Fraser Fir Christmas Trees Research Articles

Managing Cone Formation and Leader Growth in Fraser Fir Christmas Tree Plantations with Plant Growth Regulators

Early cone formation is a consistent issue in Fraser fir Christmas tree plantations in the eastern United States. Growers must remove cones by hand, resulting in significant labor costs, as cones degrade the aesthetic value of Christmas trees. In this study, we conducted two series of experiments in collaboration with several Christmas tree farms to determine the effectiveness of applying plant growth regulators (PGRs), specifically GA-inhibitors, in reducing cone formation and shoot growth in Fraser fir. In the first experiments we investigated the effectiveness of paclobutrazol, applied as a soil injection or as a foliar spray in reducing cone formation. The highest rate of soil application (300 mL of paclobutrazol per tree) reduced cumulative coning by approximately 38%. Leader growth control of soil applied paclobutrazol increased with application rate. In the second set of experiments, we compared four GA-inhibitors (paclobutrazol, chlormequat chloride, uniconazole-p, daminozide) applied as foliar sprays on coning and leader growth. Overall, paclobutrazol was the most effective compound for reducing coning and shoot growth. The results confirm earlier findings that application of GA-inhibitors can reduce, but not eliminate, coning. Likewise, PGR application can reduce shoot growth and possibly increase tree density but will not eliminate the need for shearing.

Characterization of the Entomopathogenic Fungal Species Conoideocrella luteorostrata on the Scale Insect Pest Fiorinia externa Infesting the Christmas Tree Abies fraseri in the USA

We characterized the entomopathogenic fungal species, Conoideocrella luteorostrata (Zimm.) D. Johnson, G.H. Sung, Hywel-Jones & Spatafora (Hypocreales: Clavicipitaceae), on the elongate hemlock scale, Fiorinia externa Ferris (Hemiptera: Diaspididae), infesting Fraser fir Christmas tree, Abies fraseri (Pursh) Poir (Pinaceae). Fraser fir Christmas trees that were cultivated in Michigan, North Carolina, and Virginia were intercepted in Florida during plant inspection. This study is based on the isolation in pure culture, and morphological and molecular characterization using a 4-locus (ITS, LSU, SSU, tef1) and represents the first record of C. luteorostrata on F. externa. In addition, we reviewed all previously reported natural enemies of F. externa in the USA, discussed their potential as biological control agents, and concluded the need to explore a new natural enemy of F. externa. We recommend using C. luteorostrata as a biocontrol agent for F. externa. We also suggest that our isolate could be a source of new uncharacterized active compounds and could be used in the biological control of whiteflies and scale insects, as demonstrated in other C. luteorostrata strains. We also discussed the importance of investigating biological control agents in pest and pathogen interception samples.

Arthropod and Disease Management in Fraser Fir (Pinales: Pinaceae) Christmas Trees in the Southeastern United States

Abstract Fraser fir, Abies fraseri [Pursh] Poir., is one of the most desired Christmas tree species owing to its fragrance, physical appearance, and durability. This species represents a major component of the Christmas tree industry in the southeastern United States, with production occurring in North Carolina, Tennessee, and Virginia. Fraser fir production is a multi-million dollar annual industry despite growing in a limited elevational and latitudinal range. Pest management for Christmas trees is notoriously difficult owing to the near zero-tolerance of most pests, even those causing aesthetic damage. Christmas trees are produced in monocultural environments which make them highly susceptible to several arthropod and fungal pests. We review the major pests affecting Fraser fir Christmas tree production, including their biology, symptoms, and scouting procedures, and current management strategies. In general, pest management in Christmas tree production systems has not changed significantly in the last several decades, and still relies heavily on pesticide usage. We propose several areas in need of research that could help Fraser fir Christmas tree producers mitigate the impacts of climate change and potential new pest species, as well as suggest changes to current or potentially novel integrated pest management strategies which have a chance to provide economic and ecological benefits for this industry.

Evaluating the invasive potential of an exotic scale insect associated with annual Christmas tree harvest and distribution in the southeastern U.S.

