Photos by John W. Bartok

Low-cost growing structures are used by many growers for short-term production space or winter plant protection. These are not usually heated, but sometimes minimal heat is needed to keep the temperature above freezing.

The amount of heat needed can be approximated by the formula HL = A x U x T where:

HL = Heat loss (Btu/hr)

A = Surface area of structure (sq ft), U = U-value - heat loss factor (Btu/hr – sq ft-°F) – Use 1.25 for single layer glazing, 0.8 for double layer, or 0.7 for double wall polycarbonate.

T = temperature difference between inside and outside (°F) on the coldest night.

The following discusses some of the options that growers must provide heat.

Hot air systems – As compared to water systems, air heating systems have the advantage of being low cost and easy to shut down when heat is no longer needed. Most have a blower that provides some heat distribution. Installing horizontal air flow (HAF) or perforated poly ducting can increase the uniformity of the heat in longer structures. A disadvantage to heated air systems is that very little heat gets down to the root zone in plants placed on the floor.

Vented equipment should be selected to exhaust flue gases that may contain sulfur or ethylene. Because these heaters will have limited use, look for used equipment.

Unit heaters – These are available in many sizes to accommodate most protected areas. They are usually supported from the hoops or from a frame that gets them above the plants. The fuel source can be natural gas, propane or fuel oil. High efficiency condensing gas heaters (93 percent) are available but these may have problems with the condensate freezing in cold weather unless they are drained.

Floor furnaces – These furnaces are available in sizes from 50,000 to 500,000 Btu/hr that can be fired with fossil fuels. A model with a blower instead of a fan that is attached to perforated poly ducting works well for under bench heat.

Hot water systems – There are more options with water systems. The advantages include better distribution of heat with the resulting more uniform temperature. The disadvantages include generally more expensive equipment and the system may have to be drained or blown out if it is shut down during freezing weather. Root zone heat – Locating the distribution system on benches, on the floor or buried underground will provide heat throughout the whole plant area. Heat sources can be low-cost domestic water heaters, in-line instantaneous water heaters or high efficiency condensing boilers. An additional heat source may be needed on very cold nights as there is limited heat from the root zone. Storing the excess heat from a greenhouse heating system in an insulated heat storage tank during the day and then using this heated water at night may make an economical system.

A biomass fired outdoor boiler could also provide hot water. A disadvantage is that it requires recharging late in the evening and early in the morning on cold nights. Distribution of heat could be low-output fin radiation, PEX or virgin black poly tubing or an EPDM tubing heat mat.

Heat exchangers – Water to air heat exchangers, available in many outputs, can provide heat distribution if you have a good supply of hot water. They are inexpensive as compared to fossil fired unit heaters. Location is important to get good heat distribution in low or narrow structures. Installing HAF fans can help to distribute the heat.

Low output aluminum fin radiation – This may be a good choice in cold frames or overwintering houses where a limited amount of heat is needed. Depending on the style, these have an output of 50 to 150 Btu/linear foot at 150-degree water temperature. They need to be installed so that they can be drained or blown out if the system is shut down during cold weather.

Temperature control for this heating equipment should be accurate electronic thermostats located in the center of the growing area. If freezing temperature is the main concern, locate the thermostat just above plant height. Be sure that the structure is tight to reduce cold infiltration air. Place some max-min thermometers in the growing area to monitor temperature extremes.

John is an agricultural engineer, an emeritus extension professor at the University of Connecticut and a regular contributor to Greenhouse Management. He is an author, consultant and certified technical service provider doing greenhouse energy audits for USDA grant programs in New England. jbartok@rcn.com

Over the past few years, the gutter height on new greenhouses has been increasing. Greenhouses built during the energy crisis of the 1970s usually had an 8-foot height to conserve energy. Today for various reasons, 12 feet is minimum and 16 feet is the standard with some houses being built with gutters more than 20 feet. What are the advantages of going taller? The following comments may help you decide.

Greater air volume means slower temperature change. Increasing the height from 12 feet to 16 feet increases the volume by more than 20 percent. The larger volume takes a longer time to heat up or cool down.

Natural ventilation is more effective. Natural ventilation systems operate on the principle that heat is removed by a pressure difference created by wind and temperature gradients. The ridge of a taller house receives more wind currents creating a better draft. Buoyancy is the other component. Cool air near the floor becomes lighter as it is heated and rises toward the roof. The greater distance between the floor and the roof vent, the greater the temperature difference.

Light reaching the plants is more uniform. It may not be obvious but the farther the greenhouse frame and fixtures are above the floor, the lighter the shadows become. This can result in greater uniformity and more light reaching into the lower canopy.

Room for additional energy/shade screens. Screens are valuable for both saving energy in the winter and excluding heat in the summer. A single screen can save up to 40 percent of the winter heat. Adding a second screen can reduce heat loss another 10 to 15 percent. At least 12 inches is needed to install a second screen. Usually these are located at the top and bottom cord of the energy truss for tight closure.

There are some negatives that can offset the advantages. The taller greenhouse is more expensive to build. The wind load on a tall house is increased due to the greater wall surface area. Larger support members and more bracing may be needed for the extra load. Also, additional wall glazing is needed. This amounts to 1 to 1.5 percent of the total surface area for each foot of additional height.

