Post-planting Weed Control Research Articles

Harmonized site preparation and postplant herbaceous weed control for establishment of southern pine plantations on coastal bedded sites

AbstractLoblolly pine or slash pine response and vegetation colonization are summarized for a region-wide study that included five locations on coastal soils in the southern United States. The objective was to evaluate timing of postplant herbaceous weed control (HWC) treatments following preplant site preparation with imazapyr applied at two timings (August and November) and at three rates (0.56, 0.84, and 1.12 kg ha−1). All imazapyr site preparation treatments were applied after bedding. Site preparation treatments resulted in fast-growing stands without HWC at all locations with average Year 3 dominant tree height ranging from 2.6 to 3.7 m. Imazapyr plus sulfometuron was an effective HWC treatment on loblolly pine. Vegetation control and pine response varied by surface soil texture. On coarser-textured soils, the site preparation treatments resulted in <10% vegetation cover in June of the first pine growing season. On these coarser-textured soils, loblolly pine growth was increased by second-year and not first-year HWC. On finer-textured soils, vegetation colonization was aggressive, with >20% cover in June of the first pine growing season, such that early first-year HWC provided the largest loblolly pine response of single-pass HWC treatments. Pines were highly tolerant to imazapyr site preparation treatments as evidenced by the lack of differences in slash or loblolly pine survival and growth from the doubling of imazapyr rates for applications in either August or November. There was little meaningful residual control of herbaceous vegetation into the second pine growing season from site preparation treatments or first-year HWC regardless of location. There was no consistent pine response benefit from increasing the imazapyr site preparation rate for included treatments. Cost-effective treatments would utilize low site-preparation herbicide rates followed by the appropriate timing of HWC if longer-term vegetation control is the objective.

Optimising spot weed control regimes forPinus radiataplantations

Spot spraying, in which only the area around individual trees is treated, is an important method of herbicide application during establishment of Pinus radiata D. Don (radiata pine) in New Zealand. Minimising the spot size reduces costs and has possible environmental benefits from reduced overall herbicide use. An analysis of six experiments at five separate sites tested the growth response of P. radiata to spot weed control on sites dominated by herbaceous vegetation, usually as a result of oversowing with a mixture of grasses and legumes. The analysis showed that, on sites dominated by herbaceous weeds, the reduction in rotation length achieved by applying total weed control compared with no postplant weed control ranged from 0.4 to 1.6 years and averaged 0.9 years. A spot diameter of 1 m maintained for 1 year achieved 28% of the benefit of total weed control, whereas a spot diameter of 2 m maintained for 1 year achieved 66% of the benefit. Generally, there was little benefit in maintaining spots beyond 1 year. An economic analysis indicated that weed control of any kind was generally unprofitable when the time-shift gain from weed control was 0.4 years or less but highly profitable for sites with a time shift of 1.6 years or more.

Cumulative Effects Analysis of the Water Quality Risk of Herbicides Used for Site Preparation in the Central North Island, New Zealand

Herbicide use varies both spatially and temporally within managed forests. While information exists on the effects of herbicide use on water quality at the site and small catchment scale, little is known about the cumulative effects of herbicide use at the landscape scale. A cumulative effects analysis was conducted in the upper Rangitaiki catchment (118,345 ha) in New Zealand, to determine the risk to water quality from two herbicides commonly used for post-plant weed control: terbuthylazine and hexazinone. Data from a 12.5 ha catchment study within the Rangitaiki Basin, where these herbicides were aerially applied in two consecutive years, were used to model herbicide concentrations entering the Rangitaiki River for the remaining treated areas in the catchment for the same two spray seasons. A spreadsheet model routed herbicide residues from their point of entry into the river to a flow gauge on the Rangitaiki River. Modeling of chemical residue loadings and concentrations of terbuthylazine and hexazinone indicated that potential herbicide residues in stream waters would be mainly below analytical detection limits and pose no risk to the aquatic environment or human health and safety. Safety factors for drinking water quality standards, aquatic organisms, and human Acceptable Daily Intake levels were very large.