The movement of invasive species is a global threat to ecosystems and economies. Scale insects (Hemiptera: Coccoidea) are particularly well-suited to avoid detection, invade new habitats, and escape control efforts. In countries that celebrate Christmas, the annual movement of Christmas trees has in at least one instance been associated with the invasion of a scale insect pest and subsequent devastation of indigenous forest species. In the eastern United States, except for Florida, Fiorinia externa is a well-established exotic scale insect pest of keystone hemlock species and Fraser fir Christmas trees. Annually, several hundred thousand Fraser firs are harvested and shipped into Florida, USA for sale to homeowners and businesses. There is concern that this insect may disperse from Christmas trees and establish on Florida conifers of economic and conservation interest. Here, we investigate the invasive potential of F. externa on sixteen conifer species by quantifying the reproductive potential of this insect pest and its ability to establish, reproduce, and damage these plants. We find that small amounts of heavily infested Fraser fir plant material can release several hundred juvenile F. externa for over a month. Similar to other case studies, we find evidence that host susceptibility may in part be linked to phylogenetic relatedness. Encouragingly, only six of sixteen species evaluated were susceptible to attack. Our results provide new insights into methodology for evaluating scale insect dispersal and host susceptibility. We also provide guidance for future studies investigating scale insect reproduction, dispersal, and risk for plant species of unknown susceptibility to other exotic insect pests.

Shearing Systems for Fraser Fir (Abies fraseri) Christmas Trees

Plantation-grown Fraser fir (Abies fraseri (Pursh) Poir.) Christmas trees were subjected to nine shearing regimes over nine years in a plantation in western North Carolina (USA). Treatments differed in the year of onset as well as the length of the residual leader (25 to 46 cm). Long leaders (36 to 46 cm) yielded trees that were taller than trees sheared with short leaders (25 to 30 cm), but the gain in height was offset by a lower average U.S. Department of Agriculture grade. Late in the rotation, trees sheared with 36–46-cm leaders were 17–34% heavier than those with 25–30-cm leaders. Average wholesale price of trees sheared with long leaders was 57% greater than that of trees sheared with short leaders. Assuming good bud density on leaders and branches, and considering other factors as well, the optimum leader length for Fraser fir Christmas trees in western North Carolina appears to be 30 to 41 cm (12 to 16 inches). Depending on site quality and variation in bud density and vigor among individual trees, leader length can be reduced, if necessary, to increase crown density.

Post-Emergent Control of Nuisance Cones in Fraser Fir Christmas Tree Plantations

Heavy cone production by Fraser fir Christmas trees requires significant labor inputs to remove nuisance cones. We conducted two field trials in collaboration with operational Christmas tree farms to evaluate the effectiveness of post-emergent herbicides to stop the development of newly emergent cone buds. In the first trial (2016), we applied six products (two conventional herbicides and four herbicides labeled for organic production) to trees using back-pack sprayers in operational plantations at four farms in Michigan. Three products; Scythe, Axxe, and Avenger, provided better cone kill than the other products but resulted in phytotoxicity at two locations. In 2017, we applied the three most effective products from the earlier trial at three farms either as single applications or as two applications approximately one week apart. We also evaluated a hand-held mechanical de-coning device at two farms. For all the products and the mechanical device, cone control in the 2017 trial was high (>80%). Phytotoxicity to foliage was low (mean rating, <0.3; 0 = none, 2 = severe) for single applications of the herbicides. Repeated applications increased cone control slightly but also increased risk for phytotoxicity. The mechanical device caused significant damage to shoots and foliage. We attribute the increased product effectiveness and reduced phytotoxicity between the 2016 and 2017 studies to improved coverage and earlier spray timing. Based on the current retail product cost, chemical cone control can be cost-effective compared to handpicking cones if trees have high numbers of cones that can take several minutes to remove. The effect of using surfactants and reducing product rates should be investigated along with mechanized application.

