Karen E. Varga
The other day, I was reading the local news and a piece about property values caught my eye. In the Cleveland suburb that I live in, home values have gone up almost 8 percent over the past three years. The city is becoming more desirable to live in, especially for young professionals, and houses are snapped up quickly, often selling in a matter of days or weeks. We’re seeing firsthand how the housing market is rebounding, especially this year. The planning and development director notes that there has been steady improvement over the past four or five years, which is on par with what we’re seeing nationwide.
According to an August 2015 report by Kiplinger, a Washington, D.C.-based publisher of business forecasts and personal finance advice, the housing market is steadily recovering and is showing no signs of stagnating any time soon. New home construction is up, especially of multifamily homes, contributing to a 12-percent overall increase in housing starts since late 2014, a great sign for the horticultural industry. As you well know, new housing means an increase in demand for landscaping and the plants that go into new yards.
The report also indicated that 2015 may have the best home sales since 2008. One interesting point to note though, and one that we heard keynote speaker Curt Steinhorst talk about at Cultivate’15, is that not as many young people are buying homes due to residual student debt, problems getting credit and high rent; they’re waiting longer to make the jump from renting to buying.
While the state of the housing market is far from the only economic indicator affecting the horticulture market, it’s still good news for our market. In this year’s State of the Industry Report, we found that almost all growers reported sales that were at least as good or better than last year — 24 percent with flat sales and 66 percent with increased sales. Only 8 percent were down from last year. Edibles are still going strong, but we’re also seeing an uptick in annuals/bedding color and perennials production and demand. Turn to page 13 to read the 2015 State of the Industry Report.
Have something to share about your year or a new idea that’s been working well for you? Send me an email at firstname.lastname@example.org or give me a call — I’d love to hear about it.
Editor’s note: In part I of this two-part article, author Richard McAvoy addressed managing Easter lily crop production up to bud set. You can read that article and see the complete 2016 production schedule in our September 2015 issue at greenhousemag.com.
Once lilies emerge, all focus should be on optimizing flower bud count and keeping on schedule for the early date Easter in 2016. Bud set should be completed in early- to mid-January. During this part of the crop cycle you can use insurance lighting to reach your full 1,000-hour vernalization goal, but do not attempt to speed development of the crop with high temperatures. Once bud initiation is set you will need to track height to meet production goals, leaf unfolding rates and bud development to meet targeted sales dates.
With both pot-cooled and case-cooled lilies, greenhouse forcing starts at the end of the bulb-cooling period. Typically this is 17 weeks before Easter for case-cooled bulbs and 14 weeks before Easter for pot-cooled bulbs. The difference in the two schedules just reflects the stage of shoot development. With pot-cooled bulbs, the shoots are either at the soil surface or already emerged as soon as forcing begins (Week 14). In contrast. case-cooled bulbs will take up to three weeks to emerge. So either way, the shoots on both crops should be emerging by about week 14 (Dec. 20).
Bud initiation begins soon after lilies emerge, and should be completed no later than mid-January in the 2016 crop, when shoots are 3 to 5 inches tall. The development of stem roots coincides with flower bud initiation. During this period, day and night temperatures of 60° to 65°F are desirable (63°F is ideal), but it is imperative that temperatures do not exceed 65°F until bud initiation is complete.
Leaf counting & forcing temperatures:
If you haven’t previously used leaf counting, this will be a good year to start. Begin using the leaf counting technique to track lily development as soon as bud initiation is complete. You should be able to start this by week 10 or 11 (Jan. 10 to 17). This will allow you adequate time to determine if lily development is on track, and if not, to make the necessary adjustments. Don’t wait to start leaf counting this year. Too often, growers do not realize their crop is behind schedule until after visible buds fail to appear at about week 6.
Run lower average daily temperatures (55° to 60°F) if lilies are ahead of schedule — an unlikely circumstance this season, or higher temperatures (70° to 75°F) if behind schedule. Begin to assess crop development early so that temperature extremes can be avoided later. Typical leaf unfolding rates vary from approximately one leaf/day at 53°F to 1.5 leaves/day at 63°F, 2 leaves/day at 72°F and 2.5 leaves/day at 82°F. Forcing temperatures between 55° to 70°F produce the highest quality lilies and are most fuel-efficient.
