Virus problems can occur year-round in greenhouses. The variety of symptoms caused by impatiens necrotic spot virus (INSV) never ceases to amaze me. Symptoms may include ringspots, necrotic leaf spots, blacking on stems and distorted or puckered foliage . Symptoms vary greatly depending on the host plant. Plants recently testing positive for INSV include gloxinia, coleus and impatiens.
Last, but not least, don’t forget Thielaviopsis. The first Thielaviopsis of the season arrived in the lab this week on calibrachoa. This pathogen is seen every year on both annual and perennial ornamentals. Common hosts include petunia, pansy, calibrachoa and fuchsia; this pathogen can also cause disease on a wide range of greenhouse grown perennials. Symptoms include yellowing, wilting and general lack of vigor. These symptoms are easily mistaken for a nutrient deficiency, however plants do not respond to increased fertility. |
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Dave Smitley, Entomology
March 27, 2008 -- Late March and April is the time that populations of thrips in greenhouses really start to explode. A combination of three factors is responsible for this. First, warmer temperatures and longer days give overwintering thrips the green light to reproduce. Second, an ample supply of pollen and warmer temperatures allow thrips to reproduce faster. Finally and most important, the low number of thrips present in greenhouse crops since February have now completed a second generation, turning 100 thrips into 30,000 thrips. This always comes as an unwelcome surprise in late April. The best way to avoid problems with thrips is to watch the scouting reports carefully and begin your thrips management program when thrips numbers begin to increase on yellow sticky cards.
When the number of thrips per yellow sticky card increases beyond your tolerance level (for most growers the threshold is from 10 to 100 per card), spray the infested greenhouse sections with one of the following products every five days for four applications. Conventional sprayers usually give better results than foggers. Obtaining good coverage of stems and the undersides of leaves improves control. High spray pressure and good air movement usually result in the best coverage.
Choose from the following list of products for thrips control. Using a product from a different chemical class every six weeks may help slow the development of thrips resistance. However, mixing different products together, or spraying different products in the same month will not slow the development of resistance. Chemical classes are shown in parentheses after each product name. For a description of the chemical classes see the new wall chart ‘Insect Controls for the Greenhouse Industry, MSU Extension Bulletin E-2696.
Avid (6), Mesurol (1), Orthene 97 (1), Pedestal (15), Pylon (13), Safari (4a) Sanmite (21), Tristar (4a), and Conserve (5).
Note: some thrips populations may be resistant to Conserve. |
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Erik Runkle
Horticulture
March 24, 2008 -- Grants and loans are once again available for greenhouse growers and other agricultural industries to support investments in energy-efficiency improvements and renewable energy. Last week, the USDA Rural Development Office announced that $220.9 million is available to agricultural producers and rural small businesses. Application deadlines are April 15 and June 16.
The Renewable Energy and Energy Efficiency loan and grant program was established to encourage agricultural businesses located in rural areas to create or install renewable energy systems and energy efficiency improvements. Eligible projects include, but are not limited to, investments in anaerobic digesters, biomass boilers and burners, solar collectors, wind energy, and energy efficiency improvements. Examples of energy efficiency projects include the installation of more energy-efficient motors, pumps, fans, ventilation systems, insulation, and heating and lighting systems.
Loans are available to cover up to 50 percent of a project’s cost, not to exceed $10 million. Grants are available for up to 25 percent of a project’s cost, not to exceed $250,000 for energy efficiency improvements and $500,000 for renewable energy systems.
Two separate grant competitions are available. For the first competitive window, grant-only applications must be submitted no later than April 15. For the second competitive window, grant-only applications must be submitted between April 16 and June 16. Applications for loan guarantees and loan/grant combinations must be submitted by June 16.
Last year, eight Michigan farmers and rural small businesses received over $2.3 million in Renewable Energy & Energy Efficiency Improvement grants or guaranteed loans under this program. Successful greenhouse business recipients included Neal Mast & Son Greenhouses, Inc. in Grand Rapids for a greenhouse energy curtain and Wenke Greenhouses, Inc. in Kalamazoo for greenhouse energy-efficient boilers.
For more information in Michigan, contact Rick Vanderbeek at (517) 324-5157 in East Lansing, Paula Gromak at (989) 673-8173, ext. 120 in Caro, or Lori Krause at (906) 428-1060, ext. 112 in the Upper Peninsula. In addition, visit the Energy Grants and Loans webpage on the MSU Floriculture AoE Team’s website for additional updated information. You may also wish to visit the USDA Rural Development website for more details. |
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Carolyn Randall, Coordinator Pesticide Safety Education Program
March 24, 2008 -- The long-awaited, newly revised and rewritten pesticide applicator core certification manuals will be available for sale through the MSUE Bulletin office and through county Extension offices by April 1. These manuals are currently being printed and delivery is expected by the end of March. Unlike the old core manual, which combined the private and commercial certification information into one, the new manuals will be sold separately. The new bulletin number for the private core manual is E3007. The new bulletin number for the commercial core manual is E3008. Both will be sold at a retail cost of $30. They both consist of a Michigan-specific addendum shrink-wrapped with the National Pesticide Applicator Certification Core Manual.
