Greenhouse IPM Notes. Northeast. Current Situation. March 2006 A publication of Rutgers and Cornell Cooperative Extension Vol.

Transcription

1 Northeast Greenhouse IPM Notes March 2006 A publication of Rutgers and Cornell Cooperative Extension Vol. 16, No 2 Current Situation Jim Willmott, Rutgers Cooperative Research & Extension. Early season pest management is critical this year since overlapping Easter and spring crops will limit space until mid-april. Crowding crops complicates pest management because plants are often more prone to damage and pesticide spray coverage is reduced. Keep air moving with horizontal airflow and avoid overwatering crops during cloudy, damp and cool conditions. Be sure watering crews irrigate according to crop needs, not by a schedule. Overwatering promotes algae, infectious diseases and edema. March weather conditions are variable and unpredictable and they greatly influence pest activity - consider diseases. The best conditions for plants are relatively dry, bright and not too cold or hot. Maintaining a favorable environment is challenging especially if your growing facilities are technologically challenged: State of the art, well-maintained, environmental control systems really help when spring conditions fluctuate wildly. Remember that cloudy, moist outdoor conditions influence the indoor greenhouse environment and plant physiology. This alters host susceptibility to pathogens both above and below ground. Some pathogens, such as Botrytis, Thielaviopsis and certain species of Pythium, are more prolific and damaging during cool, wet conditions. An especially aggressive Pythium blight was recently found attacking roots, crowns and foliage on bacopa in plug flats. Pythium Blight on bacopa. Photo Jim Willmott Bacterial spot has been showing up on verbena. Spots are initially red-purple and about the size of a pinhead. These enlarge into irregular shaped spots with redpurple margins and brown centers. Occasionally entire leaves die. Applications of Phyton 27 at 10-day intervals will help manage this disease when used in concert with good sanitation practices. Discard or isolate diseased plants from healthy plants, and provide conditions that will reduce relative humidity and prolonged periods of leaf wetness. Maximize air movement and avoid overhead irrigation. Myrothecium leaf spot has been common on New Guinea impatiens this season. Damage is usually minor, but symptoms look a lot like INSV. Symptoms appear as roughly circular spots, with red margins, brown centers in concentric patterns. Under moist conditions, white fungal resting structures appear on undersides of leafs within mature leaf spot. Other hosts include begonia, gardenia, pansy and snapdragon. Myrothecium

2 is considered to be a weak pathogen that will attack stressed or injured plant tissue, though once established the disease can be difficult to manage, particularly in warm and moist environments. Prevent disease by practicing good sanitation and avoiding plant injury and stress. Minimizing periods of leaf wetness and avoiding overhead irrigation and will help reduce the incidence of infection and spread of the disease. If necessary apply appropriate fungicides such as Daconil, Medallion, Cleary s 3376, OHP 6672, Terraguard, or Compass O. Symtoms of Myrothecium on New Guinea impatiens resemble INSV a much more serious problem. Photo Jim Willmott 2 Thielaviopsis (black) root rot on pansy, verbena, vinca and petunia has been common in recent years. Inspect incoming stock for uneven yellowing and stunting. Several fungicides are labeled for drench applications. Those with thiophanate methyl (such as Banrot, Cleary s 3336, Fungo Flo, OHP 6672) have been consistently effective. For crops that don t mind, keep ph on the low side about 5.5 to 5.8: Lower ph hinders Thielaviopsis. Thoroughly disinfest benches, floors and all areas where Thielaviopsis-infected crops grew last year and avoid placing susceptible crops in these areas. When Thielaviopsis is present it is also important to control fungus gnats, as they can move the fungus throughout the greenhouse. Fusarium crown rot and leaf spot were found on dracaena (spikes). The leaf spots were irregularly shaped and yellow with tan centers. Plants with crown rot showed wilting that progressed into plant death. Keep plant crowns and foliage dry and if necessary apply a fungicide such as Heritage, Medallion, Spectro, a macozeb material, or an iprodione material such as Chipco 26 GT, Chipco 26019, or Sextant. Powdery mildew affects a wide range of plants and is common on verbena, petunias, pansies, gerbera daisies, non-stop begonias, hydrangeas, kalanchoes, and roses. Last year we found a troubling powdery mildew on dahliettas. Numerous fungicides are labeled, including from bicarbonate materials, strobilurins, and DMIs such as Strike, Terraguard, and Eagle (not registered for use on Long Island). Always follow label instructions and rotation recommendations. Increase air movement to help reduce the likelihood of infection, remove any potential weed hosts, or apply a labeled fungicide for management. Thrips have been heavy in some locations this spring. Good indicator plants include gerbera daisy, brachycome and phlox hybrids. Populations can also be monitored with the use of sticky cards; blue cards should be used when you are primarily monitoring thrips, and yellow should be used when you are monitoring other common greenhouse insects in addition to thrips. It is best to act swiftly when thrips are observed to be increasing in numbers. Once flowers open, management will be much more difficult to achieve. Remove older plants that are harboring the insects, and, if practical, remove flowers promptly on infested plants. Look for early symptoms of thrips feeding before they become much more obvious. Photo Jim Willmott 2

