Seedling Loss Research Articles

Field tests of denatonium benzoate to reduce seedling damage by pocket gophers ( Thomomys talpoides Rich.)

The repellency of a bitter compound, denatonium benzoate, to reduce pocket gopher damage to conifer seedlings was tested in two independent field trials in Oregon and Idaho. In the Oregon trial (1992 to 1993), treatments included a denatonium benzoate tablet placed in-ground with the seedling roots; a tablet plus denatonium benzoate foliar spray applied to both roots and foliage; and no chemical application (i.e. control). No significant difference between treatments was noted for ponderosa pine ( Pinus ponderosa Dougl.) or Douglas fir ( Pseudotsuga menziesii (Mirbel) Franco) seedlings suffering gopher-related mortality. Non-animal mortality (58.2% of all seedlings) accounted for a greater loss of seedlings than gophers (38.2%). Composite foliage and composite soil samples collected from the treatment plots were all negative for the presence of denatonium benzoate. In the Idaho trial (1993 to 1994), similar treatments (but with an additional spray-only treatment) were used on ponderosa pine seedlings. There was no significant difference in gopher-related mortality levels between treatments. A large portion (72.5%) of all seedlings was destroyed by gophers. It appears that the bitter compound, denatonium benzoate, as evaluated in these trials, is not an effective gopher repellent.

Long-term softening of surface and buried hard seeds of yellow serradella grown in a range of environments

A 3-year field experiment was conducted to investigate seed softening in yellow serradella (Ornithopus compressus L.) in a low rainfall Mediterranean environment at Merredin, Western Australia. The study examined seeds of 4 accessions of serradella from separate growing sites (Pindar, Merredin, and Badgingarra), and included the effect of pod burial (only for accessions grown at Merredin). Pods were placed on the soil surface in December 1992 and sampled in March, June, and October for the next 3 years. Burial treatments (2 and 6 cm beneath the surface) commenced in June 1993 after pods had been on the soil surface for one summer. Samples were collected in June for the next 2 years. Softening of seeds over the first summer in the field was compared with that obtained in the laboratory with 16 weeks at a diurnally alternating temperature of 60/15ºC. Few seeds of any accession softened (generally <6%) at the soil surface during the first summer but the rate of softening increased over the next 2 years. The highest annual rate of softening was about 55% in the third year in accessions GEH72-1A and GEH72-2A. Accession of serradella hadmore influence on pattern of seed softening than site at which seeds were produced. Burial of pods at 2 cm markedly accelerated seed softening in all strains, particularly GEH72-1A and cv. Madeira, in which over 95% of hard seeds softened during the first year of burial. Softening at 6 cm was similar to that at the soil surface. Shallow burial of pods, as would occur during cereal cropping in one year,could improve regeneration of serradella, but reduce the longevity of its seed bank. Laboratory treatment at 60/15ºC generally over-estimated field softening during the first summer.The spread of germination in time in laboratory tests differed between accessions and was much wider in GEH72-2A than in others, extending up to 35 days. Such behaviour could provide insurance against total seedling loss following false breaks of season.

Common Bermudagrass (Cynodon dactylon) Management in Cool-Season Turfgrass

Common bermudagrass is an invasive, perennial weed of cool-season turfgrass in California. Complete renovation of the infested area has been the only practical method of restoring desirable cool-season turfgrasses. In studies in southern and northern California, common bermudagrass was suppressed with sequential herbicide applications, allowing seedling establishment and regrowth of established cool-season turfgrass species. One application of fenoxaprop, triclopyr, or their combinations did not control common bermudagrass. Sequential applications of these herbicide treatments resulted in 99, 94, and 100% control of common bermudagrass, respectively, and resulted in establishment of seeded perennial ryegrass in Riverside, CA, over a 2-yr period. Similar results were obtained in the recovery of established tall fescue from a common bermudagrass/tall fescue turfgrass mixture in Willows, CA. Both fenoxaprop and triclopyr can reduce emergence and stunt seedling growth of perennial ryegrass and tall fescue. Greenhouse studies showed that stunting and stand loss of tall fescue and perennial ryegrass seedlings could be reduced by delaying applications from PRE to the two-leaf stage.

