SR9076 - Root Rots of Ginseng: Identification of Candidate Fungicides for Minor Use Registration and Assessment of Fungicide Resistance

Researcher:

Dr. Richard Reeleder, Agriculture and Agri-Food Canada, London

Objectives:

1. To assess under laboratory conditions new fungicide chemistries for use in management of Cylindrocarpon diseases of ginseng.
   

2. To assess under in vitro conditions the response of Pythium and Phytophthora isolates to metalaxyl.
   

3. To determine field performance of candidate fungicides in management of Cylindrocarpon diseases of ginseng.

Expected Benefits:

1. Ontario will benefit economically as a result of increased profits obtained by ginseng growers.
   

2. Growers may increase their share of the world ginseng market.
   

3. Pesticide industries would benefit from incrase sales of new products and the environment would benefit as use of unlabelled products would be reduced.

Summary of Research Results:

The fungal pathogen Cylindrocarpon destructans causes annual crop loss in the Ontario ginseng industry that has been estimated by industry to be as high as $15 million per year. This pathogen causes rots of mature roots ("disappearing root rot") and of seeds and seedlings, is tolerant to a number of fungicide products, contributes to the replant decline phenomenon, and may be a cause of the disease "rusty root". Registered fungicides have been effective in reducing effects of other diseases of ginseng but products targeting this disease are not yet available.

We have screened new fungicide chemistries in vitro and have established field trials to evaluate their field performance. Resulting data indicate that some newer products are similar to propiconazole in vitro with respect to control of C. destructans. Some products (e.g. fludioxonil) are being tested in field trials established as a result of this project. Pythium spp and Phytophthora cactorum are known to be virulent pathogens of ginseng. Metalaxyl and related materials are used to control phytophthora root rot in ginseng and a benefit of the use of this product has been to provide some control of Pythium as well. Results of in vitro screening indicate that metalaxyl-tolerant Pythium populations are present at low levels in certain fields but there is no evidence that selection for metalaxyl-tolerance is occurring during the four-year ginseng production cycle. Fumigation of ginseng fields reduced Pythium populations to approx 100 propagules per g of soil. When, however, populations were at or below this level prior to fumigation, further reductions resulting from fumigation were limited.