A Newsletter for Professionals Growing Greenhouse Crops in the Rocky Mountain Region

Contents

• ChemSweep
• Career Day 2000
• Diseases of Lisianthus
• News from the Lab
• 1999 Poinsettia Evaluation

ChemSweep

Due to previous success and much demand, Colorado ChemSweep, a waste agricultural pesticide program, is coming again in the spring of 2000. Please help distribute the information to growers or others with waste pesticides in your county.

Click here for a registration form
requires Acrobat Reader

Note the registration deadline of February 15.

As the Environmental and Pesticide Education Specialist, I am excited about the program because it provides an opportunity for unusable pesticides to be disposed of in an environmentally safe manner. The program is conducted under the "Universal Waste Rule" which will allow MSE Environmental, Inc. to go to the site, properly package the waste, take possession of the waste and become the generator of the waste, thus reducing future liabilities for the program participants. The program meets all state and federal hazardous waste regulations.

This will be the third statewide ChemSweep. Since the program started with a pilot in 1995, 68,665 pounds of waste pesticides have been collected in Colorado from 225 participants. The cost to participants will be between $2.25 - $2.65 per pound. However, a minimum of $50.00 (approximately 20 pounds of waste) is required for MSE to make an on-site visit.

Due to this cost restriction you may want to creatively design ways for growers or others with very small amounts of waste to cooperate with each other or someone with a larger amount of waste. If I can be of further assistance, please do not hesitate to call 970-491-6027, fax 970-491-3862 or e-mail smcdonal@lamar.colostate.edu.

Sandra McDonald , Ph.D.
Environmental and Pesticide Education Specialist
Bioagricultural Sciences and Pest Management

Career Day 2000

Career Day 2000

Career Day 2000 is scheduled for February 23, 2000. This is an excellent opportunity for you to come to campus and recruit new employees or student interns. For more information, you can contact Dr. Jim Klett or our Department office. Also, you can download a registration by clicking the link below:

Download the Information Form
requires Acrobat Reader

Steven E. Newman, Ph.D.
Greenhouse Crops Extension Specialist
Horticulture and Landscape Architecture

Diseases of Lisianthus

Lisianthus has been gaining popularity in recent years, not only as a cut flower, but also as a potted plant. Since it is relatively "new" to many growers a discussion of the diseases that affect the crop may be beneficial.

As with any crop grown, effective disease management begins with 3 steps:

1. Determine if the problem is in fact due to disease. Or is it insect or environmentally related?
2. Identify the disease correctly.
3. Take a holistic or integrated approach to management.

Identifying characteristics of six diseases on lisianthus are described below.

Botrytis blight is a fungus that causes small bleached spots on petals that rapidly enlarge to blight the entire flower . On stems symptoms consist of brown lesions. Wounded or senescent tissues are more prone to attack by the fungus, however, healthy tissue may also become infected. Areas damaged by Botrytis have a characteristic gray, fuzzy sporulation, which is referred to as "grey" mold. Conditions that promote the disease include high relative humidity, standing water on plant tissues, low temperatures (generally below 60°F), and poor air circulation. Spores are carried in air currents and are commonly present at all times in the greenhouse on plant tissue. To manage the disease eliminate debris, standing water, reduce high humidity by raising the temperature or venting with lower humidity air, and increase air movement with horizontal air flow systems or fan jets.

Curvularia blight or leaf blotch begins as tiny tan specks that enlarge to form large blotches. These symptoms mimic micronutrient toxicity symptoms that may be induced by low pH. If soil pH is below 6.5, then micronutrient toxicity may be the culprit. Otherwise suspect Curvularia. This disease is favored by 75°F temperatures.

Downy mildew symptoms begin as a mottled yellowing on the leaf surface. Mycelium and spores of the fungus will be produced on the leaf underside and appear as a gray or light brown mass of mildew. High humidity, cool temperatures and prolonged leaf wetness are conducive to development of this disease. Hence, it often appears in the early spring or late fall. Downy mildew spores survive in plant debris or on weeds and are spread by air currents and splashing water. To manage the disease remove infected plant material, avoid prolonged leaf wetness, and improve air movement.

