§      Fungicide management strategies for Myrothecium leaf spot on New Guinea impatiens
§      Evaluation of Topflor for height control of poinsettia
§      Does your farm have a high capacity well?
§      Photos of downy mildew on Rudbeckia

Fungicide management strategies for Myrothecium leaf spot on New Guinea impatiens
Jeffrey Woodworth and Mary Hausbeck
Plant Pathology

Myrothecium leaf spot has been an increasing problem in the production of New Guinea impatiens for the Michigan greenhouse industry. The causal fungus, Myrothecium roridium, is considered a weak pathogen that attacks compromised plant tissues. Injuries and plant stresses associated with rooting and transplanting provide an excellent scenario for the establishment of Myrothecium in the impatiens crop. Once established, the disease can become difficult to manage, especially under warm, moist environmental conditions.

On New Guinea impatiens, Myrothecium causes necrotic foliar lesions that are often, but not always associated with the leaf margin. The lesions can become quite large (greater than 1 cm) and may coalesce together if there is more than one lesion per leaf. Lesions on the petioles and stems can lead to defoliation. Careful examination of the leaf spots reveals dark rings within the lesion. When infected leaves are placed in a very humid environment (such as a moistened sandwich bag), white tufts called sporodochia form. Green to black spore masses eventually develop on the white sporodochia and help differentiate the disease from other leaf spots, such as INSV. Please see the accompanying pictures of a sporulating leaf lesion.

Myrothecium roridium has a very broad host range and causes leaf spots and stem rots on several greenhouse crops including pansy, begonia, snapdragon, rudbeckia and gloxinia. Myrothecium spores are rain splashed and are easily spread by overhead irrigation. The pathogen survives well on organic debris, so proper sanitation of the greenhouse is imperative before any susceptible crops are placed back in the range. Rigorous fungicide spray schedules are recommended on both stock plants and transplants if Myrothecium blights have been noted in prior years.

In a recent study at Michigan State University, New Guinea impatiens were wounded to simulate transplanting injury. Fungicide sprays, representing several different chemistries, were applied at 7-day intervals. Plants were inoculated with Myrothecium spores and were placed in plastic bags to create high humidity levels. Evaluations of the number of foliar lesions were taken 7 and 14 days following inoculation. Disease pressure was severe in this trial (99.5 foliar lesions per plant in the inoculated control) and no treatment was able to completely control lesion development. Daconil Weather Stik 6F and Medallion 50WP offered the best protection, reducing the number of lesions by 75 percent compared to the control. Terraguard 50W, 3336 WP 50WP and Camelot 58EC offered moderate levels of control, reducing the number of lesions by approximately one half. The biopesticide Endorse 2.5WP (labeled only for turf currently) and the strobilurins (Insignia 20WG [labeled only for turf currently], Heritage 50WG and Compass O 50WDG) offered little disease suppression compared to the untreated inoculated control.

If Myrothecium spot is found in a crop, a fungicide rotation incorporating a chlorothalonil product (such as Daconil Weather Stik 6F) and Medallion 50WP, coupled with good sanitation and a program to minimize plant stress, should provide an effective management strategy.

*Column means followed by the same the letter are not significantly different (Tukey's Studentized Range; P=0.05).

Evaluation of Topflor for height control of poinsettia
By Erik Runkle, Cathy Whitman, David Joeright, and Royal Heins
Horticulture

By now, poinsettias are probably not on your mind.  However, we have wrapped up some research on height control of poinsettia that we wanted to share.

Topflor is a promising new plant growth regulator for greenhouse crops that is scheduled for release in 2004 or 2005. The active ingredient is flurprimidol, and the mode of action is similar to that of A-Rest, but with greater activity.  Flurprimidol has been labeled as Cutless for use on ornamental crops in the U.S. and trialed on a number of woody crops.  Topflor is effective on a wide range of greenhouse crops, and has been extensively used in Europe since the early 1990s.

Recommendations exist for European growers, but a slightly different formulation of Topflor will be available for use in the United States.  Testing of the new formulation has begun, but it has not been trialed under northern growing conditions.  Suggested rates vary by growing location, and for poinsettia, preliminary proposed rates range from 2.5 to 5.0 ppm in Indiana to 35 to 40 ppm in North Carolina.

We performed an experiment to determine appropriate rates for Michigan producers.  Poinsettia was selected for study because it is still the most valuable floriculture crop produced, and because height control is a challenge every year.  We trialed three rates of Topflor, alone or in combination with B-Nine, as well as a tank mix of B-Nine and Cycocel.

