While root rots caused by Pythium and Rhizoctonia are the most common among greenhouse crops, black root rot is a serious threat to pansies, petunias and vinca. Black root rot is caused by the fungus Thielaviopsis and may also infect cyclamen, poinsettia, primula, impatiens, snapdragon, verbena, phlox, begonia and nicotiana. Plants with black root rot often show symptoms that mimic nutrient deficiencies such as stunting with older leaves shriveling. Leaves may turn yellow and the youngest leaves become stunted and tinged with red. In mild infections, older leaves are yellow-green with the veins retaining their green color. Black root rot may also affect the lower stem on crops such as poinsettia, causing cracks that appear black.

Sanitation is the best preventive measure against black root rot. Once this fungus is established in a crop or in a greenhouse, an effective fungicide program is needed. Based on studies conducted in my lab, I recommend fungicides that have thiophanate-methyl as the primary active ingredient (Cleary’s 3336 F is an example) be used frequently at the high labeled rate. A good rotational product is Terraguard 50W since it has a different mode of action and has shown to be effective in my studies against black root rot.

Choosing an effective fungicide to control black root rot is critical because a misstep early in the disease epidemic may result in an unsalable crop. If the crop is treated for Pythium root rot when black root rot caused by Thielaviopsis is really the problem, not only will time and money have been wasted but the disease will have a head start in causing damage to the crop before it can be halted with the correct fungicide. Several new fungicides have recently become available and others will be labeled soon. While some of these new products have broad activity and fit in many management programs, others are quite specific and should be used in a more limited way.

We conducted two trials to look at how Cleary’s 3336 F and Terraguard 50W compare with new fungicides and biocontrol agents in controlling black root rot. We used pansy and vinca crops because of their frequent problems with black root rot. We evaluated plant height and death as a measure of whether the fungicide provided protection. In our pansy study, only drenches of Terraguard 50W or Cleary’s 3336 F limited plant death to 25 percent or less, compared to plant death of over 70 percent when no fungicide was used. Also, drenches of Terraguard 50W or Cleary’s 3336 F prevented the severe stunting that occurred when fungicides were not used. In our black root rot trial with vinca, few plants died overall even without fungicide treatment. We did, however, see differences in the ability of the fungicides to prevent plant stunting caused by black root rot. Drenches of Cleary’s 3336 F or Terraguard 50W provided plant protection better than all other fungicide drenches tested in this trial.

Sometimes new isn’t always better and for black root rot the standard program of Cleary’s 3336 F rotated with Terraguard 50W is the way to go. Since this was our first look at some of the products included in these studies, it is possible that higher rates and shorter intervals may be helpful in improving black root rot control. Until further testing is done, stick with the proven fungicides to ensure the best control.

A proper rooting environment is just as important as the source and quality of the unrooted cuttings (URCs) that you receive. Over the past nine years we have seen a 300 percent increase in the number of cuttings imported into the United States. Growers have little influence on the stockplant management techniques and the methods employed to harvest, store and ship these URCs, but they can improve how they propagate URCs to reduce rooting time and consequently increase profitability.

These five factors are all essential for rapid rooting and preventing cuttings from drying out. However, these conditions are also conducive to pathogen development and efforts should be made to root cuttings with the least amount of mist possible to minimize disease, leaching of nutrients and water-logged media. Growers often find that it is difficult to keep these conditions in balance because of external environmental factors. Consequently, on warm and sunny days growers may opt to heavily shade their propagation houses, increase misting frequency and duration, and vent more, leading to a stressful environment for the URCs.

Managing light intensity
Until recently, the importance of light during propagation has not been well described. When light levels are too high, plants can experience stress and wilt, which can delay rooting. When light levels are too low, root formation can be delayed, increasing propagation time. Desirable levels of light vary, depending primarily on the stage of root development.

