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skeleton weed seeds are dispersed by

Experimental evidence presented by McVean [58] indicates fairly high levels of readily available calcium and phosphorus are both important for initial establishment of rush skeletonweed seedlings. Low levels of nitrogen (0.062%) do not preclude rush skeletonweed establishment, although seedlings do better with higher levels. Rush skeletonweed seedlings are also sensitive to competition and shading from other plants [58,82].

In Australia, different types of rush skeletonweed differ in their regenerative capacity. Root cuttings from type C plants produced greater numbers of shoot buds than those of types A and B, regardless of the root diameter, plant age or depth of origin of the cutting. Bud production increased with age in types A and C, but decreased in Type B plants (Hull and Groves 1973, as cited by [67]). Similarly, Rosenthal and others [80] observed differences in root production between the early- and late-flowering biotypes in Washington. After 6 months growth in buried cans, the early-flowering type averaged 6.7 major roots per plant and the late-flowering type averaged 10.7 major roots per plant. After 18 months, the early-flowering plant showed no further increase in root numbers, while the late-flowering plants averaged 16 major roots per plant [80].

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

An integral part of any weed prevention program is to contain infestations neighboring uninfested areas, and to contain rush skeletonweed along highways, railways, and waterways [84]. In Adams County, Washington, a policy was adopted that all rush skeletonweed infestations west of a line that demarcated densely infested rangeland from the remainder of the county were to be controlled using chemical and biological controls. Buffer strips, 300 feet (90 m) in width, were established where large infestations bordered cultivated land. Complete control was maintained along rights-of-way. The purpose of the boundary line and buffer zones was to place a containment line around the worst infestations and slowly shrink those areas over the next several years [83]. No results or follow-up publications are available.

Rush skeletonweed response to cultivation depends upon frequency of cultivation, management of fields during the fallow phase, and age of rush skeletonweed plants [58,99]. Cultivation in the wheat-fallow system of cereal farming in Australia initially favored rush skeletonweed survival and spread. In this system cultivation is frequent enough to increase rush skeletonweed density due to the plant’s ability to regenerate from severed root pieces (see Asexual regeneration), but not frequent enough to decrease their survival [19,60,67]. Surviving rush skeletonweed plants thrived because they had little competition in the fallow phase. Population growth rates tend to increase with the frequency of cultivation until the interval between successive cultivations is reduced to approximately 8 weeks, when plant survival is adversely affected [19]. Daughter rosettes are easier to kill since they have smaller carbohydrate reserves than those arising from taproots. Decreases in rosette densities are greatest following cultivation in dry soil, as root fragments are highly prone to desiccation [23,58,67].

When planning a prescribed burn, managers should preinventory the project area to evaluate the extent, cover, and phenology of any rush skeletonweed or other invasive plants present on or adjacent to the site, and avoid ignition and burning in areas at high risk for rush skeletonweed establishment or spread due to fire effects. Managers should also avoid creating soil conditions that promote rush skeletonweed germination and establishment. Areas of soil disturbance (e.g., those brought about by fire suppression activities) are especially susceptible to invasive plant establishment. Invasive plant status and risks must be discussed in burn rehabilitation plans. Also, wildfire managers might consider including weed prevention education and providing weed identification aids during fire training; avoiding known weed infestations when locating fire lines, monitoring camps, staging areas, helibases, etc., to be sure they are kept weed free; taking care that equipment is weed free; incorporating weed prevention into fire rehabilitation plans; and acquiring restoration funding. Additional guidelines and specific recommendations and requirements are available [36,93].

The white and yellow seeds of skeleton weed are usually sterile while olive-green to brown seeds are usually viable.

The pappus consists of toothed, white bristles 5 to 8mm long on a stem or beak about the same length.

Method of reproduction and dispersal

Skeleton weed reproduces from a long tap-root and by seed.

Most seeds germinate when placed on the soil surface, with 90 per cent germinating when covered with 6 to 7mm of soil.

Skeleton weed prefers temperate, subhumid and semi-arid open scrublands occurring in dry situations on well drained sandy to moderately textured soils. It does not readily establish on heavy textured soils. The plant is tolerant to drought, frost and waterlogging.

Skeleton weed has yellow daisy flowers about 20 millimetres across, and usually flowers from December until May (though it has been found flowering in July in Perth). The seeds are about three to four millimetres long with a parachute to aid wind dispersal.

Status: present in WA

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When to find it: in grain crops, skeleton weed is most likely to be found at harvest time. In other situations it is most recognisable when flowering, in summer and autumn.

Who is likely to find it: potentially anyone in the South West Land Division could find skeleton weed as it is widespread and can occur in different situations. It has been found on farms in a number of Wheatbelt shires. It has also been found along railway lines, on roadsides and on industrial land in the Perth metropolitan area, Fremantle and further south as far as Albany.

Native to southern Europe, the Mediterranean and south-west Asia. Relatively long-lived perennial with a deep tap root; stems and roots exude white latex when damaged.

Seed: brown, three to four millimetres long with numerous shallow ribs. Each seed carries a pappus of white bristles, five to eight millimetres long.