Ortet Age and Clonal Effects on Growth and Market Value of Fraser Fir (Abies fraseri) Grafts as Christmas Trees

Grafting provides a means to clonally produce Fraser fir (Abies fraseri (Pursh) Poir.) Christmas trees that have desirable traits such as faster growth, greater crown density, increased pest resistance, or more desirable foliage attributes than seedling stock. Grafting Fraser fir to disease resistant rootstocks also provides a means to ameliorate the impact of root rot, predominantly caused by Phytophthora cinnamomi Rands. The influence of ortet age on growth and market value of grafts has not been studied for Fraser fir Christmas tree production. A field trial was established in 2004 near Independence, Virginia (USA), with the objectives of assessing (1) the effect of ortet age (stock plants = 6 to 8, 10 to 12, and 18 to 20 years) and (2) shearing regimes (fixed leader length versus variable leader length) on growth, quality, and market value of Fraser fir Christmas trees. Commercial height, Christmas tree grade (based on U. S. Dept. of Agric. standards), and net present value (US dollars) were assessed at the time of harvest. Cone damage to quality was rated after 8 years in the field. Scions from Fraser fir Christmas trees 2 m or taller produced grafts that expressed maturation, resulting in lower tree quality, heavier cone damage, and decreased market value compared to seedling stock. In contrast, the quality and market value of grafts was similar to that of seedlings when scions were collected from young Fraser fir Christmas trees. For Christmas tree production, scions should be collected from the upper whorls of trees no older than 2 to 3 years in the field (6 to 8 years from seed). The effect of age on Fraser fir clones varies so that pre-screening might identify some older selections suitable for use as scion donors. Fixed versus variable shearing regimes had little effect on tree value, although some individual clones responded better to one regime or the other.

Phenology and growth responses of Fraser fir (Abies fraseri) Christmas trees along an elevational gradient, southern Appalachian Mountains, USA

Fraser fir (Abies fraseri) trees are endemic to locations above 1500m in the southern Appalachian Mountains, and are also grown commercially for Christmas trees well below their native range (down to 600m). To evaluate how phenology and growth of this species will respond to climate drivers associated with warming, we assessed the timing of bud-burst, shoot growth, trunk growth, as well as shoot- and leaf-level architecture, of Fraser fir Christmas trees along an elevational gradient from 664 to 1228m. Daytime maximum temperatures and evaporative demand were highest at low elevation and cloud events and higher wind speeds occurred more often at high elevations. Bud-burst occurred 6days sooner, new shoots ceased elongation 10days sooner, and radial trunk growth ended 8days later at low elevations than at high elevations, indicating a shift and lengthening of the growing season. Final shoot length did not vary among elevations, but the percent increase in trunk diameter was greatest at middle elevations. Architectural characteristics such as specific needle mass, needle packing density, and silhouette-to-projected area ratios generally did not vary with elevation. As climate change progresses, higher cloud ceilings, increased evaporative demand, and higher temperatures may further shift the timing of the growing season and reduce growth at low elevation Christmas tree farms, but farms at higher elevations may benefit from a longer growing season.

Increased diversity of Phytophthora species in Fraser fir Christmas tree plantations in the Southern Appalachians

ABSTRACTPhytophthora root rot (PRR) disease afflicts significant economic losses to the Fraser fir Christmas tree industry. In previous surveys conducted in 1972 and from 1997 to 1998 in North Carolina, the incidence of PRR was ∼9.5% with Phytophthora cinnamomi identified as the predominant causal species isolated from infected roots of Fraser fir. Due to increased use of out-of-state planting stock since 2000, we suspected increased diversity of Phytophthora species. During 2014, we surveyed Fraser fir Christmas tree plantations in the Southern Appalachians of North Carolina, Tennessee and Virginia to determine the occurrence of pathogenic root-rotting species of Phytophthora. A weighted sampling strategy based on Christmas tree acreage was deployed to collect symptomatic Fraser fir roots from 103 commercial production fields in 14 counties. Six species of Phytophthora were isolated from infected roots sampled from 82 sites in 13 counties. Phytophthora cinnamomi, P. cryptogea and P. pini represented 70.3%, 23.1% and 1.1% of the 91 isolates. Phytophthora citrophthora, P. europaea and P. sansomeana accounted for the remaining 5.5% of the isolates and have not been identified in previously published Fraser fir surveys conducted in the region. The pathogenicity of P. citrophthora on Fraser fir was confirmed based on completion of Koch’s postulates.

