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Integrating Control of Botrytis and Powdery Mildew in a Greenhouse Crop FINAL REPORT

Integrating Control of Botrytis, Powdery Mildew, and Downy Mildew in Flower Crops

M.K. Hausbeck, Michigan State University; M. Daughtrey, Cornell University; and L. Barnes, Texas A&M University

INDUSTRY NEEDS:

Commercial flower growers must face increasing pesticide regulations while adopting environmentally-sound practices which may increase production costs and decrease profits. In addition to these challenges, growers of flower crops must manage a host of potentially devastating diseases including powdery mildew (PM), downy mildew (DM) and Botrytis.

PM is a continuing problem for poinsettia growers, especially those in the northern U.S. and Canada, and it was considered a “new” disease in the U.S. in the early 1990s (Daughtrey and Hall, 1992). The fungus which causes the disease is currently referred to as Oidium sp. since the information necessary to classify it further is lacking. More information is needed on the effect of environment on the infection and progression of PM. The ability of PM to be latent and exhibit no symptoms or signs is not understood. However, understanding this component of PM biology is critical to the production of disease-free poinsettia cuttings. Information learned regarding PM on poinsettia will be helpful in understanding PM on other crops, such as gerbera and rose, which continue to offer significant challenges to growers. New fungicides are needed for a PM management program for roses because the PM fungus has likely developed resistance to fungicides currently relied upon.

While much is known about the general biology of Botrytis cinerea, this fungus continues to cause significant losses at all stages of production. Free moisture and temperature are of primary importance for B. cinerea conidial germination and subsequent infection, although conidia can be very tolerant of drying (Good and Zathureczky, 1967). Botrytis conidial “showers” are typically associated with grower activity (Hausbeck and Pennypacker, 1991), and those occurring during and immediately after harvesting are important in disease management. In order to protect plants, fungicides that are effective against B. cinerea are used repeatedly, and continuous use of systemic fungicides has resulted in the selection of resistance in greenhouse B. cinerea populations (Moorman and Lease, 1992). Environmental modification in a commercial greenhouse has been a successful control tool to reduce B. cinerea inoculum and blight; it could be used in conjunction with a disease prediction system to reduce sole dependency on fungicides (Hausbeck, 1993). Botrytis blight has traditionally been the primary foliar disease of poinsettia causing leaf, stem, and bract blight (Strider and Jones, 1985). Botrytis also frequently causes storage blights of cut flowers. When cut roses are stored under high humidity, petal spotting caused by Botrytis may progress rapidly and blight the entire flower head. Gerbera flower blight can be a limiting factor in production, with symptoms often occurring during storage or transport and shipment, when temperature fluctuations result in high humidity and condensation on flowers (Salinas and Verhoeff, 1995).

There is little information regarding DM on floriculture crops even though this disease continues to negatively impact certain sectors of the floriculture industry. DM of roses (caused by Peronospora sparsa) results in plant stunting and foliar chlorosis. DM (caused by Peronospora antirrhini) is a devastating disease on cultivated snapdragons, especially on seedlings raised in humid conditions. DM causes yellowing of leaves and stunting of plants, and the fungus may also infect the growing points of established plants (Nelson and Strider, 1985). In general, sporulation of Peronospora spp. requires high humidity or dew and temperatures of 4-7 to 22-25 (Yarwood, 1943).There is little information regarding the influence of environment and stages of the DM fungus infection cycle.

Knowledge of the environmental effects on the establishment and progression of specific diseases would allow growers to manipulate their greenhouse environments to best avoid disease development. The judicious use and rotation of fungicides with different modes of action, the use of biocontrols, and optimizing the interval between applications would help avoid development of fungicide resistance in the fungus while providing disease control in an efficient manner.

PROJECT OBJECTIVES:

  1. Conduct fungicide trials using registered and experimental fungicides and biocontrol agents in both the greenhouse and the field to:
    • control PM in gerbera, rose, and poinsettia stock plants and cuttings;
    • control Botrytis in postharvest roses; and
    • control DM in snapdragon.
  2. Work to support additional registrations for needed fungicides on flower crops.
  3. Survey and meet with snapdragon producers to explore options for cultural management of DM and initiate research regarding the source of DM epidemics in snapdragon.
  4. Research the environmental and cultural factors affecting disease development (epidemiology) of Botrytis, DM, and PM.
  5. Develop grower recommendations for integrated control of Botrytis (rose, poinsettia), PM (gerbera, rose, poinsettia) and DM (snapdragon).