The Michigan Department of Agriculture has established a cut-off date of August 1, 2008 for taking the old core exam. In the interim, applicants will be given the choice of taking the old core exam or the new core exam depending on which manual they studied. |
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Steven Gower and Jan Byrne, MSU Diagnostic Services
March 4, 2008 -- Our plant diagnostic laboratory routinely inspects plants to determine the specific reason(s) of poor or improper growth. As diagnosticians, we logically and rationally rule out potential causal agents and hopefully come to a confident, definitive conclusion as to the reason of plant decline. Is the problem associated with plant pathogens, insect pests, parasitic nematodes, pesticides, inadequate nutrition, environmental constrains, poor site location or a host of other factors?
Two of the first things we attempt to rule out on every sample are problems related to plant diseases and insect pests. Once biotic factors are excluded, we then consider the many abiotic, non-living factors that could be at play. To help in this endeavor, we generally test the growth media for pH and soluble salt content. These two readings are simple, quick and can be very revealing as to the reason for poor growth.
Most plants have an optimal pH range in which they perform best. Some plants may prefer slightly acidic media while other plants can tolerate a much lower or higher pH. The pH of the media influences the uptake and availability of all nutrients. Growing greenhouse plants in media with a pH lower than the optimal range can result in poor uptake of macronutrients and increased uptake of some micronutrients (e.g. iron toxicity). On the flipside, micronutrient deficiencies generally occur on plants growing in media with a pH higher than the optimal range (e.g., iron or manganese deficiencies).
The soluble salt content of the media and irrigation water should be tested frequently throughout the growing process. All soluble nutrients, such as nitrate, ammonium, potassium, calcium, magnesium, chloride, sodium and sulfate, contribute to the soluble salt content of the media. A soluble salts test will alert growers if the salt level starts to creep upward and can also provide an indication of the nutrient status available for plant uptake.
Greenhouse plants vary in their tolerance to salt levels and this tolerance is often dependent upon the growth stage of the plant. Excessive soluble salts can result in reduced growth and loss of vigor, root death, chlorosis and necrosis of leaves, wilting and marginal leaf burn. Excessive soluble salts are generally a result of too much fertilizer present in the soil solution in relation to the plant’s needs. High salts may occur from miscalculation of fertilizer dilutions, poorly calibrated or malfunctioning fertilizer injectors or over-application of fertilizers. Other causes of excessive salt buildup may be inadequate leaching and poor drainage. Excessive soluble salts may be reduced in the media by leaching several times with clear water.
Total soluble salt content is determined with a solu-bridge conductivity meter and is expressed as millisiemen (mS) or millimho (mmho). Millisiemen is the preferred unit for expressing soluble salt measurements. Regardless of the unit, the value is the same. Growers often determine soluble salt content by using one part media to two parts distilled water, allowing the solution to sit idle for up to one hour before taking a reading. Many testing labs determine soluble salt content on the saturation extract. Guidelines for interpreting soluble salt levels in growth media are listed in Table 1.
We recently received a Dianthus plug sheet with stunted plants with very poor root development near the middle of the sheet compared with very healthy and well-rooted plugs along the edges (view pictures). There were no signs of plant pathogens or insect-related problems.
Because there appeared to be a pattern of injury, both pH and soluble salt content was recorded from two areas of the tray. One sample was taken along the edge of the sheet – the other from the center of the sheet. While pH did not differ across the plug sheet, the plugs near the middle of the sheet contained a soluble salt content of 2.1 mS/cm compared with 0.8 mS/cm along the edges (1 part media: 2 parts water). This constituted approximately 2.5 times the soluble salts content and severe salt injury on Dianthus plugs would be expected at this level.
The jury is still out on this sample. Are the salt levels high in the middle of the Dianthus plug sheet because some other abiotic factor inhibited growth and therefore water and nutrient uptake? Or was salt toxicity an issue from the start? We are leaning towards the later – a salt toxicity problem soon after seeding which delayed germination, emergence and plant development. However, we cannot definitively determine which problem occurred first. |
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| One healthy Dianthus seedling (left) versus two injured seedlings (right). |
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| Pattern of injury in a Dianthus plug sheet. |
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| * Warncke, Darryl D. and Dean M. Krauskopf. 1983. Greenhouse growth media: testing and nutrition guidelines. Bulletin E-1736. East Lansing, Mich.: Michigan State University Extension. |
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Christmas trees
