Carol A. Rolando

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

BackgroundThis 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.MethodsInformation 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.ResultsGlyphosate 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.ConclusionsAt present time there is insufficient information to support or refute the prohibition of terbuthylazine and hexazinone in New Zealands 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.

Using chlorophyll fluorescence to determine stress in Eucalyptus grandis seedlings

Synopsis Since several environmental factors affect the functioning of the photosynthetic system, the status of the photosynthetic apparatus is a good indicator of the plant in terms of stress and stress adaptation. The measurement of chlorophyll fluorescence with a portable fluorimeter has been shown to be a useful non-destructive method for the investigation of the structure and function of the photosynthetic apparatus. A quantitative analysis of fluorescence emission, called the JIP-test, has also been introduced by which the behaviour of the photosynthetic system in response to environmental changes can be monitored. A pilot trial was conducted to determine the effect of light, water and nutrient stress on the fluorescence emission of Eucalyptus grandis seedlings. Flourescencc measurements were made on potted plants with a Hansatech Plant Efficiency Analyser, everyone to two days from stress initiation until trial termination. The results indicate that water and light stress in E. grandis seedlings can be detected using chlorophyll fluorescence data. The quantum efficiency of primary photochemistry (Fv /Fm) is a good indicator of water stress, while a more detailed analysis of the JIP-test parameters is required for detection of light stress. These results indicate that nutrient stress may have to be severe before photosynthesis and growth are affected. As a practical tool to detect unhealthy plants this technique could be useful to the forestry industry particularly in the fields of establishment and tree breeding where drought or temperature stressed seedlings could be detected before mortality occurs. More detailed stUdies are required to confirm this.

An integrated analysis of 33 Eucalyptus trials linking the onset of competition-induced tree growth suppression with management, physiographic and climatic factors

One of the greatest difficulties associated with controlling competitive vegetation during the establishment of eucalypts relates to the timing and planning of ‘weeding’ operations. This may be due to site related variability in vegetation species distribution and abundance, climatic conditions and methods of site preparation. Using data from 33 eucalypt vegetation management trials, multivariate statistical techniques were used to determine whether any climatic, physiographic or management related variables could be related to the time taken for competition-induced tree growth suppression to occur. Altitude, the method of site preparation (burning versus not burning) and the interaction between these two factors were significantly related to the timing of tree growth suppression. Regardless of the method of site preparation, the onset of competition-induced tree growth suppression occurred earlier at lower altitudes, where the vegetation was more diverse and vigorous. At higher altitudes, burning appears to stimulate the earlier growth of vegetation, reducing the time for competition-induced tree growth suppression to occur.RésuméUne des grandes difficultés pour obtenir un contrôle de la végétation concurrentielle pendant l’installation de plantations d’eucalyptus est liée à la planification des opérations de désherbage. La difficulté provient de la variabilité de distribution et d’abondance des espèces qui constituent la végétation, des conditions climatiques et des méthodes de préparation du terrain. Des données de 33 essais de gestion de la végétation concurrente en plantation d’Eucalyptus ont été analysées avec des techniques statistiques multivariées pour identifier les variables climatiques, physiographiques ou de gestion susceptibles d’influencer l’apparition du ralentissement de croissance par la compétition herbacée. L’altitude, la méthode de préparation du terrain (brûlis ou non brûlis) et l’interaction entre ces deux facteurs ont eu un effet significatif sur ce ralentissement. Indépendamment de la méthode de préparation du terrain, le ralentissement de croissance se produisait plus précocement à basse altitude, là où la végétation était plus variée et plus vigoureuse. À plus haute altitude, le brûlis semble stimuler une croissance plus précoce de la végétation herbacée, en favorisant ainsi le ralentissement de la croissance des arbres.

Post-establishment vegetation control in a Eucalyptus grandis x E. camaldulensis stand

Synopsis In eucalypt plantations, the effect of shading following canopy closure reduces the growth of competing vegetation. In some eucalypt stands full canopy closure is not achieved and the important characteristic of complete shading is lost. This results in stands with the potential to support competitive levels of postestablishment vegetation. A trial was established on a two year old Eucalyptus grandis x E. camaldulensis stand to determine the competitive effect of post-establishment vegetation on tree growth. A weedfree treatment was implemented annually over a period of five years and compared to a weedy control to determine the time period for the post-establishment vegetation to reach competitive levels. There was no significant tree growth or survival response to competition from post-establishment vegetation for the duration of the trial.

Herbicides for use in management of certified Pinus radiata plantations in New Zealand

Summary Post-planting vegetation control in commercial Pinus radiata D.Don forests within New Zealand almost exclusively uses a mixture of the two triazine herbicides, terbuthylazine and hexazinone. However, neither of these herbicides is endorsed for use on land certified by the Forest Stewardship Council (FSC), based on criteria relating to their persistence or toxicity in the environment. This is a problem for the forest industry as these herbicides are inexpensive, are not phytotoxic to P. radiata, and their residual action enables continued control of competing vegetation for up to a year following application. Using measurements obtained from three short-term field trials where herbicides were applied as pre- and post-emergent, post-planting treatments to a wide range of competitive vegetation species, the efficacy of alternative mixes of herbicides was compared to the triazine mix (the current industry standard). As the restrictions on the use of terbuthylazine by FSC may be lifted, this herbicide was also trialled in mixes with herbicides other than hexazinone. Tree growth was quantified one year after herbicide application using a biomass index. Results from all three trials showed that the triazine mix provided the greatest level of vegetation control, with the trees in this treatment attaining the highest biomass index. Where herbicide mixes were applied as pre-emergent treatments, the best alternative herbicide, as assessed by tree growth at one year, was indaziflam applied at 300 g active ingredient (a.i.) ha–1. Compared to the triazine mix, the biomass index for this treatment was reduced by <1%. Where herbicides were applied as post-emergent treatments, the best alternatives to the triazine mix were very similar across trials and included treatments where terbuthylazine (at 7000 g a.i. ha–1) had been applied in combination with one of either mesotrione (at 150 g a.i. ha–1; 300 g a.i. ha–1), triclopyr (at 113 g a.i. ha–1), or clopyralid (at 1500 g a.i. ha–1) or where a mixture of clopyralid, triclopyr and haloxyfop (1125 g a.i. ha–1, 113 g a.i. ha–1 and 250 g a.i. ha–1) was used. Reductions in biomass index at one year in these five treatments, relative to the triazine mix, ranged between 5% and 35%, with smallest reductions being recorded for terbuthylazine used in combination with either clopyralid or mesotrione.