Once lilies reach visible bud, they will typically flower in 30 days at 70°F and 35 days at 65°F. Monitor bud development by measuring bud length. Adjust temperature as needed to stay on schedule. A “bud stick” is a useful tool to gauge the rate of lily bud development and the time needed to finish at a specific temperature. If you don’t have a bud stick refer to Table 1 to estimate the rate of bud development. I recommend you assess bud development early and adjust temperatures at that time. In late Easter seasons, growers in northern climates often hold off on forcing bud development until the last two weeks, knowing that high natural light and warm weather in early- to mid-April will assist in this effort. But this season, you will have to push in late February and early March for the early sales dates. Ask yourself, what conditions can I expect this time of year? If winter weather patterns are still likely to prevail at your site, start your push earlier.
Uneven temperatures produce uneven crops. Use horizontal airflow to equalize greenhouse air temperatures. If you need to use temperatures above 80°F to push lilies at the end, take care to maintain adequate soil moisture and humidity levels or lily development may stall and buds may abort.
Growth regulators should not be applied until after flower buds have set (early- to mid-January 2016). Use DIF to control lily height during flower initiation. Equal day/night temperatures or cool morning temperatures will produce a DIF effect and keep lilies short. The conventional PGR program uses a single application of A-Rest, Concise, Topflor or Sumagic as needed when shoots are 3 to 5 inches tall. The dose used is high enough to provide control through to about week 6. However, many growers have learned to fine-tune PGR applications to exert more precise control on the crop and with far better results. A typical program may call for weekly applications as needed to either slow stem stretch with a growth retardant such as Sumagic, or increase stretch with gibberellins such as in Fascination, or to prevent leaf yellowing in closely spaced plants (also with Fascination). Growers that use such programs are successfully applying growth retardants to lilies that are past the visible bud stage.
Even if you are inclined to be more conservative in your PGR practices, split applications are preferred as they produce the most desirable plants. With split applications, use half the normal dose at the first application and then a one-quarter to one-half dose in subsequent applications (depending on the number of applications you plan to use and the amount of control needed). Lilies exposed to high concentrations of growth retardants have a greater tendency to develop lower leaf yellowing in the later stages of production. Some growers have been applying low concentrations of Sumagic (or similar products) just as the shoot emerges and then following with a second application when the bud initiation period is over. I prefer to allow bud initiation to be completed before altering natural hormone levels in the plant. Plus, if you are maintaining 63°F day and night, as you should, you already have a zero DIF regime that will limit stretching during this phase. If you still wish to apply PGRs at this time, I recommend the lowest effective dose (an eighth to a quarter of the normal dose). Just apply enough to hold the plant for seven to 10 days rather than the typical 3 to 5 weeks.
Leaf yellowing can develop gradually in the greenhouse or suddenly and severely after lilies are sold. Gradual leaf yellowing can be a sign of chronic stress due to a persistent and unfavorable environmental condition or a telltale symptom of a diseased root system. Improper nutrition, poor media aeration or overwatering, and low light and poor air movement from tight plant spacing, are conditions that are conducive to leaf yellowing.
Sudden and severe leaf yellowing at the end of the crop is most likely to occur on lilies in poor root health and suffering from the poor nutritional and carbohydrate status associated with a bad root system. Prolonged cold storage prior to shipping and poor shipping conditions can also favor sudden, catastrophic yellowing.
To prevent early- and mid-season leaf yellowing (from seven to 10 days before visible bud until seven to 10 days after visible bud), spray Fascination at 10/10ppm. (Note: Fresco and Fascination are similar PGR formulations; both contain two active ingredients and recommendations are provided in a format that reflects the concentration of each). Apply only to lower leaves and cover thoroughly. To prevent late-season leaf yellowing and post-harvest flower senescence, spray 100/100ppm to thoroughly cover all foliage and buds. To protect leaves from yellowing during shipping or cooling, apply when buds are 3 to 3½ inches long but not more than 14 days before the start of shipping or cooling. Side effects include increased stem stretch, so avoid contact with immature leaves during early- and mid-season applications unless increased height is your objective. Growers sometimes spray these compounds at 3 to 5 ppm at seven-day intervals or as needed to increase stem stretch.
Getting ready to ship:
Lilies require adequate fertilization from planting to finish but high salts in shipping can be a problem. Apply one clear watering right before shipping to lower salt levels and enhance the keeping quality for the consumer.
Good quality lilies can deteriorate rapidly after leaving the greenhouse. Avoid holding sleeved and boxed lilies for long periods of time, especially when temperatures are high in the shipping container. EthylBloc can also be used to increase post-harvest flower life. EthylBloc works by inhibiting the damaging effects of ethylene (a naturally occurring plant hormone that greatly accelerates the onset of leaf yellowing, and flower aging and death). Plants produce ethylene naturally but ethylene can also result from the incomplete combustion of fuels in a greenhouse, shipping or warehouse environment.
