Water! Water! Water! Without doubt, one of the most valuable commodities on earth, water is a resource we must protect and respect in all aspects of our personal and professional lives. In container production systems, we have made tremendous advancements over the decades in water quality, water use efficiency, irrigation delivery methods and timing, water recapture/reuse/recycling, etc. Large multi-institutional projects (WateR3, for example), continue to innovate systems and educate growers on better water use technologies and management practices.

As new production practices and products enter the horticultural market, there is a continual need to evaluate and understand how water is utilized in these systems. Let’s take substrates for example. The development and use of “new” substrate materials, primarily wood products, has resulted in many growers having to relearn or rethink how they irrigate their crops. Of all the promises and potentials of wood substrate components in growing media, there are some adjustments that have to be made during crop production. In this article, we will highlight some of the things growers and researchers are seeing and learning relative to substrate hydration and wettability before and during crop production. But first, let’s review some of the common terms used (often incorrectly or interchangeably) to describe events and activities relating to substrate hydration and water.

Wettability — the preference and/or capability of a liquid (water) to be in contact with a solid (substrate). The interaction of fluids and solids

Capillarity — absorption and movement of water through/by capillary pores as a result of the forces of capillary action often against gravity. Also referred to as “wicking”

Evaporation — water loss due to vaporization that occurs on the surface of water as it changes into the gas phase. Can occur on substrate surface as well as container wall surfaces

Hydration efficiency — the ability of a substrate to capture and retain water in the fewest number of hydration events (water applications)

Hydraulic conductivity — the ability or ease with which water can move through substrate/soil pore spaces across a hydraulic gradient. Measured in saturated and unsaturated conditions

Water holding capacity — often referred to as “container capacity.” The percent volume of substrate pores filled with water after saturation and drainage. Maximum water holding capacity is rarely achieved in production, since irrigations do not saturate the substrate. “Maximum” substrate capacities are typically reported based on laboratory testing. “Achieved” water holding capacity is the amount of water held in containers after normal irrigation events that apply water on or in the containers. The achieved water capacity of a substrate after irrigation is most always less than the reported maximum water holding capacity.

Saturation — when all substrate pores are completely filled with water. Not achieved with normal irrigations (top or bottom) if drainage is allowed

Hydrophobicity — tendency to repel water; unable to be easily wetted. Refers to a substrate’s ability to be hydrated or rehydrated easily.

Hydrophilicity — tendency to be wetted by water with little or no difficulty.

Wood substrate products (fiber, chips, shavings, etc.) are now being offered by many of the largest substrate manufacturers in North America and Europe. It is projected that the number of wood products and commercial substrates containing wood will increase significantly in the next 18 to 36 months. There are three primary technologies (machine and process types) that create wood products: Disc-refiners, screw extruders and hammer mills (Fig. 1A). While there are variations within each of the processing types, the overall structure, particle size and shape and properties of wood products are fairly distinct. Regardless of the wood product, the moisture content of the material at the time it is incorporated with other components (like peat) will significantly influence how it blends and mixes. For example, a disc-refined wood fiber has visual and physical differences when wetted at different moisture levels (from left to right) of 25, 33, 50, 66 and 88% (Fig. 1B). The wetter the fiber, the more it clings and clumps to itself. When blended with peat, the clumps are difficult to uniformly blend with peat and can look (and function) unfavorably (Fig. 1C). Inadequate moisture content at the time of potting (not moist enough) can lead to shrinking and swelling of the substrate in containers (Fig. 1D) which can negatively affect water capture and movement during irrigation events.

