties of choice rather than ‘PeeGee’. Deer at the same location also fed on Hydrangea arborescens, Eryngium ‘Blue Glitter’ and Ilex verticillata ‘Winter Red.’ Other deer delectables include ornamental cabbage and kale and lilies. When it comes to pansies, yellow- and white-flowered plants are eaten before other colors.

For more: University of Maryland Cooperative Extension, (301) 596-9413; www.agnr.umd.edu/ipmnet.

Minimize growth regulator overdose. During the cold, cloudy weather of winter, there is a chance that growers could encounter a plant growth regulator overdose. University of Connecticut extension specialist Rich McAvoy said if an overdose spray of Cycocel or B-Nine (or a generic equivalent) is applied and the mistake is discovered before the spray dries (usually within 30 minutes of application), the material can be washed off with water and the damage avoided.

Diluting the chemical is not an option with products like Bonzi, Sumagic, Topflor or A-Rest. If the overdose is modestly high (25-50 percent too high a rate), environmental conditions that minimize stress may be enough to allow the plant to recover without further action. Adequate light levels, increased temperatures, increased fertilization and reduced water stress favor rapid growth, enabling plants to outgrow the adverse overdose effects. In situations where the dose is too high to correct in this way, a gibberellic acid treatment can be used to reverse the effect of the growth regulator.

For more: Rich McAvoy, University of Connecticut, Department of Plant Science; (860) 486-0627; www.negreenhouseupdate.info.

Screening detects Xanthomonas on geraniums. Bacterial blight caused by Xanthomonas campetris pv. pelargonii is one of the most destructive diseases of geraniums. Zonal geraniums are particularly susceptible to infection by this bacterium.

Researchers at University of Toledo devised a screening technique using polymerase chain reaction (PCR) to rapidly detect the presence of the pathogen before onset of symptoms. The resolution of this test is high and as few as 10 cells of the bacterium indicate a confirmation.

The researchers used PCR to screen 17 geranium species/cultivars for the presence of Xanthomonas and found that PCR could detect the bacterium as early as before the symptoms became visible. Efforts will now be made to design a workable, sampling protocol to screen incoming plugs. The specific objective, said University of Toledo professor emeritus Stephen Goldman, is to collect samples in an accountable manner, enabling a definitive diagnosis for infection at selected, expert testing laboratories.

For more: Stephen Goldman, University of Toledo, Department of Environmental Sciences, (419) 277-0290; www.eeescience.utoledo.edu.

Bandedwinged whitefly migrating into Maryland greenhouses. Some growers were seeing bandedwinged whitefly (Trialeurodes abutiloneus) migrating earlier into greenhouses from surrounding agricultural field crops, University of Maryland Cooperative Extension reported. The whitefly entered earlier than usual this year from weeds and field crops, including soybeans, killed by drought conditions. This usually occurs in late-September to mid-October after crops and weeds dry down.

Bandedwinged whitefly feeds on ornamental crops like cabbage, kale, asters and poinsettia. In previous years, this whitefly has also been found on petunia, geranium and hibiscus during the spring.

University of Florida entomologist Lance Osborne said bandedwinged whitefly were present in very high numbers on cole and cotton crops in Florida and Georgia during September, but that the silverleaf whitefly (Bemisia tabaci) was the main one being found there.

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For more: University of Maryland Cooperative Extension, Central Maryland Research and Education Center, (301) 596-9413; www.agnr.umd.edu/ipmnet.

Containerized perennials held over winter need protection from cold temperatures. Unlike field-grown plants, roots of container-grown plants are not buffered from cold temperatures by the soil, and the only insulation is a thin wall of plastic. Besides root hardiness, factors such as soil moisture, temperature fluctuations and root development in the container also affect plant survival.

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Perennials are susceptible to root injury over a wide range of growing medium temperatures. Generally, protection is needed in areas where the average temperature is 20°F or lower.

Different techniques can be used for overwintering, depending on the expected minimum temperatures, the length of time temperatures are expected to remain low, temperature fluctuation, container size and plants’ root hardiness. Some experimentation may be necessary to determine which method of overwintering works best.

Preparing plants for winter

Potting up. Successful overwintering begins when plants are potted up by late September or early October to allow them to become established for several weeks before cold weather arrives in late November. The more established the root system, the better the chance the plants will survive winter. The smaller the container, the more protection will be needed. Poorly established and pot-bound plants tend to overwinter poorly.

