Floriculture Greenhouse Update

This information was summarized from a recent article by Rob Wick and M. Bess Dicklow, Plant, Soil and Insect Sciences, UMass Extension published in Floral Notes, 23(1), July-August 2010

During 2008 and 2009, Downy mildew (Peronospora species) of basil occurred throughout the east coast in epidemic proportions both in the field and in greenhouses. Although the downy mildew pathogen has been detected in basil seed; seed transmission is probably a rare event. Air-borne dissemination from infected plants is more likely.

Symptoms on the top of the foliage occur as yellowing as if the plants are nitrogen or nutrient deficient. When spores are produced, a characteristic gray, fuzzy growth on the underside of the leaves is evident. Symptoms of downy mildew on basil can easily be mistaken for nutritional deficiency.

The most important environmental factors favoring disease development are high humidity and extended leaf wetness. Cultural controls are directed at reducing the amount of time leaves remain wet by reducing plant density and watering early in the day. In the greenhouse, horizontal air flow can be increased and condensation reduced by fans. Removing and destroying severely infected plants can slow disease development.Field trials conducted in southern New Jersey in 2009 determined that commonly-grown sweet basil (Ocimum basilicum) cultivars such as ‘Poppy Joe’ and ‘Nufar’ were the most susceptible to downy mildew. The least susceptible basils include the lemon and spice types such as O.x citriodorum and O. americanum  cultivars, “Lemon Std’, ‘Lemon’, ‘Lime’, ‘Spice’, ‘Blue Spice’ and ‘Blue Spice Fil’.

Few fungicides are labeled for herb plants. Copper products and phosphites are labeled for use on basil. It is the grower’s responsibility to read and follow label directions. The label is the law and any recommendations made here are superseded by the label.

At the University of Massachusetts, we are investigating methods to control this disease with biological control agents. We are interested in collecting live, infected plants.

If you think your basil plants are infected, please call or email Rob Wick, Dept. of Plant Soil and Insect Sciences; 413-545-1045, rwick@pltpath.umass.edu.

Photos: DM symptoms on top of Basil foliage, DM symptoms on underside of leaf

Robert Wick and Bess Dicklow, UMass Extension

Note: Downy mildew has also been observed recently on ornamentals in the Lamiaceae family, which includes basils (Ocimum spp), mints (Menta spp.), sages (Salvia spp) and other aromatics. According to Margaret McGrath, Cornell University, the coleus and basil downy mildew pathogens have now been demonstrated to be genetically different; therefore, these ornamental plants are not considered potential alternative host. However, there are many ornamental basils that are also hosts to pathogen affecting basil grown for use as an herb. Tina Smith, UMass Extension and Leanne Pundt, UConn Extension

Fact Sheet with photos and more details: Basil Downy Mildew (Cornell University)

Chrysanthemum white rust (Puccinia horiana) is a serious fungal disease of chrysanthemum. White rust can spread quickly in greenhouse and nursery environments causing severe crop losses.Chrysanthemum white rust (CWR) is a quarantine significant pest in the United States; therefore, occurrence of this disease leads to state and federal regulatory action. In the last few years chrysanthemum white rust is occurring with more frequency in New England.  The federal management plan for CWR includes the following measures destroying symptomatic plants, fungicide treatments on remaining asymptomatic plants, surveys of the surrounding area, and trace backs of infected stock. The full management plan can be viewed on the web on the USDA, APHIS website. The symptoms of chrysanthemum white rust are very distinct. Light green to yellow spots up to 5mm in diameter appear on the upper surface of the leaf. These spots become brown and necrotic with age. Raised beige to pink pustules form on the underside of leaves beneath the spots. Pustules become white with age. Pustules are most common on young leaves and flower bracts but may form on any green tissue or the petals. Symptoms usually occur during cool, wet weather.Infected plants may show no symptoms until environmental conditions encourage symptom development. If the warm, dry weather pattern this season in southern New England continues, symptoms may be delayed. Preventative fungicide applications, being used by some growers, will suppress disease development. For a list of treatment options see the floricast by Margery Daughtrey, Cornell University . Syngenta has a bulletin on chrysanthemum white rust that can also be downloaded.Note: Growers finding CWR are required to report the finding to their State regulator agency. There are on-going discussions concerning Chrysanthemum White Rust regulations. As a result, APHIS has established a Stakeholder Registry for those interested in receiving updated information related to these discussions. When registering, check Chrysanthemum White Rust  in Topics of Interest.

Paul Lopes, UMass ExtensionWith input from Margery Daughtrey, Cornell University

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

Update on Late Blight of Tomato and Potato for Retailers--

On 6/19 late blight was confirmed on tomato from a community garden on Long Island. The gardeners are taking out all their tomato and potato plants. On June 17 a plant pathologist confirmed late blight on tomato from a home garden in New Haven county, CT. The plants had been grown from seed by the gardener. Thus, late blight ha been confirmed in one location in New England. LB has been confirmed in NY, CT, PA, MD, KY, LA, FL and Manitoba to date this year on either tomatoes or potatoes.

