Tuesday, December 16, 2008

Become an ASHS Certified Horticulturist

Submitted on behalf of Dr. Karen Panter of the University of Wyoming

On February 18, 2009, be among the first in the country to take (and hopefully pass) the test to become a Certified Horticulturist! The national CH program is geared toward working, paid, professional horticulturists who may or may not have any formal horticultural education.

The goals of the program are simple:
  1. To promote horticultural industry standards and to provide a means to verify professional competence in the field of horticulture.
  2. To identify professionals who demonstrate an established level of knowledge, skills, and expertise in the field of horticulture and to provide prospective employers and members of the public with a means to identify qualified horticulturists.
  3. To provide horticulturists with the opportunity to validate their professional competency.
  4. To raise awareness and confidence in the field of horticulture and to acknowledge a commitment to the public and government to foster quality horticultural services.
  5. To enhance knowledge and skills in the profession through continuing education and recertification requirements.
How would this benefit you?
  1. It would advance the development of your own knowledge and skills in horticulture.
  2. It would provide others a basis to trust your own work and abilities.
  3. It would allow you, as a competent horticulturist, to distinguish yourself from others in the profession.
  4. It would afford the public and those in government and industry the opportunity to select your services and skills based on competence represented by certification designation.
  5. It would show you are a leader in the field of horticulture.
  6. It would give you an incentive to continue your ongoing professional development by initially gaining and then maintaining certification.
  7. Certification promotes you as a practitioner of best horticultural practices.
The program is national, meant to dovetail with local and state certification programs already in place. It is managed by the American Society for Horticultural Science (ASHS) and is being set up to meet the standards of the National Organization for Competency Assurance (NOCA). NOCA sets rigid standards for exam questions, exam proctors, protocol for offering and taking exams, and much more.

If you are interested, contact us at kpanter@uwyo.edu for further information. We will be offering the Certified Horticulturist exam at the Wyoming Groundskeepers and Growers Association conference in Casper in February – test date is February 18. Check the WGGA website (www.wgga.org) for further information on the conference and check the ASHS website (www.ashs.org) for info on the CH program and exam! You’ll be glad you did.

Karen L. Panter, Ph.D., C.P.H.
Plant Sciences - 3354
1000 East University Avenue
Laramie, WY 82071
phone 307-766-5117

Wednesday, December 10, 2008

Hobby Greenhouse Ventilation and Determing Solar Altitude

I recently had a communication from an extension colleague in Washington state who has a client that asked a question about ventilating a green house. The client wants to convert their back porch to a greenhouse using polycarbonate to enclose the structure. The greenhouse will be on the south side of the home. It will not get any direct sun in the summer from directly above. Some direct sun in the winter.

The question regarded what kind of ventilation would be needed. The client also wants to know the angle of the sun in the summer and winter for his latitude (about 49°N).

For venting a backporch to a greenhouse, there are many issues to consider. First, for winter ventilation one can use the greenhouse as a solar accumulator during daylight hours. To do this, install a small fan that will draw air from the greenhouse and direct it into the home. A bathroom fan may work for this application. Choose one of the more quite ones. To get the appropriate size, calcuate the greenhouse volume and calcuate your fan size (cfm) to equal about eight air exchanges per minute. For a 10-ft x 20-ft x 8-ft or 1,600 cu. ft. Then divide 1,600 cu. ft. by 7.5, which gives a resulting fan requirement of 213.33 cfm. Bathroom fans are typically rated between 50 and 150 cfm. So two mid-size fans would work in this example. Rembember to install a return air vent as well. Place the fans high to move the warm air from the greenhouse into the home and the return air vent near the floor to pull cooler air from the home.

For summer ventilation, it would be best to engineer some sort of venting mechanism near the peak. There are many different means to do this creatively. Otherwise, you could install a pair of exhaust fans near the peak of the greenhouse on either end. Plan on about one air exchange per minute in this instance, which will require a totoal of 1,600 cfm or 800 cfm per fan. You will then need to add ventilation openings allowing outside air to come into the greenhouse when the fans are in operation.

In order to determine the solar angle of the sun during the winter and summer, we first need to make some assumptions. For 49°N, or the U.S. and Canadian border and 120°W (your client appears to be in Washington) the solar attitude at 12:00 hr is 17.52° on 21 December and 64.43° on 21 June (winter and summer solstice, respectively). You can use a website to calcuate these values for any point on the globe by pointing your browser to:

The United States Navy Sun or Moon Altitude/Azimuth Table

When designing a lean-to style greenhouse for the southern exposure, it is wise to place a opaque surface overhead that will shade summer sun and the transparent surface should be perpendicular to the winter sun. The image below should better illustrate this concept.