Use of remotely sensed data to characterize weed competition in forest plantations

ABSTRACTCharacterization of weed size using remotely sensed data could provide a useful means of scheduling post-plant weed control in plantation forests. Data from four forestry stands, which included field measurements of weed competition and multispectral data collected from an unmanned aerial vehicle (UAV) and satellite platform (WorldView3), were used to (i) develop models to predict overall weed percentage cover (C), height (H), and a competition index, CI, (C × H/100) derived from these two metrics; and (ii) determine the optimal spatial resolution for imagery from these two platforms for characterizing these measures of weed competition.Bivariate analysis of the three weed metrics showed the optimal spatial resolution to be 5 m for the WorldView3 data and 1 m for data obtained from the UAV. The best multiple regression models developed to predict C, H, and CI had coefficient of determinations (R2) of, respectively, 0.33, 0.68, and 0.56 for data derived from WorldView3 and, respectively, 0.56, 0.79, and 0.71 for data derived from the UAV. Vegetation indices, derived from the multispectral UAV data and satellite imagery, were strong predictors of weed metrics for all but one of the six models developed. These results suggest that it may be possible for forest managers to use satellite imagery and UAV data to schedule weed control operations.

Herbicide concentrations in waterways following aerial application in a steepland planted forest in New Zealand

The use of herbicides to control competing vegetation in planted forests is an important component of forest management. The increasing public aversion to herbicide use includes the possible contamination of receiving aquatic environments. The risk of surface run-off, leaching and erosion processes transporting herbicide residues to waterways, is potentially higher in steepland forests containing soils with high leaching potential. The purpose of this study was to measure the concentrations of terbuthylazine and hexazinone, two herbicides commonly used in post-plant weed control in New Zealand, in waterways, when aerially applied in a steepland forest catchment with Recent Soils. Terbuthylazine and hexazinone were applied, at 6 and 1.5 kg ha−1, respectively, to 30 ha distributed over a 193-ha catchment. Herbicide concentrations were measured in stream water and sediment in a 12-ha headwater sub-catchment (W1) (57 % sprayed) and in stream water at two sites further down the catchment. These sites were monitored prior to, and for 5 months after, herbicide application. The highest concentrations in stream water were recorded on the day of herbicide application at W1 (terbuthylazine, 9.6 μg L−1; hexazinone, 5.3 μg L−1). Terbuthylazine concentrations were above drinking water standards for several hours, well below the decadal time frame required to exceed these standards. Thereafter, concentrations rapidly declined, with the highest concentrations recorded 1 month after herbicide application, 2 days after a 50-mm (24 h) rainfall event. Concentrations declined downstream and were <5 μg L−1 where the stream exited the forested catchment. Terbuthylazine only was detected in sediment for up to 60 days after herbicide application. Concentrations and persistence of both herbicides in stream water were well below toxic levels for aquatic organisms. The potential risks to aquatic environments from herbicide application in steepland conditions were partially mitigated by the 30-m ‘no-spray’ zone along the stream margins, along with logging slash in the stream channel and the spatial distribution of the treated areas within the catchment. Under these operational conditions, and when applied according to manufacturer’s instructions, the downstream risks to human health and aquatic environments appeared to be low.

A survey of herbicide use and a review of environmental fate in New Zealand planted forests

This paper examines current herbicide use in New Zealand planted forests. Compliance of key herbicides with existing Forest Stewardship Council (FSC) standards, the key environmental certification body within New Zealand, is also reviewed. Information obtained from a survey of six forest companies operating in New Zealand was used to identify major herbicides used by the New Zealand planted forest industry, estimate quantity of herbicides used on an annual basis and also determine changes in weed management practices motivated by certification. Glyphosate was the most widely used active ingredient in pre-plant weed control with terbuthylazine and hexazinone used most widely for post-plant weed control. Together these herbicides comprise 90% of the estimated 447 tonnes of active ingredient that is annually used. Average aerial application rates for these three active ingredients were estimated at 3.3 kg ha-1, 7.0 kg ha-1 and 1.8 kg ha-1, respectively. Use of terbuthylazine and hexazinone is restricted on FSC-certified forests subject to derogation. Environmental certification has resulted in a shift from broadcast application of terbuthylazine and hexazinone to greater use of spot weed control in the first year after tree planting. Spot weed control can reduce the amount of active ingredient used by up to 89%. Non-chemical weed control is not widely used by the forest industry as it is not as cost-effective as current herbicide regimes. A review of the literature indicated that, when used operationally and according to label registrations, these herbicides are unlikely to have any negative impacts on the planted forest environment. Although they have been detected in groundwater, under multiple land uses, concentrations were at levels below documented safe drinking standards. There are limited data for forest soil and no data on the effects of these herbicides on aquatic biota in New Zealand. At present time there is insufficient information to support or refute the prohibition of terbuthylazine and hexazinone in New Zealand's planted forests. This has highlighted a need to conduct field studies to determine the fate and behaviour of terbuthylazine and hexazinone in planted forests in New Zealand.