3 Various pesticides are available for thrips control, but should be used along with cultural management practices. Conserve has been an effective material for thrips management, however there have been reports of possible resistance and this material should be used only when necessary and with caution. Mesurol is another option, and some suppression can be achieved with Avid and Orthene (though Orthene is only labeled for a limited number of crops). Additionally, some growers have reported decent results when using BotaniGuard. Fungus gnat populations have also been building. Suspect plant damage from larvae where adult numbers are high. We found heavy damage to liriope. Yellow sticky cards should be installed and checked at least weekly in order to monitor populations. Information on monitoring and managing fungus gnats was discussed in the January/February issue of IPM Notes (Dan Gilrein, Winter Pest Roundup: Fungus Gnats). Are Your Blooms Blemished by Botrytis? Margery Daughtrey, Cornell University, Long Island Horticultural Research and Extension Center Botrytis blight or gray mold can lead to many unhealthy manifestations on plants: petal rot, leaf spot or stem rot. For the most part, these diseases are caused by one fungus, Botrytis cinerea, which has a very wide host range (see Table 1). This is the fungus that can be the downfall of greenhouse flower crops such as geraniums, lisianthus, bacopas, cyclamens, osteospermums, poinsettias, primulas, and snapdragons. Florists are all too familiar with Botrytis as the post-harvest destroyer of cutflowers such as gerberas and roses. Botrytis cinerea can occur on virtually any dicot and many monocots. The name gray mold comes from masses of fungal sporulation that are produced on dead plant tissue. The fungus may produce spores upon plant tissue that it has killed itself, or upon tissue injured by drought, chilling, sprays, or fertilizer. One reason that Botytis survives so well in the greenhouse is that it can act either as a plant parasite or as a saprophyte (feeding on organic matter). Visible gray mold is a clear danger signal in the greenhouse, as it is direct evidence of inoculum available to start new infections. Table 1. Some flower crop hosts of Botrytis cinerea anemone bacopa chrysanthemum cyclamen dahlia exacum fuchsia geranium gerbera lily lisianthus marigold peony petunia poinsettia rose snapdragon tulip vinca zinnia In addition to B. cinerea, there are also a few other Botrytis species that are relatively specialized. With a few rare exceptions, these other Botrytis species affect members of the buttercup family (Ranunculaceae), or monocots in the Iridaceae, Amaryllidaceae and Liliaceae. Being susceptible to another species of Botrytis does not mean that a plant is not susceptible to the generalist pathogen B. cinerea, so this means that some plants face two possible Botrytis enemies rather than just one. The common greenhouse crops that have a double-barreled Botrytis threat are tulips and lilies. On tulips, Botrytis tulipae causes diseases known as tulip blight or fire. Oval leaf spots sometimes cause the leaves to become malformed and cankers can form on the stems. Small yellow to brown spots with watersoaked edges develop on both leaves and flowers. The name tulip fire is used for the disease in cases in which the lesions enlarge dramatically and develop light-colored centers. Brown spots sometimes form on the outer bulb scale beneath the tunic. Small sclerotia may form on bulbs where the tunic cracks, or on the surface of spots on the outer scale. The sclerotia formed by B. cinerea are larger and more irregularlyshaped. The fungus Botrytis elliptica occurs on lilies and Easter lilies, in addition to autumn-crocus, dogstooth violet, gladiolus, and tuberose. On Easter lily the oval spots are orange to reddish brown, with either a purple margin or a water-soaked zone. On Asiatic hybrid lilies, the spotting can lead to severe scorching of the lower foliage of garden plants, especially in rainy seasons. Diagnosis. Because of its tendency to produce very characteristic gray-brown sporulation on infected plant parts, Botrytis blight is usually not very hard to diagnose. The leaf spots caused by Botrytis begin as 3

