Abstract
The cost to clover growth of soil-borne root disease was measured in ten New Zealand dairy pasture soils. The average increase clover growth (weight) after soil pasteurisation was 28.5 %, but ranged from a 64 % increase (Whataroa soil) to a decrease of 11.9 % (Ruakura soil). The economic cost of reduced clover growth was determined using the Farmax Dairy Pro decision support system. In Southland and Canterbury, clover root disease was estimated to cost $750 and $715 ha−1 year−1 respectively, and in the Waikato region $1506 ha−1 year−1. DNA-based testing of the soils detected the presence of diverse fungal, oomycete and nematode pathogen populations. A significant linear relationship was found between reduction in clover growth and group F Pythium spp. (P = 0.0177). The DNA-based assay indicated that Aphanomyces trifolii, a root pathogen of subterranean clover, may be present in the dairy-pasture soils. As this pathogen is currently not recognised as present in New Zealand, a definitive determination of its presence is required. Based on the high economic costs of diseases, the control of soil-borne root pathogens in New Zealand pasture is a direct means to increase profitability.
Highlights
A diverse range of pathogens are known to cause disease on the roots of forage plants in New Zealand pastures (Harvey and Harvey 2009)
In the period between 1990 and 2014, the area used for dairy pasture grew from 1.57 million ha to 2.42 million ha (Statistics New Zealand 1999, 2014)
When calculated as percentage growth change, microwave-treatment of soil resulted in clover growth increases from 64 % (Whataroa) to −11.9 (Ruakura)
Summary
A diverse range of pathogens are known to cause disease on the roots of forage plants in New Zealand pastures (Harvey and Harvey 2009) These include nematodes, fungi, and Oomycetes (Falloon 1985; Skipp and Christensen 1989; Waipara et al 1996; Watson and Mercer 2000; Sarathchandra et al 2000), which vary from highly host-specific through to broad-range generalists. In New Zealand, the bulk of research efforts were conducted in the mid 1980’s through to the early 2000’s (Falloon 1985; Skipp and Christensen 1989; Waipara et al 1996; Watson and Mercer 2000; Sarathchandra et al 2000), with relatively little work conducted for the past 15 years This is at odds with the trend for increased value of pasture production on a per hectare basis. The direct value of dairy as a land use has grown, with total export values of $2.98 billion in 1996 from 1.76 million ha, to $15.82 billion in 2014 from 2.42 million ha
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