Long-term response of weed control intensity on Scots pine survival, growth and nutrition on former arable land

The effects of post-planting weed control intensity on the cover and composition of ground vegetation, and on growth, survival and foliar nutrient concentrations of 4-year old bare-rooted Scots pine (Pinus sylvestris L.) seedlings were studied over a 15-year period with experimentation on former arable land. Weed control treatments with terbuthylazine and glyphosate were carried out 1–3 times during successive years, either as overall or as spot applications. The vegetation cover and the shading effect of vegetation decreased with increasing weed control intensity. The more intensive the weed control was, the better was the afforestation result in terms of tree seedling growth and survival. Overall application repeated three times increased seedling survival by 79 percentage points, and their final height, breast height, diameter, and stand volume after 15 years were increased by 183, 19, 15, and 822%, respectively. Weed control did not affect the foliage nutrient concentrations, except for magnesium. However, increase in weed control intensity was reflected in larger needle size 5 years after planting.

Bringing Agroforestry Technology to Farmers in Leyte, the Philippines: A Comparison of Two Extension Assistance Regimes

The response of farmers to personalised forestry and agroforestry extension assistance has not been well documented in the Philippines, thus providing the impetus for this research in which the effectiveness of extended on-farm assistance was compared with more limited assistance. In four municipalities in Leyte Island, farmers responded positively to an extended program which helped them overcome problems in germinating and growing seedlings and establishing trees on their land. A limited assistance program which sought to make use of farmers’ familiarity with growing and raising plants was relatively unsuccessful, with less preparation of tree planting sites and a higher rate of abandonment. Allowing farmers freedom to select planting sites and aspects of technical advice which suited their personal circumstances, encouraged a high degree of cooperation between extension staff and farmers, but 38% of farmers neglected post-planting weed control and 35% of sites were inappropriate for growing trees. Destruction of sites by flooding and grazing also caused farmers to blame extension staff even though these risks had been discussed with them beforehand. This suggested that a more interventionist approach would be appropriate for site selection although it may reduce recruitment. The number of farmers recruited through local government staff was low, but attendance by neighbours at locally held demonstrations was high, suggesting an avenue for further recruitment. Overall, the program was successful in shifting the initiative for further planting from extension staff to those farmers who received extended extension assistance.

Effects of management techniques on the establishment of eucalypt seedlings on farmland: a review

Research into the effects of seven management techniques on survival and growth of eucalypt seedlings planted on farmland is reviewed. The techniques include: pre- and post-planting weed control; soil cultivation; fertiliser; mulch; tree guards/shelters; and irrigation. The initial and ongoing effects of each technique are discussed—including the effects of timing, type and quantity. Consideration is given to site, species and climatic influences. A statistical analysis of the published survival rates is then presented, to provide information on the relative importance of, and interactions between, practices. The analysis shows that maximum survival may be achieved by using one or two management techniques. Combining this result with the insights gained from the review suggests that the use of soil cultivation and post-planting weed control are likely to achieve the greatest improvements in early eucalypt survival and growth.

Eucalyptus and Populus short rotation woody crops for phosphate mined lands in Florida USA