Trimming. Many perennials have top growth that dies back with the onset of cold weather, while others retain their foliage throughout winter. Plants that die back should be trimmed back to the crown and cleaned up before covering. Evergreen perennials such as Phlox subulata should be protected from direct contact with overwintering coverings either by laying pots on their side or by placing a structure over them.

Watering. Before covering, water the growing medium well to prevent desiccation, but allow the foliage to dry. Check soil moisture periodically throughout winter and avoid overwatering, which promotes root, crown and foliar diseases. In an unheated poly-covered house, water may be needed as often as once every two weeks. Ground beds covered with thermoblankets hold moisture and probably don’t need watering.

Pest control. Some growers treat plants with a broad-spectrum fungicide before covering. Overwintered perennials also need some type of rodent control. Greenhouses can be made rodent tight by burying fine mesh screen wire such as hardware cloth around the perimeter under ground and bending it outward at a 90-degree angle, leaving it at least 6 inches deep. Mowing and cleaning up natural vegetation eliminates protected areas for rodents.

Two basic methods for overwintering are maintaining plants below freezing or above freezing.

Maintaining plants below freezing

Thermoblankets. One of the simplest techniques to keep plants at a constant temperature below freezing is by placing a sheet of insulating material over containerized plants during the coldest months outdoors. Thermoblanket systems are relatively inexpensive.

In the production yard, perennials are placed pot-to-pot in an upright position on the ground; tall plants are leaned over, just like laying shingles; and plants with foliage are laid on their side. Cover plants with a thermoblanket such as 1/4-inch flexible polypropylene foam or polyethylene foam laminated to white UV-treated polyethylene film. Pull the blanket tight over the containers and secure the edges about 12 inches beyond the pots with concrete blocks. Follow the manufacturer’s recommendations.

In areas where air temperatures are likely to drop to minus 10°F, or where the site is exposed to high winds, consider using a double-foam layer, placing plants inside an unheated greenhouse under foam or putting plants in a minimally heated greenhouse.

Thermoblankets tend to trap and retain moisture, which may eliminate the need for irrigation. Problems under the blankets are difficult to detect because the blankets are opaque.

Pots tend to warm prematurely during winter thaws or near the end of storage. This can cause shoot growth that can be injured by the return of freezing temperatures. Venting may be needed during unexpected periods of warm weather.

Thermoblankets are usually so tight that ventilation is practically nonexistent. Check periodically for disease development.

Sandwich method. Place plastic sheeting or spun-bonded fabric directly over plants and then cover with a 6- to -12-inch-deep layer of fluffed straw. Cover the straw layer with another layer of white plastic sheeting. This insulating technique is especially effective in Northern regions where temperatures remain consistently low all winter. Plants are so well-insulated that they are slow to warm in spring and remain frozen until the cover is removed.

Unheated poly-covered houses with foam blankets. Containers are stored in narrow hoop houses covered with white polyethylene film. White poly reduces fluctuating temperatures and maintains lower temperatures than clear poly film. However, the lack of light in spring can cause plants to stretch. If clear poly film is used, ventilation is needed.

Once temperatures consistently drop to 25°F-30°F, pots inside unheated structures can be covered with a thermoblanket to further protect plants from extreme cold. This technique creates a microclimate 8°F to 10°F warmer than the air above the blanket inside the structure. Place the thermoblanket over the plants only during extremely low temperatures to avoid excessive moisture buildup.

Maintaining plants above freezing

Heated greenhouse or poly-covered house with roll-up sides. This is the best method for temperature control, especially if minimal heat is used. It also provides more control over moisture levels, plant growth and heat buildup. Greenhouses or poly houses covered with two layers of clear poly film are heated in the fall to 50°F until all of the plants are well-rooted, then the temperature is slowly lowered to 35°F where that temperature is maintained throughout winter. Clear poly is used in this case to allow the maximum amount of sunlight exposure to the crop. Foliage stays drier. In spring, plants break dormancy earlier allowing for early shipping.

Roll-up sides maintain the same temperature inside as outside, whether during a winter thaw or in the spring when warm sunny days cause a rapid rise in the greenhouse temperature and push the plants along too quickly. Rolling up the sides is also useful for hardening off plants in spring and dropping them for protection if unexpected cold weather or snow arrives.