Fraser Fir Tolerance and Weed Control with Hexazinone + Sulfometuron-methyl

Experiments were conducted to test a new herbicide for posttransplant application in Christmas trees. A premix containing 68.6% hexazinone and 6.5% sulfometuron-methyl was applied at 3.0, 4.5, 6.0, 7.5, and 9.0 oz/acre plus 0.25% v/v nonionic surfactant (NIS) to recently transplanted fraser fir (Abies fraseri) Christmas trees and trees transplanted for 1 year in Spring 2008. The treatments were repeated on the same plots in 2009 and 2010. At Gobles, MI, trees treated with 7.5 oz/acre of hexazinone plus sulfometuron had increased stem diameter, after one growing season, and trees treated with 9.0 oz/acre had reduced leader length the second year. After 3 years, fraser fir trees treated with hexazinone plus sulfometuron at 9.0 oz/acre had reduced tree height. Stem diameter, leader length, and number of leader buds were not statistically different from the untreated control. At Horton, MI, trees treated with 9.0 oz/acre of hexazinone plus sulfometuron had reduced leader length after 1, 2, and 3 years. After 3 years, trees treated with hexazinone plus sulfometuron at 6.0, 7.5, and 9.0 oz/acre were shorter than the untreated controls. There were no differences from the untreated trees in stem diameter of trees treated with hexazinone plus sulfometuron after 3 years.

Recent results of Czech-American fir hybridization research

Fraser fir (Abies fraseri) Christmas tree plantations in North Carolina are infested by root rot caused by Phytophthora cinnamomi. This disease kills almost 100% of Fraser fir material and leaves the soil permanently infested. Control crossings of Mediterranean fir hybrids Abies cilicica × Abies cephalonica with Abies fraseri were performed to ensure possibly resistant hybrid material of desired Christmas tree parameters. Pollen of various clones of A. fraseri was shipped to the Czech Republic by NCSU. Control pollinations were performed in April/May 2010 and 2011 in our hybridization seed orchards. Female strobili were isolated in the period of their highest receptibility. Cones were collected during September. Cones were dried and completely disintegrated. Basic parameters of cones and seeds were assessed for each seed lot. Seed samples of the individual seed lots were X-rayed for assessment of the final share of full seeds. In 2010, the most successful combination CZ2 × NC81 brought 7% of viable seeds. In 2011 the most successful combination was CZ2 × NC26 with 18% of viable seeds.

Fungicide Efficacy in Prevention of Root Rot Incited by Phytophthora cactorum and Phytophthora drechsleri in Fraser Fir Seedlings

The most serious disease problem in fraser fir (Abies fraseri) Christmas tree production is phytophthora root rot (PRR). The efficacies of six fungicide treatments in preventing PRR incited by Phytophthora cactorum and P. drechsleri in 2-year-old fraser fir seedlings were evaluated in 2010 and 2011 in central Pennsylvania. The study examined five fungicide drench treatments [dimethomorph, fosetyl-aluminum (fosetyl-Al), hydrogen dioxide, mefenoxam, propamocarb hydrochloride] and one soil spray treatment (mefenoxam) in raised planting boxes. Dimethomorph applied on 14-day intervals prevented foliar disease symptoms and mortality in fraser fir seedlings exposed to either P. cactorum or P. drechsleri. One-time application of fosetyl-Al or mefenoxam were effective at times in preventing foliar disease symptoms and mortality in fraser fir seedlings exposed to P. drechsleri but were not as effective against P. cactorum.

