© vladteodor | Adobestock

When pests are discovered in the greenhouse, they were likely reported by a scout.

The first thing you need to consider when you think about scouting is to come to grips with who’s actually going to do it. Some growers have full-time scouts, some have part-time scouts, but for most operations scouting is part of someone’s responsibilities — not an entire job description on its own.

“Don’t think you have to have a paid, titled, credentialed scout do the scouting,” says Timothy Malinich, horticulture educator in agriculture and natural resources with the Ohio State University Extension’s Erie County office. “Scouts can just be people that have been empowered to go out there and look for things, see those things and report them back to the people that will need to treat them.”

Scouts could be site managers. If a greenhouse has multiple locations, it could be the manager of each site. It could be all employees at the greenhouse. It could be the employees on the potting line or employees managing inventory in the shipping yard. In many cases, it’s the applicator.

Greenhouse managers can empower everyone in their organization to scout, but you need to make it part of the job description. You must give the people you are empowering to scout time to do the work and be flexible about when they do it.

You should also provide some basic training on what scouting entails. Though even without formal training, if an employee sees something that doesn’t look normal, they can report it and you can use it as a point of data.

Thomas DeHaas, an agriculture and natural resources educator at Ohio State University Extension’s Lake County office, says every employee is likely to have one of the most powerful scouting tools right in their pocket: the smartphone.

“They can take a picture and text somebody,” DeHaas says. “If you have a central person who gets that info, you’ve already improved your scouting program 100%.”

DeHaas suggests growers think outside the box to incentivize employees to scout in addition to their responsibilities. For instance, you could offer $1 for each picture sent that turns out to be a problem.

“If it’s worth doing, it’s worth paying for,” DeHaas says. “Giving people time to do it is going to cost you money, but it saves money, too.”

There are several financial and plant health benefits to a robust scouting program. Because your trained scout or scouts can find pests before they become a problem, you’re able to reduce pesticide inputs, preserve your beneficial insect supply, and reduce the chance of pesticide resistance.

Scouting tools

The tools of the trade can vary widely in price and effectiveness. If you ask a large amount of your employees to scout, you won’t outfit all of them with Canon Rebels and pricey magnifying lenses. But everyone should at least have the basics listed below. Here are some options:

Basic tools

Smartphone, loupe, pen and waterproof paper, pruners, marking tape, flags, acetone with cotton balls, hand sanitizer, map of greenhouse (to mark where pest was found), yellow sticky cards.

Midrange tools

Digital magnifier, EC/pH meter, clip-on lenses for smartphone (ex. CamKix), Hand-lens with 10x power and/or optivisor (headset with magnifying glass), Resource information such as pesticide labels, pictures and life cycles of key pests.

High-end tools

Field microscope, “real” camera (D-SLR style), laptop for image manipulation, clip-on lenses like olloclip.

Source: Reporting by Matt McClellan and information from the University of Massachusetts Amherst

Emma: Weed control is a constant battle for greenhouse and nursery growers. Can you tell us about some of the key weed species we run into in indoor production and why they are problematic?

Chris: Despite our best efforts, weeds will usually find their way into a greenhouse by some way or another. The greenhouse is a perfect environment for many different weed species but certain species like bittercress (Cardamine spp.), woodsorrel (Oxalis spp.), and liverwort (Marchantia polymorpha) can really thrive and spread exponentially inside a house. Bittercress and woodsorrel grow fast, produce many seeds, and the seed pods explode when they are ripe, spreading the weeds throughout the house. Liverwort is problematic mostly because it loves two things: moisture and nitrogen. Propagation mist beds are perfect for liverwort. Liverwort spreads both vegetatively and via spores, and can spread throughout a house extremely quickly. It is also almost impossible to hand weed. Once any of these species gets into the actual crop, there isn’t much that can be done other than manual removal.