Microbial Inoculants for Sustainable Forests

Fungal root pathogens are widespread and may cause substantial seedling losses in conifer nurseries. Furthermore, poor seedling survival and growth on reforestation sites results in reduced forest regeneration. Use of microbial inoculants for disease control and plant growth promotion has become an important endeavour. A microbial culture collection of 500 strains was assessed for biological control of fungal root pathogens and/or plant growth promotion of conifer seedlings. Seven of these strains showed significant suppres-sive effects on various soil-bome fungal pathogens. On Douglas fir, two strains, RAL3 and 64-3, reduced disease caused by Fusariumby. 7-42% in repeated growth room assays. The same strains significantly increased healthy stand of white spruce seedlings inoculated with Fusariumand Pythiumin a conifer nursery, and increased the survival of bare-root white spruce seedlings planted on a reforestation site by 19-23%. Both strains also significantly increased new root and total plant dry weights. Strain RAL3 in commercial formulation maintained a viable population of about log 8-9 cfu/ml for over a year when stored at 5°C. Strain survival on seed varied with conifer species. No decreases in bacterial populations were observed on seeds of jack pine or Douglas fir after 37 to 44 days storage at 5°C, but decreases were observed on seeds of white spruce and Scots pine. This study has provided candidate beneficial microbial inocu-lants which offer promise for development of commercial inoculants for the forestry industry.

Suppression of common root pathogens by helper bacteria and ectomycorrhizal fungi in vitro

Root pathogens cause considerable loss of tree seedlings in nurseries and are generally difficult to control using conventional methods. Inoculation with ectomycorrhizal fungi may provide some suppression of pathogens. Bacteria (so-called mycorrhization helper bacteria) have been isolated that stimulate mycorrhiza formation on seedling roots and enhance seedling growth; however, their role in pathogen inhibition has not been explored. Four strains of helper bacteria were inoculated together with the ectomycorrhizal fungal species Laccaria bicolor, L. proxima and Suillus granulatus on culture plates to determine inhibition of the pathogens Fusarium oxysporum and Cylindrocarpon sp. Buffered medium was used to rule out acidification of the medium as a mechanism of inhibition. None of the ectomycorrhizal fungal species alone inhibited the growth of Fusarium but all showed slight inhibition of Cylindrocarpon growth. Helper bacterium strain MB3 (Bacillus subtilis) was effective in inhibiting both pathogens and, when inoculated with either L. proxima or S. granulatus, inhibition of Fusarium growth was enhanced over MB3 alone. With Cylindrocarpon, however, only S. granulatus inoculated along with MB3 showed enhanced inhibition over MB3 alone. The other three bacterial strains had little effect on the growth of Fusarium or Cylindrocarpon. More research is necessary to determine if these inhibitory effects are reproducible in situ.

Gas exchange and water relations of Fraxinus americana affected by flurprimidol.

Effects of flurprimidol on plant water relations and leaf gas exchange were investigated in one-year-old white ash (Fraxinus americana L.) seedlings subjected to soil water deficits. Flurprimidol (20 mg kg(-1) of soil equivalent) was applied to the soil surface of pot-grown seedlings after shoot growth was completed. Two months after flurprimidol application, water was withheld from one-half of the seedlings. Leaf water relations and gas exchange parameters were measured 5, 7, 10, 14, 18 and 22 days after withholding water. Under both irrigated and nonirrigated conditions, flurprimidol treatment resulted in reduced net CO(2) assimilation rate and transpirational water loss of seedlings as a result of decreased stomatal conductance. Consequently, flurprimidol-treated seedlings had higher leaf water potential and relative water content than untreated seedlings. Nonirrigated flurprimidol-treated seedlings also had greater turgor and sap osmolality and lower osmotic potential at full turgor than seedlings in the other treatments, indicating that flurprimidol increased osmotic adjustment. Under water-stress conditions, water use efficiency was lower and gas exchange efficiency was higher in flurprimidol-treated seedlings than in untreated seedlings, suggesting that flurprimidol treatment enhances survival of plants subjected to soil water deficits.

