American Rose Trials for Sustainability (A.R.T.S.) continues its work to trial and award roses with superior performance, providing growers and retailers the chance to profit from this iconic crop. These acclaimed selections also give consumers the chance to successfully grow roses. Eleven roses have earned 2020 A.R.T.S. Local Artist awards. Local Artist awards are regional awards recognizing superior performing roses tested under low-maintenance conditions. Of these winners, Screaming Neon Red is the sole 2020 winner to earn the highest A.R.T.S. award, A.R.T.S. Master Rose (roses winning four or more Local Artist awards), and becomes only the 12th Master Rose to date. The new and past A.R.T.S. winners will help industry members and gardeners alike enjoy 20-20 vision for roses as they seek to grow well-adapted roses that have a proven track record for excellence in their region.
Each year, more rose breeders send their most promising introductions to the A.R.T.S. national trial gardens to be evaluated under low-input conditions across the various U.S. climate regions. Each year’s set of trial roses are grown side by side with two industry standard/control roses that have well-documented strong performance in past research-Carefree Beauty (‘BUCbi’) and Knock Out (‘RADrazz’). The bar is definitely set high. After two full years of testing, the scores of the two industry standards are averaged to create a benchmark score. The test roses that outperform this benchmark in each climate region and have at least two-thirds of the trial roses in the region surviving to the end earn an A.R.T.S. Local Artist award. Gardeners selecting an A.R.T.S. Local Artist award winner for their region can expect to be very successful with this rose when providing basic plant care.
All deserving roses earn A.R.T.S. Local Artist awards, and there is no minimum or maximum number of awards. Having a solid and consistent benchmark eliminates the practice used in many trials of “grading on a curve” to ensure yearly winners. The debut of the 2020 A.R.T.S. Local Artist roses in May 2019 gives industry professionals an advanced opportunity to secure inventory of these strong performing and in-demand roses.
A step above
The A.R.T.S. testing methodology is the strongest, most scientifically-sound trialing protocol for a multi-site rose trialing awards program in the U.S., and possibly the world. Besides using industry standards in each trial as benchmarks, other solid scientific hallmarks include: ample spacing between plants to observe natural plant habit; plants of each trial cultivar are randomized separately throughout the beds with data taken monthly on each plant; and the evaluation protocol is straightforward. The thorough evaluation protocol, scientific rigor, focus on regional performance within a coordinated national program, use of modest nutritional inputs, no pesticides on the roses and strong trial site partnerships have allowed A.R.T.S. to raise the bar for independent, scientifically based rose trialing.
The A.R.T.S. Local Artist and Master Rose awards meet two key desires of the American gardening public. First, consumers desire, yet struggle to find, objective, accurate and research-based information from an independent source to guide their purchasing decisions. Second, to make the best use of limited time and hard-earned resources, people want to grow roses, as well as other plants, that have proven to be as sustainable, hardy, pest resistant and as beautiful as possible in their region. The A.R.T.S. team (university scientists, extension educators, public garden professionals and industry members with rose expertise) has made meeting these two goals the core of the A.R.T.S. mission.
The “regionality” of the A.R.T.S. awards means that nursery and landscape professionals along with home gardeners can be sure they are selecting plants that will perform well in their neck of the woods. Not every plant is going to thrive in every climate. While a particular cultivar may do well in the short, cool growing season of Maine, it may perform very poorly in the much longer and warmer conditions found in inland California. A.R.T.S. national test sites are strategically located throughout the continental U.S. and are hosted by partners that share the A.R.T.S. mission including botanical gardens, arboretums, municipalities, colleges and universities. A.R.T.S. defines its climate regions using the Köppen climate classification system, which is the preferred means used by ecologists. This system not only takes into account temperature, but also seasonal precipitation and humidity. The A.R.T.S. evaluation protocol has 45% of the score reflecting subcomponents of the health and quality of the foliage, 42.5% the presentation and quality of the flowers and 12.5% reflecting the plant’s growth habit. Climate can greatly impact all three of these evaluation categories. To find out which climate region of the country your garden is in, consult the Köppen climate map (pictured on page 17).