4 small, circular areas, but they tend to enlarge in every period of high humidity, creating a zonate leaf lesion that is oval or irregular in outline. Spots are dark brown when fresh, but become paler after they dry. Stem symptoms usually begin at a cutting wound or leaf scar, or may develop at a node where a blighted leaf was attached. Stem symptoms also may be dark initially, but become lighter in color with time. The sporulation of Botrytis is very distinctive, and its presence on a leaf or stem lesion is a fairly reliable clincher for diagnostic purposes. If plant parts appear to be diseased with Botrytis, place them into a sealed plastic bag with a moist paper towel for hours, and watch for development of the tell-tale sporulation. Dealing with Botrytis Margery Daughtrey, Cornell University Long Island Horticultural Research and Extension Center and Nora Catlin Cornell Cooperative Extension of Suffolk County Inoculum management. Minimizing infection incidence is partly achieved by minimizing the number of spores that are present. Remove plants or plant parts that have been killed for any reason, as these provide a substrate upon which the fungus can build up threatening inoculum. Although B. cinerea is probably found within every greenhouse, it is poor management to allow significant reservoirs of sporulation to persist within the structure. This will help to control Botrytis disease during production and on foliage and flower parts postharvest as well. Plant debris should be kept under cover in the greenhouse, and avoid injuring or stressing plants. Avoid overcrowding plants, since lower leaves that are starved for light and in a high humidity environment can die and become massive Botrytis inoculum breeding grounds. Excessive fertilization, dry-down events, or spray injury can also generate dry brown leaf edges that give Botrytis a foothold. Environmental management. Having good command over environmental conditions in the greenhouse is key to managing Botrytis. Botrytis blight is a gray weather disease, and is hardest to control outside the heating season when there are no infusions of heated air to mop up excess moisture that has been generated by transpiration and by the evaporation of water used for irrigation. Generally, greenhouse relative humidity (RH) lower than 85% is not favorable for Botrytis blight development. It is unlikely that anything can be done to entirely eliminate Botrytis from the greenhouse environment, so steps taken to avoid the high relative humidity that triggers disease outbreaks are very critical. The most dangerous environmental conditions from the perspective of Botrytis management are those that generate condensation on plant surfaces, as these provide the free moisture needed for germination of the Botrytis spores. Practices that can help reduce humidity are: irrigate only when necessary and do not irrigate late in the day, make sure your floors are well drained avoid generating puddles and standing water, vent out the high-humidity air and slightly heat the incoming cooler air (since this keeps the greenhouse at a good growing temperature, and reduces the capacity of the air to hold moisture even short bursts of heat will help), and circulate the air constantly in the greenhouse using HAF fans or any fans available. Cultural control. The nutritional status of a crop will have an effect on its likelihood of developing Botrytis blight. Any plant nutritional deficiency that leads to premature senescence can predispose a plant to Botrytis blight. Additionally, calcium deficiency should be avoided because of its role in strengthening cell walls that present a physical barrier to fungal penetration. High levels of nitrogen may also be conducive to Botrytis disease since high levels of this nutrient can produce denser plant canopies that hold humidity. The spores of B. cinerea need a supply of nutrients for germination: free water is not sufficient. The nutrients available to the pathogen are to some degree regulated by the activities of other microorganisms on the leaf surface, which indicates a possible mechanism for effectiveness of biocontrol agents. Keep in mind that pollen can be a good source of nutrients for Botrytis. Chemical control. The chemical control of Botrytis blight is largely limited to contact action materials, meaning that the grower has a constant duty to deliver 4

5 fungicide to all susceptible plant surfaces on a weekly basis whenever the environment favors the disease. The more crowded the plants are, the greater the need for good spray coverage, and yet the more difficult it is to obtain. Fungicide trials over the past have indicated that Decree and Medallion as well as Daconil and other chlorothalonil materials give excellent control-but note that label precautions must be followed to avoid phytotoxicity. In spite of some partial dicarboximide resistance in Botrytis cinerea populations, iprodione (found in Chipco 26GT, 26019, Sextant, etc.) is still often very effective. Reductions in disease incidence and/or severity are also seen with copper (e.g. Kocide, Phyton 27, Camelot) and mancozeb (e.g. Protect T/O, Dithane) materials and strobilurins (Compass and Heritage are labeled for use on Long Island). Resistance to benzimidazoles, including thiophanate methyl (in Cleary 3336, OHP 6672), has eliminated this fungicide group as an option for Botrytis management. Biological control. Biological control for B. cinerea has been