Friday, November 21, 2008

Fertilizer Calculations: Proportioners

Liquid feed fertilizer programs used in greenhouse crop production allows a grower to manipulate plant nutrition conveniently. This is done by using different fertilizers containing equal ratios of nutrients and adjustment of specific fertilizer elements within a fertilization program. These ratios are calculated using the formulas discussed in the previous issue.

To apply soluble fertilizer to a crop in its final dilution, fertilizer injectors are used to introduce the fertilizer into the irrigation water. There are two major categories of injectors: proportional fertilizer injectors and positive displacement fertilizer pumps (non-proportioning types).

Proportional fertilizer injectors

There are three categories of proportional injectors based upon their principle of operation. They include: 1) pressure differential injectors, 2) water motor injectors, and 3) water meter injectors.

Differential pressure injection may be accomplished by a pressure differential such that the pressure of the point of injection is less than at the intake of concentrated fertilizer. Concentrated fertilizer is then pulled into the irrigation water. This is accomplished by connecting a hose to the vacuum side of the irrigation pump and placing the other end in the concentrated fertilizer solution. An adjustable valve in the hose or a series of valves are used of control the volume of concentrated fertilizer solution withdrawn. This is done to vary the fertilizer concentration without modifying the concentrate. The injected fertilizer concentration can inadvertently be altered by changes in pump speed and line pressure due to leaks, clogged nozzles, and faulty valves- If air is allowed to enter the stock fertilizer suction line, the system will probably have to be reprimed.

Venturi type proportioners are similar in principle to the system described above. As water flows through a constriction in the proportioner, the water speed increases and pressure decreases. A tub attached at the constriction facilitates movement of fertilizer from the concentrated solution into the irrigation water. The Siphon Mixer uses the venturi principle and has a dilution ratio of about 1:15 with inlet water pressure of 30 psi. Changes in inlet water pressure, flow rate, or any factor creating back pressure on the output side of the proportioner such as a constrictive nozzle or a kink in the hose, will alter the dilution ratio. Generally, 50 feet or less of hose is used although some line pressure drop is experienced regardless of hose length. The Siphon Mixer has a dilution capacity of one gallon of concentrate in five minutes.

Displacing concentrated fertilizer dilution into the irrigation water is another example of pressure differential injection. There is a bag inside a metal tank. As water fills the tank, the bag (containing fertilizer concentrate) collapses forcing fertilizer concentrate into the irrigation water. This type of injector contains few moving parts; however, inlet water pressure and flow rate does alter injection accuracy. Flow control valves are used to compensate for variations in inlet flow rate.

Water motor controlled injectors use water flow to operate a piston or diaphragm that injects or forces fertilizer into the irrigation water by positive displacement. As water flows through the injector, the water moves a cam to turn and push a piston back and forth. Consequently, oscillation of the piston varies with water flow.

Water meter controlled injectors use a water meter mechanism to determine the flow rate and water powered diaphragm pumps to inject the fertilizer.

Positive displacement fertilizer pumps displace a fixed amount of concentrated fertilizer each time fertilizer is forced into the irrigation water. A piston or piston and diaphragm is used to displace the fertilizer. Injectors of this type are usually driven electrically and should have a common electrical circuit with the irrigation water pump so the injector will stop when the irrigation pump is stopped.

When positive displacement injectors are use, a blend-tank may be needed in the water line immediately following the point of injection to ensure adequate mixing of water and fertilizer. This is especially true if the fertilizer passes thorough pipe lengths insufficient to adequately mix the fertilizer.

Injection Calculations

After selecting an injection system for proportioning concentrated fertilizer into irrigation water the amount of fertilizer to be dissolved into the concentrate must be calculated. Regardless of the type of proportioner or ratio, the first step of determining the amount of fertilizer is to determine the volume of irrigation water to be applied. To do this, note the proportioner rate given by the manufacturer. These values are given as a ratio, for instance 1:100. What this means is that for each 100 units of water, 1 unit of concentrate is mixed for a total volume of 100 units. Therefore, 50 units of concentrate will yield 5,000 units of fertilizer and irrigation water. Note that "units" can be changed to gallons, liters, quarts, or any other volume to suit your needs.

After the total volume has been calculated, all that is left to determine is the amount of fertilizer to mix a concentrated solution. Take the value 8.09 oz. ammonium nitrate / 100 gal. of water which yields 200 ppm N calculated in Part 1, and simply multiply by 5,000. This results in the value 404.5 oz. or 25.3 pounds of ammonium nitrate that must be dissolved in 50 gallons of water using a 1:100 proportioner.

When mixing concentrated fertilizer salts in water, remember to use hot water. As salt dissolves in water, an endothermic reaction occurs. This means that heat is removed and the water chills. This is the same reaction used to chill ice cream in a hand crank freezer. Therefore, if hot water is not used, the fertilizer concentrate may chill to a temperature too low for adequate blending.