The active ingredient in EthylBloc, 1-methylcyclopropene or 1-MCP, is released as a gas and therefore lilies must be treated in an enclosed environment. A sealed shipping container or truck, or sealed greenhouse can be used to treat plants. Flowers must be fully developed before treatment. To extend flower-life, treat lilies with EthylBloc just prior to harvest, or immediately after harvest, or just prior to shipping, or upon arrival from a supplier, or just prior to sale. Note that repeat applications are not harmful and are recommended on species such as lily that bloom sequentially over time.
Richard McAvoy is professor and extension specialist at the University of Connecticut.
Born with a green thumb, Nick Baker was destined for horticulture, even if at first he didn’t know it.
As a small child, he watched his family found Baker’s Acres, a garden center and greenhouse operation in Alexandria, Ohio. With a passive interest, he saw the company grow. He was always around growers and their plants, but never wanted to plant seeds of his own or thought of it as a potential career.
“I was never really interested in it,” he says. “It was just kind of there. There were just greenhouses in the backyard.”
So, Baker bolted and headed for the green hills of Athens, Ohio, where he enrolled at Ohio University. After a couple of years, he decided to transfer to upstate powerhouse, Ohio State University, in Columbus.
But eventually, the collegiate lifestyle lost its shine and Baker lost interest in his studies. He dropped out.
In 2007, he found a new direction.
“I went back to work for my parents [at Baker’s Acres],” he says. “Surprisingly, I was good at the work. So I stayed with it.”
Within a year, Baker was doing what he calls “serious growing.” Now, 35-year-old Baker is the company’s head grower, and has taken over the primary greenhouse duties, though his father still works in the greenhouse on a near-daily basis.
How things change
Now Baker’s days involve monitoring all of the greenhouse’s growing systems, delegating to the staff at Baker’s Acres, propagation and crop maintenance. There are other office-bound duties that he must also attend to. But, he says, he’d prefer to be working with the plants.
“I spend a lot of time in the office,” he says. “But I’m not great there. I’d rather be in the greenhouse, working with plants. So, I try to divide my day as best I can between the business side of the operation and the growing side.”
Baker’s typical day is not unlike that of other head growers. He arrives early, with his dogs. He walks his pets around the facility before heading into the greenhouse. Once inside, he inspects the plants and the growing systems. Then, depending on the time of year, he issues direction to the staff. In the winter, he and his wife will begin propagating and working on the next year’s crops.
“We water by hand in the greenhouse,” he says. “It’s a lot of watering.” He says the greenhouse waters by hand because that's what they “have available.”
Baker’s Acres grows almost 100 percent of its own crops, including the annuals, they offer. He says that the only crops they receive finished are tropicals, trees, shrubs and some perennials.
“Everything else we grow ourselves. In fact, we propagate ourselves too, including the succulents and begonias,” he says.
For Baker, there are a few special treats to grow. He likes annuals. He loves succulents. He even describes himself as a “big succulent nerd,” noting his large collection. In fact, the plants that he loves to grow are only united by one, simple characteristic — they’re exciting.
“I don’t really like boring plants. Cool leaves, cool foliage, cool blooms, that’s what I like,” he says. “Begonias, coleus — I enjoy working with those types of plants.”
This focus on exciting plants has helped Baker’s Acres develop a repertoire of rare and exotic varieties. Baker calls his retail operation a “boutique garden center.”
A vibrant future
Beneficial insects are another aspect of Baker’s job that he describes as “exciting.” Baker’s Acres has transitioned, completely, to the use of beneficials and biologicals. The company no longer uses any chemicals, he says.
The decision to make the jump was made in the summer of 2014. Baker and his team cleaned out the property and then let it “bake for a couple of months” before bringing back all of the stock plants. They introduced their beneficials at the same time.
“It’s been interesting seeing what happens in a greenhouse when you stop spraying and you just use beneficial insects,” he says. “You start getting things chewing holes in your plants that you wouldn’t normally see.”
He says that caterpillars, a pest that had never presented a significant problem for Baker’s Acres, are now hungrily munching through the company’s coleus. And caterpillars are just one of many new opponents. Baker says it has been “fun learning and seeing what happens next.”
“Before, we were trying to battle thrips, nonstop, with chemicals. But we could never really control them,” he says. “But with beneficials, thrips are one of the easiest to control. It’s pests like aphids that are suddenly a problem, suddenly harder to control.”