Needle Collection Time for Nutrient Evaluation in Christmas Tree Production

Christmas tree needle sampling to evaluate nutrient need is an established practice. Data to support the recommended fall sampling time in Oregon and Washington were not found. In addition, the recommendation for needle sampling of Fraser fir in North Carolina was made without data from winter months. The goal for this article is to affirm or modify recommended needle sampling time. Needles of Douglas fir, Turkish fir, Nordmann fir, Noble fir, Grand fir, and Fraser fir Christmas trees were collected monthly for a year, dried, and analyzed for nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and boron (B). No single period was found for any species when needle nutrient concentration was stable for all elements determined. Needle collection time was chosen by integrating cultural practices, likelihood of nutrient deficiency, and needle nutrient concentration changes for species grown in an area. Needle collection is recommended during February in western Oregon and Washington. The current sampling time, fall, is logical for Fraser fir Christmas tree production in North Carolina.

Design and Implementation of a Soil Matric Potential-based Automated Irrigation System for Drip Irrigating Fraser Fir

Irrigation of fraser fir (Abies fraseri) in Christmas tree production is gaining importance in the upper midwestern United States because of the intensive planting of this species out of its natural range. However, current scheduling practices rely on empirical observations with no monitoring of soil moisture and no use of automated irrigation system. The goal of this project was to design, construct, and implement a tensiometer-based automated irrigation system for fraser fir Christmas tree plantations that would (1) use existing technologies, (2) apply water based on changes in soil moisture content, (3) provide operational flexibility, and (4) interface with a computer for system changes, data collection, and system modifications. Soil tensiometers equipped with 4- to 20-milliampere transducers were installed at two drip-irrigated tree farms. Water on demand was controlled by soil moisture tension levels that triggered the stimulation of a relay wired to solenoids delivering irrigation water to the various treatments. The system functioned according to the design as expected. However, several issues associated with the need for regular maintenance of tensiometers, computer programming, and system wiring created some challenges regarding the reliability and transferability of similar system to commercial facilities.

Design and Implementation of a Soil Matric Potential-based Automated Irrigation System for Drip Irrigating Fraser Fir

Irrigation of fraser fir (Abies fraseri) in Christmas tree production is gaining importance in the upper midwestern United States because of the intensive planting of this species out of its natural range. However, current scheduling practices rely on empirical observations with no monitoring of soil moisture and no use of automated irrigation system. The goal of this project was to design, construct, and implement a tensiometer-based automated irrigation system for fraser fir Christmas tree plantations that would (1) use existing technologies, (2) apply water based on changes in soil moisture content, (3) provide operational flexibility, and (4) interface with a computer for system changes, data collection, and system modifications. Soil tensiometers equipped with 4- to 20-milliampere transducers were installed at two drip-irrigated tree farms. Water on demand was controlled by soil moisture tension levels that triggered the stimulation of a relay wired to solenoids delivering irrigation water to the various treatments. The system functioned according to the design as expected. However, several issues associated with the need for regular maintenance of tensiometers, computer programming, and system wiring created some challenges regarding the reliability and transferability of similar system to commercial facilities.

Naphthaleneacetic Acid Reduces Leader Growth of Fraser Fir Christmas Trees

Two methods of application, the Danish Easy Roller and the German Sprühsystem, were tested to evaluate the effectiveness of naphthaleneacetic acid (NAA) at reducing leader growth (tips of primary axes) of fraser fir [Abies fraseri (Pursh) Poir.] Christmas trees. A commercial product, Sucker-Stopper RTU (1.15% ethyl 1-NAA), was applied to leaders at concentrations of 0 to 500 mL·L−1 when leaders were 8 to 15 cm long. As the concentration increased, leader elongation decreased. The Easy Roller reduced leader growth the most, but leader mortality was unacceptable at concentrations 20 mL·L−1 or greater. Although less effective than the Easy Roller, the Sprühsystem caused negligible mortality of leaders. Applying 40 mL·L−1 with the Easy Roller yielded ≈50% of leaders with target lengths of 20 to 36 cm with little mortality. The Sprühsystem gave similar results at 250 mL·L−1. NAA might be useful for producing dense trees with minimal shearing or for producing more natural, open trees during shorter rotations.

