by George Looby, DVM
The historic Publick House located on the Sturbridge town green in Sturbridge, MA was the site of the Greenhouse Management and Production Meeting for 2017 presented by the UMass Extension Service. Tina Smith acted a moderator for the event which began with a presentation by Dr. Ryan Dickson from the University of New Hampshire. Dickson reviewed how light, temperature, and relative humidity affect plant growth in greenhouses.
Managing light is critical to maximize plant growth through photosynthesis, with most crops being light saturated at 4,000 ft. candles. Another unit of measure used in determining total light coming into a greenhouse is DLI (daily light integral). There are instruments available that can measure the total light coming into a structure to aid the operator in adjusting the amount of light coming in. Among the aids that can adjust the level of lighting are retractable shade curtains and the use of whitewash in the interior of the greenhouse.
Plants react differently to the hours of daylight they are exposed to, thus plants may be classified as long day plants or short day plants. When plants are exposed to high light and longer days the crop time is shortened. Plants also respond differently to different colored lights — an example of which might be that blue lights tend to produce a more compact plant while red lights favor the development of leaves and stems.
Although it may seem like a small item, hanging baskets can pose a real problem in light control and management. Given the number of baskets found hanging in many greenhouses it is easy to see how they can interfere with the amount of light reaching the beds below.
The average daily temperature (ADT) must be monitored and an attempt made to maintain it at 68-75 degrees, the temperature range favored by most plants. Another measure is the DIF, the difference in the day and nighttime temperatures. As an example, an increase in the root zone temperature in pansies shortens the time to the flowering phase.
There is a factor called base temperature — the temperature at which crops stop growing — and plants vary considerably in their base temperature. Cold tolerant plants, when grown in conditions that are too warm, tend to stretch out. In managing greenhouse temperatures, the lower the humidity the easier it becomes to maintain an optimal temperature.
The combination of high temperatures and humidity favor the development of some diseases, especially fungi, and in addition it may interfere with the uptake and transpiration of calcium.
Dr. Mandy Bayer, UMass Extension, talked about greenhouse irrigation with its many manifestations. Consider all of the plant factors where water is involved — transpiration, metabolic activity, growing media, fertilizer, salt build up and many more. Growing media holds water and assists in anchoring the plant with the size and distribution of the particles, making the media of considerable importance. Large particle size favors drainage while small particle size favors water retention.
Irrigation is an essential part of greenhouse management and can be accomplished in several ways. Manually watering the crops is labor intensive and can be wasteful and uneven, where some areas get too much and others too little. On the positive side, the investment in equipment is minimal. Automated equipment comes at a price but it has the advantages of being labor efficient, reducing human error, and can be programmed to recycle water. Deep lines have the advantage of allowing the foliage to remain dry with good volume control.
The subject of greenhouse plant nutrition was discussed by Dr. Rosa Raudales from UConn. Any evaluation of greenhouse nutrition should start with an analysis of the water used in the operation. Particular attention should be paid to water quality — alkalinity, electrical conductivity (EC), specific ions, and pH evaluated. Alkalinity can be considered to be dissolved limestone in its mode of action. EC is a measurement of the ability of a solution to move electrical charge. When considering pH, elements react differently in the way they respond to different levels of pH. Some plants grow best when the pH of the media is in the range of 5.4 to 6.0 while others do best when the range is 6.0 to 6.6. The same may be said for EC — some do best when it is high while others do better when it is low.
Controlled released fertilizers are mainly used to finish off a given crop prior to its being offered for sale. In summary, Dr. Raudales offered these words; Check water quality, match fertilizer to crop needs and water quality, trust no one! Test new batches of growing media, monitor pH and EC of the growing media and switch temporarily to an acid or basic fertilizer.
With neonicotinoids falling into disfavor, a variety of control measures are now being advocated to take their place. To discuss alternative control measures Kerri Stafford of Cavicchio Greenhouses and Amanda Gioacchini of Pioneer Greenhouses were invited to discuss how they are approaching the change. Kerri is employing biological controls to control thrips. Two of the products she has employed are Amblyseius sp. and Orius sp. For the control of aphids she has used a species of parasitic wasp. Other pests that she deals with have also been controlled using biological means.
Amanda stressed the importance of good sanitation employing an automatic table washer for the tables and an uptake spray on pathways and gutters. Scouting and excellent record keeping are critical to any good control program. Hanging barley plants are used for aphids reproduction, and the introduction of control measures, Amblyseius sp., are used for mite control.
In the rapidly changing world of disease and pest control, both of these operations are poised at the very edge of what is new and current. Much of what was presented at this meeting is very detailed and the prizes will go to those who invest their time and talent into incorporating this material into their own operations.
Greenhouse management and production for 2017
by George Looby, DVM