Impatiens necrotic spot virus has the potential for extreme crop value loss and is difficult to eradicate. Symptoms of the virus in lisianthus include stunting, circular to irregularly shaped necrotic leaf spots, and distortion of leaves and shoots. Management of this virus is dependent upon elimination of infected plants and control of western flower thrips, the vector of the disease.

Fusarium crown and stem rot causes a gradual loss of green coloration in leaves, followed by browning of leaf veins, and the eventual tanning of the entire leaf. Wilting, stem rot and rapid plant death occurs. Orange spore masses will appear at the base of the stem. The spore masses and the veinal browning are diagnostic for this disease. The fungus is spread by contaminated transplant trays and on pruning tools.

Root rots can be caused by several fungi, most notably Pythium and Rhizoctonia. (Rhizoctonia will cause a root and crown rot). Both fungi will cause leaves to turn yellow and wilt. Rhizoctonia will also cause a browning or discoloration at the stem base. When plants are extracted from the soil, root systems will be notably discolored and the outer covering (cortex) of the root will slough off. Root rots are common in overly moist soil with poor aeration and drainage. The pathogens are spread by splashing water, plant and soil debris.

Several fungicides are labeled for management of these diseases. However, before using the chemical make sure to clean up debris, make sure growing medium provides adequate aeration and drainage, improve air circulation and watch fertility and water amounts.

Fungicides labeled for disease management

No endorsement of products mentioned is intended nor is criticism implied of products not mentioned. As always, before using any pesticide, consult the label.

Laura Pottoff
Extension Pathology Agent
Jefferson County

News from the Lab

Plant Hormones

Now that you have been introduced to a few members of the Jones' lab I would like to begin a new series of small reports for the next few months. The subject of these reports was inspired by the recent ProGreen conference. While at ProGreen, in my class on how plants grow, I received a number of inquiries from people about plant hormones- what are they? and how can I find out more about them? After realizing that there really was no good reference that would cover the practical uses of plant hormones within the horticulture industry, I decided that this would be a good forum to provide some information on the subject. This month I would like to present some general information about plant hormones, and then in the subsequent months I will present the specific uses of plant hormones and their effects on plant growth and development.

What is a plant hormone?

Much research has been devoted to determining how plants grow. We know that plants require light, water, and nutrients for proper growth, but they also require internal chemical messengers called plant hormones. Plants are complex organisms and the development of a normal plant is a fairly complex process. Growth of the plant requires communication between different organs (roots, stems, and leaves) and even between individual cells within an organ. For example, if the roots are experiencing a water stress they can communicate this to the leaves and the plant will close the stomata to conserve water. Hormones control this process. Another characteristic of plants is that they are immobile, if environmental conditions change they can not move to a better location. Hormones allow the plant to alter patterns of growth in response to their environment. For example, when plants are grown in a windowsill they will tend to grow toward the light. This response is also controlled by plant hormones.

These substances are called plant hormones after their counterpart in animals, which are also chemical messengers. Plant hormones are synthesized by the plant and active at very low concentrations. These concentrations are much lower than the plants requirements for micronutrients for example. While the term plant hormone is often generalized to include all substances that show these types of activities in the plant, the term plant growth regulator is more common in the horticulture industry. Growth regulator is a term that the chemical industry has adopted to include man-made chemicals that have the same activity in plants as the hormones produced by the plant.

The most commonly recognized hormones fall into five classes: ethylene, gibberellins (GA), auxin, cytokinins, and abscisic acid (ABA). I will present more on the gaseous plant hormone ethylene next month.

Michelle L. Jones, Ph.D.
Assistant Professor of Floriculture
Horticulture and Landscape Architecture

To see more of the results, go to:

1999 Annual Poinsettia Evaluation

Steven E. Newman, Ph.D.
Greenhouse Crops Extension Specialist
Horticulture and Landscape Architecture