During crop production, one of the most frequent comments from growers has to do with surface drying of substrates that contain wood products. The drying of the substrate surface is much quicker and more severe than the normal expected surface drying of peatlite mixes. The surface drying of substrates (Fig. 2A) containing wood is normally seen in late spring or summer production times when water use and demand (from the plant and from the surrounding environment) are greater. The quickness and severity of drying (and the resulting substrate color change) can often lead to premature irrigations and thereby overwatering issues during production. Just because the surface is dry it does not mean that there isn’t sufficient water in the container. The surface drying is a result of the wood particle sizes and shapes, the light and fluffy nature of the material (low bulk density), the very high air porosity and different hydraulic conductivity rates compared to peatlite mixes. During late winter or early spring production when water demand is lower, surface drying is rarely a problem and often times can remain wet and prone to algae growth (but no worse than traditional peatlite mixes) (Fig. 2B). This also occurs often in propagation substrates and systems.

As a result of container surfaces often drying faster than what is normally expected, it is important that the substrate be able to be rewetted sufficiently and easily. The wettability and hydration efficiency of wood products is a topic of much focus and interest at the moment. Substrate hydration is critically important at the time of substrate blending/mixing, at the time of pot filling, transplanting and throughout a plant’s production time.

There are many ways researchers and substrate manufacturers test substrates for their wettability, re-wettability, evaporative losses, need for surfactants, etc. At North Carolina State University, the two most common techniques we use to quantify these parameters are: 1) overhead/drip hydration efficiency test (Fig. 3B&C); and 2) capillary rise ebb-in-flood efficiency test (Fig. 3A). These techniques simulate different irrigation delivery methods to test the water capture, retention, movement and release in substrates. Based on wettability, hydration, capillary, etc., substrates can be better engineered, formulated and chosen to best function (in regard to water) based on the irrigation method, pot size and height, etc. of individual growers.

The addition of wood products (primarily fiber) has been shown to improve the wettability of peat substrates at low moisture contents. When dry, peat can be very hydrophobic and difficult to properly wet. Wood by itself is less hydrophobic and in some instances (based on fiber size) can be slightly hydrophilic. As an example, peat was tested at low (25%) and high (50%) moisture contents. Ten overhead irrigation events were applied to the substrate samples and the amount of water retained after each event was measured. After the 10 hydration events, the maximum water holding capacity of the samples was determined and are represented on the graphs (Fig 4A.) as the solid red lines across the top, while the water retention is plotted with the blue line. Peat by itself at 25% moisture only, had a maximum water capacity of 25% and the irrigation events never even got to that level. At 50% moisture, peat’s maximum water holding capacity increased to 68%, but yet again, the irrigation events were never able to achieve that capacity (Fig. 4A). When 10% (by vol) ForestGold wood fiber was added to the same peat materials, the water holding capacity increased in the dry peat to 58% (compared to 25% in peat alone) and at 50% testing moisture, maximum hydration was achieved after four irrigation events (Fig. 4B). Similar results were seen with Berger wood fiber (Hydrafiber) at both the 25% and 50% moisture tests (Fig. 4C) with maximum hydration occurring at the seventh irrigation event. Both wood products shown here are disc-refined materials. Other wood products produced with different methods or of different sizes can behave differently.

Current and future initiatives in the Horticulture Substrate Laboratory at North Carolina State University are focused on substrate-water-plant interactions. Research on irrigation water in container crop production systems is a three-pronged approach: delivery, movement and fate. Delivery encompasses the different means and methods of irrigating crops in indoor and outdoor production systems. The need for substrates to capture and retain water is a critical step in production efficiency. Water movement entails how water, once captured by the substrate, moves vertically up and down a pot and also laterally from side to side in a root ball/pot. Water movement can depend on irrigation delivery method (from top or bottom), size/height of container, substrate components, dryness or wetness of substrate at the time of irrigation, presence of wetting agent, etc. Water fate includes draining/leaching after irrigations, evaporation from the substrate surface, evaporation from the container walls (if non-plastic), bound in substrate particles unavailable to plants or transpiration from the plants themselves. Understanding water delivery, movement and fate as it relates to substrate properties and grower management practices will be critical in the future as more and more emphasis (and dare I say — regulations) will be placed on water usage and management. How can we engineer or formulate substrates to be better (more efficient) at capturing, moving and retaining water? How can we mitigate water loss from the substrate? How can we extend plant water availability in post-production environments to extend plant shelf-life and quality? Many questions. Many opportunities.

