Management Strategy for Vegetation State C
There are a number of options to replace these Hieracium communities with more productive systems: Agricultural development, Grazing management, Forestry, and Biological control
Pasture improvement and fertiliser application can successfully control Hieracium and directly addresses the fundamental problem Hieracium poses for pastoral systems, limitation of stock feed. A seven year trial at two sites the Mackenzie basin showed H. pilosellaremained dominant at nil or low fertiliser inputs but was reduced by legume introduction and high fertiliser application within two years, and was rare by six years, on a deep, moderately productive soil. On a shallower, less productive soil, the legume sward took 5-6 years to begin decreasing the Hieracium content (Scott et al. 1990). Two further trials at Mt. John, Lake Tekapo, monitored for nine years, similarly showed Hieracium decreased or disappeared under high fertiliser and sowing inputs, particularly with irrigation, but became an increasingly important component with decreasing fertiliser inputs (Scott 1993). Lupin (Lupinus pollyphylus) was the best legume at low and moderate fertility levels and alsike (Trifolium hybridum) or white clover (T. repens) at the high fertility levels. Rate of phosphate fertiliser had greater effect than corresponding rate of sulphur. The effect of different grazing intensities was relatively minor. Approximately 200,000 ha of the South Island high country may be suitable for such development, requiring investment of around $40 million, assuming costs of $200/ha (McMillan 1991). The economic feasibility of development determines the applicability of this strategy for specific properties.
Recent research indicates that grazing management is potentially one of the most feasible current strategies for slowing and limiting Hieracium spread on unfertilised or low-input land. The effect of low-intensity grazing in reducing the flowering, cover and density of erect growing Hieracium species has important management implications for both pastoral farming and nature conservation. Makepeace (1985) observed massive seed production with both H. pilosella and H. praealtum but considered the probability of successful establishment from seed to be negligible, about 1 in 230,000. This formed the basis for previous management recommendations largely ignoring seeding control. Subsequent research in the Canterbury (Espie 1992), Otago (Espie 1995) and Marlborough (Rose and Frampton 1999) demonstrated that Hieracium species can successfully established large numbers of seedlings, particularly during seasons with wet summers and autumn. As Hieracium recruitment from seed is important, then management strategies that reducing flowering will effectively reduce establishment. This is consistent with much anecdotal evidence from farmers and from fenceline effects, where many set-stocked summer grazed blocks carry less Hieracium than adjoining blocks that were spelled or conservatively grazed.
Grazing may reduce the density and abundance of the upright species (Espie 1995) but will not control H. pilosella once it has become established. Its mat-forming growth habit is a successful evolutionary adaptation to grazing pressure. To control it a 'tall grass' management system, resulting in accumulation of standing herbage is required. H. pilosella cover was consistently lowest under treatments accumulating high herbage in a 17 year grazing trial at Tara Hills (Espie 1995). Management for long term pastoral viability will therefore entail light grazing at conservative stocking levels, both for improved per animal performance and for minimising H. pilosella. A potential option is complete destocking and spelling of fertilised hill blocks for extended periods to allow herbage accumulation to limit H. pilosella. These blocks would then be intensively mob stocked to reduce the H. praealtum and other upright species. The goal will be to maintain a balance that keeps the Hieracium content to an acceptable minimum as a pasture component but to prevent it gaining dominance. Improving production from low-altitude blocks will be necessary to provide the forage and management flexibility lost from the hill country.
The extensive areas of low-input pastoral tussock land will require new management strategies designed to co-exist with, but minimise, the impact of Hieracium. Different species of Hieracium will require different management. Low-intensity grazing during spring and early summer is recommended to reduce Hieracium seed spread and limit the abundance of upright Hieracium species. Cessation from grazing, allowing accumulation of standing herbage, is necessary for limiting the mat-forming H. pilosella.
Other successful options for Hieracium control involve alternative land uses such as forestry. In many semi-arid areas these options will be less uneconomic, but where sufficient rainfall and finance is available, plantations can provide a viable land-use for currently very low-value Hieracium dominated former tussock grasslands.
Biological control will be important for long term management of Hieracium on the agriculturally un-improvable land. European fungi pathogenic to Hieracium are being evaluated at present, in particular a rust Puccinia herracia var piloselloidarum specific to stoloniferous species of Hieracium and a powdery mildew Erysipe cichoracearum. They are capable of depressing growth rates by 2 - 12 %. Over 1200 European strains of fungi have been screened for virulence and activity. The best strains can achieve 80% infection (Jenkins, pers. comm.). The rust causes a low intensity (1-5%) infection, throughout the year in Europe. It appears the best option for H. pilosella control and is likely to be most effective in the higher rainfall runs. The powdery mildew appears better suited to hot dry conditions. Both the rust and powdery mildew have been widely dispersed at a series of sites throughout the high country to aid rapid dispersal.
Insects that attack Hieracium are also being investigated by the Hieracium Control Trust. A European gall-forming wasp, Aulacidea pilosellae, and three moths, Oxptilis spp., have been investigated, among others, as potential biological control agents (Scott 1985, Syrett and Sarospataki 1993). Native broad-nosed weevils Niceana cervinata and N. cinerea have also been shown to feed on H. pilosella and H. praealtum seedlings, causing up to 54% mortality in a laboratory experiment (Evans, pers. Com). The gall wasp and plume moth have recently been released in the high country and populations are currently being monitored (Allan Innes, pers. comm.). This appears the best option for Hieracium control on conservation lands.
Hieracium species are resistant to herbicides and a complete kill is seldom achieved (Meeklah et al. 1981, Mitchell pers. comm.). Results vary from 20 - 85%, depending on formulation, application rate and time of application. Hi-ester 2-4-D at 1 l/ha with clopyralid 0.51 l/ha and a penetrant, a mecoprop/MCPA/dicamba mixture at 1.-3 kg a.i./ha have produced the best results. Late spring- early summer is the best time for treatment or if in autumn, using a glyphosate/penetrant combination at 1.08 kg a.i /ha. Application costs are high, around $55-80/ ha, and multi-applications are usually necessary, in early (September) and late spring (October/ end November) and autumn (Feb./ March). This effectively limits their practical use to localised spot control or in combination with pasture introduction.