Once late blight is detected, it is important to pull and destroy infected plants as soon possible. Any infected plants left in the ground have the potential to provide inoculum that can spread to other gardens and farms many miles away.

Protection with Fungicides. All potato and tomato crops should be protected with fungicides on a regu­lar basis.  Products containing chlorothalonil or copper can be suggested for home gardeners.

New Fact Sheets:

More information and photos can be found in the updated fact sheet by Dr. Sharon M. Douglas titled Late Blight of Tomato and Potato in Connecticut--2010.

And to help distinguish LB from other leaf spots on tomatoes see this new fact sheet: Recognizing Tomato Blights (University of Massachusetts)

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

Bacterial leaf spot on pepper transplants was identified at a retail garden center.

Bacterial leaf spot of pepper caused by Xanthomonas campestris pv. vesicatoria is the most common and destructive disease of peppers in the Northeast. Different strains or races of the bacterium are cultivar specific, causing disease symptoms in certain varieties only.

The bacterium is carried within seed, or in solanaceous weeds and crop debris. Tomatoes are also susceptible. Disease development is favored by high nighttime temperatures and high moisture and may be arrested during prolonged dry spells. Bacteria spread from plant to plant by splashing water, blown by high-pressure sprayers, or on workers hands and equipment.

Resistant varieties offer the best protection against this disease. Start with certified disease free seed or treat seed with hot water or dilute solutions of bleach. Grow transplants in a clean, disinfected greenhouse, rotate crops, control solanaceous weeds, rogue infected plants, and minimize leaf wetness periods by proper irrigation practices and plant spacing.

Streptomycin can be applied before transplant. Maintain adequate fertility, especially nitrogen in the field and apply copper bactericides at a 7-10 day schedule as soon as disease is detected. Sprays can be stopped with the arrival of cooler and drier weather. Bactericides are only marginally effective when environmental conditions are conducive for disease development; sanitation and environmental control are important disease management principles.

M.Bess Dicklow, UMass Extension Plant Diagnostic Clinic and Paul Lopes, UMass Extension

Be on the watch for Bacterial Canker Clavibacter michiganensis pv michiganensis and Late Blight caused by Phytophthora infestans. These two diseases can be very destructive to tomatoes in Massachusetts.

Initial symptoms of Bacterial Canker are the result of primary, systemic infection that first affect the lower leaves causing leaf curling, wilting, chlorosis, and shriveling. In advanced stages, the pathogen spreads throughout the plant and causes poor growth, wilt, and plant death. Foliage throughout the canopy wilts, yellows, turns brown, and collapses. Stems can split resulting in open breaks or cankers and stems break easily. Secondary infections occur from water splash onto foliage, stems, and fruit. Spots occur on green fruit and are very characteristic: white to yellow spots, 3-4 mm with raised brown centers (“bird’s eye spots”).

Late blight appears on potato or tomato leaves as pale green, water-soaked spots, often beginning at leaf tips or edges. The circular or irregular leaf lesions are often surrounded by a pale yellowish-green border that merges with healthy tissue. Lesions enlarge rapidly and turn dark brown to purplish-black. During periods of high humidity and leaf wetness, a cottony, white mold growth is usually visible on lower leaf surfaces at the edges of lesions. In dry weather, infected leaf tissues quickly dry up and the white mold growth disappears. Infected areas on stems appear brown to black and entire vines may be killed in a short time when moist weather persists.

 Note: The symptoms for Bacterial Canker and Late Blight most often do not appear early in the growing season, but can be introduced and symptoms noticed on plants grown and shipped to New England from the south.

Photo: Cut stem of a potted tomato plant with Bacterial canker

Late Blight information and photos (scroll down for photos)

Paul Lopes, University of Massachusetts

Mum cuttings are arriving at some growers. Begin the season by reviewing your fertilizer program and teaching new employees to recognize Chrysanthemum white rust symptoms.

Mums are heavy feeders during the first few weeks. Growers use a variety of ways to fertilize mums. Some growers use 100% water soluble fertilizer through a drip system, some use 100% controlled-release fertilizer and some use a combination of water soluble and controlled-release. Regardless of the program you use, start plants off right and prevent premature buds by:

Using moistened soil when potting up plants, then water-in freshly planted cuttings with a fertilizer solution. Many growers are successfully using 200 to 300 ppm of 20-20-20 immediately after planting. The cuttings establish faster and grow more rapidly.

Do not stress the young plants during their first 4 to 5 weeks of growth, and especially during the first 10 days of the crop or plants will develop buds prematurely and plants will be short. Keep plants moist, well fertilized and properly spaced.

Also check plant roots regularly to monitor plant health.