Poinsettia 'Freedom Red' plants were placed under short days on October 7, 2002 and spray applications (listed below) were made on October 8, 2002 beginning at 8:30 AM.  Plants were grown at 68°F (20°C) with a 9-hour photoperiod.  Capsil surfactant was added to all treatments at the rate of 16 oz/100 gallons.  All treatments were applied as sprays at a volume of 2 quarts per 100 ft². 

Treatments:

On the date of the first PGR spray application, plant height was measured (from soil level to tallest shoot apex) and recorded. Two days after spray application, the plants were observed for phytotoxicity. At anthesis, the date was recorded, plant height was measured, and area of the three largest bracts was measured.  

All the plant growth regulator treatments reduced final plant height compared to untreated plants (Figures 1 and 2). The most compact plants were those treated with Topflor at 20 ppm, which were 27 percent shorter than untreated plants. Height reduction in response to B-Nine (at 1250 or 2500 ppm) was between 21 and 22 percent.  Combining Topflor and B-Nine in a tank mix did not increase their effectiveness significantly. The B-Nine + Cycocel tank mix was the least effective treatment. 

All treatments reduced bract size, but the reduction caused by Topflor was less than that caused by B-Nine. Topflor at 20 ppm reduced bract size by 16 percent, while the reductions from B-Nine ranged from 26 to 34 percent.  None of the treatments influenced time to flower, and no phytotoxicity was observed in any treatment.  

These results indicate that Topflor was effective for height control of poinsettia, and caused less reduction in bract size than B-Nine.  This chemical appears to offer growers a good option for height control, but more studies are needed to fine-tune rates, times of application, and assess its effect on bract size if applied later in production.

We thank the Detroit Metro Flower Growers Association and the Western Michigan Greenhouse Association for helping fund this project.

Two recent water-use laws were passed in Michigan that will affect many farm operations. These public acts will be changed to the Natural Resources & Environmental Protection Act (NREPA).
A copy of the complete act may be found at http://www.michiganlegislature.org

Both acts use the like definitions for "large capacity well" that the acts apply to. Large capacity wells are those with the capacity to withdraw 100,000 gallons per day (70 gallons per minute) average in any consecutive 30-day period. The combined capacity of the wells 100,000 gallons or greater capacity per day (70 gallons per minute) on a site, also meets the large capacity well definition. Water use reporting will also include surface water withdraws. All agricultural water uses will apply to these laws.

Act PA 177 Aquifer Protection and Dispute Resolution: this will be a new part 317 of the NREPA. This establishes a system within the Michigan Department of Agriculture (MDA)/Michigan Department of Environmental Quality (MDEQ) to receive complaints from small well users against high capacity well users and work toward a solution.

Act PA 148 Groundwater Mapping and Water Use Reporting: this act amends part 327 of the NREPA. This law will create a groundwater resource map of the state and establish a groundwater advisory committee to direct groundwater protection efforts in the future.

The MDA will assemble township-based reports annually and forward to the MDEQ. If a producer has a site that exceeds the 70-gallon per minute threshold, then he must start filing annual water use reporting forms in January 2005.

Large capacity water users will be required to report the following:
(a) The amount and rate of water withdrawn on an annual/monthly basis in either gallons or acre inches
(b) The type of crop irrigated, if applicable
(c) The acreage of each irrigated crop, if applicable
(d) The source or sources of the water supply
(e) If the water withdrawn is not used entirely for irrigation, the use or uses of the water withdrawn
(f) If the source of water withdrawn is groundwater, the static water level of the aquifer or aquifers needs to be identified
(g) Applicable water conservation practices and an implementation plan for those practices

Estimating the producer's water use could be accomplished by several methods:
§    Pump capacity multiplied by run time: run time timers are less costly and more trouble free than flow meters
§    Flow meter: meters actual flow, maintenance and calibration
§    Water application multiplied by number of applications, plus estimate of additional water use
§    Industry average numbers (Mid West Plan Service or ASAE ) with appropriate adjustments.

Conducted correctly, any of these systems or combination of them could produce estimates that meet the needs of the law. Producers need to evaluate their water use and devise a simple, low cost, low time input method, to accomplish the goal of the legislation that may improve the management of the operation. Most farm supply houses, greenhouse supply houses and irrigation supply houses carry flow meters and run time timers.

MSU Extension will be working with growers to develop the easiest and most accurate methods to estimate greenhouse water usage. Stay tuned for more information this winter.

In the last issue of the Greenhouse Alert, Dr. Willie Kirk wrote an article entitled Control of downy mildew in Lamium (Lamium maculatum “Purple Dragon”) with Subdue MAXX and Cygnus 50WG.

This week, we have photos that show the damage of downy mildew on rudbeckia.