RESEARCH CONDUCTED:

Conduct fungicide trials using registered and experimental fungicides and biocontrol agents in both the greenhouse and the field to:

  • control PM in gerbera, rose, and poinsettia stock plants and cuttings;
  • control Botrytis in postharvest roses; and
  • control DM in snapdragon.
  • Over the course of this grant, there have been two trials for PM on gerbera, 14 trials for PM on rose, six trials testing fungicides on PM on poinsettia, two trials for Botrytis on cut roses, and one trial for DM on snapdragon.

PM on gerbera

  1. Eight fungicides and 15 treatments were investigated for their ability to control PM on gerbera. The systemic fungicides, Systhane (applied at 14-day [14d] or 21d intervals) and Terraguard (4 or 8 oz at 7d), provided complete PM control throughout the course of the trial. Strike (1 vs. 2 oz, 30d) failed to provide adequate PM control beyond 21d after application at either rate. Triact (0.5%) and ZeroTol (1%), contact, surface-active products, provided generally good PM control at 7d intervals. Soluble Silicate provided fair-to-good control at 2000 ppm, however, it left noticeable residue on the plants.
  2. Five fungicides (Pipron, Terraguard, Strike, and Systhane) applied at 10d intervals were compared for their ability to control PM on gerbera. Although there were no significant differences between treatments, the highest rate of Systhane (12 oz) had the least percentage of infected leaves and the lowest foliar rating during the course of the experiment.

PM on roses

  1. A 1996 study at MSU compared BAS 114 UBF (Milsana), BAS 490/Cygnus and the industry standard Strike. All treatments were effective compared to the untreated control. BAS 490/Cygnus (0.2 lb) was significantly more effective than other treatments in reducing incidence and severity of PM. BAS 114 UBF (0.5 or 1%) was similar to Strike in disease control.
  2. BAS 490/Cygnus (0.2 lb, 7d) was compared to Rubigan (6 oz, 7d) in New York in 1996. By the end of the experiment, both products had significantly decreased the percentage of leaves with PM (0 to 0.8%) compared to the controls (84.6%) for cv. Red Sunblaze.
  3. Terraguard (4 oz) at 7d and 14d intervals was compared to Latron (1 pt) at 7d intervals at New York in 1997. Terraguard at 7d intervals resulted in significantly better control of PM throughout the experiment.
  4. A 1997 trial at New York compared eKsPunge and/or Latron B-1956 with Terraguard. All treatments significantly reduced foliar PM compared to the untreated control. EksPunge was significantly more effective at 7d than 14d intervals.
  5. Another study at New York in 1997 compared monopotassium phosphate product (eKsPunge) with and without spreader-sticker to Terraguard (Daughtrey and Macksel, 1997b). Treatments of Latron, eKsPunge + Latron, and Terraguard at 7d intervals provided significant reduction of disease, but the level of control was acceptable only with the Terraguard treatment. Terraguard 7d was superior to the other treatments.
  6. An experimental fungicide (WAC-72) was compared to Cleary’s 3336 and Pipron + Latron B-1956 (Daughtrey and Macksel, 1997c). At the final rating, the most effective treatments were Pipron (8oz) + Latron B-1956 and the combination of these two materials with Cleary’s 3336 (16 oz).
  7. A new fungicide (Recover FL) was compared with Pipron, Strike, and Terraguard. All fungicides significantly limited PM on foliage and flowers compared with the untreated control. Pipron, Strike, and the high (300 ppm) rate of Recover were especially effective in limiting the number of flowers infected (<0.3%) (unpublished data; Hausbeck et al., 1997).
  8. The experimental fungicide BAS 490/Cygnus + Latron B-1956 was compared with Strike + Latron B-1956. Both fungicides significantly limited PM on flowers and foliage in comparison to the untreated control. There was no significant difference between type of fungicide used or length of treatment interval (7d vs. 14d).
  9. Cleary’s 3336, Pipron, and combinations of these two fungicides with Clearspray T/O were tested for their ability to control PM. All fungicides significantly limited PM on foliage compared with the untreated control. Cleary’s 3336 WP + Pipron LC + Clearspray T/O, Cleary’s 3336 WP, and Cleary’s 3336 WP + Clearspray T/O significantly limited the number of flowers with PM compared with the untreated control.
  10. In a study at Cornell (1998/99), a trial comparing WAC-72 (recently registered as ‘First Step’), Kaligreen, Pipron, and a baking soda + horticultural spray oil “home remedy” preparation (not legal for commercial greenhouse use) was conducted. All of the products provided equally good control in all treatments. Few, if any, colonies were visible on the bicarbonate-treated plants.
  11. In a second study conducted at Cornell (1998/99), 7d treatments at all rates of WAC-72 tested provided excellent control, as did the Pipron sprays. PM was reduced, but less effectively, by combinations of thiophanate-methyl and either Pipron or WAC-72 applied on a 14d basis. Cleary’s 3336 (14d) was less effective than the combinations including Pipron or WAC-72, while treatments alternating with Strike every 14d did not give any significant control of the PM.
  12. A trial comparing varying rates and application intervals of Heritage against Strike, an industry standard was conducted at MSU in 1998. Although there were no significant differences, trends noted. Strike and the untreated control had higher percentages of foliage and flowers infected than Heritage at both rates (4 and 8 oz), regardless of being applied at 7, 14 or 21d intervals.
  13. A trial in 1999 (similar to the 1998 study) at MSU compared various rates and application intervals of Heritage against Strike, an industry standard. Again, there were no significant differences among treatments; however, Strike limited disease on the foliage compared to the untreated control. Heritage (4 or 8 oz) provided foliar PM control comparable to the Strike standard when applied every 7 or 14d.
  14. A second study at MSU in 1999 compared Cygnus alone or in combination with Latron B-1956, Latron alone, Strike + Latron, Heritage, BAS 114 UBF (Milsana), and Systhane. Cygnus (0.1 or 0.2 lb, 7 or 14d) and Systhane (5 oz, 14d) held PM to <5% on foliage. Cygnus, Cygnus (0.1 or 0.2 lb) + 2 oz Latron B-1956 (7 or 14d), and Systhane resulted in a rating of <1.0 (where 0=no PM) for PM on foliage and on flowers.Heritage (2 oz, 14d) also had a rating of <1.0 on flowers only.

