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Strategies for Control of Root Rot in Apiaceae Crops

The Apiaceae vegetables, such as parsley, coriander, parsnip and carrot, are prone to root rots, cankers and cavity spot diseases that can significantly affect yield and marketability of produce.

Between 2009 and 2011, a series of field trials were conducted in Victoria, Tasmania, Queensland, New South Wales (hydroponic systems), and Western Australia.

These trials evaluated a range of control options for Pythium related diseases of Apiaceae vegetable crops, including fungicides, biological and cultural controls, and varieties.

Key Outcomes and Conclusions

  • In parsnip trials, disease symptoms developed gradually during the cropping season but the greatest increments of disease incidence and severity were observed in spring, coinciding with relatively higher rainfall, increasing temperatures and day length, and rapid growth of parsnip roots. Soil properties (sand or loams) and rainfall were associated with higher disease levels and 100% yield loss in crops grown on medium clay soil in the season of relatively high rainfall.

  • Of the many disease management options evaluated in parsley and parsnip trials in Victoria, only fungicide treatments and new parsnip varieties gave significant reductions in disease and improved yields. However, fungicide treatments were not consistent, being effective in only one of two trials in parsley and one of four trials in parsnip.

  • Autumn sown parsley and parsnip crops are at the highest risk of root disease, being exposed to relatively warm temperatures and autumn and spring rains.

  • Three different biological control agents, Bacillus subtilis, Streptomyces lydicus andPythium oligandrum, did not provide any significant control of root rot in field grown parsley, parsnip or hydroponically grown coriander.

  • There was evidence that Bacillus subtilis treatments stimulated the growth of parsnip and coriander.

  • Two disease management options that provided disease control and improved yields were fungicide treatments and varieties. Metalaxyl, applied to the soil, reduced the severity of root rot in parsley and canker in parsley, resulting in improved yields. This fungicide is active against the “water mould” pathogens such as Pythium. However, results were not consistent.

  • Fungicides were not effective in one of two trials in parsley and one of four trials in parsnip. Heavier soil types appeared to be a major constraint. Some parsnip cultivars evaluated in the field proved to be much less susceptible to canker, returning up to 3 times more marketable crop than the standard variety. These varieties may be an option for cultivation when the disease risk is very high.

  • Cultural control treatments of hilling soil over the parsley and parsnip crowns, and blanketing soil with organic mulch, did not reduce root disease, although both hilling and mulch treatments stimulated plant growth in some trials.

  • Recommendations for control of these Pythium induced root rots include rotation with non-Apiacaea crops (e.g. Brassica), selection of fields/beds with relatively good drainage, and early applications of fungicides such as metalaxyl in the granule form to ensure a good distribution in soil.