Stage 1: stick to callus formation
During the early stages of propagation (from stick to callus formation), maximum recommended light intensity is between 120 to 200 μmol·m^-2· s^-1 (600 to 1,000 footcandles) to provide enough energy for callus formation and root initiation without causing desiccation. In addition, light transmission through the propagation house should be indirect or diffuse. White wash or exterior shade in combination with retractable shade curtains can provide a good system for light modulation, especially in the spring and summer. Curtains alone are an effective way to modulate light transmission, as they can remain open on cloudy days or in the morning and late afternoon on sunny days. Curtains should be closed during the brightest hours of the day to prevent excessively high light levels. Stage 2: after root initiation
Once roots have initiated (generally 5 to 12 days after stick), maximum light intensity can be increased to 200 to 500 μmol·m^-2· s^-1 (1,000 to 2,500 footcandles). Again, the light should be diffuse.

Plant container laws: A sign for the times
Dean Krauskopf
Extension Educator

When you sell a plant, you are selling a packaged product, which, by law, must have some information about the product easily accessible by the consumer. Every container sold must comply, including nursery stock, perennials, vegetables and herbs. Failure to comply with the law by any retailer can result in a “stop order” where the retailer will not be permitted to sell the plants (and they will most likely die on the bench). Potentially worse, fees can be levied on a per case (or pot) basis. Here is a brief summary of how to comply with the law proactively, before a complaint is placed, an inspection occurs or a stop order or fine is issued.

There are three types of information that should be readily accessible:
1)    Declaration of identity
2)    Declaration of net contents
3)    Declaration of responsibility

The three types of information must appear either on the sign displayed with the plant material or on the tag. The easiest way to comply with the law in 2005 might be to adjust signs to include all three types of information. Information can be displayed on tags.

Declaration of identity must describe the product or plant. It can be the common name (mum) or scientific name (chrysanthemum). When more than one plant is grown in the container, describe all plants or use the terms “mixed annuals” or “mixed annuals and perennials” or another term that accurately describes the container contents.

Declaration of net contents must describe the volume or measurement (diameter at pot top and bottom, and pot depth) in both English and metric units. For packs, list the measurements (English and metric) for the individual cells, the number of cells per sales unit (e.g. 6-pack etc) and total measurements for sales unit. Measure all containers sold to determine the full volume each container can hold. The easiest approach is to list volumes (English and metric), as it requires only two listings rather than six or more. List volumes using the largest whole unit, for instance: use 3.5 qt, not 7 pt or 0.875 gal; use 3.31 l, not 3,312 ml. List that volume using the largest whole unit. Use gallons or liters or pints. Use a decimal place or fraction for parts of the whole unit. Don’t report ounces; use gallons or another larger measure. Don’t report milliliters; report liters.

Declaration of responsibility must provide the consumer with the producer(s) or retailer of the product. The simplest way to comply with this aspect of the law is to report “grown for (insert retailer’s name).” However, if you grew the product on-site, it should read “grown by (insert retailer’s name).”

Declarations of identity and net contents must appear in close proximity on the sign and must be clearly discernable from other information on the sign. Declaration of responsibility can appear with or separately from the other two, but again it must be clearly discernable. Retailers should inspect every sign that is placed on the retail sales floor, bench or banner to be sure all three types of information are included for every product sold. Two examples of how to display the three necessary types of information are shown here.

This information was adapted with permission from Industry Guide to Marketing Container Plants published in the Ohio Florists’ Association Bulletin (January/ February 2005) Number 888 (http://www.ofa.org/pdf/container121304.pdf). The OFA article was prepared in cooperation with the American Nursery and Landscape Association and the Southern Nursery Association. Contact the NIST at: http://www.nist.gov/or NIST Weights and Measures Division, Gaithersburg, MD 20899.

If you have questions, contact MSU Extension’s Jeanne Himmelein, himmele1@msu.edu, Tom Dudek, dudek@msu.edu, or Dean Krauskopf, krauskop@msu.edu

Disclaimer: The information presented here is provided with the understanding that the contributors are not engaged in rendering legal advice. Every effort has been made to present accurate information. Additional information can be obtained by contacting the NIST directly.