The author is an associate professor and director of the Horticultural Substrates Laboratory at North Carolina State University. You can reach him at Brian_Jackson@ncsu.edu

Photo © eoneren | iStockphoto

Glyphosate, a popular nonselective pre-emergent herbicide commonly known by the trade name Roundup, has been in the news lately due to several high-profile lawsuits. In August 2018, a jury in San Francisco ordered Roundup’s manufacturer, Monsanto, to pay $289 million in damages to a school groundskeeper who claimed the product caused his cancer. A judge upheld that decision, but reduced the payout to $78 million. Recently, another jury in San Francisco ruled against Monsanto, concluding that glyphosate was a substantial factor in causing the non-Hodgkin lymphoma in a Sonoma County man.

Bayer, the company that bought Monsanto in 2018, responded by saying there was more than four decades of extensive science and the conclusions of regulators worldwide that support the safety and non-carcinogenic nature of their glyphosate-based herbicide.

The International Agency for Research on Cancer (IARC) did list glyphosate as a probable human carcinogen (Group 2A) in 2015. But that puts it on the same level as burning wood, eating red meat, high-temperature frying or late-night work shifts — other Group 2A carcinogens.

In 2016, the Environmental Protection Agency’s office of pesticide programs released a report stating there was no evidence of a correlation between glyphosate exposure and the numerous cancer claims. In 2017, EPA released a draft statement that also concluded that glyphosate was not a likely carcinogen to humans.

The difference in the two opposing conclusions comes down to the dose, said Jeffrey Derr, professor of weed science at Virginia Tech University. Derr addressed glyphosate use in nursery/landscape situations in a June 24 webinar hosted by AmericanHort. In his article in the May/June edition of the “Virginia Turfgrass Journal,” Derr said the IARC did not consider dose in their analysis, while the EPA did consider it to be relevant to the interpretation of data.

Christine Olinger of the EPA’s Office of Pesticide Programs also took part in the webinar to answer question about the EPA research. She said she saw some tumors in animals dosed high above the recommended levels.

Scott Senseman, head of the University of Tennesee’s Department of Plant Sciences, is the past-president of the Weed Science Society of America. In that role, he has drafted a statement on glyphosate cancer risk. However, the challenge is how to communicate science to non-scientists.

“We’re in a society that is made up of a lot of kinds of individuals,” he said. “Trying to come up with a statement that encompasses all of those is a tall challenge.”

In the June 24 webinar, Senseman said the WSSA Committee on Glyphosate Cancer Risk had also drafted a symposium proposal. The symposium would assist green industry professionals with interpreting results from long-term exposure studies, explaining the methodology used to assess toxicological risk, as well as looking at the situation from an attorney’s perspective.

Derr suggested a few alternatives to glyphosate-based herbicides.

“There’s no easy replacement for glyphosate,” he said. “There’s not one particular product that can do everything.”

Glufosinate is the top alternative he recommended. It’s a contact herbicide with some systemic action, available in the trade as Finale, Cheetah Pro and others. It offers activity within one to four days and is used at a rate of 2-4 quarts per acre. It carries a “Warning” signal word. Glufosinate is better than contact herbicides on perennial weeds, but somewhat less effective than glyphosate on them. It provides good control of cutleaf evening primrose, doveweed, dayflower and white clover. Derr cautions growers and other green industry professionals to keep glufosinate off the bark of young trees.

If you need weed control and you don’t want to wait one to four days, Derr said that diquat is an excellent option. This is the most effective contact herbicide alternative to glyphosate, he said. In fact, it’s the contact part of the popular, effective Roundup QuikPro product (which is glyphosate + diquat).

“On a warm, sunny day, if you treat an area in the morning you’ll see results by that afternoon,” he said.