Monday, November 10, 2008

Leaf Wetness Sensors

The Leaf Wetness Sensors were created by Spectrum Technologies, Inc. as a low-maintenance tool in IPM systems for disease prediction and spray scheduling of outdoor field-grown crops. The logger records values of simulated leaf moisture between 0 (dry) and 15 (wet) which are used in quantifying cumulative hour above some disease threshold. Our work evaluated this instrument in a commercial hydroponic tomato greenhouse for the purpose of disease prediction and humidity control at various levels within the crop canopy. Data indicate that the sensors may also be used to improve irrigation scheduling with regard to disease prevention.

Spectrum Technologies’ Leaf Wetness Data Logger and LogBook Software were used to record leaf wetness values over two 18 day periods. For the 18 day maximum interval, recordings are taken every 12 minutes. Relative humidity values and irrigation timings were recorded on the greenhouse’s Priva environmental control system. The sensor was stationed 1 meter above the floor within the crop canopy, at the same location for both monitoring periods.

Examining the figures below, it can be observed that spikes in the leaf wetness values are generally preceded by irrigation intervals (red columns), with some cumulative effects occurring during periods of frequent irrigation. The timing of irrigations is controlled by the Priva system according to maximum time intervals over four periods during each day, and to quantities of incoming light received following the previous irrigation. It may be assumed that by analyzing daily leaf wetness fluctuations during the different seasons, environmental control settings can be selected which will allow for more appropriate irrigation timings in regard to reduced leaf wetness and disease prevention.

Leaf wetness (columns), relative humidity (blue line), and irrigation time (red columns) measured mid-December

Leaf wetness (columns), relative humidity (blue line), and irrigation time (red columns) measured early February.

Tuesday, October 28, 2008

Disinfecting Irrigation Water for Disease Management

High quality water for agricultural use is becoming limited. Runoff and irrigation return flow from containerized nursery and greenhouse facilities may contain nitrogen, phosphorus, pathogens, certain pesticides, various salts, and trace metals. Traditional greenhouse irrigation practices recommend watering to 10% excess, with application scheduled just prior to incipient wilting. The use of trickle tube irrigation can reduce the volume of irrigation water consumed in a greenhouse.

Closed and subirrigation systems are widely used by European greenhouses to comply with government imposed regulations to limit environmental contamination from pesticides and fertilizers from greenhouses. Ebb and flood irrigation is one subirrigation system that is being adapted by U.S. growers to reduce fertilizer and water waste. Closed recirculating irrigation systems can reduce the consumption of water and fertilizer.

Plant disease can potentially be introduced through irrigation water. Fungicides are often considered to be the first line of defense and often applied to the substrate, but not the irrigation water. Therefore alternative disease control strategies or integrated pest management (IPM) should be employed when using recirculated irrigation water.

Many growers using recirculated irrigation water employ several water disinfection methods to prevent the spread of soil borne disease organisms, including UV-C radiation, heat treatment, chlorination, ozone, and activated hydrogen peroxide.

Ultraviolet Radiation of Irrigation Water

Ultraviolet (UV) light is electromagnetic radiation with wavelengths between 200 and 700 nm. Visible light is from about 400 to 700 nm. UV disinfection water systems use UV-C radiation at 254 nm. Microorganisms absorb most of the energy at this wavelength resulting in a germicidal effect. The photochemical reaction alters essential molecular components (DNA and RNA). This process essentially eliminates most fungi, bacteria and viruses.

Heat Pasteurization of Irrigation Water

Heat pasteurization of root zone substrates is a common practice, but not so for irrigation water. Yet in The Netherlands, heat pasteurization is the most common water treatment system. Typical recommendations for heat pasteurization of irrigation water require that the water or nutrient solution pass through a heat exchanger and heated to 203°F (95°C) for 30 seconds, yet viruses can be inactivated at 131°F (55°C) and 158°F (70°C) for 90 and five minutes, respectively.

Oxidation Reduction Disinfection of Irrigation Water: Chlorine, Ozone and Hydrogen Peroxide

Oxidation reduction reactions originally referred only to reactions that involved the reaction of oxygen with another element or compound and reduction was used to indicate the removal of oxygen from a compound. Common oxidizing compounds include chorine, bromine, ozone, sodium and calcium hypochlorite, hydrogen peroxide. Common industrial uses of oxidation-reduction include water disinfection, odor control, cyanide destruction, chrome reduction, and metal etching.

Chlorine is the most typical water sanitizing agent and its oxidation characteristics can best describe oxidation reduction chemistry. Chlorine activity is typically reported as free residual chlorine or total chlorine. Chlorine exists in water as HOCl (hypochlorous acid) or OCl- (hypochlorite).