PM on poinsettia

  1. A study in 1996 at New York compared Milsana 1114 005, BAS 490/Cygnus, Pipron + Latron, Terraguard and Strike, all applied at 7d intervals, for control of PM on poinsettia. All treatments significantly reduced the number of PM colonies on leaves and bracts compared to the untreated control. Terraguard (8 oz) and Pipron (8 oz) + Latron (0.06%) resulted in no colonies on the bracts, while Strike (4 oz) resulted in no colonies on the leaves.
  2. In a study conducted in New York (Daughtrey and Macksel, 1997a), all treatments gave significant control of PM on leaves compared to the untreated control. Weekly sprays with eKsPunge + Latron or Latron alone gave significant control of foliage, but were ineffective on bracts. On bracts, the best control (no colonies) was seen in Terraguard treatments. A strobilurin fungicide, BAS 490/Cygnus, was also tested at 14d intervals and provided control of PM on bracts that was statistically similar to Terraguard, although a few scattered colonies were visible. Weekly treatments with the experimental fungicides AC-72 and WAC-73 was also effecttive at controlling disease on bracts although leaf and bract tip burn was observed. An experimental biocontrol was also tested and provided bract control significantly better than the untreated control, but not as good as Terraguard.
  3. A 1997/98 trial at MSU compared 0.2 lb BAS 490 + 2 fl oz Latron B-1956 (7 or 14d), Systhane (4, 8 or 12 oz, 14d), Strike (2 oz) + Latron (7 or 14d), Pipron (4 fl oz, 14d), Terraguard (4 oz, 14d), WAC-72 (2.5 or 5 lb, 7 or 14d) and Cleary’s 3336 (1 lb) + Latron B-1956 (14d) for control of PM on poinsettia. At the last observation date, all treatments were significantly better than the untreated control with the exception of WAC-72 (2.5 lb, 14d). Only the high rate of WAC-72 (5 lb) at 7d intervals resulted in phytotoxicity.
  4. A second study in 1997/98 at MSU compared Phyton-27 at varying rates alone or in combination with Latron B-1956 (1 fl oz) at 7d intervals against the industry standard Strike (4 oz, 14d) for control of PM on poinsettia. Phyton-27, regardless of rate or whether a spreader-sticker was added, showed significantly more disease than Strike for percentage of infected leaves and bracts and for infection severity; it was comparable to the untreated inoculated control on all observation dates.
  5. Sixteen materials, including strobilurins, industry standards and alternative chemistry products applied at at 7 or 14d intervals, were tested in New York in 1998 (Daughtrey, et al., 1999). All treatments significantly reduced PM severity on bracts and leaves in comparison to the untreated control. No PM colonies were detected on plants treated with the sterol biosynthesis inhibitors (SBI) Strike, Terraguard and Systhane (all 14d); or Pipron, eKsPunge (MKP), or Terraguard alternated with eKsPunge (all 7d). Other materials tested which significantly suppressed disease were Cleary’s 3336, BAS 114 UBF (Milsana, extract of giant knotweed), ZeroTol 27% (hydrogen dioxide), Phyton-27, and WAC-72 (bicarbonate) (all 7d), and the strobilurins, Cygnus, CGA 279, and Heritage (all 14d). Spray residue on plants treated with eKsPunge and Cleary’s 3336 (7d) was unacceptable; treatments alternating between Cleary’s 3336 and WAC-72 showed less residue. White bract spotting occurred with hydrogen dioxide treatment and dark spotting with BAS 114 UBF.
  6. Michigan’s 1998-99 fungicide trial included all products tested in New York plus 10 additional materials. The area under the disease progress curve (AUDPC) was used as a means of summarizing the number of PM colonies occurring on the bracts over time. Cleary’s 3336 + Latron B-1956 failed to provide control significantly better than the untreated control. Applying a low rate (2 oz) of Heritage at a 14d interval was similar to using a higher rate (3 oz) at a 21d interval. Also, using a higher rate (3.2 oz) of Cygnus at a longer interval was no different than using a lower rate (1.6 oz) every 7d. While there were no significant differences in the XDE-795 (quinoxyfen) rates tested, the lowest rate (5 ppm) had more disease than the higher rates tested. Similarly, there were no significant differences among the CGA 279 rates tested although the lowest rate (0.5 oz) had the most disease. Both rates of Systhane completely prevented the development of disease. While Cleary’s 3336 + Latron B-1956 did not effectively control PM, alternating this application with WAC-72 was effective. A number of treatments provided a significant level of protection 60d after the last fungicide application and included the following: Heritage (2 oz, 14d), Cygnus, XDE-795, CGA 279 (1 and 2 oz), and Systhane. Systhane applications completely prevented PM development even 60d after the last fungicide application. PM development on the leaves was negligible, and not reported.

