Plots In May Research Articles

Strategies for Mixed‐Grass Prairie Restoration: Herbicide, Tilling, and Nitrogen Manipulation

AbstractLarge areas of North American prairie have been planted with grasses introduced from Eurasia. We examined three strategies (herbicide, tilling, and nitrogen manipulation) for enhancing the establishment of seedlings of native species and suppressing the introduced grasses Agropyron cristatum (crested wheat grass) and Bromus inermis (smooth brome). Plots (5 × 15 m) were subjected to one of three levels of tilling (none, intermediate, complete) and four levels of nitrogen (none, intermediate, high, and sawdust added to immobilize nitrogen). Treatments were applied in a factorial design with twelve treatments and ten replicates. Seeds of 41 native species were drilled into the plots in May 1992. Following the failure of seeds to establish in 1992, a subplot (5 × 13 m) within each main plot was sprayed with the herbicide glyphosate in April 1993. The nitrogen treatments were repeated in Spring 1993. In August 1993, the density of native seedlings in sprayed subplots was 20 times that in unsprayed subplots. Within sprayed subplots, native seedling density and the cover of bare ground decreased significantly with increasing nitrogen availability. Plots receiving sawdust had significantly higher mean cover of bare ground and significantly lower concentrations of soil available nitrogen. Native seedling density was significantly higher in plots receiving the highest intensity of tilling. The responses of native seedlings to all these factors point to the importance of neighbor‐free establishment sites as a prerequisite for prairie restoration.

Impact of Forcing Summer Asparagus in Coastal South Carolina on Yield, Quality, and Recovery from Harvest Pressure

The objective of this study was to determine the effect of forcing summer asparagus (May to October) and age at first harvest after transplanting on yield and quality. Ten-week-old `UC 157 F1' asparagus seedlings were field-planted on Sept. 1986 and forced to emerge from 1988 to 1992 by mowing fern in separate replicated plots in May, June, July, August, September, or October. Forcing treatments were not spring-harvested. Forced yields were compared to normal spring harvests (emerging from January to April). Harvesting began for the first time ≈18 or 30 months after transplanting. Spring 1988 yields were greatest of all, but declined yearly for 5 years. Summer forcing in either July or August maintained acceptable yields through 1992. The warmer climate during summer forcing caused most plants to reach the prescribed cutting pressure (eight spears per plant) within a standard 6-week harvest season. Cooler temperatures during spring harvest seasons slowed spear emergence and prevented the plants from reaching prescribed cutting pressure. Forcing in May and June was too stressful to plant recovery after the harvest season by reducing fern regrowth and increasing plant death. Cooler temperatures during October forcing inhibited spear emergence. Forcing in September yielded less than forcing in July and August, but September asparagus would command higher market prices. There was no advantage at any harvest time to delay first harvests from 18 to 30 months after transplanting. Forcing in July through September has potential as an alternative enterprise in coastal South Carolina.

Reversing the Fragmentation Perspective: Effects of Clearcut Size on Bird Species Richness in Maine.

The effects of clearcut size on bird species richness in a forest-dominated landscape were examined. Forty-five clearcuts, ranging in size from 2 to 112 ha and in age from 3 to 10 yr post-cut were selected as study sites in eastern Maine. At least 10% of each clearcut was censused using 1-16 fixed-radius (50-m) circular plots in May and June of 1989 and 1990. Species richness increased with clearcut size but the number of species present per plot did not differ significantly over the size range of cuts. There was some evidence of increased richness in clearcuts up to 20 ha. Of the 15 most common clearcut species in both years, 10 (1989) and 12 (1990) increased in abundance between 2 and 20 ha, beyond which no preference for clearcut size was found. Additionally bird species locations throughout clearcuts were largely independent of distance from the forest edge.

Revegetation of a contaminated zinc smelter site

Over 800 ha of forest vegetation are dead on Blue Mountain at Palmerton, Pennsylvania. The major cause was emissions of Zn, Cd, Cu, Pb, and SO 2 from a zinc smelter operating since 1898. In 1985, a research effort was initiated to develop a remedial action program to mitigate the environmental damage. Field plot studies were conducted to determine the feasibility of using mixtures of dewatered municipal sludge and fly ash as amendments to facilitate the establishment of vegetation on the highly contaminated soil. Three mixtures of sludge (S) and fly ash (FA) were evaluated (1S:1FA, 2S, and 3S:1FA). The amendments were applied on 0.4-ha plots in May 1985. Five grass and legume seed mixtures were hydroseeded on subplots for evaluation. In addition, seedlings of 10 tree species and hybrid poplar cuttings were planted on the plots. After two growing seasons, results indicate that all three sludge-fly ash mixtures were successful in facilitating vegetation establishment.