‘Listen’ to your local artists
With 30 roses now receiving Local Artist awards, a dozen of which are designated as A.R.T.S. Master Roses because of their wider adaptability, the momentum of A.R.T.S. continues to build. It is clear that A.R.T.S. is here to stay.
This spring, 15 A.R.T.S. national test gardens have already received, planted and begun evaluating a new set of trial roses. The spring 2017 A.R.T.S. plantings leading to the 2020 winners were planted in four U.S. climate regions. Thankfully, as of this year, A.R.T.S. has expanded to represent eight of the nine major Köppen climate regions of the continental U.S. The only one missing is the tropical southern tip of Florida. We believe A.R.T.S. has become the premier U.S. rose awards program and we are committed to continuing to strengthen the program.
For more: americanrosetrialsforsustainability.org
* Trial sites that hosted the 2017-2018 trials that determined the 2020 A.R.T.S. Local Artist awards.
After a lengthy and rigorous dissection of its practices, Loma Vista Nursery entered a program that will drastically reduce pest-related risks and enrich the company. Late last year, the nursery received SANC certification. SANC — Systems Approach to Nursery Certification — is administered by the National Plant Board, a non-profit organization that includes plant pest regulatory agencies representing each of the states and the Commonwealth of Puerto Rico and Guam. The program is voluntary, audit-based and designed for production nurseries to reduce pest risks associated with movement of nursery stock.
Nursery owner Lyndsi Oestmann learned about SANC from a longtime customer who thought they could benefit from the program because they ship to multiple states.
Soon afterward, Lyndsi and members of her key leadership team attended a SANC panel at Cultivate.
When Lyndsi told the leadership team she wanted to pursue SANC, the first question asked was, “Will this sell more plants?” But she was looking at it from a different perspective. It wasn’t about sales, it was about being accountable.
“I really like the fact that SANC holds us accountable to the practices we should be doing,” she says. “Because when it gets really busy at the nursery, it’s easy to slip out of habits, and SANC is how we get consistency throughout the year.”
Emerging and ongoing pest problems directly affect the bottom line. Through SANC, this systems approach can lead to healthier plants and facilitate commerce for all sizes and types of nurseries.
A competitive spirit was another motivation to go through the meticulous risk assessment. When Lyndsi told the inspector from the Kansas Department of Agriculture about the nursery’s plans, he said he didn’t think they could do it. That lit a fire under her and her dad, Mark Clear, who co-owns the nursery.
“My dad and I are both very competitive,” she explains. “He was a professional baseball player and I grew up playing competitive sports. If someone says we can’t do something, we’re going to do it.”
But it wasn’t just someone’s lack of faith in their ability. Lyndsi also knew it was the right path for the nursery to take.
“Deep down I knew it was something great for our team to do together.”
First, the nursery had to get the state of Kansas on board before they could even be accepted into the program. When the state gave its stamp of approval, the nursery’s inspector — the same one that didn’t think the nursery could pull off SANC and all of its requirements — really got into the process and was volunteering to help at every turn.
“He’s from a nursery background, so he understood how SANC could make both the inspection process and our relationship better,” Lyndsi says. “Inspectors don’t want to put a no-sale on a crop. Our inspector knows we’re doing things to prevent that.”
Once accepted into the program, the nursery hired a manager to solely help implement the program. She led the nursery’s SANC committee and eventually helped write the SANC manual.
Step one in the process is the risk assessment where every detail of the nursery is put under the microscope. The team identified potential pest pathways and strategies to assess them.
“We’d never looked at IPM or production so closely before,” Lyndsi says. “It was a huge process that involved almost every single person in the nursery.”
During the risk assessment, Lyndsi was pleased to find out they were already doing several things to reduce pest risks and all they needed to do was document those processes.
