Paul Flower Report on Herbicide Spraying
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Bitou Bush Helicopter Boom Spraying in NSW Paul Flower 2004 Bitou Helicopter Boom Spraying in NSW i Credits Elizabeth Teakle for proofreading, John Toth who provided incalculable assistance, Andrew Leys for constructive comments on the final draft, Dr. David Teakle for generous help with references and proof reading, . Bitou Helicopter Boom Spraying in NSW ii Executive Summary Helicopter spraying of glyphosate herbicides has achieved high levels of control of Bitou in many sites in NSW, but has achieved only 70 % or less kill of bitou at approximately one third of the total areas sprayed (see figure 2). The herbicides used in Bitou Helicopter Boom Spraying (BHBS) are predominantly glyphosate herbicides. Of the areas sprayed, 55% has been with Roundup®, 41% with Roundup Biactive®, and 5% of the area were sprayed with metsulfuron-methyl as Brush-Off ® Brushcontroller (see Figure 5). The factors reducing the effectiveness of glyphosate were reviewed from the scientific literature. Water stress was most commonly attributed by BHBS managers to result in low kill rates of bitou by BHBS. However other environmental conditions associated with drought, such as low relative humidity and salt build-up on leaves, have been found in studies to be important in reducing kill rates of glyphosate herbicides. Low humidity at the time of spraying can result in the solidification of the herbicide on the leaf surface and reduced herbicide uptake. The majority of native plant species monitored through BHBS with glyphosate are not considered sensitive to this procedure. A smaller number of species have been observed to be commonly killed by BHBS and are listed in this report as highly sensitive. Another set of species are heavily impacted and require an extended period to recover, and these are referred to as moderately sensitive. A list of plant species according to their observed response to BHBS has been constructed (see Table 1). The many factors which influence herbicide injury sustained by plants by BHBS with glyphosate herbicides are reviewed from the scientific literature and from monitoring studies of BHBS. A major factor reducing the impact of herbicide on sensitive plants is the effect of sheltering of smaller plants by higher canopies of leaves. Several possible factors may increase the injury of herbicide on native plants and are speculated in the review, including increased activity of pathogenic soil fungi following spraying leading to a reduction in seedling recruitment. Coincidence of high levels of sea salt aerosols deposited on leaf surfaces after spraying may increase the damage to plants after BHBS. Plants flowering at the time of BHBS are expected to be much more susceptible to damage from BHBS. The data collected from monitoring of BHBS operations in NSW has many deficiencies, the greatest of which is its incompleteness. There is no data on seedling injury in BHBS possibly because very low levels of seedling recruitment have been observed in many BHBS operations. Increased levels of sand erosion may occur after death of bitou following BHBS in some areas because of the large volumes of sand trapped by well established thickets of bitou bush. BHBS is considered to have significant potential to create chemical drift and damage off-target native plants and plant communities. Some of the factors contributing to this situation are discussed. Cumulative injury of native plants from exposure to low levels of glyphosate created by drift from BHBS is discussed. The technique of BHBS has achieved satisfactory levels of effectiveness when the aims are simply to control bitou bush. BHBS has not achieved high levels of effectiveness when gauged as a biodiversity management tool due to inadequate use of precautionary measures and the inadequate monitoring of herbicide injury of native plants. Bitou Helicopter Boom Spraying in NSW iii Contents Introduction................................................................................................................... 1 1 .0 Overview of Bitou Helicopter Boom Spraying ............................................................3 1.1 Advantages of Helicopter Boom Spraying in Controlling Bitou Bush.......................................3 1.2 The challenges of BHBS ............................................................................................................4 1.3 The Aims of BHBS ....................................................................................................................4 1.4 Where is the Uncertainty? ..........................................................................................................5 1.5 Scope for Unknown Impacts ......................................................................................................6 1.6 The Need for a More Precautionary Approach...........................................................................8 2.0 Effectiveness of BHBS in Biodiversity Management .................................................10 2.1. Factors Reducing the Effectiveness of Glyphosate .................................................................12 2.2 Control of Bitou Bush with Metsulfuron..................................................................................20 3.0 Susceptibility of Native Plants .....................................................................................22 3.1 Glyphosate Herbicides .............................................................................................................22 3.2 Factors Affecting the Phytotoxicity of Glyphosate ..................................................................24 3.3 Seedling Injury .........................................................................................................................35 3.4 Cumulative Phytotoxic Effects.................................................................................................39 3.5 Seasonal Variations in Plant Sensitivity...................................................................................39 3.6 Post BHBS Plant Communities................................................................................................41 3.7 Erosion after BHBS..................................................................................................................45 3.8 Herbicide Drift .........................................................................................................................46 3.9 Environmental Activity of Metsulfuron-methyl.......................................................................52 3.10 Monitoring of Plant Injury......................................................................................................55 3.11 Categorisation of Plant Sensitivity .........................................................................................63 4.0 Suggestions for Further Research ...............................................................................72 5.0 Recommendations.........................................................................................................73 6.0 References......................................................................................................................74 7.0 Appendices Aims of This Report.......................................................................................................................91 Bitou Helicopter Boom Spraying in NSW iv List of Figures Figure 1 Estimates of the Area of BHBS from 1979 to 2002............................................. 1 Figure 2 Effective Kill of Bitou Bush using Helicopter Boom Spraying in NSW........... 12 Figure 3 Mean Maximum June Temperatures in NSW.................................................... 15 Figure 4 Mean Minimum June Temperatures in NSW..................................................... 15 Figure 5 Herbicides used to Helicopter Boom Spray Bitou Bush in NSW ..................... 23 Figure 6 Average Wind Speed and Direction at 9am along NSW Coast ........................ 50 Figure 7 Average Wind Speed and Direction at 3pm along NSW Coast ........................ 50 Table 1 Sensitivity/Tolerance of Plant Species to BHBS of Glyphosate ......................... 64 Table 2 Tolerance of Plant Species to BHBS of Brush-off® Brushcontroller................. 67 Table 3 Susceptibility to Reproductive Impacts from BHBS........................................... 68 Bitou Helicopter Boom Spraying in NSW 1 Introduction Bitou bush is a serious invasive species of our coast and currently infests 80% of the NSW coastline and has increased by 36% from 1982 (Thomas and Leys, 2002). Bitou bush invasion has many damaging effects on plant and animal biodiversity and hence has been listed as a key threatening process under the NSW Threatened Species Act, 1995, and as a Noxious Weed in NSW. With the finalizing of the Threat Abatement Plan (TAP) for bitou bush invasion, managing authorities will be obliged to control bitou. Helicopter Boom Spraying (HBS) has been widely used to apply herbicides to bitou bush along the NSW coast over the last 10 years, with over 4000ha being sprayed. Phytotoxic effects have been observed in a number of native plant species, despite treatments occurring in winter when most native plants are not actively growing (Toth et. al., 2003; Toth et. al., 1997; Kholer and Whelan, 1993). Glyphosate has been the main chemical applied by bitou helicopter boom spraying (BHBS) which applies low rates of glyphosate in small water carrier volumes compared with other methods of perennial plant control. Spraying