The chemical regulation of polyisoprenoid synthesis in Parthenium argentatum with 2-(3,4-dichlorophenoxy)-triethylamine

Applications of 2-(3,4-dichlorophenoxy)-triethylamine (DCPTA) to guayule plants ( Parthenium argentatum) increase the enzymatic polymerization of isopentenyl pyrophosphate (IPP) to polyisoprene. The purpose of this study was to determine the effectiveness of DCPTA in increasing polyisoprenoid rubber synthesis at the end of the winter period of rubber synthesis in plants expressing a high level of polymerization activity. Guayule seedlings were transplanted to desert field plots in May, 1987 and treated with DCPTA. The polymerization activity in the stems was monitored throughout the year and the rubber content of the stems was determined in April, 1988. Treatment of plants with DCPTA increased the enzymatic polymerization activity in stem homogenates. The polymerization activity in control plants increased from 4 nmol h −1 g fresh wt. −1 in July to 183 nmol h −1 g fresh wt. −1 in January and the activity in plants with 1000 ppm DCPTA increased from 7 nmol h −1 g fresh wt −1 in July to 340 nmol h −1 g fresh wt. −1 in January. The high mol.wt. rubber polymer in the stems was determined by solvent extraction and 13C-NMR spectroscopy. Applications of different concentrations of DCPTA to guayule plants resulted in a statistically significant increase of 7–33% of the rubber content of the stems. The application of DCPTA to guayule seedlings stimulates the synthetic pathway for the production of secondary products in mature plants.

The capability of the predacious fungus Arthrobotrys oligospora (Hyphomycetales) to reduce numbers of infective larvae of Ostertagia ostertagi (Trichostrongylidae) in cow pats and herbage during the grazing season in Denmark.

Artificially prepared cow pats containing Ostertagia ostertagi eggs were deposited on two pasture plots in May, June and July 1986. Half of the cow pats, placed on one plot, were inoculated with 2000 conidia per gram faeces of the predacious fungus Arthrobotrys oligospora. On the other plot fungus-free control cow pats were placed at the same time. In the faeces generally fewer infective O. ostertagi larvae developed in the inoculated than in the control cow pats. On the herbage around the control cow pats deposited in May, June and July a maximum concentration of infective larvae was found at the same time on the 6th of August 1986. At that time the herbage larval infectivity around inoculated cow pats deposited in May, June and July was subject to a reduction of 48%, 89% and 46%, respectively, compared with fungus-free control cow pats. This experiment indicates that a concentration of 2000 A. oligospora conidia per gram faeces results in a significant lowering of the herbage larval infectivity during the grazing season in Denmark.

Control of striped chafer,Odontria striataWhite (Coleoptera: Scarabaeidae), in pasture using lindane

Abstract A field trial carried out in North Otago was designed to determine the most beneficial time (April or June) and rate of application (1 or 2 kg a.i./ha) of lindane granules to pasture to control striped chafer (Odontria striata White) and alleviate pasture damage in spring. Only the 2 kg a.i./ha rate of lindane applied in April reduced larval density in the field (48%) compared with control plots when sampled in September. However, all lindane treatments gave good control of the next generation (85 – 92%) when sampled in February in the following year. Soil cores taken from the field trial plots in May and September were used in laboratory bioassays to investigate the effect of lindane on adult striped chafers. The bioassays showed that lindane caused adult mortality in winter (77 – 84%) and spring (92 – 100%) with no difference between the rates or times of application. Striped chafer larval density was low in the field trial area (31/m2 before treatment) and no differences in pasture production ...

BIOLOGICAL CONTROL OF ROOT PATHOGENIC FUNGI BY TRICHODERMA

Abstract The antagonist Trichoderma harzianum can protect against many pathogenic fungi. Glasshouse trials with biological control of black root of cucumber ( Phomopsis sclerotioides ) grown in rockwool with T. harzianum were carried out. Seeds and rockwool mats were treated with spores of the antagonist. After a growing season (February-July), the total yield in plants attacked by the pathogen was 14 % higher in the plots treated with the antagonist than in the untreated plots. Besides an increased yield was observed before pathogen inoculation, indicating that T. harzianum may stimulate plant growth. The root test showed a correlation between a high content of Trichoderma and an increased yield in treated plots in May and June. Trichoderma population on the roots declined through the growing season and, thus, eventually the antagonist was unable to inhibit the pathogen sufficiently to prevent attack. Improvement of the treatment with the antagonist and research into its growth-stimulating effect on different crops should be carried out.