Emma: So frequent scouting, along with strict sanitation practices, is critical to keeping weed populations in check. Despite our best efforts, sometimes weeds can get the upper hand and unfortunately, there are relatively few herbicides that are labeled for use indoors due to volatility concerns.

Chris: Certain herbicides that have high vapor pressure can turn into a vapor after they have been sprayed (or applied as a granular) and these vapors can injure plants. This is problematic for fully enclosed greenhouses because the vapors get trapped inside. Whereas something like a shade house (only covered in shade cloth) doesn’t pose the same concern because vapors can dissipate more easily. Plants that are treated with preemergence herbicides and moved inside a house soon thereafter are also susceptible to volatility injury. Ensure that the herbicide that is being used inside the house is labeled for that use. Also, make sure to time your preemergence application so that it is made at least 2 to 3 weeks (depending on label) before you have to move the plants inside.

Emma: Herbicide options for enclosed structures are fairly limited but there are great options available. Post-emergent herbicides like glufosinate (Finale® XL T&O herbicide) can be used indoors while plants are present. This allows for cleaning up weeds under benches, along walkways and around equipment.

Chris: Other post-emergent herbicides include diquat (Reward) and Scythe or Axxe (pelargonic acid/ammonium nonanoate). These are all contact or minimally translocated herbicides so thorough coverage is needed for control. Be sure to turn off air circulation fans during the application. For grassy weeds, clethodim (Envoy Plus) and fluazifop-butyl (Fusilade II) could be used. Indaziflam (Marengo) is a broad-spectrum preemergence herbicide that could be applied either alone or in a tank-mix with a postemergence herbicide on the floors or under benches to prevent weeds from coming. When the house is empty (and will be for 24+ hours), you have a few more options such as glyphosate (RoundUp Pro and others) for postemergence control and flumioxazin (SureGuard) for preemergence control.

Emma: When we start talking about herbicides for outside the greenhouse or even outdoor production areas, we definitely have more options. What should growers consider when selecting herbicides for outside and around the greenhouse?

Chris: Poor weed control outside of the greenhouse will inevitably lead to poor weed control inside the house. Frequent mowing, weed fabric, gravel, basically just general sanitation, are good practices to keep weed pressure low. Most of the postemergence herbicides labeled for use in and around ornamentals in nurseries can be used around a greenhouse, but the main thing you want to avoid is the use of volatile herbicides that could drift into the house through doors, vents, etc. A major herbicide group to avoid is the auxin type herbicides like 2,4-D and dicamba. These are mostly used in turf and can be prone to volatilization. Soil sterilant herbicides like dichlobenil (Casoron) should also be avoided when treating in close proximity to production areas. It is always a good idea to shut vents and windows when treating large areas around the house.

Emma: In addition to weeds being an unsightly greenhouse pest all their own, weeds can also serve as harbors for insects and other pests and can act as additional hosts for some plant pathogens like impatiens necrotic spot virus (INSV) and tomato spotted wilt virus (TSWV).

Jen: Greenhouse weeds also provide a significant reservoir for insect and mite populations to build and thrive. They can be missed with spray applications, and even fogs and beneficials may not reach spider mite nurseries under the bench, or thrips, whitefly and aphid populations living in weedy corners or behind greenhouse structures. Don’t forget that algae is also a greenhouse weed, and it feeds and harbors shore flies and fungus gnats, allowing them to lay more eggs and be present in the range all year long. These flies and others associated with wet conditions, like drain flies, are not only plant pests and nuisance pests as they dart around workers’ faces, they can also move pathogens between plants and crops.

©Tammimild | Adobestock

More often than not, the phrase ‘holiday plant’ still means poinsettia. Come October, November and December, shelves at big-box stores and independent garden centers (IGCs) are stocked with poinsettias, primarily in traditional red with more colors being added over time.

“We haven’t seen anything of significance rise to replace it,” says Plantpeddler owner Mike Gooder. “And I think in the consumer’s eye, the poinsettia is the plant for Christmas.”