Diquat carries a “Caution” signal word and is used at a rate of 1-2 pints per acre.

The author is managing editor of sister publications Nursery Management and Garden Center.

What does “funky” mean to you? For many, it can relate to smell, a rhythmic dance or even trendy clothing. But for Jen Browning, technical service specialist for western turf and ornamentals at BASF, the term “funky” relates to pests. In the third part of the Funky Pests series, Browning discusses a commonly overlooked issue that complicates pest management for growers.

“My funky pest is weeds in the greenhouse,” she says. “Weeds are competing for resources with our plants — they’re hogging water and nutrients. But the real reason why weeds are a funky pest is because they are a Trojan horse for insects and disease.”

According to Browning, weeds can be hosts to powdery mildew, aphids and other pests. If allowed to flower, there can be thrips hiding inside the buds, which essentially creates a reservoir of crop-visiting pests.

She says the weeds that grow under a bench or in between sidewalk cracks can be easy to overlook because scouts tend to focus on the plants where insects and diseases are more obvious. However, weeds can actually make the insect and disease pressure worse.

While most growers do pull greenhouse weeds, Browning says they’ll sometimes end up in an open trash can and hang out there for days, dispersing insects and disease back onto the crop.

“The spores and bugs bounce out of the trash can, or get transferred to workers who reach inside,” Browning says. “It spreads the pests around the greenhouse — but this can be remedied by something as simple a tight-fitting lid on the container and frequent trips to the main trash collection area.”

Some example of weeds that Browning classifies as detrimental to greenhouse cleanliness are algae and liverwort. They are a food source for shore flies, which in turn may transfer pathogens around the greenhouse. Because they eat algae and carry diseases — like powdery mildew spores — they add to the disease pressure by flying around and touching crops.

“They can transfer pathogens right onto the plants,” Browning says. “Meanwhile, the grower’s thinking, ‘Why do I keep having this problem? Where is it coming from?’ It’s coming from the weeds in the greenhouse. That’s why sanitation is so important.”

Weeds themselves are one of the lesser pests in greenhouses, so their impact on IPM can be overlooked — this is why Browning considers them to be funky.

“I think of funky as the unexpected,” Browning says. “Funky can be when you don’t know the pest or don’t know where it’s coming from.”

In her breakdown of pests, Browning — who is also a trained entomologist and horticulturist — categorizes them as “funky,” “maybe funky” and “not funky.”

“Funky pests” are the ones that surprise you, like weeds sneaking in bugs and disease. “Maybe funky” are the ones you need help identifying — maybe they are a problem, and maybe they’re aren’t. “Not funky” are the ones you recognize immediately and know how to deal with: aphids, mites, powdery mildew.

But Browning says even known pests like aphids and thrips can be funky because of their ability to create an unexpected situation. Aphids can build up large populations seemingly overnight, which Suzanne Wainwright-Evans mentioned in the previous Funky Pests article. (bit.ly/unusual-aphids). Browning notes that warm temperatures in greenhouses enhance rapid development of pest populations. “The higher the temperature, the faster they go from being an egg to a reproductive adult,” she says.

“And sometimes the pest isn’t who you think it is,” she says. “You may deploy an insecticide or biological control agent that doesn’t work — because the pest you are seeing isn’t the right target for that tool.”

But weeds aren’t so complicated. They hide in plain sight and there are some simple tricks to keep them from making your pest problems funkier than they need to be.

“Greenhouse sanitation is not a sexy topic,” Browning says. “People don’t want to spend a lot of time thinking about this — it’s boring! And it’s entwined with labor issues. We have fewer people to do more work than ever in the greenhouse, so pulling those weeds, even if they’re little, and quarantining them in a closed container works. Include the weeds you do see in your spray regimen — fungicides and insecticides should be applied to them as well between weeding cycles. These are some easy ways to help defunk the greenhouse.”