Other methods

Other techniques have been used to protect containerized herbaceous perennials during winter, including retractable-roof greenhouses, covered cold frames, earthen pits, sunken frames, root cellars, barns and sheds, covering with evergreen boughs or fleece (thick felt) and deep snow.

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- Tina Smith

Roses in the United States have been plagued by downy mildew since the 1800s. Downy mildew is especially destructive to both greenhouse-grown and outdoor-grown potted roses. This disease may occur sporadically in some areas of the country, but is a predictable pest in other regions.

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The downy mildew pathogen that infects rose is specialized and does not cause disease on other ornamentals. There are many different pathogens that are responsible for downy mildew diseases, and most are restricted to only one or a few plant types. If you’ve been struggling with downy mildew on coleus, snapdragon or impatiens, for example, the rose downy mildew pathogen is not the culprit.

Downy mildew symptoms

On roses, downy mildew occurs on all aboveground plant parts, blighting leaves and canes. Sometimes the first symptoms of downy mildew are confused with a nutrient deficiency or spray injury. On leaves, spots may be purplish or brown and appear square since they may be limited by the larger veins. The downy mildew that infects roses doesn’t always produce a fuzzy mat on the underside of the leaves that is noticeable without magnification.

Infected leaves turn yellow and drop from the plant. A downy mildew infection may leave the plant nearly devoid of foliage. Once diseased leaves start dropping, the downy mildew is advanced and stopping it becomes very difficult.

When the canes become infected, purple spots occur and expand into a blight that affects large sections of the canes.

Disease-favorable weather

Downy mildew is very responsive to weather cues. When the weather favors downy mildew, symptoms on rose can explode almost overnight. Wet weather, high relative humidity and overcast conditions are triggers for downy mildew disease. Fog provides near-perfect conditions for an outbreak.

During wet weather, a fine weft of fungal threads can coat the underside of the rose leaves. This is where the downy mildew pathogen reproduces via a spore type called sporangia.

The lemon-shaped sporangia are produced on spore stalks. The sporangia develop and ripen during the night as long as there is darkness and at least six hours of continuous moisture. When the environment begins to dry in the early to mid-morning hours, the air currents pluck the sporangia from their spore stalks and carry them to nearby healthy rose foliage.

Downy mildew is most favored at about 64.4°F. Temperatures that are too high (80.2°F and above) or too low (39.9°F and below) stop the disease. If the weather becomes hot and dry, the downy mildew pathogen will be halted, at least for awhile. It is possible, however, for the downy mildew pathogen to lay quiet in infected rose tissue and wait for cooler weather.

Since the downy mildew pathogen can lay quiet in rose tissue without noticeable blighting, it is possible to receive rose plants that appear healthy only to have downy mildew symptoms develop later. It is also possible for the downy mildew pathogen to persist in a production facility, causing disease from one season to the next.

Fungal threads of downy mildew can survive in diseased rose canes. It is also possible that a specialized spore (oospore) can remain dormant in infected rose debris and soil, surviving harsh weather conditions and allowing the downy mildew pathogen to survive between rose crops.

Testing chemical controls

Newer fungicides are available to prevent and limit downy mildew on roses. When fungicide studies were conducted on site with a commercial nursery in the southeastern United States , several products were effective. Double Knock Out roses appeared to have mild downy mildew symptoms when they were received by the nursery.

Fungicide sprays in two studies were applied on a weekly schedule. An exception to this was Subdue MAXX EC that was applied as a drench every 30 days. The weather during the trials allowed downy mildew to progress but the disease never exploded as it can when conditions are especially wet and humid.

Rose plants were rated for downy mildew by counting the total number of infected leaves per plant. Plants that were not treated had nearly 20 leaves per plant infected with downy mildew.

In the first study, all fungicides that were tested limited the number of infected leaves compared with plants that were not treated. Products that limited downy mildew infection to five or fewer leaves included: Daconil WeatherStik (1 pint/100 gallons), Heritage WDG (4 ounces/100 gallons), Stature DM (12.8 ounces/100 gallons) and Junction DF (3.5 pounds/100 gallons). Some phytotoxicity was seen with applications of Daconil WeatherStik (1 pint/100 gallons).