“We found we didn’t have to make huge, sweeping changes. We weren’t re-inventing the wheel,” she says.
Throughout this tedious process, Lyndsi helped put things in perspective for those involved.
“This is about our livelihood — the livelihood of 100 other people. Healthy plants mean a healthy business,” she says.
Loma Vista worked with its state qualifying agency to create a customized plan (also called the SANC manual) that addresses identified pest risks and maintains records of what is done. A subsequent audit by industry and state regulatory agencies assesses the grower’s plan and provides checks to identify if the plan is working.
The nursery set timelines to complete the necessary steps and met each one. They were certified in a shorter amount of time than any company in the program to date. Loma Vista’s SANC manual was used as the sample in national training for other state inspectors, she adds.
Lyndsi’s goal was to have a plan in place that was not only documented but could be repeated year after year despite any management changes.
“In the past, we’ve struggled when someone left and we didn’t have all of their processes documented. When our head grower retired, we realized he had so many things stored in his head,” she explains.
The nursery’s SANC Manual is now part of its daily business and drives training sessions for new employees.
“Each member of the team has responsibilities to SANC that are critical to the health of our plants and the success of our nursery,” she says. “They have always had those responsibilities, but with the level of SANC training we now administer, they are stated front and center. Everyone knows what they need to do and does it.”
One of the important changes that came out of the risk assessment is restricting visiting vehicles to certain parts of the nursery.
“We used to not consider all the trucks that would drive through here. Customers would drive right up to a bed to load plants in some cases. Now, we require everyone to check in at the office and we restrict where vehicles can go in the nursery,” she says.
The nursery’s team of scouts is about three times larger than it was prior to SANC certification. And growers from one growing section scout different sections for a fresh set of eyes.
Loma Vista is in the maintenance phase and has been audited by the state. SANC has improved the nursery/state relationship.
“At our last audit, I asked them to list the top five things on their radar that they were looking for. It’s more like a partnership now,” she says.
SANC also provides transparency and trust with the nursery’s state ag department.
“They are privy to our company’s best-management practices and plant health care plans, so they know we are going above and beyond to ship the healthiest plants we can,” she says. “This makes their jobs easier because they have confidence in the plants we are exporting and shipping within the state.”
Training is paramount to keep crews on point and not stray from the plan. New employees go through a training protocol. And the nursery makes sure all front-line employees understand what’s required to be compliant with the plan, what role they play in the plan and how it’s important to the business.
“The SANC training board lays out the responsibilities of every section in words and pictures. And the state comes in and helps by providing pest identification workshops. AmericanHort has been a great resource for us, too,” she adds.
The initial risk assessment was a year and a half ago, and occasionally the nursery finds something they should have addressed.
“Last winter, someone brought up the fact that our racks sit at our customers’ facilities and we don’t know what plants are put on them or where they’ve been stored. They could easily have a pest or plant pathogen on them when they come back to the nursery.
If the nursery needs to make changes to the manual, they have to be approved first by the state and then by the National Plant Board.
Lyndsi and the rest of the leadership team realized the absolute importance of teamwork during a process such as SANC certification.
“Challenge your team to get out of their comfort zone and outside the box,” she says. “Everyone was involved in some way and now the team has a sense of ownership in the SANC process. Our team is laser-focused on healthy plants, and I can see that affecting how they feel at work.”
The nursery celebrated wins during the process and celebrated when they attained certification. The leadership team established an incentive program for the scouting team to complete their duties in a timely matter. Within a six-week period, if everyone turns in their scouting records on time, lunch is brought in. If records are turned in on time all year, the team receives a personalized scouting notebook.
For the nursery’s team of front-line employees, if they identify an issue such as a pest, disease, water problem, etc. and report it to their supervisor, their name is entered in to a drawing for Loma Vista apparel, hats and gift cards for $20 to the local grocery stores.