Survival, Growth, and Fertility of Carpinus Hybrids

Parents Ht Stem diam Female Male Survivalz (m) (cm)y The need for a wider choice of small trees maturing at 10 to 13 m in height and capable of enduring the stressful environments of urban landscapes prompted my interest in the hornbeams (Carpinus). The first control-pollinated hybrids in Carpinus were made in 1973 and 1974 (Santamour, 1978). The chromosome numbers of the individuals used as parents were C. betulus L. (2n = 8x = 64), C. japonica Blume (2n = 2x = 16), C. orientalis Mill. (2n = 2x =16), C. tschonoskii Maxim. (2n = 4x = 32). True hybrids, verified by chromosome counts, were obtained from C. orientalis x C. tschonoskii (2n = 3x = 24), C. betulus x C. orientalis and reciprocal (2n = 5x = 40), and C. betulus x C. tchonoskii (2n = 6x = 48). No interspecific hybrids were obtained from crosses of C. japonica with the other three species. Sargent (1896) recognized two botanical sections in Carpinus, with C. japonica being classified in Sect. Distegocarpus and the other species in Sect. Eucarpinus (= Sect. Carpinus). Self-pollinations were made in all four parental species, but intraspecific crosses were limited to three species because I had only one plant of C. orientalis. Seed set from selfing was extremely low, indicating a high degree of self-incompatibility in these species. Only in C. betulus were the selfed seedlings vigorous enough to grow to outplanting size in 2 to 3 years. Also, in C. betulus, two different intraspecific crosses gave about the same seed set, but only one cross produced seedlings. The loss of several hybrid seedlings severely limited the numbers of plants available

Mortality and height growth losses of coniferous seedlings damaged by the black army cutworm

Growth and survival of seedlings were determined for 1 to 3 years following defoliation by black army cutworm, Actebiafennica (Tausch.). Ten data sets were collected on three sites and included four species of seedlings: interior Douglas-fir, Pseudotsugamenziesii var. glauca (Beissn.) Franco; lodgepole pine, Pinuscontorta Dougl.; western larch, Larixoccidentalis Nutt.; and Engelmann spruce, Piceaengelmannii Parry. Mortality following defoliation cannot be assessed until after the flush in the next growing season because completely defoliated seedlings often regenerate new foliage and survive. More than 90% of the total mortality that did occur was detected at that time. Mortality of up to 39% occurred when seedlings were defoliated more than 60%; most of this occurred when planting was carried out concurrent with defoliation. Synergistic root stress effects caused by poor planting, dry sites, or drought significantly increased mortality. Height growth was significantly reduced when defoliation was greater than 60%; the greatest effects occurred when terminal bud destruction accompanied needle loss. Growth losses were greatest the year of defoliation; recovery of height growth of lodgepole pine was complete by the 2nd year on good growing sites. On poor sites, retardation of lodgepole pine height growth was still evident after 3 years.

Gophers love oak — to death

Weed competition, insects, and small mammals all account for oak seedling loss. High populations of pocket gophers, as at Lopez Lake County Park in San Luis Obispo County, can destroy 90% of 2 to 3-month-old transplanted valley oak seedlings in the first year. Without effective protection from pocket gophers, any control of or protection from other small mammals and control of competition may be of little value

Fungal Pathogens inPinusandEucalyptusSeedling Nurseries in South Africa: A Review

SYNOPSIS Fungal diseases are responsible for severe losses of Pinus and Eucalyptus seedlings in South African forest nurseries. Pathogens such as Botrytis cinerea, Fusarium oxysporum, Rhizoctonia solani, Phytophthora cinnamomi, Cylindrocladium scoparium and Colletotrichum spp. are commonly associated with disease symptoms. Control can be achieved by means of cultural, chemical and biological methods, while ectomycorrhizae could also play an important role in resistance of seedlings to pathogens.