Virginia Creeper (Parthenocissus quinquefolia) and Wild Grape (Vitisspp.) Control in Fraser Fir

Virginia creeper and wild grape are troublesome perennial vines that often infest Christmas tree plantations. Field studies were conducted to evaluate Fraser fir injury and Virginia creeper and wild grape control with directed applications of triclopyr (1,680 g ai/ha) alone and in combination with 2,4-D (1,120 g ai/ha), clopyralid (280 g ai/ha), and halosulfuron (36 g ai/ha). Additional treatments included 2,4-D, clopyralid, glyphosate (1,120 g ai/ha), halosulfuron, hexazinone (560 g ai/ha), mesotrione (105 g ai/ha), and sulfometuron (71 g ai/ha) applied alone; and a mixture of hexazinone plus mesotrione. In the triclopyr-containing treatments, Fraser fir injury ranged from 6 to 13% at 1 mo after treatment (MAT) and was 4 to 8% at 11 MAT. Leader growth was not impacted by the herbicide treatments. At 11 MAT, all triclopyr-containing treatments controlled Virginia creeper 93 to 98% and wild grape 98 to 100%, which was greater than the control observed with glyphosate at 63 and 59%, respectively. Virginia creeper and wild grape control with 2,4-D was 88 to 90%. Clopyralid, halosulfuron, hexazinone, hexazinone plus mesotrione, mesotrione, and sulfometuron provided less than 66% control of both perennial vines. Directed applications of triclopyr-containing treatments or 2,4-D were effective management tools for selective removal of wild grape and Virginia creeper from Fraser fir Christmas tree plantations. Additional research is needed on the potential sensitivity of other commonly grown Christmas tree species to triclopyr-containing treatments.

Weed Control in Christmas Trees with Flumioxazin and Other Residual Herbicides Applied Alone or in Tank Mixtures

Four studies were conducted from 2001 to 2004 in Michigan to determine Christmas tree tolerance and weed control with flumioxazin and other herbicide treatments. In Study 1, fraser fir (Abies fraseri) leader length was greater with fall-applied flumioxazin (0.38 lb/acre) than with halosulfuron (0.21 lb/acre), isoxaben (1 lb/acre), oxyfluorfen (1 lb/acre), simazine (2 lb/acre), or sulfentrazone (0.5 lb/acre). Flumioxazin applied in the fall provided preemergent control of common ragweed (Ambrosia artemisiifolia), field violet (Viola arvensis), and hoary alyssum (Berteroa incana) 79% to 98% the following summer. Preemergence weed control with the other herbicides was more variable. In Study 2, fraser fir treated in the spring with oxyfluorfen had the shortest leader length (terminal stem growth of the current growing season) at 4.3 inches. Trees treated in the spring with flumioxazin, isoxaben, simazine, and sulfentrazone had leader lengths of 6.7 to 8.7 inches. Flumioxazin applied preemergence in the spring controlled common ragweed 80%, but controlled field violet, hoary alyssum, and white campion (Silene alba) only 43% to 64%. In Study 3, fall-applied flumioxazin alone did not injure colorado blue spruce (Picea pungens). However, mixtures of flumioxazin plus pendimethalin (3 lb/acre) caused 5% and 6% tree injury at 6 months after treatment (MAT) and sulfentrazone plus pendimethalin caused 9% and 23% injury at 6 MAT in 2003 and 2004, and 52% injury at 9 MAT in 2004. There was no significant injury to the trees treated with isoxaben plus pendimethalin, oxyfluorfen plus pendimethalin, or simazine plus pendimethalin in 2003 and 2004. Leader length was reduced by sulfentrazone plus pendimethalin compared with flumioxazin plus pendimethalin and oxyfluorfen plus pendimethalin. Flumioxazin plus pendimethalin provided 84% to 88% preemergence control of annual grasses, common catsear (Hypochoeris radicata), horseweed (Conyza canadensis), and virginia pepperweed (Lepidium virginicum). In Study 4, spring-applied mixtures of flumioxazin plus pendimethalin resulted in minor (2%–10%) visual injury to colorado blue spruce, although leader length at the end of the season did not differ significantly from the control. In summary, flumioxazin controlled several weed species with acceptable selectivity in colorado blue spruce and fraser fir Christmas trees.

