The viability and moisture content of yarrow (Achillea millefolium L.) rhizomes: A dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Agricultural Science with Honours in the University of Canterbury

The effect of desiccation on yarrow (Achillea millefolium L.) rhizomes was studied in three series of experiments at Lincoln College during 1982. Desiccation in growth cabinets at 11°, 18° and 25°c led to the total death of 5 cm long rhizome fragments within 10 - 14 hours. Rates of death and moisture loss increased with increasing temperature. Water content was found to be a more reliable analysis of water stress than water potential. There was a linear relationship between moisture content and survival of the rhizomes, and 50% viability occurred at moisture contents between 40 and 49%. High soil moisture decreased the effect of desiccating temperatures on rhizome viability. On the surface of soil at field capacity, 0 88% of the rhizome fragments were viable after 12 hours at 20°C, while on air dry soil all the rhizomes were dead. Seven per cent of the rhizomes were still viable after 6 days burial in air-dry soil. Viability decreased slowly in rhizomes buried in wilting-point soil. No rhizomes survived longer than 3 days when placed on the soil surface during hot, dry weather in February, but there was no apparent loss in viability over 8 days of rhizomes placed on the soil during cool,wet weather in April. Emergence of buried rhizomes in the February trial was about 40% less than those considered viable in the laboratory. Total death of rhizomes placed on the soil surf ace in May did not occur until 14 weeks had passed. Initial death was rapid though, and less than 15% remained viable after 4 weeks. It was concluded that the desiccation of yarrow rhizome fragments on the soil surface was a successful method of controlling the rhizomes. Tillage techniques would need to be devised to enable a significant proportion of the rhizomes to be brought to the soil surface. Warm, dry weather and dry soil would be optimum conditions for desiccation.