To encourage soft growth that branches freely, many growers use 250-300 ppm 20-20-20 or a fertilizer that is at least 60% ammonical nitrogen as a constant feed during the first 2-3 weeks for all fertilizer programs. Then, growers using 100% water soluble fertilizer throughout the season, switch to 200-250 ppm 20-10-20 constant feed for 3-4 applications and then rotate to a calcium nitrate based fertilizer such as 15-0-15 for 1 application, then repeat. The 20-10-20 contains less ammonical nitrogen. Once plants start to show color, fertilizer is reduced to 100 ppm constant feed.

If using controlled-release fertilizer, keep in mind that the rate of release is affected by its formulation (rate of release), soil temperature and frequency of irrigation. Most formulations release at temperatures of 70°F or above, therefore during cool temperatures, fertilizer is going to be slow to release. We often have cool temperatures in June when plants need the most fertilizer. This is the reason liquid feed becomes important, to get plants growing and create vegetative growth.

Garden mums initiate flower buds easily and develop rapidly if plants are stressed in any way. If terminal flower buds are observed when cuttings arrive, plants should still perform satisfactorily. When cuttings with terminal flower buds are planted, they should be pinched hard (allow 4-5 leaves to remain) when they are turgid (4-5 days after planting). This will force out lower breaks which tend to be more vegetative. If both terminal and lateral buds have developed when cuttings arrive, it is best not to plant them, as they most likely will not perform satisfactorily.

Tina Smith, University of Massachusetts

For more information see:

Fact Sheet: Garden Mums for Fall Sales. University of MassachusettsFact Sheet 2008: Chrysanthemum White Rust. University of Massachusetts.Grolink: Belgian Mum Cultural Information Fact Sheet. Garden Mums from Cell Paks. Griffin Greenhouse Supply Company.

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

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

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

Late Blight caused by Phytophthora infestans – a very destructive and very infectious disease killed tomato and potato plants in gardens and on commercial farms throughout the eastern U.S. during 2009. Late blight occurs at some locations in the Northeast each year, however in 2009 infected plants were distributed through large local retail stores throughout the region (Ohio to Maine) during June, and outbreaks were reported over this entire region by early July. Never before had such an extensive distribution of infected plants occurred, especially so early in the season. This, combined with the cool, wet growing season and the exceptionally contagious nature of the disease during cool, rainy, windy weather all contributed to a disastrous year for farmers. Garden retailers can help prevent the spread of late blight in gardens and on farms this growing season and provide customers with the facts about this disease. Grow your own transplants from seed or purchase locally grown plants Late blight is not seedborne in tomatoes (however, it is tuber-borne in potato), so tomato plants started from seed locally would be free of the disease. Growing your own transplants from seed or purchasing from a reputable local grower will ensure a healthy start to the season for your customers and local farms. Provide disease-resistant or tolerant varieties       Tomatoes: Disease-resistant or tolerant varieties of tomatoes exist, however seed is in limited supply this year. ‘Mountain Magic’, ‘Plum Regal’, and ‘Legend’ are three varieties with resistance or tolerance to late blight. Note that the variety ‘Legend’ is the only late-blight resistant variety for which seed is readily available this year. In addition to late blight, each year tomatoes become infected with early blight and Septoria leaf spot, which look very similar. If possible, also provide tomato plant varieties that are resistant or tolerant to early blight for your customers, such as the varieties ‘Mountain Fresh’, ‘Mountain Supreme’, and ‘Plum Dandy’ and others.       Potatoes: Purchase certified, disease-free seed potato from a reputable source, and ask your supplier about their source of seed and if it was inspected in the field for late blight. Seed potato from the northeast are less likely to carry the disease. Inspect transplants for signs of disease If you purchase plants to sell, inspect all transplants for stem, petiole cankers or leaf blight as long as plants are on the shelf. Teach your staff what to look for, using the web-links below. If you suspect a late blight infection, use your Plant Diagnostic Lab to confirm if late blight is present. Know the FACTS for Staff and Customers Train employees and provide information to your home gardening customers. * Potatoes that freeze or fully decompose will not carry the pathogen over winter. * Tomatoes will not carry late blight over the winter, because freezing kills the whole plant. *  Tomato seed, even from fruit that was infected with late blight, will not carry the pathogen, so no need to worry about the tomatoes left behind in the garden or compost pile. Certain perennial weeds can become infected with late blight, but none of their above-ground tissues live through the winter. *  Late blight will not survive on tomato stakes and cages. * The biggest threat for overwintered disease in New England is on potatoes. In the spring, advise home gardeners to inspect last year’s potato plot and any compost or cull piles for volunteer potato plants that might come up. If they find potato plants, pull them out and put them in the trash or destroy them. If tubers were infected and survive, then the late blight could grow upward from the tuber, infecting the stem and producing spores when weather conditions are favorable. These spores could then disperse to other tomato and potato plants. * During the growing season, pay attention to pest alerts to learn about whether late blight has been observed in New England, and what actions you need to advise to customers. Pest alerts will be updated on the UMass Extension Vegetable Program Website, www.umassvegetable.org   

Photos: Symptoms on stems, leaves and fruit (Cornell) Photos, FAQ, Fact Sheets (Cornell)

Tina Smith, University of Massachusetts