“This helps keep people engaged and rewards them for paying attention to plant health. Even though we have a formal scouting program and a formally trained scouting team, everyone on the nursery is a scout,” she says.
Sue Markgraf contributed to this story.
The single photon avalanche diode (SPAD), such as the Minolta SPAD-502 from Spectrum Technologies, is a chlorophyll content meter that is commercially available, portable and used to measure “greenness” based on optical responses when a leaf is exposed to light that in turn is used to estimate foliar chlorophyll (Chl) concentrations. The SPAD-520 makes instantaneous and non-destructive readings on a plant based on the quantification of light intensity (peak wavelength: approximately 650 nm: red light-emitting diode [LED]) absorbed by the tissue sample. A second peak (peak wavelength: approximately 940 nm: infrared LED) is emitted simultaneous with red LED to compensate for thickness of the leaf. Percival et al. (2008) found, irrespective of the species that they investigated, Acer pseudoplatanus, Quercus robur and Fagus sylvatica, high correlations were recorded between SPAD readings, total leaf Chl and carotenoid content, foliar nitrogen (N) content, and leaf photosynthetic efficiency as measured by chlorophyll fluorescence Fv/Fm values; however, a poor correlation between SPAD values and the ratio of total Chl: carotenoid were obtained.
Much of leaf N is incorporated in Chl, so quantifying Chl content gives an indirect measure of nutrient status (Richardson et al., 2002). However, Chl generally accounts for less than 10% of a plant’s total N, whereas proteins account for approximately 80% of total plant N (Imsande, 1998). Additionally, the assessment of leaf photosynthetic pigments (Chl and carentoids) is an important indicator of senescence because breakdown of leaf Chl is associated with environmental stress (Brown et al., 1991). Another indicator of stress is the variation in total Chl/carotenoids ratio. A rapid increase in total leaf carotenoid content versus Chl is a widely recognized plant response to stress (Hendry and Price, 1993). Kitao et al. (1998) found that deciduous tree leaves showed their maximum photosynthetic performance in late-June, in their study, which occurred three months after first flush at their location.
In higher plants, carotenoids generally consist of 7% to 9% of total leaf photosynthetic pigments, consistent with values indicated by Hall and Rao (1999), Lawlor (2001), and Percival et al. (2008). Chl contains N but carotenes do not. Therefore, when N deficient plants are given N they increase their Chl concentrations but not carotenes and may develop a dark-green hue (Terry 1980; Val et al., 1987). This explains why trees fertilized with only N can be more susceptible to insect and disease infestations as the Chl: carotenoid ratio is imbalanced. Carotenoids are the “quenching” substances in the plant. Initial plant stress response is stomatal closure to conserve transpirational water loss, this in turn results in the production of high-energy reactive oxygen species (ROS) such as superoxide and singlet oxygen (Lawlor, 2001). Buildup of ROS results in oxidization damage to leaf membranes, i.e., chlorophyll bleaching and cellular membrane destruction. To minimize the effects of oxidative stress, plants have evolved an antioxidant system consisting of carotenoids that function as protective photooxidative pigments responsible for the quenching of these ROS (Kraus and Fletcher, 1994). Because an increase in total leaf carotenoid content is a widely recognized plant stress response (Peñuelas and Filella,1998), quantification of total leaf content can provide indicators of plant responsiveness to stresses frequently encountered in urban and landscape environments (Hendry and Price, 1993; Strauss-Debenedetti and Bazzaz, 1991; Vieira, 1996).
In the Percival et al. (2008) study, SPAD readings for Acer and Quercus ranged from 1 to 49. These were slightly higher on the low end, and slightly lower on the high end, than those reported by Richardson et al. (2002) for Betula papyrifera.