Our short-rotation woody crops (SRWC) research in central and southern Florida is (1) developing superior Eucalyptus grandis (EG), E. amplifolia (EA), and cottonwood ( Populus deltoides , PD) genotypes, (2) determining appropriate management practices for and associated productivities of these genotypes, and (3) assessing their economics and markets. Reclaimed clay settling areas (CSA) and overburden sites in phosphate mined areas in central Florida are a potential land base of over 80,000 ha for SRWC production. On CSAs, PD grows well in the absence of cogongrass ( Imperata cylindrica ) but is not as productive as the non-invasive EG and EA. SRWC establishment on CSAs requires strict implementation of the following cultural practices: thorough site preparation through herbiciding/disking and bedding, superior trees, watering/packing seedlings, fertilization with ammonium nitrate at planting and annually thereafter as feasible, high planting density possibly including double row planting, and winter harvesting so that coppice regeneration suppresses weeds. PD cultural requirements, that may require post-planting weed control to suppress herbaceous competition, exceed those of the eucalypts. EG SRWCs on CSAs are at risk of blowdown 3–4 years after planting or coppicing; younger PD, EG, and EA SRWCs appear much less susceptible to wind damage. Genetic improvement must continue if EG, EA, and PD are to increase in commercial feasibility. SRWC cost competitiveness will depend on establishment success, yield improvements, harvesting costs, and identifying/using incentives. Strong collaboration among public and private partners is necessary for commercializing SRWCs in Florida.

Effects of competing vegetation and post-planting weed control on the mortality, growth and vole damages to Betula pendula planted on former agricultural land

Effects of competing vegetation and weed control methods (fibre board mulch, cover crop of clover, various herbicides) on the survival and growth of and vole damage to silver birch (Betula pendula Roth) were analysed based on data from a field experiment established in southern Finland. The cover percentage of competing vegetation and its shading effect were assessed, and seedling size and vitality were recorded several times during the 11-year research period. Mean seedling height and height increment decreased linearly with increasing vegetation cover. Seedling mortality started to significantly increase once the vegetation cover had reached the level of 60–80%. Herbicides significantly retarded increase of weed cover on the initially weedless areas for two to three years, and a cover crop promoted increase in cover percentage. Successful weed control with herbicides significantly increased seedling growth and survival. After 11 years, the average stem volume on the herbicide-treated plots (28.9 m3 ha–1) was 2.5-fold as compared to that of the control plots (11.6 m3 ha–1). Furthermore, seedling mortality on the control plots (21%) was almost 3.5-fold as compared to the seedling mortality on herbicide-treated plots (6%). Having a cover crop proved to be an ineffective weed control method both in terms of seedling growth and survival. The application of mulch had only a slight effect on height increment (0.6 m in 11 years), but on the other hand, it considerably decreased seedling mortality (control: 21%, mulch treatment: 1.5%). These differences were not, however, statistically significant. Small seedling size, high shading class, and high vegetation coverage percentage increased the risk of voles damaging the seedlings.

Revegetation to combat tree decline in the Midlands and Derwent Valley Lowlands of Tasmania: Practices for improved plant establishment

Summary The results of site assessment and information survey of 13 plantings established between 1995 and 2000 from the Tasmanian Midlands and Derwent Valley Lowlands are presented. Establishment success of tubestock plantings ranged from 2 to 100% and that of direct seeding from 860 to 20 000 seedlings/ha. Successful establishment of tubestock and direct seeding was associated with first year watering and good rains, respectively. Browsing damage was evident in direct seeded plots with eucalypts most affected and acacias and She‐oak (Allocasuarina verticillata) least affected. Treeguards appeared to prevent browsing of tubestock, but those poorly constructed by inexperienced planters tended to collapse and smother seedlings. Larger seedlings appeared to exhibit better survival and growth than smaller seedlings under conditions of drought. While only two sites were mounded, mounding appeared superior over ripping as a site preparation technique, particularly where ripping on heavy, black cracking clays induces cracking, drying of the soil profile and seedling mortality when planted too close to rip lines. Recommendations are listed for best practice establishment techniques based on the site assessment and survey results. Of the recommendations, the requirement for postplanting weed control and the benefits of detailed records of plantings are emphasized. Most plantings surveyed would have benefited from postplanting weed control and it is suggested that this has been a major deficiency in previous revegetation programs. Furthermore, there has been little accountability of the success of projects undertaken. Improved record keeping would benefit landholders and particularly extension officers and researchers in the industry.