In the second study, all fungicides were applied as sprays. Mandipropamid, a new product that is not yet registered, has targeted activity against downy mildews and other related pathogens. Mandipropamid was compared alone and in combination with other fungicides for activity against downy mildew on rose.

Plants that were not treated with any fungicide had approximately 25 infected leaves per plant. Products that limited disease to eight or fewer leaves included Mandipropamid (8.2 fluid ounces) alone or mixed with Heritage WG (1 ounce) or Subdue MAXX (1 fluid ounce). Subdue MAXX EC (2 fluid ounces) applied alone as a spray was also effective. Subdue MAXX EC is currently labeled only as a drench.

Downy mildew control tactics

* Use a combination of techniques to prevent and control downy mildew. Keep the environment dry, practice good sanitation and use effective fungicides. Early detection helps in the timing of fungicide applications.

* Look for dark, purplish spotting on leaves and canes as early symptoms of downy mildew.

* Keep air moving around plants whenever possible so that relative humidity is kept low. In outdoor production facilities, arrange plants in rows that take advantage of the prevailing winds to dry the foliage.

* Choose effective fungicides and reapply frequently, especially when the weather favors the disease. In some instances, a five- to seven-day spray fungicide spray schedule may be needed.

* Alternate fungicides so that label restrictions regarding the application interval are not violated. Help delay resistance to fungicides by alternating products with each application.

* Fungicides must be sprayed so that roses are thoroughly covered with the spray. Even though some products offer systemic movement in the plant, the entire plant must be covered with the fungicide spray for the needed protection.

* All plants with downy mildew should be disposed of or destroyed at a location far from the production facility. Cull piles must be avoided because these would be a likely place for the downy mildew pathogen to survive and cause problems for new crops.

The author thanks Michigan State University Department of Plant Pathology research assistant Blair Harlan and plant pathologist Amanda Gevens for technical assistance. This research was funded in part by the USDA-Agricultural Research Service through a cooperative agreement as part of the Floriculture and Nursery Research Initiative and by American Floral Endowment.

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- Mary Hausbeck

Blooming Nursery in Cornelius, Ore., is a wholesale operation that grows herbaceous perennials, groundcovers, herbs, ornamental grasses, vines and shrubs. The grower offers finished containers -- marketed under the Blooming Advantage name -- and plugs, liners and bare-root plant material.

Several of Blooming Nursery’s greenhouses are equipped with highly efficient ebb-and-flood watering systems. Eliminating or reducing overhead watering cuts down on disease and helps to conserve valuable natural resources.

Steve Taylor is Blooming Nursery’s sales and marketing manager. Taylor provided GMPRO with some of his top picks in plant material.

Aquilegia vulgaris ‘Leprechaun Gold’ has striking golden and green marbled foliage with granny-bonnet, violet-purple flowers. It grows 24 inches tall and 18 inches wide. It’s hardy to USDA Hardiness Zone 4.

Ocimum ‘Pesto Perpetuo’ is a columnar basil that grows 4 feet tall, but is only 12-15 inches wide. Its light-green foliage has striking creamy-white edges. “Since it does not flower, this is a great culinary basil, keeping its sweet flavor year-round. It never turns bitter,” Taylor said. “But most people use it as an annual ornamental foliage plant.” Although it will not overwinter outdoors in most places, it thrives in hot, humid conditions better than many perennials. As with any basil, there are almost no insect or disease problems.

Dicentra spectabilis ‘Gold Heart’ features a rosy-pink flower in spring set off by glowing, chartreuse foliage. “Even when it’s out of bloom, it stands out because of the outstanding foliage,” Taylor said. It grows 3 feet tall and wide, and it’s hardy to Zone 3. It’s not for resale in Canada, he said.

Blooming Nursery

Founded: 1982 by George Dinsdale.

Location: Cornelius, Ore.

Crops: More than 2,000 varieties of perennials, herbs, ornamental grasses and flowering shrubs.

Production space: 150,000 square feet of heated greenhouses; 150,000 square feet of shade structures and cold frames and 5 acres of outdoor production.

Market: Liners, plugs and bare-root material are shipped nationwide, and finished material is shipped in the Pacific Northwest.

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For more: Blooming Nursery, (503) 357-2904; www.bloomingnursery.com.

- Kelli Rodda