Ozone is a form of oxygen O3) typically generated by a corona discharge system by passing dried, oxygen-containing gas through an electrical field. The electrical current splits the oxygen molecules (O2). The resulting oxygen atoms (O-), seek stability and will bond to other oxygen molecules (O2), forming ozone (O3). The ozone is then injected into irrigation water where it inactivates microorganisms by disrupting cell membranes through oxidation.

Hydrogen peroxide (H2O2) a strong oxidizer, but is not very stable. Hydrogen peroxide is water (H2O) with an extra oxygen molecule attached and is a natural compound found in trace amounts in rain and snow. One commercially available hydrogen peroxide formulation is currently labeled as a greenhouse pesticide/disinfectant. Hydrogen dioxide (ZeroTol) kills bacteria, fungus, algae and their spores immediately on contact.

For the complete article, click here.

Tuesday, October 21, 2008

Common Diseases in Commercial Floriculture Greenhouses

Diseases of greenhouse crops can be caused by pathogenic bacteria, fungi, viruses, and phytoplasmas. Many abiotic or non-infectious conditions mimic diseases or lead to plant disease. It is important to be able to distinguish between the two. If a disease is suspected and a pesticide is applied to remedy the situation caused by an abiotic stress, then undo expense, labor, risk has occurred.

Planning an integrated pest management (IPM) program for disease control includes sanitation techniques, monitoring techniques, and management strategies. Pesticides should only be used when monitoring reveals that they are required.

There are four basic forms of plant disease causal organisms that commonly infect greenhouse crops, fungi, bacteria, viruses, and phytoplasmas. Yet many microorganisms are beneficial. The occurrence of plant disease is a result of a complex interaction of a susceptible host plant, the presence of a pathogenic causal organism, and the environment.


Fungi are difficult to describe because they are organisms found differing in many forms, behaviors, and life cycles. These organisms are characterized by a chitinous cell wall and filamentous growth called hyphae, which forms mycelium.

Botrytis blight or gray mold will infect most greenhouse crops and is one of the most important pathogens of above ground plant parts typically caused by Botrytis cinerea. The symptoms include brown, water-soaked spots or decay on leaves or petals.

Often confused with powdery mildew, downy mildew almost always is found in patches on the underside of foliage as soft and fluffy gray, purplish, or light brown sporulation. It is sometimes found on stems or buds. Peronospora and Plasmopara species are the primary causal fungal agents on flowering greenhouse crops.

Powdery mildews are a group of fungi including the genera Erysiphe, Leveillula, and Sphaerotheca that produce gray or white powdery growth on leaves, Figure 4. Many species are host species specific. For instance, Sphaerotheca pannosa var. rosae only infects members of the Rosaceae family.

Powdery mildews are obligate parasites existing only on living tissue and do not require plant stress or injury to infect host plants. Warm greenhouse temperatures during the day and cool at night favor powdery mildew infection. Free water is not required for spore germination. Management of powdery mildews relies on early detection, sanitation, cultural practices, environmental control, and fungicides.
Soil-borne diseases include the species Pythium, Phytophthora, Rhizoctonia, and Thielaviopsis, which collectively include the majority of the fungi that infect roots and crowns of plants. Most greenhouse crops are susceptible to one or more of these causal organisms.

Damping-off is a term that generally refers to sudden plant death in the seedling stage due to the attack of soil-borne fungi. Pythium infection is more common in wet and poorly drained soils, Figure 5. It infects young plant tissues, typically root tips, and spreads into primary roots. It causes a soft dark brown to black wet rot that disintegrates root cortical tissues, which will sluff leaving only the vascular stele.

Rhizoctonia solani is the most common species to cause root rots of greenhouse plants. Rhizoctonia infection typically results in moist, brown lesions or cankers on crowns and roots.

Thielaviopsis basicola infected roots will become very black and thickened, hence the name black root rot. The lesions will be dry compared to those found with Rhizoctonia infection.

Bacterial diseases found that infect greenhouse plants are difficult to control other than through prevention, sanitation, and removal of infected plants. Disinfectants can be used to sanitize greenhouse tools, benches and pots to provide some protection.

Viruses can be defined as non-cellular organisms. These organisms consist of nucleic acids, RNA and DNA surrounded by protein, which obligately reproduce inside host cells using the host’s metabolic machinery and ribosomes. This reproductive process forms products called virions, which protect the virus and are transferred to other cells. Plant viruses are transmitted directly through sap by contact through plant wounds with contaminated tools, hands, or by animals, mainly aphids, leafhoppers and thrips, feeding on the plant. The virus then spreads systemically throughout the plant via the vascular system.

Phytoplasmas are considered to be specialized bacteria that are obligate plant parasites found in the phloem. Aster yellows is the most significant phytoplasmas that infects greenhouse plants and is vectored by leafhoppers.

For the complete article, click here.