He says that the greenhouse, with all the buzzing beneficials flying around, is more vibrant and alive than ever.
Expand the customer base
Currently, Baker’s Acres sells to other independent garden centers.
“Mostly we sell them begonia liners or coleus planters, that sort of thing,” he says. They do some special orders, but the majority of its business comes from its retail presence.
However, being a boutique garden center and greenhouse operation isn’t the end of Baker’s Acres development, Baker says. He wants to start reaching new and varied customers. To do that, he’s experimenting with new growing techniques (like solely using beneficial insects for pest management) and streamlining other production methods, trying to become more efficient. Partly, Baker wants to keep up with rapidly changing practices, but he also wants to find out what appeals to younger crowds. His hope is to expand the reach of the gardening industry and make it more appealing to everyone.
“I’d like to try and get into grocery stores. I feel like millennials like to shop at Whole Foods and other stores like that,” he says. “They’ll walk in, see a cool succulent and want to buy it. That can be a gateway to other gardening.”
He also wants to produce foolproof plants, plants that are almost impossible to fail with. “Our goal is to streamline our plants. We want them all to be really great for the customer,” he says.
LEDs for the greenhouse industry: A perspective
By Cary A. Mitchell, Director, SCRI Project for Developing LED Lighting Technologies and Practices for Sustainable Specialty-Crop Production & Professor, Department of Horticulture & Landscape Architecture, Purdue University
Growers of specialty crops have become intrigued with the possibility of using light-emitting diodes (LEDs) to meet their greenhouse lighting needs. LEDs have a mystique that appeals on many levels, but is enough known to risk replacing the tried-and-true of today with the spark and passion of tomorrow for ongoing commercial production?
Pros and cons
LEDs have a reputation for expending less electrical energy than traditional greenhouse lighting sources, as well as having a longer lifespan. And engineering continues to improve the efficacy of LEDs to convert the energy of electricity to the energy of light, and the cost of their manufacture continues to come down. The main obstacle that makes growers hesitate is the capital investment of equipping greenhouses with LED fixtures. For supplemental photosynthetic lighting, it takes a higher up-front investment to provide equivalent light intensity with LEDs than by staying with traditional lamps. So, where do these tradeoffs come out? It leaves growers asking, “Should I invest now, or should I wait?”
Unfortunately, there is no simple answer to these questions. It depends not only on capital investment vs. energy savings in a given region, but also on specific crop responses to narrow-spectrum vs. broad-spectrum light. Optimum “LED light recipes” combining spectrum, light intensity and photoperiod have not been worked out in detail yet for every cultivar of every specialty crop, and they do vary. Growers with contracts to meet cannot afford to guess about crop responses just to save energy, especially when the ante to get into the LED poker game is salty compared to traditional light sources. Comprehensive economic analyses must be conducted using experimental or pilot crop-response data.
Those of us conducting LED research applied to greenhouse specialty crops typically recommend that growers interested in trying LEDs, but worried about making costly mistakes, take it slowly and conduct some of their own trials on a small scale. Only after satisfying themselves that they can get as good or better crop response with LEDs should they consider the economic tradeoffs. If the projected break-even time works for them, then they can make a gradual transition as traditional lighting sources require replacement.
Promising Possibilities for LEDs in the Greenhouse
Control of flowering
The obvious application for LEDs in the greenhouse is photoperiodic control of flowering ornamentals (Figure 1). LED fixtures for photoperiod control cost more than (disappearing) incandescent light bulbs, but not nearly as much as high-intensity discharge (HID) lighting fixtures, and they fit right into standard screw-in light sockets. What’s more, the intensities of light required for night-break induction or inhibition of flowering are vanishingly small, so the energy bill is relatively low. That said, research is not finished regarding spectral optimization of photoperiod control for different crops, so even this likely application for LEDs in the greenhouse is not yet a turnkey deal for commercial application. Investigating effects of different spectral blends on floral control and accompanying plant development is still a work-in-progress. Growers will have to conduct some of their own trials, await the published results of public-sector research or trust manufacturer claims before jumping in with both feet.
Intracanopy photosynthetic lighting
High-light-requiring, high-wire trellised vegetable crops such as tomato, cucumber and pepper are self shading in the greenhouse, and production is particularly limited during low-light seasons and/or in low-light climates. The unique property of LEDs to be relatively cool because waste heat is rejected remotely from emitters allows LEDs to be placed close to plant tissues, including within the foliar canopy of vertically dense foliar canopies (Figure 2). Research is showing potential for intracanopy lighting to save considerable energy, stimulating yield without accompanying overhead HID lighting. But the technology and protocols are still under development.