Botrytis on cut roses

  1. Eight shipments of three cultivars (pink ‘Dolores,’ dark red ‘Royalty,’ red ‘Kardinal’) of long-stemmed cut roses were received at MSU with the buds wrapped in cellophane and stems packed with ice. The treatments were postharvest flower dips of l lb/100 gal of Decree, 12.5 oz/100 gal of Phyton-27, and the untreated control. Roses were inoculated with Botrytis spores or misted with water. ‘Royalty’ seemed to be the most susceptible cultivar. When averaged across shipments, an application of Phyton-27 to uninoculated roses resulted in significantly more healthy roses than the untreated control.
  2. In a second set of experiments at MSU, red ‘Robina’ roses were treated by either dipping or spraying the flower to runoff. Roses were misted with Botrytis spores and later rated for disease development. All controls became blighted. Ornalin FL effectively limited Botrytis blight with 16.7% healthy roses in experiment 1 and 25% healthy roses in Experiment 2, but left a slight residue on the flowers in both experiments. Timsen 40WP (experiment 1) was the only other treatment with healthy flowers; it had 33.3% healthy roses 3d after inoculation, but all showed some sign of infection after 5d. All treatments delayed the development of blighting in Experiment 1. In Experiment 2, several treatments resulted in substantially less blighting than the untreated control and included WAC-73, ESC11 (Pseudomonas syringae), ESC10 (P. syringae), and Ornalin FL. TopShield (Trichoderma harzianum) and a new experimental fungicide, PrimaStop (PreStop, Gliocladium catenulatum) in Experiment 1 left heavy residues on the flowers and did not provide control.