Effect of weed control with fibre mulches and herbicides on the initial development of spruce, birch and aspen seedlings on abandoned farmland

Post-planting weed control methods on abandoned farmland were studied in three field trials in southern Finland using a completely randomized design with four treatments and 30 to 40 replications. Mulches of 60 x 60 cm [sheet mulch – strips of plane waste and plastic fibre, newspaper – waste paper slurry, wood chips, pure wood fibre slurry], herbicides [i.e. glyphosate or terbuthylazine alone or mixed and dichlobenile applied to 1 m2 spots] and hoeing treatments were compared to an untreated control plot. The study material consisted of two-year-old containerized aspen (Populus tremula L.), silver birch (Betula pendula (L.) Roth) and Norway spruce (Picea abies (L.) Karst.) seedlings planted in spring 1996. The ground vegetation was dominated by Elymys repens, Deschampsia cespitosa, Cirsium arvense and Epilobium angustifolium. Monitoring of the trials over a 3-year period showed a moderate effect of weed control, which varied according to the method used and by the crop species. Significant growth responses were found with herbicide in spruce, wood chips in spruce and birch and with sheet mulch in aspen seedlings. Sheet mulch also encouraged vole nesting thus increasing damages. Generally, slurry mulches proved to be insufficiently durable. Mulching had a clear insulating effect, which may increase the risk of winter drought.

Is site preparation necessary for bur oak receiving post-planting weed control?

Le labourage et le hersage sont recommandes avant l'etablissement de plantations d'especes feuillues de haute valeur sur des terres agricoles abandonnees et envahies par des especes herbacees competitrices. Toutefois, il n'est pas toujours possible d'effectuer la preparation mecanique du sol. L'utilisation de traitements de repression post-plantation des herbacees pourrait permettre de reduire l'effort de preparation du site. L'etude compare trois methodes de preparation du site (labour et hersage ; labour, hersage et herbicide simazine ; un temoin), dont les parcelles ont ete separees en deux pour recevoir l'un ou l'autre de deux traitements post-plantation (herbicide glyphosate, paillis de plastique noir) appliques par bandes de 120 cm sur la rangee de plants de chenes a gros fruits (Quercus macrocarpa Michx). Apres 5 ans de traitements de repression des herbacees, la preparation du site par le labourage et hersage n'a pas produit des resultats de croissance superieurs relativement au temoin. Toutefois, la croissance etait superieure lorsque la preparation mecanique etait combinee a l'application de l'herbicide simazine. La hauteur et le diametre des plants de chenes etaient superieurs avec l'utilisation de paillis de plastique en comparaison a l'application de glyphosate. Ces resultats permettent d'envisager le reboisement en especes feuillues sur des sites ou la preparation mecanique du sol est impraticable, si des traitements de repression des herbacees sont appliques apres la plantation.

Effect of post-planting applications of granulated atrazine and fertiliser on the early growth of Eucalyptus nitens

A factorial experiment was established in a plantation of Eucalyptus nitens in southern Tasmania on a site which had formerly carried native eucalypt forest. Before planting, the site had been cleared of weeds with foliar translocated and pre-emergence herbicides. The first factor of the experiment examined the effects on tree growth of no post-planting weed control, control by hand or with three levels of application of granulated atrazine, 0.9, 1.8 and 8 kg ha−1. The second factor examined the effects of no fertiliser application or the application of nitrogen as urea at 200 kg ha−1 N plus triple superphosphate at 120 kg ha−1 P. Tree growth responses to treatments were examined at 11, 16, 23 and 29 months of age. Fertiliser application increased tree height and diameter growth. Application of atrazine generally reduced height and diameter growth, but this was statistically significant only at the highest rate of application. Growth reduction occurred even though atrazine reduced post-planting weed cover on the site and hence potential competition with the tree crop for site resources. Hand weeding reduced the weed crop on the site even more than atrazine, but this did not increase growth of the tree crop. Given satisfactory establishment practices which include the use of herbicides pre-planting, it was concluded that post-planting weed regeneration was not sufficiently vigorous to warrant post-planting weed control on these sites. The use of atrazine for post-planting weed control could even be deleterious to eucalypts.