There are changes in the market, however. There is no replacing the poinsettia, but changes are occurring and developing on the margins. For one, more colors — whites, greens, oranges and more — are being bred, trialed and then reaching consumers. Poinsettia growing season is changing too, with the hope that poinsettias can be sold in early fall and after Christmas in colors that fit those moments.

“They are getting harder and harder to sell,” says Nicole Bent, president of Shelmerdine Garden Centre in Manitoba. “I look at them as a commodity plant that you can find in any big-box store — Walmart, Safeway, wherever. It’s harder for the garden center to sell them without making them look like something above and beyond what is available at a big-box store.”

A retail point of view

According to Bent, one of the steps Shelmerdine has taken in recent years is to begin “dressing up” poinsettias more.

“We have gravitated to using better pot covers and using glitter to make them look like the special plant they are,” she says. “You also have to watch your pricing too because when you can buy a poinsettia at Walmart for $9.99, why would you spend $14.99 at a garden center?”

Pricing she says, has to be monitored carefully as to not be too far out of line with what customers can buy at a competitor, even if what Shelmerdine offers is more unique.

Bent adds that, in recent years, the business has started to diversify what it offers around the holiday season. One project they’ve focused on are amaryllis bulbs — a trend they found was successful in Europe and are hoping will translate in North America over time. The hope is that if they are losing market share on poinsettias to big box stores, offering amaryllis bulbs will help replace any lost revenue.

“It hasn’t totally hit yet, but we think it will get bigger in the next few years,” she says. “One thing we really think will help are the wax bulbs that have been introduced over the last several years. It’s basically an amaryllis bulb that has been dipped in wax. Everything the plant needs to live is in that wax cover, so the bulb just grows. You can decorate around it, put it on a plate to showcase it and the flower just continues to grow and bloom.”

The only downside, Bent says, is that the wax-covered bulb will die after the holiday season ends. Traditional amaryllis bulbs can be saved and re-grown year after year, so there is some downside for the customer expecting a long-lasting plant.

“We did notice in 2019, the first year that we sold wax bulbs, that people just didn’t get it [as a concept],” Bent says. “But last year, even with COVID and online ordering, they were totally sold out.” This year, with COVID-19 not keeping customers at home quite as much, will see if the trend holds since people will assumedly be out more.

As for poinsettias, Bent estimates that Shelmerdine produces around 10,000 poinsettias per year with 9,000 allotted for fundraising programs and the remaining 1,000 sold in store. That split has been consistent for the last 15-20 years and the in-store poinsettias are 75% red, 15% white and the remaining a mix of “novelty” colors of pink and burgundies. Unique wraps are used to differentiate the more standard design available at larger retailers. Smaller alternatives like Princettia and poinsettia trees have gained some steam, but have not made nearly the impact that poinsettias do on the bottom line.

“We also would have a hard time making a profit without the volume of the fundraising program,” Bent says. “And with new items, we have to keep looking for the next thing.”

Trialed improvements

At Cresco, Iowa-based Plantpeddler, Gooder and his team operate one of the biggest poinsettia trials in the United States. (Others include N.G. Heimos’ trial in Millstadt, Illinois, and Lucas Greenhouses’ trial in Monroeville, New Jersey.) Over the past several years, he says poinsettia genetics available from breeders has improved greatly.

“Poinsettias can be a difficult crop to grow,” he says. “But in the last three to five years, a number of important enhancements have been made. People says ‘oh, the poinsettia has plateaued,’ but that could not be farther from the truth.”

“We are seeing incremental breeding improvements and that’s really important,” he continues. “One of the things breeders are working on is early ‘blushing’ but late flowering.” The idea, he says, is that in the past, some varieties wouldn’t be ready to ship when the bracts began opening up, but the color wasn’t right. With new breeding, the plant won’t fully open up as early.