Prescribed burning in uneven-aged stand management of ponderosa pine/douglas fir forests

The purpose of this study was to examine the effects of low intensity prescribed fires on wildfire hazard reduction, site preparation and tree mortality of uneven-aged managed ponderosa pine/Douglas fir ( Pinus ponderosa/Pseudotsuga menziesii ) forests. The study also provided the opportunity to determine the effects of uneven-aged silviculture on fire hazards. Burning followed the individual-tree selection cutting and full-tree utilization of an uneven-aged silvicultural prescription, which was developed for two stands in western Montana, U.S.A. Prescribed burning, following the full-tree utilization, proved to have no usefulness on fire hazard reduction. Uneven-aged cutting without any fuel management treatment showed substantial fire behavior potential, far beyond the control limit of direct attack methods. Residual duff depth was not significantly different between the burned and the unburned treatment units. Mineral soil exposure of the burned unit was significantly greater than the unburned unit in only one of the study stands. Removal of the litter fuels was significantly greater in the burned units, contributing to a receptive seedbed for natural regeneration of shade-intolerant tree species. Fire succeeded in eliminating Douglas fir regeneration. Losses of ponderosa pine seedlings were substantial, but a few saplings and seedlings did survive the fire. Fire also killed 6·5 to 9% of the overstory trees (over 3 m in height). Overstory mortality was statistically significant, but this mortality was confined to smaller trees (less than 12 cm in d.b.h.). Guidelines are offered for a safe and effective prescribed burning under standing timber in ponderosa pine stands.

Seedling mortality caused by Hylastes cunicularius Er. (Coleoptera, scolytidae) in Picea abies plantations in Northern Sweden

Mortality of Picea abies seedlings caused by Hylastes cunicularius was studied by analysing damage reports and by repeatedly inspecting 12 000 individually marked seedlings in 59 plantations. The findings indicated that H. cunicularius caused more damage in the northern parts of Sweden than in the more southern parts. Feeding by H. cunicularius was the most frequent cause of spruce seedling death in plantations during 4 to 6 years after cutting of the previous stand. Although accumulated seedling losses sometimes exceeded 30%, yearly loss rates were generally moderate. The long period over which damage can occur is one of the reasons why H. cunicularius has rarely been identified as an important cause of seedling mortality in spruce plantations.

Germination of Piptochaetium Napostaense (Speg.) Hackel and Stipa Tenuis Phil. And Seedling Survival Under Field Conditions.

The objectives of this work were to investigate the germination of Piptochaetium napostaense and Stipa tenuis under laboratory conditions and to evaluate the effects of different plant canopy cover on seedling emergence and survival of the two species in the field. Fresh seeds of both species present a high level of dormancy associated with the lemma and palea, preventing seedling emergence immediately after the seeds fall in NovemberPecember. Seventy per cent of the seedlings of both species emerged in autumn. The germination behavior of these grass species may be an ecological adaptation serving to avoid seedling loss through exposure to the high temperatures and drought occurring during summer in the Calden District. Seedling survival was greater in the grazed, low plant canopy cover site, indicating that a certain degree of disturbance to reduce neighbouring plant interference favours seedling establishment in both species.

Influence of Moisture Loss During Storage on New Growth of Conifer Seedlings

Abstract The relationship between moisture loss from bare-root 2-year-old seedlings of Colorado spruce (Picea pungens glauca Engelm.) and percent survival and performance after extended storage at 0°C (32°F) was investigated. Moisture loss was examined by percent weight loss and moisture content (g H2O/g FW) during postharvest handling and storage. To generate different levels of moisture loss, seedlings were stored in various packages that differed in water permeability with a 0 and 1 day delay at 20°C (68°F) prior to 5 or 7 months of storage at 0°C (32°F). Depending on treatment, percent weight loss of seedlings varied from 0 to 60% and seedling survival ranged from 0 to 100%. When percent weight loss was below 25% all bare-root seedlings survived 5 and 7 months storage. Seedlings expressed a great degree of tolerance to desiccation stress, as demonstrated by those few which survived nearly 60% weight loss. Between 20 and 40% weight loss there was no direct relationship between moisture loss and percent survival. Bare-root Colorado Spruce seedlings grew with 100% survival following 5 and 7 months storage at 0°C (32°F) if packaged in either unsealed perforated or nonperforated polyethylene film.