Weed Control in Christmas Trees with Flumioxazin and Other Residual Herbicides Applied Alone or in Tank Mixtures

Four studies were conducted from 2001 to 2004 in Michigan to determine Christmas tree tolerance and weed control with flumioxazin and other herbicide treatments. In Study 1, fraser fir (Abies fraseri) leader length was greater with fall-applied flumioxazin (0.38 lb/acre) than with halosulfuron (0.21 lb/acre), isoxaben (1 lb/acre), oxyfluorfen (1 lb/acre), simazine (2 lb/acre), or sulfentrazone (0.5 lb/acre). Flumioxazin applied in the fall provided preemergent control of common ragweed (Ambrosia artemisiifolia), field violet (Viola arvensis), and hoary alyssum (Berteroa incana) 79% to 98% the following summer. Preemergence weed control with the other herbicides was more variable. In Study 2, fraser fir treated in the spring with oxyfluorfen had the shortest leader length (terminal stem growth of the current growing season) at 4.3 inches. Trees treated in the spring with flumioxazin, isoxaben, simazine, and sulfentrazone had leader lengths of 6.7 to 8.7 inches. Flumioxazin applied preemergence in the spring controlled common ragweed 80%, but controlled field violet, hoary alyssum, and white campion (Silene alba) only 43% to 64%. In Study 3, fall-applied flumioxazin alone did not injure colorado blue spruce (Picea pungens). However, mixtures of flumioxazin plus pendimethalin (3 lb/acre) caused 5% and 6% tree injury at 6 months after treatment (MAT) and sulfentrazone plus pendimethalin caused 9% and 23% injury at 6 MAT in 2003 and 2004, and 52% injury at 9 MAT in 2004. There was no significant injury to the trees treated with isoxaben plus pendimethalin, oxyfluorfen plus pendimethalin, or simazine plus pendimethalin in 2003 and 2004. Leader length was reduced by sulfentrazone plus pendimethalin compared with flumioxazin plus pendimethalin and oxyfluorfen plus pendimethalin. Flumioxazin plus pendimethalin provided 84% to 88% preemergence control of annual grasses, common catsear (Hypochoeris radicata), horseweed (Conyza canadensis), and virginia pepperweed (Lepidium virginicum). In Study 4, spring-applied mixtures of flumioxazin plus pendimethalin resulted in minor (2%–10%) visual injury to colorado blue spruce, although leader length at the end of the season did not differ significantly from the control. In summary, flumioxazin controlled several weed species with acceptable selectivity in colorado blue spruce and fraser fir Christmas trees.

Effect of Two Fire Retardants on Postharvest Drying and Flammability of Douglas Fir and Fraser Fir Christmas Trees

SafeTree Christmas Tree Fire Retardant was applied to freshly harvested Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] boughs, and RapidCool FRX Christmas Tree Retardant was applied to freshly cut Fraser fir [Abies fraseri (Pursh) Poir.] boughs. The flame retardants were sprayed onto the foliage. Fire retardant accelerated the drying rate of Douglas fir boughs, which increased flammability. RapidCool fire retardant did not slow the drying rate of Fraser fir boughs, and had no effect on moisture content (MC) at ignition, flame time, total burn time, or total foliage consumed. For both species, initial ignition and spread of flame occurred at 60% to 70% MC. Fresh boughs did not ignite in burn tests and were not a fire hazard. Twig MC of nontreated Fraser fir increased 20% during display in water, further decreasing the possibility of ignition when exposed to a flame. Neither product was effective as a fire retardant on boughs of Christmas trees.