Transplants in the greenhouse? Maybe.
End-of-day, daylength extension or supplemental lighting with LEDs can stimulate growth and development of young transplants during low-light seasons in the greenhouse (Figure 3). Manipulation of spectral composition with LEDs may alter morphology of seedling or grafted transplants as well as total growth in desired ways (Figure 4). Because dense LED arrays block considerable sunlight from reaching crops in the greenhouse when positioned close above crop surfaces, the question is, Is more sunlight blocked than supplemental light provided? If the LED light can be sole-source with even better crop-response outcomes (growth, morphology, color, phytonutrient content), why not propagate young plants in warehouses under LEDs rather than in greenhouses under partial solar and partial LED light? The tradeoffs appear to be complex, relating not only to energy utilized or saved, but whether LED light enhances desired effects of solar light, or whether solar light negates desired effects of LED light. There is growing evidence that all such scenarios are possible. The research jury is out on this one as well, and the choices likely will vary from species to species and cultivar to cultivar.
Large-scale overhead lighting? Maybe not.
Individual LEDs tend to be relatively low in wattage, even the high-output ones, compared to a high-powered HID lamp. The way LED arrays put out significant light intensity is by populating boards densely with individual LEDs so that their emission beams overlap, and by actively heat sinking them with cooling air or recirculating water. Heat-sinked LED arrays can put out significant light intensity at a distance from crop surfaces, but this does not take advantage of the unique advantage of LEDs. Because they lack the radiant-heat output of HIDs, LEDs can be placed much closer to plant surfaces. Therefore, closely placed LEDs can deliver as much photosynthetic light as more distant HIDs but with much less input power. Close positioning also is a current weakness of densely arrayed LEDs. They block solar light in the greenhouse, and of course the arrays are expensive. Thus, it is hard to envision large propagation or production greenhouses with massive arrays of LEDs delivering energy-efficient supplemental light at the intensity of HIDs, or for the fixture costs of HIDs.
As the shakeout continues, LEDs will find niches in the greenhouse industry, different niches in the warehouse-based plant-factory industry and HID lamps will continue to survive, mostly in greenhouses, for a while. LED applications for greenhouse propagation and production will continue to evolve as LED light-delivery technology advances, and should eventually become the dominant lighting technology for specialty-crop production, until something better comes along.
Can white LEDs control flowering?
By Qingwu Meng and Erik S. Runkle, Michigan State University
When the natural days are short (October to March), lighting during the middle of the night (night interruption, NI) can create long days. The spectrum and intensity of the light source is critical for its efficacy. For instance, blue light does not influence flowering at a low intensity (e.g., 2 µmol·m−2·s−1), but does at a moderate intensity (e.g., 30 µmol·m−2·s−1). In addition, at a low intensity, a mixture of red and far-red light effectively promotes flowering of long-day plants, whereas only red light is needed to inhibit flowering of short-day plants.
Incandescent lamps have been used for photoperiodic control, but they have been phased out of production. Replacing incandescent lamps with compact fluorescent lamps may delay flowering of some long-day plants. Light-emitting diodes (LEDs) have emerged as an alternative because of their energy efficiency, longevity, and spectral controllability. LEDs with a similar red-to-far-red ratio to incandescent lamps are effective at controlling flowering. However, some growers wondered whether more affordable white LEDs would also be effective.
White LEDs, which are really blue LEDs coated with a phosphor, cast a broad spectrum but emit little far-red light. They are categorized into cool, neutral and warm types based on light appearance. We grew five long-day plants (calibrachoa ‘Callie Yellow Improved,’ coreopsis ‘Early Sunrise,’ petunia ‘Wave Purple Improved,’ rudbeckia ‘Indian Summer’ and snapdragon ‘Liberty Classic Yellow’) and two short-day plants (chrysanthemum ‘Cheryl Golden Yellow’ and marigold ‘American Antigua Yellow’) at 68°F under nine-hour short days with or without one of five NI lighting treatments from LEDs: red, blue+red, cool-white, warm-white or red+white+far-red.
