Preserve Selection and Design Considerations: If grasses are dominant in a selected area, fertilization can tip the balance in favor of grasses (see Management procedures).
There is some evidence (Watt 1981b) that over time a population of mouse-ear hawkweed senesces and is replaced by diverse species.
Management Requirements: Hieracium pilosella needs to be managed to prevent it from displacing native species. Management procedures which have been used in pasture lands are discussed below.
Management recommendations in rangelands include introducing productive grasses and legumes and establishing planned rota- tional grazing (Anonymous 1980). Good competitors include white, alsike and red clovers, smooth brome and tall oatgrass. Watt (1981b) showed evidence that with time, a mouse-ear hawkweed population senesces of its own accord. It is not shade tolerant (Davy and Bishop 1984).
Davy and Bishop (1984) studied the effects of the addition of inorganic nutrients on Hieracium in Breckland grass-heaths. Quantities and compositions of salt mixtures used were the same as those used by Willis (1963), i.e., (weight in grams for treatment of one square yard of vegetation) 21.2 g (NH4)2HPO4; 10.6 g (NH4)2SO4; 21.1 g K2SO4; and 42.4 g MgSO4.7H2O. Nitrogen alone was added as NaNO3 (Davy and Bishop 1984). Applications were made by hand sprinkling dry mixtures on 11 occasions at about four-month intervals between October 1975 and March 1979. Fertilization on plots which were 50% or greater grasses was found to prevent the spread of mouse-ear hawkweed, with the effectiveness of NPK > NP > NK > N > no treatment (Davy and Bishop 1984). The decline of hawkweed populations in nutrient treated quads was rapid and striking due to two different mechanisms: (1) direct physiological and demographic responses to the increased nutrient supply; and (2) indirect effects arising from responses of competitors to increased nutrients (Davy and Bishop 1984). Fertilization should only be used to control hawkweed in areas where it can be expected to give preferred and established grasses a competitive edge. In this case, hawkweed can be shaded out.
Reader and Watt (1981) found a similar response to 336 kg/ha/yr NPK fertilizer for Hieracium floribundum. One application increased growth of POA COMPRESSA and temporarily halted hawkweed patch formation.
Makepeace (1985b) found that 2,4-D ester + "versatil" (active ingredient chloropyralid) at 1000 + 400 g/ha or 750 + 300 g/ha gave good control of hawkweed but also reduced the vigor of alsike clover. The clover recovered over time, the hawkweed did not. Three years of herbicide treatment with oversowing of clover were necessary to essentially eliminate the hawkweed.
Monitoring Programs: A survey of the literature showed that Hieracium pilosella is a threat to pasture land in New Zealand and appears as a weed in Canada and the United States. The most recent research survey was published in 1985, and it is not known whether current research is ongoing.
Management Research Needs: Research is needed to determine whether methods which have been used to control Hieracium pilosella in pasture lands, where the primary concern is to encourage the growth of agronomically important species, are compatible with the management goals on Nature Conservancy preserves.