Toward predicting reproductive success in submersed freshwater angiosperms

Reproduction is central to changes in distribution and abundance patterns of submersed freshwater macrophytes. In this paper we seek to identify potential ‘bottlenecks’ limiting sexual or vegetative reproduction or its predictability for these plants. To this end we consider the regulation of seed production, seed fate, vegetative propagule production, and vegetative propagule fate in turn, both in general terms and for the perennial Vallisneria americana Michx. in particular Plant biomass appears to be an important determinant of the incidence of flowering for greenhouse-grown Vallisneria americana: 88% of 425 plants either failed to flower if below a threshold dry weight of 0.75 g, or flowered if above it. The number of flowers (in females) or inflorescences (in males), however, was only moderately well correlated with Vallisneria biomass, and the flowering ‘threshold rule’ weakened considerably in the field. Closer examination of the dependence of seed output on plant biomass and pollination intensity, and of the importance of seed or fruit abortion is needed for submersed species. Our ignorance of seed fate is exemplified by the paucity of quantitative studies on dispersal distances and seed deposition patterns, on seed banks, and on features of seed microenvironments pertinent to germination, although the sensitivity of seed dormancy and germination to a variety of environmental conditions has been tested in the laboratory for many species. Further, losses of seeds and seedlings as a result of unfavorable environments, sediment disturbance, flotation, pathogens, and herbivores are generally not well characterized. Overall, the principal limiting step for sexual reproduction may in some cases be lack of floral induction, and in others, ineffective pollination, but dispersal away from the local population, failure of seeds to germinate, and the challenges of seedling establishment cannot be ruled out. Plant size is well correlated with vegetative propagule production for both greenhouse and field Vallisneria populations. As with seed germination, the germination of vegetative propagules has been relatively well studied in the laboratory, but important regulators of germination and establishment in the field warrant further study. We suggest that more investigations at two interfaces of physiological ecology and demography may be particularly fruitful. Regarding propagule production, experimental focus on allocation patterns which ‘translate’ accumulated resources into seeds or vegetative propagules should prove rewarding. Regarding propagule fate, post-dispersal mortality of seeds and vegetative propagules may be rooted in phytiological tolerance limits, but could also be attributable to pathogen or herbivore attack.

Aliette-Rovral Disease/Compatibility Test with Temik 15 G, 1989

Abstract The test was conducted at the Northeast Research Station, St. Joseph, LA. Terraclor Super-X (TSX) 10 lb (FORM.)/acre and Ridomil PC 8 lb (FORM.)/acre were used as standard fungicides. Aliette-Rovral combinations were applied in granular and wettable powder formulations. Plots were replicated 4 times in a randomized complete block design and were 4 rows wide (40-inch spacing) × 65 ft long. ‘Stoneville 453’ cotton was planted on 8 May, on a commerce silt loam soil which was cover cropped with vetch and fertilized preplant with 50 lb N/acre. Treatments were applied ihfurrow with a John Deere 7300 series planter which was equipped with granular applicator split boxes. Infurrow spray treatments were applied with a compressed air power sprayer system attached to the infurrow nozzles on the planter. Major pest and/or secondary pest control was initiated in late Jun and continued on an “as needed” basis through Aug. Stand data were recorded by counting all plants on the third row on 30 May. Plant height data (in) were recorded on 13 Jun. Plant disease ratings were made on 14 Jun. Twenty plants/plot were harvested and the root lesion size was measured and assigned a rating value. Yield was estimated by harvesting the 2 center rows of each plot with a mechanical harvester on 19 Oct. The seeding rate on the John Deere 7300 planter was set to deliver 84,500 seeds/acre. Cool/wet conditions followed planting. May rainfall was 5.29 inches occurring from the 5th to the 19th and Jun rainfall was 10.06 inches. Plant populations in the treatments ranged from 49,181 to 62,551 plants per acre after emergence. The cool/wet environment caused slightly higher than normal seedling loss which ranged from 26-42%.