Cresswell and Weir (1997), working with woody plants in Australia, found the percentage leaf N associated with woody plant health ranged between 1.7% and 2.5% with values less than 1.7% being associated with a low foliar N content. Percival et al. (2008) investigated the relationship of % N to SPAD and Chl. Percival et al. (2008), found in their genera of Acer, Fagus and Quercus sp. that SPAD critical values of between 22 and 25 correlated to Cresswell and Weir’s (1997) low foliar N of 1.7%. Consequently, Percival et al. (2008) concluded SPAD value less than 25 are the level when N fertilization should start in these species to prevent N-related deficiency problems. Perry and Hickman (2000), did a survey of 25 woody landscape plants species in California with species from the following genera, Betula, Fagus, Buxus, Abies, Fraxinus, Ilex, Juniperus, Larix, Pinus, and Picea. Perry and Hickman (2000) only measured leaf %N and found for Quercus lobata leaf concentrations of total N ranged from a minimum of 2.14%, to a maximum of 2.85%, and an average of 2.32%. Acer saccharinum leaf concentrations of total N ranged from a minimum of 2.03, to a maximum of 3.39%, and an average of 2.52% (Perry and Hickman, 2000) and Betula pendula had a minimum of 2.16%, to a maximum of 3.39%, and an average of 2.69%. (Perry and Hickman, 2000). Percival et al. (2008) N levels for Acer pseudoplatanus ranged from 0.25% to 3.25% with coinciding SPAD readings between 0.5 – 49. N levels for Quercus robur ranged from 1% to 3.4% with coinciding SPAD readings of 1-49 (Percival et al., 2008).
There are several discrepancies in the reported leaf %N levels of Cresswell and Weir (1997) for general woody plant health and those reported by Perry and Hickman (2000), for the two genera that were common to those investigated by Percival et al. (2008). Percival et al. (2008), reported Acer minimum N% levels were considerably lower than Cresswell and Weir (1997). Perry and Hickman (2000), although, their maximum values reported did concur with Percival et al., (2008), they did not with Cresswell and Weir (1997). Likewise, Percival et al. (2008), Quercus minimum %N levels were considerably lower than Cresswell and Weir (1997) and Perry and Hickman (2000). Percival et al. (2008) Quercus %N, however, was much higher than reported by Perry and Hickman (2000) and Cresswell and Weir (1997).
Many studies support that top dress applications of N fertilizers in landscape or nursery field trees provided no benefit in growth versus no fertilizer (Day and Harris, 2007; Harris et al., 2008; Robbins, 2006). In other words, doing nothing was as good as fertilizing with N. Also, N fertilizers did not speed establishment, increase shoot extension or leaf nitrogen (Day and Harris, 2007). However, three factors that affect tree caliper growth beyond N application rate and timing that possibly confounded these “no benefit” studies were illustrated by other researchers and include soil compaction, groundcover(s) present and N form (Fare, 2006; Rao and Rains, 1976; Warren et al., 1993). Nitrate is the preferred form of N application if soils have high pH (above 6.0). Even though Nitrate N is preferred in alkaline soils, Nitrate absorption is more rapid at low pH (Rao and Rains, 1976). Another, issue is type of fertilizer. Controlled release fertilizers (CRFs) which contained minor nutrient packages were found to significantly increase caliper growth and time of development in a study by Mathers et al. (2012) which took place over three years. CRFs containing increased Zn and Mn may be more important to the growth of Acer rubrum ‘Red Sunset’ versus Pyrus calleryana ‘Chanticleer’ or
Dr. Elton Smith (1991), performed the only long term (18 years) study ever conducted in woody nursery/ landscape trees and created many of the current recommendations still used today. Dr. Smith’s recommended rates for top dress (surface for nursery) or (drilled, sub-surface or surface for landscape) were 220 to 264 lb/ac (nursery) (Smith, 1991), or 6#/ 1000 ft2 or 29.3 g/m2 (landscape) (Smith, 1986). Smith (1991) was conducted with Tilia cordata ‘Select’, Malus ‘Snowdrift’ and Acer saccharum ‘Monumentale.’ Despite soluble agricultural grade (SAG) fertilizers having been found to prove no benefit and CRFs with minor package being found to be effective, SAGs are still commonly used in nursery. Soluble or controlled release fertilizers (CRFs) are used in landscape, however, these do not always contain minor packages. The applications of soluble fertilizers are normally split (spring and fall) to be completed in late spring on or before mid to late June and mid to late autumn before a normal freeze. Thus, the questions of when? – with what? and rate? continue in woody plant studies and practices today.