explored extensively; this area will probably see more development in the future. Products currently on the market containing Bacillus subtilis and Trichoderma species have shown some suppression of Botrytis blight. There are promising results from recent research which used a species of Trichoderma as a media additive to control Botrytis and is discussed in more detail below. Botrytis attacking New Guinea plugs. Photo Jim Willmott How Does Crop Fertilization Affect Thrips and Two-spotted Spider Mite Populations? Steven K. Rettke, Rutgers Cooperative Research & Extension The following article contains a review of a research summary presented by Kimberly Williams (Associate Professor, Kansas State Research & Extension) at the OFA Short Course Conference in Columbus, Ohio (July, 2005). Various research reports support the conclusion that nutritional fertilizer can promote the growth and development of two-spotted mite and thrips infestations on crops. However, the ranges of fertilizer concentration used in these studies were often too extreme when comparing pest impacts. They typically were too deficient or toxic of macronutrients such as nitrogen (N) or phosphorus (P) and hence produced crops that were not saleable. Recent research by Chen et al. (2004) attempted to determine if certain fertilization rates could be used to help minimize pest outbreaks. Their objective was to investigate N and P fertilization rates that would produce commercial quality crops and provide significantly different nutrient tissue levels for the pests to feed on. A study using ivy geraniums and varying levels of nitrogen fertilization that produced plants that could be sold, showed no appreciable affect on mite populations. The nitrogen fertilization sources used contained 60% nitrate and 40% ammonium. The N tissue concentrations ranged from a low of 112 ppm to a high of 448 ppm. Although the dry weight and width of the plants having 112 ppm of N were noticeably less than those having 234 ppm, 338 ppm, and 448 ppm of N, the impact on mite populations were negligible. A similar study conducted with ivy geraniums, using varying levels of phosphorus fertilization rates, showed only a slight affect on two-spotted spider mite infestations. The results indicated that plant tissues having 46 ppm and 92 ppm P 2 O 5 promoted only slightly more mites after 8 weeks than plant tissue having only 23 ppm of P 2 O 5. 5

6 An additional study involved determining any affects produced from varying concentrations of N and P on thrips feeding on Impatiens wallerana.. The general trends that were found with mites, discussed above, were also found in this study. Tissue concentrations ranging between 112 to 280 ppm N showed no effect on thrips infestation levels. Additionally, it was curious to note that with P levels, the Impatiens plant tissues containing only 23 ppm P 2 O 5 had slightly higher thrips infestation levels than the tissues having 92 ppm P 2 O 5. The lower P concentrations produced higher thrips numbers, which was the opposite result shown in the study with two-spotted spider mites. The conclusions that can be drawn from this particular research study are that when using fertilization rates that result in commercial quality crops the impact on thrips and mite numbers are generally not significant. As a result, the manipulation of specific fertilization rates cannot be used to help minimize pest outbreaks. These results are good news for growers who may have had concerns about encouraging pest outbreaks by increasing fertilization rates to produce larger, faster growing crops. To the contrary, the higher fertilization rates (within the commerciallypracticed range) enabled plants to more effectively recover after damage from minor infestations. As a final comment, it is generally assumed that new, soft, and succulent stem and leaf tissue growth will promote increased aphid populations. The research study reviewed in this article did not include the effects of fertilizer rates on aphid infestations. However, previous research that has indicated a positive correlation between increased aphid populations with increased fertilization failed to limit N and P rates within an acceptable range to produce a crop that could be sold. Watch out for INSV!! Margery Daughtrey, Cornell University Long Island Horticultural Research and Extension Center Some growers in the Northeast encountered impatiens necrotic spot virus (INSV) on their lobelias this spring. Fortunately, the supplier issued a warning indicating that there was a chance of INSV in the plant material. Note that plants with INSV are a very dangerous item to leave on the greenhouse bench. Even plants not showing symptoms might be a source of virus for Western flower thrips (WFT) larvae and these will be able to spread the INSV once they become winged adults. Without prompt disposal of suspect plant material, a small INSV problem can become a large one. Adult WFT will feed on many different species of spring annuals and perennials, most of which are susceptible to INSV. Symptoms will vary a lot from plant to plant. The stunting and the necrotic leaf spots on these small lobelias (see