Cylindrocladium root rot in Ontario bare-root nurseries: estimate of spruce seedling losses

Estimates of cylindrocladium root rot losses in three black and three white spruce compartments at five Ontario bare-root nurseries were determined through visual field assessment and seedling isolation. The causal fungus, Cylindrocladiumfloridanum Sob. & C.P. Seym., was isolated from 10–77% of the symptomatic and 0–28% of the apparently healthy seedlings in each compartment. In five compartments, estimates of mean incidence based on seedling isolations and visual assessment, were higher than those based on visual assessment alone. The percentage of living spruce (apparently healthy or symptomatic) estimated to be infected in each compartment was 0.1–32.7%. No fungus isolations were attempted from dead seedlings. Mortality in the plots in the six compartments was 0.02–17.7%. The correlation between the level of Cylindrocladium incidence and the inoculum density was significant (p < 0.01) in two compartments. The use of inoculum density to predict disease incidence warrants further investigation.

Evaluation of seed dressing and in-furrow treatments with fungicides for control of seedling disease in cotton caused by Rhizoctonia solani

Seven fungicides, together with the standard compounds quintozene and benodanil, were tested against Rhizoctonia solani in the laboratory and were then evaluated for the control of seedling disease in cotton grown in field plots, inoculated with R. solani. Both seed dressing and in-furrow applications gave some measure of control with all fungicides tested, but in-furrow treatments were the more effective, especially against postemergence damping off. Compounds giving the best control of seedling loss were tolclofos-methyl as a seed dressing and pencycuron plus captan in-furrow, reflecting results from the laboratory test. However, several other compounds were also as effective as the standard compound, quintozene, in controlling seedling loss.

SEEDLINGS

SummaryThe factors which cause the death of seedlings were examined and an attempt was made to determine the selective forces to which they are subjected in the field. After briefly dealing with the difficulties of defining a seedling, I examine a few cases from the recent literature in which the causes of seedling mortality are identified and quantified either by monitoring populations under natural conditions or by manipulating the environment experimentally. The special vulnerability of the immediate post‐germination phase is illustrated and the consistent underestimation of seedling loss in many studies is suggested. Some interesting cases of the effects of neighbours on seedling mortality are examined and it is shown that nearest neighbours may affect a seedling's chance of being grazed. It is concluded that since the causes of seedling mortality‐are so varied and unpredictable in most habitats, individual plasticity may provide a better strategy for survival than highly specialized adaptations to specific mortality factors.

Grasses as Hosts of Meloidogyne Naasi Franklin: Ii. Study of Nematode Populations and Their Effects On Yield of Three Varieties

The yields of Italian and hybrid ryegrass cvs Promenade and Inca respectively and of tall fescue cv. Pastelle were decreased by M. naasi for the three first months of their growth. The second stage juvenile populations within the roots during establishment were responsible in 1984 for losses of seedlings of Inca and Promenade. Negative correlations were statistically significant between these root populations and the height of both varieties, but dry and fresh plant weight was diminished only in cv. Promenade. The initial population in the soil (Pi) was significantly negatively correlated with dry weights of the plants of all three cultivars after three months growth. At the time of the second yield assessment cvs Inca and Pastelle were tolerant to M. naasi, by contrast with cv. Promenade. The study of the relationships relating to Pi and the root populations of the nematode revealed that J2 invaded the roots of grasses independently of the Pi, but three months after sowing, the number invading was proportional to the Pi. The increase of J2 populations in the roots may have been the consequence of invasion throughout the experiment only at the highest levels of infestation. The development of J2 into females in cvs Inca and Pastelle was negatively related with infestation level, but was independent of Pi in cv. Promenade.