Impact of pH
Nutrient availability to plants is affected more by pH than by any other factor. In high pH soils, ions of micronutrients such as iron (Fe) and manganese (Mn) precipitate and the availability of these elements decreases. Plants, thus, may express deficiencies of iron (Fe) and manganese (Mn) in these conditions. Phosphorus may also become deficient in alkaline conditions as it complexes with calcium (Ca) to form insoluble calcium phosphates. Deficiencies of most of the micronutrients can be corrected by adjusting soil pH. However, it is very difficult to adjust pH downwards. It is much easier to raise pH. In some cases, the soil pH may be so high that the sulfate reducing bacteria necessary to convert elemental sulfur (S) to the only form in which plant can take it up (SO4-) are in such low numbers that no conversion will occur (Reisenauer et al., 1973). Many regions of the Midwest have high pH or alkaline soils and have the scenario listed above, where sulfate reducing bacteria are limited.
Transplant mortality is a significant concern and expensive in terms of replant, warranties, customer satisfaction and time for landscape managers. Also, in the landscape correcting nutrient deficiencies is more important early in the life of the tree versus as the tree matures. Smith (1991) showed that trees over 6 years of age showed a marked decline in response to fertilizer or requirement. Smith (1991) showed that Tilia declined in nutrient requirements by 16 years, Malus at 10-12 years and Struve (2002) indicated Acer at 14 years.
Three common caliper trees sold for the urban landscape market in the Midwest are Quercus ellipsoidalis (northern pin oak), Acer rubrum 'Frank Red' (Red Pointe maple) and Betula nigra 'Cully'. These species prefer acidic soils and as pH increases above 7.0, iron (Fe) chlorosis develops with pin oak which prefers pH 5-6.5, and ‘Cully’ which prefers pH 3 to 6.5 and manganese (Mn) chlorosis with Red Pointe maple which prefers 5.1 to 7. The preferred pH ranges cited by species above, agree with the greatest availability of Fe or Mn for these species. Not only do genera and species differ in pH preferences, but differences exist in ability to absorb and translocate nutrients and ability to accumulate. The difference in Fe requirements, for instance, are much higher in Quercus palustris (nursery average 139 ppm) versus Betula nigra (survey average 107 ppm) (Jones et al., 1991) although both develop Fe chlorosis. Whereas, with Mn, Acer rubrum has a lower demand (survey average 20 ppm) versus Betula nigra (survey average 29 ppm) and a high demand for Fe (683 ppm) (Jones et al., 1991) even though Acer rubrum will develop Mn chlorosis and Betula nigra Fe chlorosis.
Pronounced chlorosis of either Fe or Mn deficiency results in reduced chlorophyll (Chl) synthesis (Abadía et al., 2011 ). Fe deficiencies actually reduce all the photosynthetic piments in leaves, i.e. (Chl) a, Chl b, carotene, and xanthophyll (Terry, 1980). Carotene and xanthophyll are the two groups that make up carotenoids in plants. Chl is essential not only as a photosynthetic pigment, but also as a structural component in living organisms. The reduced level of Chl molecules decreases the photosynthetic efficiency (Wang et al., 2018). Fe is also a cofactor in at least 139 enzymes that catalyze unique biochemical reactions. Fe thus plays many essential roles in plant growth and development including thylakoid synthesis and chloroplast development but also as indicated above photosynthetic pigments synthesis).