DM on snapdragon

  1. Experimental materials, “Exp 1,” “Exp 2,” and “Exp 3" were tested at Cornell for their ability to prevent DM on snapdragons. Only one yellow spotted plant (3%) with sporulating DM was noted in the Exp 1 (higher rate) treatment and only 3 spotted plants (10%) in the lower rate treatment. Plants treated with Exp 2 also were well protected, showing only 1 spotted plant (3%). None of the Exp 3-treated plants showed yellow spotting, while 30% of the plants treated with Protect T/O and 73% of the plants treated with Banol developed yellow lesions. Protect T/O acts as a protectant whereas the experimental materials are at least locally systemic. Exp 3, although suppressing symptoms well, was not as effective at preventing sporulation as the higher rate of Exp 1 or Exp 2. Exp 2 and the higher rate of Exp 1 gave the best results overall, since suppressing sporulation is important for managing an epidemic.
  2. Work to support additional registrations for needed fungicides on flower crops. At the time this grant was initiated, the fungicide Strike 25WDG was the only industrial standard available for the control of PM on poinsettia. During the course of this grant, based on the results of fungicide trials, the following products have been registered for use on poinsettia: Systhane, Terraguard, Phyton-27, Pipron, Cleary’s 3336.
  3. Survey and meet with snapdragon producers to explore options for cultural management of DM and initiate research regarding the source of DM epidemics in snapdragon. Researchers visited with producers and cut flower growers to assess current cultural management strategies. A spore monitoring project was initiated with a grower cooperator and is ongoing.
  4. Research the environmental and cultural factors affecting disease development epidemiology) of Botrytis, DM, and PM.

PM on poinsettia

A scanning electron microscope (SEM) was used to determine that PM conidia began to germinate within 2 hours of landing on a poinsettia leaf at 20 C (85% RH). Conidial germination peaked at 76% within 36 hours after inoculation. Within 24 and 48 hours after inoculation, 32.5 and 51.0%, respectively, of germinated conidia had the structures (appressorium and haustorium) necessary to infect the plant leaf. Using SEM, unique morphological features of the powdery mildew fungus were observed including an arced basal cell and thin ridges on the subterminal cells of some conidiophores (Celio and Hausbeck, 1998). Conidial germination was reduced, and development of secondary germ tubes and haustoria was severely limited when incubation temperatures were 30 C (Celio and Hausbeck, 1998).

Microscopy studies of the infection process were conducted in relative humidity (RH) chambers (35-92% RH) at 15, 20 and 25C, in which leaf disks cv. Freedom Red) were incubated for 48 hours (Byrne and Hausbeck, 1998). All aspects of the infection process were limited at 15C. Infection rates were highest at 20C under 35-50% RH. The highest temperature evaluated, 25C, favored maximum germ tube elongation and development of secondary germ tubes and appressoria. In previous studies, 32C was found to inhibit the infection process. The effect of temperature on sporulation was quantified using leaf disks placed on agar disks and incubated in petri dishes for 14d at 15 or 20C (Byrne and Hausbeck, 1999). The number of conidiophores and length of conidial chains on the leaf disks were recorded. The number of conidiophores produced did not vary with temperature. Sporulation was initiated 9d after inoculation. Maximum conidial chain lengths were 4 and 7 conidia at 15 and 20C, respectively. The percentage of conidiophores bearing no conidia were 33 and 15%, at 15 and 20C, respectively.

DM on snapdragon and rose

A Burkhard spore trap and weather-monitoring equipment were placed on site at two commercial grower cooperators. One grower is a producer of cut snapdragons and the other a producer of potted roses. Rainfall, relative humidity, temperature, leaf wetness, wind velocity, and direction were monitored with average values recorded hourly. The trials were conducted from December through April, and analysis of the data is ongoing. Spores of the DM fungus were detected in the atmosphere just prior to the grower report of the first DM occurrence in field snapdragons. It was noted that spore release of the DM fungus typically occurred in mid-morning during a time when the relative humidity decreased and the wind speed increased. This followed a dew period occurring the previous evening that likely provided the necessary conditions for the spores to develop. Similar information is currently being generated regarding the DM fungus that affects roses.

Develop grower recommendations for integrated control of Botrytis (rose, poinsettia), PM (gerbera, rose, poinsettia) and DM (snapdragon).

Development of a PM spray program for finishing and postharvest phases of poinsettia production

Based on the fungicide trials that were conducted during the course of this grant, the following products completely prevented development of PM colonies on poinsettia: Terraguard and Pipron + Latron for bracts and Strike for leaves (trial 1); Terraguard (trial 2); Strike, Terraguard, Systhane, Pipron, eKsPunge, Terraguard alternated with eKsPunge (trial 5); Systhane (trial 6). Good control of PM was achieved with the following products: WAC-72 (leaf/bract tip burn observed), WAC-73 (leaf/bract tip burn observed), Cygnus (trial 2); Strike (trial 4); Cleary’s 3336, BAS 114 UBF (dark spots observed), ZeroTol (white spots observed), Phyton-27, WAC-72, Cygnus, CGA 279, Heritage (trial 5); Cleary’s 3336 alternated with WAC-72, Cygnus, XDE–795, CGA 279 (trial 6). These products give growers alternatives to systemic fungicides (Systhane, Terraguard, Strike) in the management of this disease. Further development and registration of the experimental fungicides listed here will increase the alternatives available to growers.