Training new employees how to water is very difficult — greenhouse staff and owners concur. Many growers have told me that watering is their No. 1 training need. Why is it so difficult to learn or teach how to water properly? Many argue that there is art in this practice, and that art is unteachable. Teaching someone how to paint like Leonardo da Vinci is impossible. Yet, anyone can learn the basic skills of drawing and painting.

Watering is not an easy task. Individuals need to consider multiple factors before deciding whether to irrigate or not. Hence, teaching it is not simple either. I argue that when training new employees, we need to communicate better and more often and emphasize the whys and the hows.

Tip No. 1: Define watering.

New employees must understand that irrigating crops is not about pouring water or turning on a water valve. Watering is about maintaining AIR and WATER balance in the root-zone — that is the ultimate goal.

Tip No. 2: Explain WHY watering is difficult.

Regardless of the operation size, all greenhouses producing ornamental plants are EXTREMELY diverse. Walk with your team in the greenhouse, point out the diversity and explain WHY watering everything with the same volume and frequency is not appropriate. For example, you can see a small greenhouse dedicated to retail and another greenhouse producing for wholesale. Both have the same “diversity problem.” For example, on the top scenario, you can point the different materials of the hanging baskets (coconut fiber will allow the media to dry faster than plastic), small containers need less volume per irrigation but higher frequency, hanging baskets receive direct light while plants on the bench are partially shaded, each container contains a different mix of crops, and the canopies are dense or the crop is too high, making it difficult to visually assess moisture. Workers who are aware of the differences are more likely to pay attention while doing the task. Explain how fluctuating weather patterns makes watering difficult. We tend to talk about seasons as a parameter, but the truth is that the oscillation of temperature and sunlight that we see within a week in spring and fall is broad. In Connecticut, we can go from a snowy-dark-cold day to a sunny-bright-warm day in less than 24 hours. Prepare your staff to respond to these unplanned changes.

The weather itself calls for a watering decision. On top of that, workers must decide what to do instead of watering. Workers may fear being perceived as if they are not working hard enough and the easiest way out is to grab a hose which may be WHY some workers overwater. Head growers must communicate with their staff to make sure they all agree about how weather patterns will affect daily tasks. If the staff member’s role is to water a section, but the crop doesn’t need it, then the staff should have a clear directive about what alternative activities to conduct.

Tip No. 3: Discuss WHY plants need water and WHY excessive or insufficient levels affect crops.

Photosynthesis is the process in which solar energy converts to chemical energy. For photosynthesis to occur, a water molecule must be broken down. Hence, without water, there is no photosynthesis; without photosynthesis, plants will not grow. Water also carries nutrients and helps maintain cell/plant turgidity. The take-home message is that plants need water to maintain structural integrity and perform basic functions. Plants also need oxygen in the root zone to maintain essential plant functions. That is why we cannot keep the substrate saturated. Explain physical properties of the growing media. When we fill containers with growing media, there will be gaps between the media particles. If we cover the bottom of the container so nothing comes out, and then add water — the water will fill those spaces, leaving no room for air. If we then let the free water drain, a portion of the water will remain adhered to the media particles and there is also air space. This is known as container capacity.

Tip No. 4: Agree on HOW and WHEN to water.

The instructions for most activities in the greenhouse are specific — hence why they are easy to learn or teach. For example, dip the cuttings before transplant, after (x) number of days transplant (#) liners to an (x) size container, a given amount of product per area or container, spray every number of days, prune to a given height, etc. However, most operations don’t communicate that specifically about watering. I recommend that every operation develops clear guidelines for watering. I know it’s not a simple task (that is why we started acknowledging the complexities), but it must be done. Everyone in the operation MUST agree on what is the criteria to irrigate or not to irrigate. Dry media does not always call for action and growing on the dry side has many benefits for ornamental crops.

Tip No. 5: Retain your employees

Retrain to make sure the staff has not deviated from the original guidelines.

The author is an assistant professor and greenhouse extension specialist at the University of Connecticut. You can reach her at rosa.raudales@uconn.edu.