Tenth-Year Results of Herbaceous Weed Control in a Loblolly Pine Plantation

Abstract Herbaceous weed control influenced the growth of planted loblolly pine (Pinus taeda L.) over a 10-yr-period. Five treatments were examined: (1) Untreated control: seedlings were planted in the established herbaceous vegetation; (2) Glyphosate: glyphosate was broadcast in September 1981 before planting; (3) Disked: plots were cross-disked in September 1981 before planting; (4) Glyphosate-PPWC: glyphosate was broadcast before planting as in Treatment 2, and postplant weed control (PPWC) herbicides were broadcast yearly for 4 yr (1982, atrazine plus simazine ; 1983, atrazine plus oxyfluorfen; 1984 and 1985, hexazinone ); and (5) Disked-PPWC: plots were disked before planting as in Treatment 3, and the PPWC herbicides were broadcast as in Treatment 4. Four years of PPWC did not affect survival and resulted in greater height, dbh, and volume per loblolly pine through 10 growing seasons. The disked-PPWC plots were the most productive through 8 growing seasons, but higher than average mortality after 8 yr on the disked-PPWC treatment resulted in the glyphosate-PPWC plots producing more volume per acre after 10 growing seasons. Total volume production was 253 inside bark ft³/ac greater on the two PPWC treatments than on the untreated controls. South. J. Appl. For. 18(3): 105-109.

Establishment of white spruce and black spruce in Boreal Ontario: Effects of chemical site preparation and post-planting weed control

Five-year results of a field experiment to evaluate the effects of vegetation control either before or after planting on the performance of planted white spruce (Piceaglauca [Moench] Voss) and black spruce (P. mariana [Mill.] B.S.P.) transplants and black spruce containerized seedlings are reported. Annual vegetation control with and without chemical site preparation significantly (P &lt; 0.05) improved height growth, ground-level stem diameter, and health of the planted seedlings. Survival and seedling growth were significantly (P &lt; 0.05) higher with chemical site preparation than with chemical release in August of the year after planting. From the beginning of June to the first half of August, soil temperatures were higher in the plots with no competing vegetation than in the control plots. The difference in temperature reached a maximum of 5 °C at 5 cm of depth and 4 °C at 12 cm of depth. Key words: black spruce, chemical site preparation, glyphosate, growth response, Picea glauca, Picea mariana, release, tending, vegetation management, weed control, white spruce

Effects of Weed and Invertebrate Control on Alfalfa Establishment in Oat Stubble

Crop residues in conservation tillage can provide excellent habitats for invertebrates that feed on alfalfa seedlings. The impact of invertebrate feeding on seedlings has been assessed for alfalfa no-till seeded into wheat (Triticum aestivum L.) stubble and grass sods, but not oat stubble. Thus, our objective was to determine the influence of weed and invertebrate control on alfalfa (Medicago sativa L.) establishment in oat (Avena sauva L.) stubble. Alfalfa was drilled into a plowed seedbed or into oat stubble. Postplant weed control (none or sethoxydim) and slug and insect control (plowing, methiocarb bait [3,5-dimethyl-4-(methylthio)phenol methylcarbamate], carbofuran [2,3-dihy-dro-2,2-dimethyl-7-benzofuranyl methylcarbamate], methiocarb plus carbofuran, and none) treatments were evaluated during the establishment of alfalfa at the Rock Springs Agricultural Research Center in Centre County, PA, on a silt loam (Typic Hapludalf; fine, mixed, mesic) soil. Slug numbers were measured 1,3, and 6 wk after planting. Seedling frequency and invertebrate feeding were measured 3 and 6 wk after planting. Morphological development was measured 6 wk after planting. Yields were taken the spring following planting. Reducing weed populations increased seedling shoot weight, trifoliolate leaves per plant, and production year first-cut yields. Invertebrate management decreased gray field slug (Derocerus reticulatum) populations and increased seedling frequency during initial seedling growth. Controlling volunteer oat was the major factor affecting establishment and yield of alfalfa no-till seeded into oat stubble.

Loblolly Pine (Pinus taeda) Response to Weed Control in Central Louisiana

Herbaceous weed control was studied on a loblolly pine planting site in central Louisiana. Pine growth was enhanced without eradicating weeds; reducing weed biomass about 50% increased the mean inside bark volume of loblolly pine saplings 53% on the weeded treatments compared to the untreated control after five growing seasons in the field. Pines receiving both preplant weed control with glyphosate or disking and postplant weed control with a series of yearly treatments (1982, atrazine plus simazine; 1983, atrazine plus oxyfluorfen; 1984, hexazinone; and 1985, hexazinone) had 62% greater volume than pines on the preplant-only treatments. So, the best gains in loblolly pine volume required postplant weed control.