Irradiated digested sewage sludge: Effects on plant-symbiont associations in the field

Anaerobically digested sewage sludge was irradiated with high energy electrons as a means of disinfestation at Boston's Deer Island Treatment Facility and transported to the Suburban Experiment Station of the University of Massachusetts, at Waltham. In May 1977, it was applied to limed field plots as liquid surface applications. Three plots were given a single application at the rate of 4·7 metric tonnes/ha dried sludge. Three other plots received double this amount (9·4 metric tonnes/ha). Three additional plots served as controls and received 111 kg/ha each of 10-10-10 N, P, K inorganic fertiliser. These applications were repeated with the same plots in May 1978. In both 1977 and 1978 sludge applications at both rates inhibited rhizobial nodulation of bush bean Phaseolus vulgaris L. ‘Contender’ and VA mycorrhizal infection in onion Allium cepa L. ‘Downing Yellow Globe’. Heavy metal accumulation in soil and plant tissue, pH, soluble salt levels and N and P status of sludge and soil were monitored throughout the experiment as possible explanations for these inhibitions. No readily discernible explanation was found.

Effects of Releases and Varying Infestation Levels of the Twospotted Spider Mite on Strawberry Yield in Southern California1

Effects of releases and varying infestation levels of Tetranychus urticae Kock on fruit yield were studied on strawberries in southern California. In the winter planting, fruit yield and size were significantly higher in the 20–25 density treatment level (DTL) plot (seasonal accumulation of 1,298 mite-days/leaflet) than that in the 90–100 DTL plot (6,371 mitedays/leaflet) in May only. There was no difference in fruit yield or size between the early release and untreated check plots (seasonal accumulations of 24,734 and 23, 135 mite-days/leaflet, respectively), but fruit yields in these 2 plots were significantly lower than that in the 2 DTL plots in May and June. In the summer planting, seasonal accumulations of 1,135 and 2,950 mite-days/leaflet in the 20–25 and 90–100 DTL plots, respectively, did not result in significant differences in fruit yield or size between the 2 levels. Fruit yield and size in May and fruit yield in June were significantly lower in the early release plot than that in the late release plot (seasonal accumulations of 11,343 and 8,168 mite-days/leaflet, respectively). Fruit yield in the early and late release plots in May and in the early release plot in June was significantly lower than that in the check plot (seasonal accumulation of 9,267 mite-days/leaflet). Also, fruit size in the early release plot in June was significantly lower than that in the check plot. Eight insectan predators were present with the cecidomyiid, Arthrocnodax occidentalis Felt, being the predominant species followed by the sixspotted thrips, Scolothrips sexmaculatus (Pergande).

Lodgepole Pine and White Spruce Establishment After Glyphosate and Fertilizer Treatments of Grassy Cutover Forest Land.

Perennial herbaceous vegetation, mainly marsh reed grass, (Calamagrostis canadensis (Michx) Beauv.), was sprayed with glyphosate on the day before planting one-year-old plugs of lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) and white spruce (Picea glauca (Moench) Voss) on cutover forest land north of Edson, Alberta. Spraying at 4.5 kg ai/ha, included spot and strip applications in June 1976, compared with unsprayed scalps and controls. At the same time, all treatments were repeated plus a 9 g, 22-8-2 fertilizer tablet for each seedling. Another experiment at the same site, begun on August 1, 1976, compared scalp, unfertilized control and glyphosate strip treatments, followed by planting of pine seedlings the day after spraying 4.5 kg ai/ha glyphosate. An adjacent experiment, also commenced on August 1, included dosages of 1.1 to 5.6 kg ai/ha with planting of pine seedlings in 4.5 kg/ha and in control plots in May 1977. August application of 2.2 kg/ha provided excellent initial vegetation control, as effective as the larger amounts applied at that time, and was superior during the first 12 months to 4.5 kg/ha applied in June. Twenty-six months after the spring planting new shoot growth of fertilized pine in the glyphosate strips was statistically significantly greater than that for all other treatments and growth in fertilized scalps was also very good. At the same time leader growth of spruce in fertilized scalps was significantly greater than that for other treatments but growth in glyphosate strips did not exceed that of unfertilized controls. Contrary to results of spring planting, there was marked injury and mortality of pine planted in August in glyphosate plots which had been sprayed on the preceding day. Seedlings planted in glyphosate-treated strips nine months after the August spraying exceeded the growth of control plants but not until the year after they were planted.

PERSISTENCE OF LINURON IN SASKATCHEWAN SOILS

The persistence of linuron, at rates equivalent to 2.2 kg/ha, was studied at four sites in Saskatchewan using small field plots. Following applications made in May 1972, plots were sampled regularly and the residues remaining in the 0- to 5- and 5- to 10-cm soil levels extracted and determined colorimetrically. By November 1972, between 28 and 42% of the applied linuron was recovered from plots at the four locations. Losses over winter were slight with approximately 30% of the initial herbicide treatment being recoverable from all soil types in May 1973. Linuron residues were still detectable in plots at all sites 18 mo after application. During winter persistence studies, 50–60% of the linuron applied in October 1972 was recovered from plots in May 1973, while 30% was detected in May 1974 following October 1973 treatments. In all samplings, linuron was found in the soil from the 0- to 5-cm level, with less than 5% of the initial applications being observed in the 5- to 10-cm depths, thus indicating negligible leaching under field conditions.