Development of a PM spray program for the stock plant and cutting phases of poinsettia production

Studies were initiated to determine whether an application of a systemic fungicide to a stock plant could provide protection to the cuttings that would subsequently be removed from that plant. Stock plants were given a single treatment with Terraguard or Systhane eight days before cuttings were taken. After the cuttings were removed from the stock plant, they were inoculated with powdery mildew conidia and maintained in an environment conducive to disease development. The Terraguard treatment suppressed PM development for approximately 29 days. The Systhane spray controlled PM infection for 55 days. In another study, when cuttings were removed two months following fungicide application they became as diseased by PM as cuttings from stock plants receiving no fungicide sprays (Unpublished data; Byrne and Hausbeck, 1998). Fungicide trial 5 found that Systhane completely prevented PM development even 60d after the last application, and the following products gave a significant level of protection 60d after application: Heritage (s oz, 14d), Cygnus, XDE-795, CGA 279 (1 and 2 oz).

Screen poinsettia cultivars for resistance to PM

Cultivars with red bracts (Freedom Red, Red Sails, V-14 Glory, Supjibi Red) had significantly more bracts infected (>91.2%) than the cultivars with pink (V-14 Pink, Hot Pink) (85%), white (Topwhite, V-14 White, V-17 Angelika White) (53-96%), or variegated bracts (Jingle Bells 3, Pink Peppermint, V-17 Angelika Marble) (53-79%) (Celio and Hausbeck, 1994; Celio and Hausbeck, 1997).

BENEFITS TO INDUSTRY:

Conduct fungicide trials using registered and experimental fungicides and biocontrol agents in both the greenhouse and the field to:

  • control PM in gerbera, rose, and poinsettia stock plants and cuttings;
  • control Botrytis in postharvest roses; and
  • control DM in snapdragon.

PM on gerbera

Several novel fungicides, Triact, Soluble Silicate, ZeroTol, showed promise as new and alternative tools to systemic fungicides for PM management.

PM on roses

New fungicides are needed for the industry because the PM fungus has likely developed resistance to currently relied upon fungicides. A biocontrol (Recover), strobilurins (Cygnus, Heritage) and alternative chemistries (BAS 114 UBF, eKsPunge, Kaligreen, WAC-72), were investigated for their usefulness in a PM management program for roses. Research studies will help to identify new fungicides that offer promise for commercial development and use, which will offer growers additional tools to manage fungicide resistance of PM.

PM on poinsettia

The registered SBI fungicides (Strike, Systhane, Terraguard) are currently providing excellent PM control. However, considering the history of other PMs developing resistance to this group of fungicides, resistance management programs must be developed and im0plemented now to delay the development of resistance. This project has identified a number of new products with different modes of action that can be used reliably in a management program. These include alternative chemistries (BAS 114 UBF, eKsPunge, WAC-72, ZeroTol), and strobilurin fungicides (Cygnus, CGA 279, Heritage). Further, this research has identified products that provide PM protection for up to 60d following the last application.

Botrytis on rose

In our studies, blighting of rose petals was the most severe symptom caused by Botrytis. The industry standard Ornalin FL consistently limited blighting caused by Botrytis in both experiments. The commercially available Phyton-27 is also effective in limiting Botrytis blight. Based on our results and using blighting as a primary criterion, the following products should be pursued in additional Botrytis trials: alternative chemistry products Timsen 40WP and WAC-73, and the biocontrol ESC10.

DM on snapdragon

  1. Further product development and registration of experimental materials, Exp1, Exp2 and Exp 3, should yield some superior new DM controls for snapdragon.
  2. Work to support additional registrations for needed fungicides on flower crops. Growers need a variety of products and biocontrols available for disease control to allow rotation of fungicides used which would avoid development of resistance in the pathogen causing the disease.
  3. Survey and meet with snapdragon producers to explore options for cultural management of DM and initiate research regarding the source of downy mildew epidemics in snapdragon. A better understanding of DM and an evaluation of whether cultivars differ in their susceptibility to this disease will be crucial in development of an effective management program.
  4. Research the environmental and cultural factors affecting disease development (epidemiology) and delayed symptom expression (latency) of Botrytis, DM, and. Investigate the efficacy of heat treatments in eliminating active and latent infections.