Mn plays an important role in oxidation and reduction processes in plants, such as the electron transport in photosynthesis (PS), especially PSII (Jones et al., 1991). Mn also plays a role in Chl production and activates IAA oxidases (Jones et al., 1991). Mn acts as an activating factor which causes the activation of more than 35 different enzymes (Mousavi, et al, 2011). Due to the metabolic role of Mn in the nitrate-reducing enzyme activity and activation of enzymes which play roles on carbohydrate metabolism, use of fertilizers containing Mn increases efficiency of photosynthesis and carbohydrates synthesis such as starch (Mousavi et al, 2011). Mn deficiencies decrease PS efficiency and therefore crop yield and quality are reduced in turn. Mn is taken up and transferred in the form of Mn2+ in plants (Mousavi, et al, 2011). Transfer in the meristematic tissues is gradual, thus the young organs of plants are rich of Mn and deficiencies show first in young tissues as do Fe deficiencies. Nitrogen (N) deficiencies by contrast appear first in older tissue. This is due to nutrient mobility in the plant, with Fe and Mn are phloem non-mobile, and N is phloem mobile. Calcareous soils, soils with high pH and especially in soils with poor ventilation (compacted) are prone to Mn deficiency.
Nitrogen is one of the most widely distributed elements in nature. It is present in the atmosphere, the lithosphere and the hydrosphere. The atmosphere is the main reservoir of N (Delwiche, 1981). The soil accounts for only a minute fraction of lithospheric N, and of this soil N, only a small proportion is directly available to plants. Both nitrate (N03-) and ammonium (NH4+) are forms of N that can be taken up and metabolized by plants. Nitrate is often a preferential source for plants, but much depends on the plant species and other environmental factors. A number of reports indicate that the uptake of both N-forms is temperature dependent, rates of uptake being depressed by lower temperatures (Clarkson and Warner, 1979). The most important difference between N03- and NH4+ uptake is in their sensitivity to pH. NH4+ uptake takes place best in a neutral medium and it is depressed as the pH falls. The converse is true for N03- absorption. Uptake of N03- is more rapid at low pH values (Rao and Rains, 1976). N is the highest required nutrient in plants. It is also the most common macro-nutrient deficient in plants. Not only is N required in large amounts, it is constantly leached and volatilized away. N deficient plants are often stunted, slow growing, exhibit weak growth and produce small leaves (espeically older leaves). General chlorosis progresses from light green to yellow and can be accompanied by excessive bud dormancy. Chlorosis can progress to necrosis of leaves and eventually abscission in advanced stages of more severe N deficiencies (Jones et al., 1991).
Despite the discrepancies reported above and the lack of specific information for the three species we are discussing, we assume the common genera values of the 1.7% N level reported by Cresswell and Weir (1997) and supported by Percival et al. (2008) are the critical N level for Quercus and Acer as found by Percival et al. (2008) with coinciding SPAD readings of less than 25. In our studies with the species discussed in this article, and based on the other research reported above, we found the SPAD-502 meter was a useful tool in determining when to fertilize with the critical %N, Fe and Mn levels lined up with SPAD readings below 25. Considering that it is difficult to get a response from N fertilizer applied to trees, as it is difficult to know when and with what fertilizer to use, it seems the SPAD-502 meter may provide help with your fertilizer budget decisions. The cost of natural gas and thus NH4 has remained quite stable since 2016, but as we know, under-fertilizing, or over-fertilizing with only N, always cuts into the bottom-line and reduces transplant survival including winter hardiness, all the while increasing pest and disease controls and establishment times.
Dr. Hannah Mathers, PhD, is owner of Mathers Environmental Science Services. She has been an independent researcher and consultant in nursery/landscape weed science, nutrition and cold stress since January 2015. Previously she was a professor at Ohio State University, an assistant professor at Oregon State University, Provincial Nursery Specialist for British Columbia and Provincial Nursery Specialist in Alberta, Canada. www.mathersenvironmental.com