Thursday, October 16, 2008

Insects, Mites and Other Invertebrate in Commercial Floriculture Greenhouses

Pest and disease damage on ornamental products is not tolerated by consumers requiring a sizeable investment in pesticide applications. These practices led to a total of 5.36 million pounds of active ingredients applied to nursery and floriculture crops in California, Florida, Michigan, Oregon, Pennsylvania, and Texas alone for the year 2000 (NASS, 2002). Of that total, 39% or 2.1 million pounds of active ingredient were applied to floriculture crops. Recognizing that these six states represent 55% of the national reported value of the nursery and floriculture industry (NASS 2003), one can project on a national scale, 9.75 million pounds of active ingredients, are applied to floriculture and nursery crops annually. Of that total, 3.8 million pounds of active ingredient are applied to floriculture crops. Understanding the investment that a greenhouse grower must consider when choosing a pest control strategy, proper pest identification is extremely important.


Aphids are small soft bodied insects that feed on plant sap through piercing and sucking mouthparts. The most common species in the greenhouse is the green peach aphid (Myzus persicae). Aphids feed in groups on stems and leaves, usually closely associated near phloem tissue along leaf veins. Some aphids transmit certain viruses that cause diseases in flowering crops. Aphids that feed on young leaves and buds will cause chlorotic pinpoints and distorted foliage. They also excrete honeydew, a sticky sugary sap. Honeydew if left unchecked will develop into a black sooty mold rendering ornamental plants unsalable.

Fungus Gnats, Shore Flies and Moth Flies

Fungus gnats, shore flies, and moth flies are often confused in that they are similar in appearance and appear under wet, over watered conditions. They are easily distinguished when they are at rest. A fungus gnat (Bradysia sp. and Sciara sp.), at rest holds its wings slightly spread when viewed from above. Shore flies (family Ephydridae, commonly Scatella stagnalis), are a bit more robust in appearance with bristle-like antennae, which are shorter than the head. Moth flies or drain flies (family Psychodidae), are grayish in color with many fine hairs.

Adult fungus gnats are commonly found on soil and other surfaces with standing water. They mostly feed on dead and decaying tissue being primarily a nuisance. The larvae typically feeds on soil fungi and decaying plant matter as well, but in high populations will attack roots and other soil-borne plant organs such as tubers and corms.

Shore flies typically feed on algae and not plant tissue. They do, however, appear under the same conditions as fungus gnats and are often confused. Adult shore flies are larger and more robust than fungus gnats. The adults are primarily a nuisance. Use the same cultural control strategies for shore flies as fungus gnats.

Moth flies also thrive under moist and over watered conditions. Excess fertility creating algal scum in and around drains and bench supports tend to attract drain flies. Moth flies have been reported to feed on plants, but little documentation is available. Like shore flies, moth flies are primarily a nuisance and cultural management is the best control.

Leaf miners

Moths and flies from several families have larvae that cause damage by tunneling through leaves. The serpentine leaf miner (Liriomyzia trifolii) and the chrysanthemum leaf miner (Pytomyza atricornis) are the two most prevalent species in the greenhouse. The adult female punctures the leaf using an ovipositor, inserting her eggs. The larvae hatch within the leaf and tunnel through the leaf for about two weeks. Afterwards, they drop from the leaf and pupate in the soil.


The citrus mealybug (Planococcus), is the most common mealybug found on greenhouse crops, but the longtailed mealybug (Pseudococcus longispinus) is also found as well. Adult females are grayish, soft-bodied, wingless insects that are elongated, segmented, and coated with a whitish cottony wax. It is the wax coating that protects the mealybug making contact insecticides less effective. Contact sprays are most effective at the first instar nymphal stage. Surfactants can improve insecticide penetration through the waxy protection.


Mites are arachnids and not insects. Arachnids include tics and spiders. They do not have segmented bodies, wings, or antennae. Mites common to the greenhouse include the spider mites and red mites [carmine mite (Tetranychus cinnabarinus), privet mite (Brevipalpus obovatus), and two spotted mite (Tetranychus urticae)] tarsonmed mites [broad mite (Polyphagotarsonemus latus), cyclamen mite (Phytonemus pallidus), and bulb scale mite (Steneotarsonmemus laticeps)], bulb mites (Rhizoglyphus spp.), and bud mites [carnation bud mite (Aceria paradianthi)]. Of these mites listed, the two spotted mite is probably the most common; however, others are becoming more prevalent with crop diversity.

Scale insects

There are many genera of scale insects common to greenhouse crops, all from the order Homoptera. They feed on plant tissue by piercing plant tissue and sucking sap. They also inject toxins that stunt growth as well as spot and streak the foliage. Some species produce honeydew much as aphids, mealybugs, and whiteflies.

There are two groups of scale common to the greenhouse, armored and soft. Armored scale (family Diaspididae) has a plate like covering that protects the soft insect body underneath. Armored scales do not secrete honeydew. The surface of soft scales (family Coccidae) is smooth and brown. Soft scales are typically larger than armored scales.