All NI lighting treatments similarly promoted flowering of calibrachoa and rudbeckia. In coreopsis, petunia and snapdragon, the most rapid flowering occurred under the red+white+far-red LEDs (Fig. 1). Surprisingly, the white LEDs did not create long days for snapdragon at all. Therefore, they were sometimes not as effective as the LEDs that emitted both red and far-red light. In contrast, the white LEDs were very effective at inhibiting flowering of the two short-day plants. Chrysanthemum plants did not flower under the white LEDs. Also, flowering of marigold was delayed under the white LEDs. In addition, some plants (e.g., coreopsis and marigold) were shorter under the warm-white LEDs than under the red+white+far-red LEDs (Fig. 1).
In summary, the white LEDs were generally as effective as the red and blue+red LEDs as an NI. These lamps stimulated flowering in four of the five long-day plants. However, flowering was delayed in some long-day plants compared to those grown under the red+white+far-red LEDs. Therefore, lamps that emit both red and far-red light are recommended for the most rapid flowering of long-day plants. General white LEDs may be useful to inhibit flowering of short-day plants, but additional research is needed before large-scale implementation.
Qingwu (William) Meng is a Ph.D. student and Erik Runkle (email@example.com) is a professor and floriculture extension specialist in the Department of Horticulture at Michigan State University. They thank the USDA National Institute of Food and Agriculture’s Specialty Crop Research Initiative and MSU’s Project GREEEN for funding this research, C. Raker & Sons and Syngenta Flowers for donating plant material and Nate DuRussel for technical assistance.
Impatiens necrotic spot virus (INSV) is a constant threat to eggplant, lettuce, peppers, tomatoes and other greenhouse vegetable crops. This is because INSV is invisible, can spread before symptoms appear and is vectored by thrips, which are notoriously difficult to control. It is also impossible to cure. Therefore, INSV management has to start by monitoring plants and managing thrips.
You are probably familiar with Western flower thrips (Frankliniella occidentalis). They feed on hundreds of plant species including most vegetables, ornamentals and herbs. They also vector INSV. Western flower thrips can only acquire INSV by feeding on infected plants during their first larval stage. Once the thrips are infected, they can transmit the virus to other plants throughout their life.
Monitor for adult thrips with yellow sticky cards throughout the greenhouse. Also look for signs of thrips feeding. Thrips feed by scraping plant tissue then sucking the juices that are released. This leaves abraded patches of tissue that often become silvery. Thrips also leave small black fecal pellets at these feeding sites. When thrips feed on young leaves or meristems, the leaves become distorted because the damaged cells do not expand properly.
Inspect plants with these or other unusual symptoms
Many plants with INSV will eventually exhibit symptoms including ring-patterned spots, necrotic spots or streaking on leaves or fruit. Stems may have dark necrotic patches or wilt. However, symptoms may not show up for weeks or months after infection. Some plants never show symptoms. One of the most sinister aspects of INSV is that thrips can acquire the virus from asymptomatic plants and spread it throughout the greenhouse before you ever know it is there.
Many growers use indicator plants to provide early warning that INSV is present. Indicator plants are plants that are particularly attractive and symptomatic to a particular pest or disease. For INSV, growers often use petunias, gloxinia, or fava beans as indicator plants, which typically show symptoms within a week. Spread a couple indicator plants throughout your greenhouse and inspect them frequently for INSV symptoms.
At the first sign of INSV, bag and discard the indicator plants so any thrips on them (which will likely be infected) do not move to crop plants. Then begin a zero-tolerance thrips management program because any thrips in the house could be infected. Thrips are only susceptible to insecticides as larvae and adults. Eggs are tucked safely within plant tissue and pupae are safe in the soil. Thus, even if you could make an insecticide application that would kill every larvae and adult thrips (you can’t), new larvae would hatch from eggs and new adults would emerge from pupae the next day. Therefore make at least three applications at five-day intervals to kill new larvae and adults, and break the population cycle. Monitor your crop and immediately bag and discard any plants with suspicious symptoms. Also set up new indicator plants to determine if infected thrips are still in the greenhouse.
Because plants cannot be cured of INSV and it is very hard to rid the disease from your greenhouse, prevention is key. Inspect new plants and cuttings for thrips or disease. Thrips often acquire INSV from weeds outdoors. Prevent thrips from entering your greenhouse with thrips screen and reduce movement of plants and people from outside to inside. Rid your greenhouse of weeds, pet plants, old stock plants and other non-essential plants, as these can be reservoirs for thrips and INSV.
INSV can be devastating if it becomes established in your greenhouse. But with constant monitoring, proper sanitation and effective thrips management, you can protect yourself from this threat.
Steven D. Frank is Associate Professor and Extension Specialist at North Carolina State University. He conducts extension and research related to greenhouse pest management.