photo) are a strong indication of INSV. Any time you suspect the presence of INSV-infected plants in your greenhouse, test them and/or dispose of them without delay. You should also use yellow sticky cards to determine whether there are thrips present that could vector the disease. These lobelias are showing symptoms that indicate INSV. Photo by Chris Logue. A New Avenue for Botrytis Control Margery Daughtrey, Cornell University Long Island Horticultural Research and Extension Center An interesting new indirect approach to Botrytis blight control has been demonstrated by researchers in Israel and at Ohio State. The Ohio study reported in 2005 looked at the addition of a biocontrol agent, Trichoderma hamatum 382, to a light sphagnum peat mix, both with and without a cow manure compost amendment. In their set of experiments there was no direct contact between the Trichoderma and the plant tissues attacked by Botrytis. The T. hamatum 382 added to the peat growing medium reduced Botrytis 6

7 effects on hiemalis begonia cv. Barbara as effectively as weekly chlorothalonil (Daconil) sprays, and also increased shoot dry weight and salability. Surprisingly, the compost medium alone also had this beneficial effect, which was attributed to accidental colonization of the compost by a beneficial microbe during the curing process. The mechanism behind the observed control of Botrytis by T. hamatum T382 is considered to be the phenomenon of Induced Systemic Resistance or ISR. This effect of topgrowth benefit from soil treatment, possibly due to ISR, has been seen with isolates of other Trichoderma species as well, including T. asperellum, T. harzianum, and T. virens. Two of these Trichoderma species are already marketed to the greenhouse industry as biocontrol agents, within products such as PlantShield and SoilGuard. In the future it is likely that new biocontrol products will be made available to provide ISR advantages to flower crops, but in the meantime there is a possibility that by using biocontrols containing Trichoderma fungi as soil treatments, you may be helping your crop s foliage to resist disease. SAF Pest Management Conference in California The Society of American Florists (SAF) sponsors a pest management conference each February, with sites alternating between California and Florida. The audience includes growers as well as educators and tradespeople who serve the nursery and greenhouse industry. This year s meeting, held in Norwalk, CA, featured two days of presentations by plant pathologists and entomologists, as well as a pre-meeting tour of Hines, El Modeno Gardens and Rogers Gardens. Subjects of discussion during the tour included the quarantine program for red imported fire ant and the challenges of production in suburbia, including elimination of nursery runoff. The presentations at the conference focused on important entomology and pathology topics for greenhouse and nursery growers, including emerging new diseases and insect pests, management of rusts, tospoviruses, powdery and downy mildews, sudden oak death, and Q-biotype whitefly. SAF has Pest Management booklets containing the text of the talks available for purchase. The booklet is $19.95 for members of SAF and $29.95 for nonmembers; the texts of the talks are also available on CD. Booklets or CDs can be purchased online at alog&super=05&catalog=pm&aff=saf or by calling Subscription Information: Greenhouse IPM Notes is available, in full color, for postal delivery for an annual fee of $50.00 (9 issues). Anyone wishing to subscribe may do so by sending a check for $50.00 payable to Greenhouse IPM Send to: Rutgers Cooperative Research & Extension of Camden County, Attention Agricultural Program, 152 Ohio Avenue, Clementon, NJ Editor Comments and suggestions welcomed. Please contact the editor: James D. Willmott Rutgers Cooperative Research & Extension 152 Ohio Avenue Clementon, NJ ext willmott@aesop.rutgers.edu The use of trade names does not imply endorsement by Rutgers or Cornell Cooperative Extension. This publication contains pesticide recommendations. Changes in pesticide regulations occur frequently and human errors are possible. Some materials mentioned may no longer be available, and some uses may no longer be legal. All pesticides distributed, sold or applied in New York or New Jersey must be registered with the New York State DEC or New Jersey DEP. Questions concerning the legality and registration status for pesticide use should be directed to the appropriate Cooperative Extension Specialist or your regional DEP or DEC office. READ THE LABEL BEFORE APPLYING ANY PESTICIDE. Cornell Cooperative Extension in New York State Provides Equal Program & Employment Opportunities, New York State College of Human Ecology, and New York State College of Veterinary Medicine at Cornell University, Cornell Cooperative Extension, County Governing Bodies and United States Department of Agriculture, Cooperating. Cooperating agencies: Rutgers, The State University of New Jersey, US Department of Agriculture and Camden County Board of Chosen Freeholders. Educational programs are offered without regard to race, sex, handicap, color, national origin or age. 7