Slugs and snails

Slugs and snails are not insects, but mollusks. Slugs are differentiated from snails in that they lack a shell. Slugs and snails feed at night and during daylight, they hide in cracks and crevices on the bench, beneath pots, or in plant litter on the ground. They prefer dark and moist hiding places. Slugs and snails are most active when the conditions are cool and moist.


Thrips (order Thysanoptera) commonly attack many greenhouse crops. The western flower thrips (Frankliniella occidentalis) is the most serious thrips problem in greenhouses. Thrips damage is often not apparent until sometime after feeding. They feed on flowers, buds, terminals, bulbs, and corms. Thrips hide deep in these tissues and the damage is not visible until after the tissue elongates.

Adult and larval stages of thrips feed on plant tissue by puncturing cells and feeding on the oozing sap. The tissue, as it grows, becomes silvery, stippled, blotched, streaked, or deformed. Western flower thrips also feed on pollen and some mites.


Whiteflies are in the order Homoptera and are not true flies, which is the order Diptera. The primary whiteflies that infest greenhouse plants are the greenhouse whitefly (Trialeurodes vaporariorum), and the silverleaf whitefly (Bemesia argentifolii).

Whitefly nymphs and adults feed on plants with piercing and sucking mouth parts and are associated with phloem tissue. Whitefly feeding can stunt plant growth and kill young plants. Whiteflies produce honeydew much as aphids, mealybugs, and scale.

For the complete article, click here.

Tuesday, October 14, 2008

Integrated Pest Management in Greenhouses

Consumers of greenhouse grown floriculture crops maintain high standards of quality. Pest and disease damage on floral products is not tolerated by consumers, which often requires a sizeable investment in pesticide applications. To maintain profitability, greenhouse growers are relying on softer, more environmentally friendly pesticides, integrated pest management, and beneficial organisms to manage pests and diseases.

The United States Environmental Protection Agency (EPA) defines integrated pest management (IPM) as an effective and environmentally sensitive approach to pest management that relies on a combination of common-sense practices. EPA outlines a generic four-tiered approach to IPM. These four steps include setting action thresholds, monitoring and identifying pests accurately, and prevention.

Expanded IPM in a greenhouse includes pest prevention, sanitation and exclusion, management of the greenhouse environment, monitoring the greenhouse crop, mechanical control, environmental control, cultural control, biological control, and chemical control.

Pest Prevention

Pest prevention in the greenhouse includes advanced planning of the crop to be grown and IPM programs, the practice of good sanitation and pest exclusion methods, the proper management of the greenhouse environment and other cultural practices, and the monitoring or scouting, which refers to regular, systematic inspection of crops and growing areas.


Sanitation involves clean practices in the greenhouse. Clean practices include eliminating weed infestations inside and outside the greenhouse. Weedy plants under the bench or around the perimeter of the greenhouse may harbor pests and diseases.


Exclusion methods include screening of vents doorways and other openings, inspection of newly introduced plants or plant shipments, the use of pest-free stock, controlling weeds, removal of crop debris, prompt removal of infested plants or plant parts, and maintaining the growing area as pest-free as possible.

Management of the Environment

Management of the greenhouse environment includes preventing plant stress. Plants under stress are predisposed to pest infestations.

Monitoring Crops

Monitoring the greenhouse crops is a strategy to detect any pest or disease outbreaks early and at a time when they are easy to manage. Many refer to monitoring as scouting. Scouting is the regular, systematic inspection of crops and growing areas.

Mechanical Control

Mechanical pest control in a greenhouse implies the use of labor and equipment to reduce pest populations directly. Mechanical control may be as simple as removing infested plants.

Cultural Control

Cultural control measures to prevent pest outbreaks include choosing crop species or cultivars that are less susceptible to infestations than others, rotation of crops from susceptible to not susceptible, altering planting times, and adjusting the duration and frequency of irrigation intervals.

Beneficial Organisms

Beneficial organisms can be used in a greenhouse to reduce pest populations. Biological control methods to be effective must be integrated with other methods, such as exclusion and sanitation.

Chemical Control

Chemical control implies the use of a pesticide. The United States Environmental Protection Agency defines a pesticide as any substance or mixture of substances intended for preventing, destroying, repelling, or mitigating any pest.

For the complete article, click here.

Friday, October 10, 2008

Fertilizer Calculations: Understanding Parts per Million

While teaching greenhouse and nursery management classes, I have found that students often have the most trouble learning how to calculate fertilizer and plant growth regulator ratios. All of these are typically based on parts per million or ppm. Most fertilizer bags and PGR labels have all the calculations printed on them, but often a refresher on the calculations is in order.