Heating costs are increased. As heat loss is directly related to the surface area of the greenhouse, the extra wall area adds some to the heat needed. Larger heaters may be needed.

Greater ventilation fan capacity is needed. For greenhouse gutter heights less than 12 feet, most engineers calculate fan capacity at 8 cfm/square foot of floor area. Recommendations for heights above that are better designed with fan capacity at 10 cfm/square foot.

Increased horizontal air flow (HAF) fan capacity is needed. As there is more air to move, it requires more power to move it. A good recommendation for houses with greater than a 12-foot gutter height would be to design with about 2.5 cfm of fan capacity for each square foot of floor area.

Labor costs may increase. If taller crops will be grown, employees may have to use elevating platform equipment to tend and harvest them.

When planning a new gutter-connected greenhouse, review the above factors based on the crops to be grown and the level of environment control desired.

John is an agricultural engineer, an emeritus extension professor at the University of Connecticut and a regular contributor to Greenhouse Management, a sister publication. He is an author, consultant and certified technical service provider doing greenhouse energy audits for USDA grant programs in New England. jbartok@rcn.com

1) Fig. 1: Eggs are oblong, approximately 1.0 mm in length, and creamy-white. 

2) Fig. 2: Adults are shiny black, and about 9 mm in length with a reddish head.

3) Fig. 3: Adult males tend to be smaller than adult females.

4) Fig. 4: Adults feed on the upper and lower leaf surfaces causing leaf skeletonization.

5) Fig. 5: Severe damage to plants reduces aesthetic quality and marketability.

The redheaded flea beetle, Systena frontalis, has emerged as a major insect pest in nursery production systems. Adults feed on many different ornamental plants; however, based on our experience and feedback from producers, Itea sp., Hydrangea sp., Cornus sp., and Weigela sp., are highly susceptible to redheaded flea beetle adults. In fact, specific cultivars tend to be more susceptible, including Itea virginica ‘Little Henry,’ Hydrangea paniculata ‘Vanilla-Strawberry’ and ‘Bobo,’ Cornus sericea ‘Kelseyi,’ and Weigela florida ‘Fine Wine.’ We have been conducting studies on redheaded flea beetle for five years at Loma Vista Nursery, one of the largest nursery operations in Kansas, and have obtained information related to biology and management.

Biology

The life cycle of the redheaded flea beetle consists of an egg, larva, pupa, and adult.

Eggs are oblong, approximately 1.0 mm in length, and creamy-white (Figure 1). Larvae are 5-10 mm long, creamy white, and have a brown head capsule when mature. The last body segment has a fleshy projection that curves upward, with hairs on the end. There are three larval instars. Larvae are located belowground in the growing medium/soil, and feed on plant roots. However, the larvae are less of a problem to plants than the adults. There is minimal information available on the pupal stage.

Adults are shiny black, and about 9 mm in length with a reddish head (Figures 2 and 3). Adult males tend to be smaller than adult females. Females lay eggs individually. Adults possess an enlarged hind femur that allows them to jump/hop similar to a flea—hence the common name. Adults feed on the upper and lower leaf surfaces causing leaf skeletonization and creating holes in leaves (Figures 4 through 6). In addition, adults deposit black fecal material on leaves during feeding.

On Itea virginica ‘Little Henry,’ adults tend to feed on the new growth where leaves are folded and pointing upward. Severe damage to plants reduces aesthetic quality and marketability. Adults can also feed on many weeds commonly associated with nursery production including common lambsquarters (Chenopodium album), pigweed (Amaranthus sp.), smartweed (Polygonum sp.), and velvetleaf (Abutilon theophrasti) among several other species. Adults may be present from June through November with possibly two to three generations per year; however, this is contingent on temperature and availability of suitable host plants. The number of generations in Kansas has not been determined. Based on experiments in which field containers of plants were collected and placed into a greenhouse (Figure 7), we have quantitatively shown that redheaded flea beetles emerge as adults from containers (Figure 8). From May 21 to June 18, 2018, we collected 10 redheaded flea beetle adults from 30 containers associated with I. virginica and H. paniculata plants.

Management

Weed removal from within the nursery, including containers, will help reduce potential food sources of redheaded flea beetle adults. Redheaded flea beetle adults may enter nurseries from surrounding vegetation; especially if the plants or weeds are a viable host. It is important to develop and implement an aggressive scouting program by monitoring for adults weekly, focusing on plants that are highly susceptible to redheaded flea beetle adults, and then conducting spray applications accordingly. Apply insecticides weekly when adults are active. We have found, in our efficacy trials, the following insecticides to be effective in protecting plants from damage caused by redheaded flea beetle adults: acetamiprid (TriStar), dinotefuran (Safari), and cyfluthrin (Tempo). Thorough coverage of all plants is important, as well as, the growing medium/soil as redheaded flea beetle adults may be able to sense changes in air pressure. Consequently, the adults will hop off plant leaves and land on the surface of the growing medium/soil (Figure 9) or the leaves of adjacent plants. Systemic insecticides can be used; however, adults still have to feed on plant leaves to be negatively affected, and depending on numbers, may still cause substantial aesthetic damage.