“This means we can ship over a longer window,” Gooder says. “Instead of having varieties to gap multiple weeks, they can cover multiple weeks by picking [better genetics].” Branching characteristics have improved too, he says, noting that branching has become more uniform.

©Studio Gi | Adobestock

The impact of color

According to Gooder, the biggest advancement in recent years has been white poinsettias. Before, many of the poinsettias were what he called a “dirty white.” Now, what’s available is often brighter and feature more of the clean, white look customers prefer.

Red, however, still remains king. Chris Berg, a senior product manager at Dümmen Orange, says red remains the most common color in their portfolio and in every breeder’s portfolio.

Dümmen, Berg says, also divides its poinsettia catalogue into different seasons. Reds, he says, primarily play for Christmas, with greens and oranges hitting the market aimed at fall consumers who aren’t looking for a Christmas plant just yet.

“It’s looking at the retail partners we have and looking into how we can tap into what they are doing and pushing,” he says. For Dümmen, breeding work occurs in Ecke, California, where breeding manager Ruth Kobayashi oversees efforts to bring new options to market.

“It’s a funny candy shop and there’s so much there to work with,” Berg says. “So we can go in there, see what’s available, match it with what’s been popular as far as holiday decor goes. From there, we can start working and sometimes fast track varieties that we think can make an impact for us.”

In Plantpeddler’s trials, Gooder notes that the best varieties available aren’t just coming from the biggest breeders in the industry.

“There are really great selections right now from every major breeder and every minor breeder,” he says. “Steve Rinehart, a new player who came from Ecke, has a few whites that we absolutely love. If you go program by program, there’s great stuff from Selecta, Syngenta, Beekenkamp, the Dümmen Orange program or Lazzeri, the new Italian breeder.”

“Gerbera ‘Red Glitter’ is the best glitter type, the best Jingle type, on the market in my opinion. It’s from Lazzeri, a new player. Those competitive dynamics help improve everybody’s game,” Gooder adds.

Future nostalgia

According to Berg, the biggest step forward for poinsettias is not so much increasing sales around Christmas and doubling down and what has been done already. It’s not even Princettia varieties or poinsettia trees. Instead, the idea is to expand the season over time with new genetics and new colors.

For example, this could mean developing more whites that fit the tone of traditional New Year’s decor vs. the reds of Christmas.

“For instance, the Ecke company was trying to develop that fall crop for years. And in some cases that has gotten really strong,” Berg says. “And we will see if we can extend into the New Year.”

At Shelmerdine, Bent says the holiday season has evolved over time for the business, with decor, ornaments and other trinkets available at the garden center becoming more popular during the holidays. In recent years, she says that there has also been an interest in tropicals and succulents being given as gifts vs. a poinsettia.

“But I don’t think we’d feel like a Christmas store — or that it would feel like Christmas — without us having poinsettias,” she says. “And we take a lot of pride in growing them in-house. It’s not a bread-and-butter crop like an annual, but this bridges us throughout the winter and allows us to keep people employed and our grower busy.”

Gooder, meanwhile, says that Plantpeddler will produce about 1.75 million poinsettias for the upcoming holiday season. Princettias and other novelties are showing good growth as well. Painted poinsettias and other novelties are around, but poinsettias still lead the way. He expects that to continue.

“For a crop that a lot of people say doesn’t make any sense and doesn’t make any money, there’s been a lot of money and time spent in breeding efforts to improve the product,” he says.

Using an unvented heater in the greenhouse, either for back-up or as a primary heat source can significantly increase disease, pollution and moisture problems.

An unvented heater is one that is designed without a flue connection so that the heat and products of combustion are exhausted into the greenhouse. Dumping these flue gases into the greenhouse may improve the overall efficiency rating as compared to a conventional heater, but the pollutants and added moisture from combustion may put your plants in jeopardy.