Parts Per Million

The use of liquid feed fertilization programs in greenhouse and greenhouse crop production is the standard of our industry. Many growers use either a constant feed program fertilizing with each irrigation, while others use a pulse feed program fertilizing on a regular periodic schedule. The program selected is determined by crop requirements, available equipment, and personal preference. The most important concern, no matter which program is used, is accuracy in calculation of fertilizer concentrations.

Crop nutrition requirements and most published fertilizer schedules use the terminology "parts per million" or ppm. There are fertilizer tables provided by most fertilizer producers for easier reference. With a little knowledge, a calculator, and patience, the tables are not necessary.

Many growers are familiar with the Quick "75" Method for calculating ppm. To calculate the amount of fertilizer required, divide the desired ppm by 75 and then divide by the decimal fraction of the desired nutrient (such as nitrogen, potassium or phosphorous) contained in the fertilizer. This results in the number of ounces of fertilizer to use in 100 gallons of water.

To use this equation, assume that the fertilizer recommendation calls for 200 ]ppm of nitrogen from ammonium nitrate (33% N)-Using the above equation, divide 200 ppm by 75 resulting in 2.67,and then divide by 0.33. The answer is 8.09 ounces of ammonium nitrate which dissolved in 100 gallons of water will yield 200 ppm nitrogen.

Confused? Some examples of what one part per million represents under various conditions are: 1 crystal of salt in 5 lbs., 1 drop in 16 gallons, 1 inch in 158 miles, 1 minute in 1.9 years, 1 pound in 500 tons, and 1 cent in $10,000. Therefore, to calculate ppm in 100 gallons of water, first multiply 100 gallons by 8.34 pounds per gallon which equals 834 pounds. Multiply 834 pounds by 16 ounces per pound which equals 13,344 ounces per 100 gallons. Therefore, 13,344 ounces per 13,344,000,000 ounces equals 1 part per million, or more simply 0.013344 ounces per 100 gallons of water equals 1 PPM.

  1. 100 gal. * 8.34 lbs./gal. = 834 lbs.

  2. 834 lbs. * 16 oz/lb. = 13,344 oz.

  3. 3,344 oz/100 gal.

  4. 13,344 oz./13,344,000,000 oz. = 1 PPM

  5. 0.013344 oz./100 gal. = 1 PPM

The next step is to multiply the desired PPM by 0.013344, which is 74.94. By rounding 74.94 to 75, it must by understood that the result will not be entirely nor mathematically accurate, but perhaps is close enough for practical purposes. Within the units of the ratios commonly used in fertilizer solution, the error will be 0.02 or less per 100 gallons.

For those who can think in metric terms, there is an easier way to calculate PPM By definition, 1 milliliter (ml) of water weighs 1 gram (g), therefore 1 liter (1000 ml) weighs 1000 g. Thus 1 liter (L) of water weighs 1,000,000 milligrams (mg). This tells us that 1 PPM equals 1 mg/1,000,000 mg of water or 1 mg/L of water. To calculate PPM in liters, simply multiply the desired PPM by 1 and divide by fraction of the fertilizer. This results in the number of mg of fertilizer to use in 1 L of water.

To illustrate this equation, use the same fertilizer recommendation as before, 200 PPM N from ammonium nitrate (33%N). Substituting in the above equation, multiply 200 by 1 resulting in 200, and then divide by 0.33. The answer is 606 mg of ammonium nitrate, which dissolved in 1 L of water will yield 200 PPM nitrogen.

To increase this to irrigation volumes, multiply this result by the required volume. Multiply 606 mg by 380 L (100 gal) which equals 230,280 mg or 0.507 pounds (8.12 oz).

Wednesday, October 08, 2008

Time to Check Your Heating Systems

In Colorado, it has been a beautiful indian summer, yet blowing snow and sub-freezing temperatures are just around the corner. It is time to make sure that your heating systems are ready to function efficiently.

Greenhouse growers who use boiler systems typically have had all their annual inspections and have completed their annual maintenance, but growers who rely on gas fired unit heaters are often not quite so conscience of the conditions of their heaters. It is way past time to inspect your heaters. Regular maintenance will easily pay for itself this season with high gas prices predicted.

Inspect the flue pipe. Wind is responsible for most damage to flue pipes, however, one can always expect some degradation of the joints in the greenhouse. Check for rusting unions and for any debris that may have collected in the flu pipe. If the flue pipe has an exhaust fan to move exhaust gasses through the flue, make sure that it is operating properly.

Inspect the heat coils. Greenhouses are humid environments and metal equipment is subject to rust. If the heat coils are rusted through, exhaust gasses can contaminate the greenhouse environment.

Inspect the gas manifold. Dirty gas orifices will cause incomplete combustion of the fuel, which will result in exhaust gasses that will contaminate the greenhouse environment.