PM on poinsettia

Information from our research may further the progress in accurately classifying the PM fungus and therefore increase our knowledge regarding host range and origin of this pathogen.

Temperature manipulation may be a useful tool in managing PM on poinsettia. For example, it would be advisable for growers to drop the greenhouse temperatures temporarily immediately following detection of PM to discourage rapid reproduction of the fungus. Slowing down the ability of the fungus to reproduce via temperature manipulation can greatly increase the efficacy of fungicide control programs and reduce losses due to reduced plant quality.

High temperature eradicative treatments might be feasible when vegetative growth is desired such as during stock plant production or following rooting of cuttings. In may be advantageous for rooted cuttings to be exposed to a high eradicative treatment since the plant size is small, requiring treatment of a much smaller area than if treating larger stock plants. While these treatments would not be helpful in a situation where reinoculation is possible, it may be helpful in situations where propagators are interested in treating rooted cuttings prior to shipment to insure the poinsettia cuttings are free of powdery mildew. Though it is unlikely that heat treatments can be used alone, there may be the potential to incorporate temperature manipulation with scouting and fungicide applications to further reduce growers’ powdery mildew management costs.

DM on snapdragon

Currently, there is little information regarding the environmental factors that trigger a DM epidemic. Knowledge of the environmental factors that are favorable for DM development could alert growers that sprays need to be initiated or intensified to avert or limit a disease epidemic.

Develop grower recommendations for integrated control of Botrytis (rose, poinsettia), PM (gerbera, rose, poinsettia) and DM (snapdragon).

A PM management program for all susceptible flower crops emphasizes early disease detection via weekly scouting (especially important when the environment favors disease development), removal of infected leaves or plants in bags to contain spores, and appropriate fungicide selection and timing of fungicide applications.

A PM management program for poinsettia: Poinsettias are susceptible to PM regardless of bract color. Since cultivars with red bracts are particularly susceptible to PM, additional attention should be paid to red-bracted poinsettias when scouting. While cultivars with white bracts are less susceptible to PM, it is worth noting that detection of PM in a commercial setting may be delayed due to low visibility of PM on white bracts. Effective fungicides have been identified that have systemic properties and offer superior control of PM. Timely applications of products tested in our studies have been the key for many growers in turning around a PM epidemic and ensuring that PM colonies do not reappear after leaving the greenhouse.

Propagators using Terraguard or Systhane on stock plants can anticipate an extended period of protection for those cuttings removed from the stock plant soon after fungicide application. As a result, fungicide applications to cuttings could be delayed from one to two months depending on the fungicide used. This strategy would save unnecessary fungicide expense. Decreasing fungicide use is important so that the PM fungus does not become resistant to our most effective systemic fungicides. Studies indicate that high (30 C) temperature eradicative treatments might be helpful in situations where propagators are interested in treating rooted cuttings prior to shipment to insure the poinsettia cuttings are free of PM.

A PM management program for rose: Trials carried out during the course of this grant showed that while none of the fungicides completely prevented PM on roses, there are products which significantly decreased the disease, and they should be used in conjunction with scouting, and removal of infected leaves where feasible.

FUTURE RESEARCH NEEDED AND FUTURE BENEFITS TO INDUSTRY:

Epidemiology and management of PM:

  1. Observe and quantify the effects of RH and temperature on the sporulation of PM on poinsettia leaf tissue.
  2. Determine the long-term effects of a high temperature treatment on the infection process of PM of poinsettia.
  3. Investigate the longevity of latent PM infections on poinsettia.
  4. Determine the factor(s) prompting the release of conidia into the greenhouse atmosphere.
  5. Determine the efficacy of standard fungicides, biocontrol agents, naturally-derived fungicides and novel fungicides in controlling PM on poinsettia, gerbera, and rose.
  6. Determine which gerbera cultivars are especially susceptible to PM.

Epidemiology and management of DM:

  1. Determine the environmental factors that are conducive to disease and prompt release of sporangia. After two years of research, compile data and develop and test a disease prediction system. This system would be useful where DM occurs annually, alerting growers when the environment is favorable for DM thereby prompting fungicide applications.
  2. Determine which snapdragon varieties are especially susceptible to DM.
  3. Determine the efficacy of standard and novel fungicides in controlling DM on snapdragons and roses.