Unvented heaters can be fired with natural gas, propane or kerosene. These fuels and the heaters are advertised as clean burning. This is generally true if they are new or the burner has been recently serviced, otherwise it can emit unwanted and harmful pollutants into the greenhouse that can affect the plants and the people working with them. Let’s look a little further at the fuels and the combustion process.

Natural gas (NG) consists of more than 85% methane with varying amounts of ethane, propane, butane and inert gases such as nitrogen, carbon dioxide and helium. It has a heat value of from about 950-1050 Btu/cu ft. The flue gases usually contain nitrogen dioxide, carbon dioxide, carbon monoxide, volatile organic compounds and particulate matter.

Liquefied Petroleum Gas (LP-gas) is obtained from gas wells or as a refinery by-product and consists primarily of propane with traces of proplyene, butane and butylenes. It is handled as a liquid and contains from 90,000-98,000 Btu/gal. Propane has much of the same pollutants as natural gas.

1-K kerosene is a low-sulfur petroleum product whose composition varies widely depending on what part of the world it comes from. Its heat value is about 135,000 Btu/gal. The major pollutants that result from burning kerosene are nitrogen dioxide, carbon monoxide, carbon dioxide, sulfur dioxide and formaldehyde.

The combustion process for both natural gas and LP gas are very similar. Here is the formula for burning natural gas.

1 cu ft NG + 10 cu ft Air + Flame ? 8 cu ft Nitrogen + 1 cu ft Carbon dioxide + 2 cu ft Water vapor

Air supply

The above formula is for complete combustion. Usually, excess air is needed to get complete combustion as greater mixing occurs and more of the fuel particles will make contact with the oxygen. Incomplete combustion reduces the amount of heat that is obtained and increases the amount of pollution. A common problem in many newer greenhouses is that they are very tight. As the heater operates, oxygen is used and combustion efficiency decreases unless makeup air is available. A free air inlet of at least 1 sq in/1000 Btu/hr input is needed. Each winter there are several instances of tight greenhouses that have frozen up when the heaters were starved for air and the heat output decreased.

Carbon dioxide

One of the byproducts of combustion is carbon dioxide which can enhance plant growth. One of the problems is that carbon dioxide is most effective when light levels are the highest during the day and the carbon dioxide is mainly produced at night when the heater operates the most.

Water vapor

Another byproduct is water vapor. This is added to the greenhouse at night when moisture levels are already high and can condense out on the cold glazing surfaces and drip on the plants. Increased moisture levels can cause increased incidence of disease problems including fungi, blight and molds.

How much water do we get? Burning 1 ccf of natural gas produces about 1.25 gallons. With propane, 0.81 gal H2O per gallon burned and with kerosene 1.5 gal H2O per gallon burned. For example, if you have a 400,000 Btu/hr nonvented natural gas heater, it will produce about 5 gallons of water/hour. If the heaters were vented, the moisture would have been exhausted outside along with the flue gases. This moisture added to the normal transpiration and evaporation could keep the relative humidity well above 90%.

Other combustion products

All fuels contain traces of sulfur, some more than others depending on its source. During combustion, sulfur in the fuel is combined with oxygen to form sulfur dioxide. Levels as low as ½ part per million (ppm) can cause injury on some plants. Once the sulfur dioxide enters the plant through the stomates, it reacts with water to produce sulfuric acid that will cause leaf burn, flecking and general chlorosis. Tomatoes and white petunias are very sensitive to this and will show signs in as little as one hour. They therefore make good indicator plants.

Ethylene gas is another pollutant formed during combustion. Levels as low as 0.01 ppm can create symptoms such as malformed leaves and flowers, stunted growth, bud abscission, epinasty and flower senescence. Levels are usually highest near the heater and can be diluted by air circulation.

Care should be taken if you install unvented heaters. Be sure to have an adequate makeup air supply and provide frequent maintenance. Use indicator plants near heaters or commercially available indicator tubes to warn of excess levels of pollutants.