Check the ignition modules and gas valves. These devices do wear out and require periodic service. These devices should be inspected and serviced by a licensed technician. Inefficient operation of gas fired unit heaters can lead to a lot of problems in the greenhouse. Primarily we think of carbon monoxide, which is deadly to the staff, but one must also think about ethylene gas as well.

Ethylene levels as low as 20 ppb (that is parts per billion) have been shown to damage Cattleya species and 500 ppb are sufficient to cause flower abortion in tomatoes. Concentrations of 50 ppb for extended periods (how long? two to four hours) are just as deleterious as high concentrations.

There has been some interest in using carbon monoxide (CO) detectors for estimating ethylene in a greenhouse. In Holland they have studied these detectors. They conclude that the ethylene level would be less than 0.1 of the critical 50 ppb if the CO content of the undiluted flu gasses did not exceed 50 ppm. The presence of CO, however, does not guarantee the presence of ethylene and vice versa. But they are cheap. Some growers use tomato plants underneath their unit heaters and if the leaves exhibit epinasty, they assume that there is ethylene contamination. Tomato plants are typically more sensitive than other floriculture crops to ethylene. (you can read more in Dr. J.J. Hanan's text, Greenhouses: Advanced Technology for Protected Horticulture)

Prevention is the key to ethylene gas control in the greenhouse. Maintain your gas-fired heaters in good condition. Clean the manifolds regularly and check for cracks in the heat exchangers. Flue pipes must be clean and free of debris. They must also have the correct clearance over the building if they are not connected to a forced air exhaust system. IR-radiant heat systems are not immune to ethylene contamination. Mount the exhaust fans as close to the end of the flue as possible to prevent any back pressure from a prevailing wind. Finally, make sure that your gas supply is adequate for the unit heater and that you are supplying adequate oxygen for combustion.

If you suspect that you have an ethylene gas problem, contact the Floriculture faculty at North Carolina State University for testing.

Tuesday, October 07, 2008

Greenhouse fuel economy during tough times

Heating greenhouses this next winter will remind many growers of fuel costs during the 1970s during the Arab Oil Embargo. I have found reports from the Department of Energy that forcast the price of natural gas to be at $12.31 per dekatherm. If we have a cold winter, there may be gas shortages. During September, Hurricanes Gustav and Ike shut down 32 million barrels of crude oil and 165 billion cubic feet (Bcf) of natural gas production in the Federal Gulf of Mexico. Recovery is ongoing and expected to continue at least through October.

According to the National Oceanic Atmospheric Administration’s (NOAA) most recent projection of heating degree-days, the Lower-48 States are forecast to be 2.4 percent colder this winter compared with last winter, but 1.7 percent warmer than the 30-year average (1971 to 2000). However, regional heating degree-day projections vary widely; for example, the West North Central region is projected to be almost 5 percent warmer than last winter.

What is the greenhouse owner/manager to do? Many buy gas on the open market as a coopertive to lock in prices. Others negotiate directly with their gas provider. Rregardless of what fuel you use and your fuel prices, we still need to make cropping decisions. Do we grow Easter lilies or just grow spring bedding plnats. Do we put in quick turn crop of cut flowers for Easter or do we start our own plugs and cuttings. These are just a few decisions a grower must make.

To ease some of these decisions and relate them to fuel, Jonathan FrantzUSDA-ARS@utoledo.edu of the USDA-ARS in Toldeo, Ohio has put together a modeling system that you can access help you make your decisions. Below is a discription of the product from the USDA-ARS website.

Virtual Grower is a decision support tool for greenhouse growers. Users can build a greenhouse with a variety of materials for roofs and sidewalls, design the greenhouse style, schedule temperature set points throughout the year, and predict heating costs for over 230 sites within the US. Different heating and scheduling scenarios can be predicted with few inputs.

You can download the current version of Virtual Grower at: http://www.ars.usda.gov/services/software/download.htm?softwareid=108

Monday, October 06, 2008

The Commercial Greenhouse, 3E

Finally, after more than two years of work, the third edition of The Commercial Greenhouse, 3E has been released. I was honored to have been asked to provide the updates of Dr. James Boodley's classic textbook on greenhouse production. I have included many new photographs and updated the material where relevant. If you liked the first two editions, the third is a must. Here is what the editors say:

The Commercial Greenhouse, third edition, is a complete reference for the modern commercial greenhouse grower, educator, and student. The book is a complete reference on greenhouse systems and technologies and the science of growing crops. The third edition is supplemented by new color photographs that provide modern images of greenhouse production, as well as updated information on pesticides, including updates on soil sterilants, and a new section on integrated pest management, that provides tangible guidelines for greenhouse operations. The clear and concise presentation of fundamental concepts in The Commercial Greenhouse, third edition makes this text a must for every greenhouse professional's shelf.

You can find it online at any of your favorite booksellers. Look for ISBN-13: 978-1-4180-3079-7 .