Survival and growth of Pinus patula at two years in response to harvest residue and pest management, in Mpumalanga, South Africa

Synopsis Previous research has indicated that the presence of harvesting residues, post-planting tern perature and rainfall, and insect pests and diseases, are among the main causes of mortality during re-establishment of Pinus patula stands. The main objectives of this work were to confirm previous observations on the effects of these factors on initial survival and growth of P. patula seedlings. Three harvest residue management treatments (burning, harvesting residues left in situ or removed) and four pest management treatments applied at planting (fungicide, insecticide, fungicide and insecticide, and a control, where no pesticides were used) were tested in combination with each other. For the first two years after planting, there was a significant effect of harvest residue and pest management on survival. At two years, survival in the burned treatment was 59 %, possibly due to the presence of Rhizina undulata. Where the harvest residues were not burned, the survival was 88 %. Application of a fungicide and insecticide at planting improved survival in all harvest residue treatments, especially the burned treatment. Tree growth was the best where both a fungicide and insecticide had been applied at planting, followed by the individual application of either a fungicide or insecticide, with the poorest growth occurring in the control treatment.

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

ABSTRACT Characterization 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.

An aerial spot-spraying technique: a pilot study to test a method for pest eradication in urban environments

BackgroundPest eradication strategies that use pesticides require application methods that have the lowest environmental and human health impact while maintaining the highest probability of success. This is highly important when eradication takes place in sensitive areas, such as urban or riparian zones. A new aerial application method, the spot-gun, was developed to provide good pesticide coverage on host species while minimising off-target exposure. This type of targeted aerial approach is useful in areas where conventional broadcast aerial spraying was historically used but was not ideal due to the quantity of pesticide hitting non-host species and going off-target. An even distribution of the active component is essential for eradication.FindingsThe spot-gun method was tested and found to provide an even distribution of dye on the adaxial and abaxial leaf surfaces as well as in the top and middle regions in both the inner and outer portions of the canopy. The form of the deposits on the leaf surface was very different from that obtained using a broadcast aerial application with a conventional spray boom.ConclusionsThe distribution results imply that the spot-gun method treatment will provide good efficacy. The implications of the different deposit pattern on efficacy are not known at this stage. This aerial spot-spray method has considerable potential as a tool for targeted aerial application of pesticides to small areas of difficult to reach canopies.

The Effect of Formulation, Dose, and Adjuvants on Uptake of Phosphite Into Pine Foliage

The aim of this investigation was to determine the effect of dose and adjuvant on uptake of two phosphite products (Phos-A and Phos-B) into Pinus radiata needles. In experiment 1, uptake of 6 kg ha-1 phosphite, applied as Phos-A, in 100 liters of water, together with an organosilicone superspreader (0.2%), was high (>60%). Uptake at doses greater than 6 kg ha-1 (12, 15, 18, and 24 kg ha-1) and applied in volumes less than 100 liters of water (75 and 50 liters) was poor (1 to 30%). Using stability tests and NMR spectroscopy in experiment 2, this appeared to be linked to a concentration dependent reaction resulting in the degradation of the organosilicone adjuvant that facilitated uptake of Phos-A. In experiment 3, uptake of phosphite applied as Phos-B, between 6 and 24 kg ha-1 in 100 liters of water, was tested alone and with four adjuvants (an organosilicone, alcohol ethoxylate, lecithin, and esterified seed oil). Uptake of Phos-B without any adjuvant was high (>50%) across all doses, indicating the formulation was optimized for P. radiata needles. Uptake of Phos-B increased with concentration up to 72% at 24 kg ha-1 in 100 liters of water. Symptoms of phytotoxicity were observed at rates of ≥12 kg ha-1. This study highlighted the effect of formulation, dose, concentration, and adjuvant on the uptake of phosphite into P. radiata needles.

Critical water stress levels in Pinus patula seedlings and their relation to measures of seedling morphology

A pot trial was implemented to determine the effect of soil water stress following transplanting on shoot water potential and stomatal conductance of Pinus patula seedlings. The relationship of seedling morphology to measures of water stress was also investigated. The trial consisted of two watering treatments: a control (no water stress) and a severe water stress (no further water after planting). The treatments were applied to recently transplanted seedlings selected to reflect a range of sizes typical in an operational environment. Measures of shoot water potential and stomatal conductance, root and shoot growth and environmental variables were made. The results indicated that P. patula seedlings tolerated high air and soil temperatures (above 35°C) and low soil water availability (−1.5 MPa). The water potential threshold for changes in stomatal conductance was in the region of −0.8 to −0.9 MPa and stomatal closure had occurred at a shoot water potential of between −1.8 and −2.1 MPa. Mortality occurred when shoot water potential declined to below −3.0 MPa. There was variability between seedlings in their potential for survival and growth. Inherently bigger seedlings had a greater capacity for new root growth following planting. Mass of new roots was significantly and positively related to higher rates of transpiration under conditions of low soil moisture.