Author’s note: We want to thank Michael Sellers, Duane Huss, Thomas Minter and Lyndsi Oestmann of Loma Vista Nursery in Ottawa, Kansas, for their assistance and allowing us to conduct research on the redheaded flea beetle.

Raymond A. Cloyd is a professor and Nathan J. Herrick is a research associate in the Department of Entomology at Kansas State University.

Nurseries are beginning to purchase small unmanned aircraft systems (sUAS), or drones, to accomplish several tasks including sales and marketing, crop inventory, and crop monitoring. Nursery operators are faced with a number of business decisions before adopting this emerging technology. To generate useful images, a nursery would need to purchase an appropriate aircraft, sensor, computer, and image processing software.

Like any other business decision, the nursery needs to evaluate what option makes the most sense based on the cost outlay of each option and the type and frequency of needs that the business has. For example, Nursery A only needs a high-quality video/images of their overall operation which can be used on the company webpage and for use at trade shows. Nursery B wants to use the sUAS for weekly crop monitoring. Nursery A may find that it is more cost effective to pay a third party provider that specializes in flying the sUAS and has the hardware and software to generate the video product. However, Nursery B may determine that it is more cost effective to purchase the aircraft, sensor, and software so they have the capability in-house and can easily fly on-demand.

Aircraft

There are two broad categories of sUAS, rotary and fixed wing. In a majority of cases, the best aircraft option for nurseries would be a rotary aircraft. While fixed-wing platforms can cover more surface area in the same amount of time (e.g. likely 6 times more) compared to rotary aircraft, fixed wing are more expensive, less stable for collecting imagery compared to rotary, and require some kind of assistance in take-off and landing. Rotary aircraft range from two to eight (octocopter) blades with 4 (quadcopter) being the most common. The advantages of more blades are stability and redundancy. Most sUAS are made of lightweight materials such as plastic, aluminum, and carbon fiber. Power is most often provided by lithium ion Polymer(LiPO) batteries. As a beginner, a ‘bundle’ might be a good purchase decision, so you get spare parts and a carrying case in the package. The most dramatic enhancements in the past three years has been in the flight navigation software. Even very low cost aircraft come with powerful automated flight software to help plan and execute flight plans. On some units, the flight plan can be saved which is especially useful if the flight pattern needs to be repeated. To get a useful professional aircraft, you will likely spend between $800 and $5,000. Some of the more common manufacturers are DJI, Autel, Parrot, and Yuneec. To help one better understand the process and terminology in purchasing an aircraft, a must read is the University of Arkansas fact sheet on ‘Features to Consider When Purchasing a Small Unmanned Aircraft System (sUAS)’. It is worth noting that the ‘s’ in sUAS describes a new category (small) created by the FAA as a part of the permanent guidelines called Part 107. To be consider in this ‘small’ category the entire system (aircraft, sensor, battery) must weigh less than 55 pounds.

Sensor

Understanding that payload weight is critical when flying sUAS, sensor manufacturers have responded by quickly miniaturizing sensors. There are seven categories of sensors (Table 1). A major reason nurseries will limit themselves to certain sensors will be cost. An alternative to owning your own sensor is to hire an outside service for more expensive operations.

Nurseries are most likely to own an RGB camera, modified RGB camera, or multispectral sensor. An RGB camera would be useful to take still images or high-quality video that can be used in sales & marketing, plant inventory, and simple crop monitoring. These low-cost cameras can also be used to safely inspect greenhouse/hoop houses coverings or structural elements. A modified RGB camera would be useful to generate a ‘vegetative crop index’ such as NDVI (Normalized Difference Vegetation Index). To generate a NDVI image requires a sensor with Red and NIR bands and software to process the image. Moving up in cost would be a multispectral sensor which is useful for more complex crop monitoring.

Software

The final piece in your aerial imaging system would be software. Some examples of software that you may use for processing aerial images include open-source or free software such as QGIS, Microsoft ICE, ImageJ, MeshLab and commercial software such as Agisoft Photoscan and Pix4D. Remember, instead of owning the software yourself, another option is to pay a third party provider to process your images. Examples of data processing services include DroneDeploy, Airinov, and Agremo (formerly AgriSens).

It is likely that a nursery would want to ‘stitch’ multiple aerial images together into a single composite image. To give you an example of what is involved we recently collected some images at Willoway Nurseries (see photos on this page) and processed them using the free software from Microsoft called ICE (Image Composite Editor).

It is likely that within five years almost every nursery will own a sUAS for even simple tasks such as infrastructure inspection or sales and marketing. Like any capital investment, nurseries need to crunch some numbers to evaluate how deep to extend into this emerging technology themselves or whether it makes better financial sense to hire a third-party provider for specific services.

James Robbins is a professor at the University of Arkansas System CES, jrobbins@uaex.edu. Joe Mari Maja is a sensor engineer at Clemson REC, jmaja@clemson.edu.

No endorsement is implied or discrimination intended for firms or references included or excluded in this article.