Epidemiology and management of Botrytis:

  1. Determine which cut rose varieties are especially susceptible to Botrytis.
  2. Determine the efficacy of standard fungicides, biocontrol agents, naturally-derived fungicides and novel fungicides in controlling Botrytis on cut roses.
  3. Test a Botrytis forecaster developed for other crops for its suitability for use in floriculture.

Future Benefits to Industry:

Knowledge of the environmental effects on the establishment and progression of specific diseases would allow growers to manipulate their greenhouse environments to best avoid disease development. Knowing the susceptibility of popular cultivars to specific diseases would allow growers to either select varieties that offer some disease resistance or know that susceptible varieties need to be closely monitored for appearance of disease. The judicious use and rotation of fungicides with different modes of action, the use of biocontrols, and optimizing the interval between applications would help avoid development of fungicide resistance in the fungus while providing disease control in an efficient manner.

ADDENDUM

Literature Cited:

Byrne, J.M., and Hausbeck, M.K. 1998. Influence of temperature and relative humidity on infection processes and sporulation of Oidium sp. on poinsettia foliage. Phytopathology 88:S134.

Byrne, J.M., and Hausbeck, M.K. 1999. The effect of temperature on sporulation of Oidium sp. on poinsettia foliage. Phytopathology 89:S10.

Celio, G.J., and Hausbeck, M.K. 1994. Susceptibility of poinsettia cultivars to Oidium sp. Phytopathology 84:1158.

Celio, G.J., and Hausbeck, M.K. 1997. Evaluation of poinsettia cultivars for susceptibility to powdery mildew. HortScience 32:259-261.

Celio, G.J., and Hausbeck, M.K.. 1998. Conidial germination, infection structure formation, and early colony development of powdery mildew on poinsettia. Phytopathology 88:105-113.

Daughtrey, M., Byrne, J.M., and Hausbeck, M.K. 1999. Management of a new powdery mildew on poisettia. The First International Powdery Mildew Conference, Aug. 29-Sept. 3, Avignon, France.

Daughtrey, M., and J. Hall. 1992. Powdery mildew - A new threat to your poinsettia crop. Grower Talks, September, pp. 23-31.

Daughtrey, M., and Macksel, M. 1997a. Evaluation of treatments for control of powdery mildew on poinsettia. Long Island Horticultural Research Laboratory Annual Report p. 17.

Daughtrey, M., and Macksel, M. 1997b. Control of powdery mildew on miniature roses with monopotassium phosphate. Long Island Horticultural Research Laboratory Annual Report p. 19.

Daughtrey, M., and Macksel, M. 1997c. Control of powdery mildew on miniature roses with the experimental fungicide WAC-72. Long Island Horticultural Research Laboratory Annual Report p. 19.

Good, H.M., and Zathureczky, P.G.M. 1967. Effects of drying on the viability of germinated spores of Botrytis cinerea. Phytopathology 57:719-722.

Hausbeck, M.K. 1993. Biological control and environmental manipulation for control of Botrytis. Proceedings for the 9th Conference of Insect and Disease Management on Ornamentals, SAF, Alexandria, VA, pp. 73-79.

Hausbeck, M.K., and Pennypacker, S.P. 1991. Influence of grower activity and disease incidence on concentrations of airborne conidia of Botrytis cinerea among geranium stock plants. Plant Dis. 75:798-803.

Moorman, G., and Lease, R. 1992. Benzimidazole- and dicarboximide-resistant Botrytis cinerea from Pennsylvania greenhouses. Plant Dis. 76:477-480.

Nelson, P.E., and Strider, D.L. 1985. Snapdragons. In: Diseases of Floral Crops - Vol. I, Praeger Publishers Division, Westport, CT. Strider, D.L., ed. Pages 497-500.

Salinas, J., and Verhoeff, K. 1995. Microscopical studies of the infection of gerbera flowers by Botrytis cinerea. Eur. J. Plant Pathol. 101:377-386.

Strider, D.L., and Jones, R.K. 1985. Poinsettias. In: Diseases of Floral Crops - Vol. II, Praeger Publishers Division, Westport, CT. Strider, D.L., ed. Pages 351-404.

Yarwood, C.E. 1943. Onion downy mildew. Hilgardia 14:595-691.

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