J.W. Potter’s research while affiliated with Agriculture and Agri-Food Canada and other places

The biodiversity of soil-inhabiting nematodes in Canada is incompletely known, as large areas of Canada's landmass have not been surveyed for nematode fauna. Nematodes considered as indigenous are generally well adapted to a variety of ecological niches and climatic zones. Much of the available information is based on agricultural ecosystems and agricultural species, and thus is biased toward conditions in disturbed ecosystems and away from "primeval" ecology. Introduced nematode species are frequently quite pathogenic, even to exotic host plants from the same geographic point of origin. Estimates of crop loss due to single species infestations of pathogenic nematodes and the costs of nematode control using chemicals are reasonably well known, averaging about 10% of crop value, but ranging to 100% depending on the situation; the cost of damage by multiple-species infestations is less defined. Nematode-suppressive mechanisms are understood in only a few plant species; sulfur appears to be important as a constituent of active compounds in suppressive plants of agricultural origin. Similarly, some native plants are equally adapted with allelopathic chemicals that suppress nematodes. Management of nematode populations in agricultural soils by integrated crop management methods is at an early stage, requiring research to quantify effects of nematode-suppressive plants and soil amendments containing nitrogen. An integrated program could include nematode-suppressive plants, appropriate soil amendments, and the promotion of microbial antagonists. Different mathematical methods may be required to analyze and explain multi-factor nematode control systems. Less-toxic management systems could benefit the soil-inhabiting nematodes that predate arthropod soil pests. Further research on soil-borne nematodes may demonstrate the value of nematodes as indicators of agroecosystem health and environmental pollutants.

Experiments on the distribution and survival of pin nematode Paratylen- chus projectus in potato growing systems and on its control by various mechanisms are described. Preferable management strategies for the pin nematode include the use of flax or a high-glucosinolate mustard or canola, the use of 'Trudan 8' sudangrass to add organic matter into the soil, and shallow but thorough tillage of a sandy soil in the fall or in early spring to disrupt the soil. In general, many grasses and legumes should be avoided as cover crops. (Fluctuations des populations du nématode de goupille Paratylenchus projectus sous différents systèmes de production de pomme de terre) Des expériences sur la distribution et la survie du nématode de goupille Paratylenchus projectus dans des systèmes de production de pomme de terre et sur son contrôle par divers mécanismes sont décrites. Les meilleu- res stratégies de gestion pour le nématode de goupille incluent l'utilisation du lin textile ou d'une moutarde ou canola à haut-glucosinolate, l'utilisation de 'Trudan 8' sudangrass comme ajout de matière organique dans le sol, et le labourage peu profond mais complet d'un sol sablonneux en automne ou au début du printemps pour perturber le sol. En général, plusieurs graminées et légumineuses devraient être évitées comme cultures de protection.

Studies were conducted at Simcoe, Ontario from 1992 to 1996 to evaluate various cover crop species as possible alternatives to fumigation prior to potatoes (Solanum tuberosum). Cereal rye (Secale cereale), a common overwinter cover crop in vegetable production systems, is an excellent host for the root-lesion nematode (Pratylenchus penetrans) and provides a suitable overwintering host on coarse sandy soils. Vorlex Plus CP and Telone IIB fumigants were compared to 'Domo' mustard (Brassica juncea) for the 1993 and 1994 potato crop years. Rye plus red clover (Trifolium pratense) was included as a known host cover crop system. Cyanogenic plants including 'Domo' mustard (1994) or 'Cutlass' mustard (1995, 1996), 'Forge' canola (Brassica rapa), 'Sordan 79' and 'Trudan 8' sorghum- sudangrass hybrids (Sorghum bicolor), and flax (Linum usitatissimum) were compared to Vorlex Plus CP fumigant and 'NK557' sorghum (Sorghum vulgare) for effects on potato yield and nematodes. Shallow (15 cm) and deep (45 cm) fumigation with Vorlex Plus CP were also compared prior to potatoes for the 1994 to 1996 crop years. There was little detectable difference in percent or days to 50% emergence of potatoes following any treatment. Highest total and marketable yields resulted from Telone IIB fumigation, then Vorlex Plus CP fumigation and 'Domo' mustard, followed by control and rye plus red clover cover. Populations of nematodes surpassed the threshold of 1000 kg -1 soil in all treatments and were highest in potatoes following rye plus red clover. Yield and nematode control following sorghum- sudangrass hybrids and mustards appeared to be intermediate between fumigated and not fumigated. All of the cover crops appeared to be root- lesion nematode hosts in the field, and reduction of population levels appeared to result after incorporation or nematode winterkill. Nematode mortality was excellent with fumigation and next best from kill over the winter after 'Sordan 79' incorporation. 'Sordan 79' grown over at least part of the summer followed by incorporation was an alternative to fumigation prior to potatoes. Deep chiselling appears to reduce nematode population,

Because of the need to find plants that suppress root lesion nematodes for use in rotation or cover-crops, 16 native sand-prairie species were evaluated for host status for 6 years. Plants were grown on a Fox sand soil at a local prairie plant nursery. Soil cores were taken in the spring, summer, and fall and assayed for plant parasitic nematodes. Five species supported very low numbers (less than 100/kg soil) of root lesion nematodes. Brown-eyed Susan ( Rudbeckia hirta ) had no detectable nematodes for the duration. Switchgrass ( Panicum virgatum L.) and Indiangrass ( Sorghastrum nutans L., Nash) samples produced detectable nematodes on only two sampling dates over the 6 years and were statistically not different from brown-eyed Susan. Butterfly weed ( Asclepias tuberosa L.) also had very low detectable nematodes as did sand dropseed [ Sporobolus cryptandrus (Torr.) Gray.]. New Jersey tea ( Ceanothus americanus L.), little bluestem [ Schizachyrium scoparium (Michx.) Nash], and big bluestem ( Andropogon gerardi Vitman) were poor hosts with <200 nematodes/kg soil. Mountain mint ( Pycnanthemum virginianum L), wild bergamont ( Monarda fistulosa L), horsemint ( Monarda punctata L), and dwarf blazing star ( Liatris cylindracea L) all had root lesion populations over 3000/kg soil. Horsemint and wild bergamont plants died out, possibly as a result of nematode infestation. Root lesion nematodes have an extremely wide host range in current agronomic and horticultural crops, and weeds and are difficult to manage using nonchemical means. Indiangrass, switchgrass, big bluestem, and little bluestem have all been used agriculturally for pastures and consequently have potential as beneficial long-term rotation crops for nematode management and soil building.

Le nematode des lesions des racines (Pratylenchus penetrans), le nematode phytoparasite le plus important du sud de l'Ontario, possede une gamme d'hotes extremement large. A cause de la necessite de reprimer ces parasites avec des cultures recouvrantes qui sont peu ou pas hotes, plusieurs especes indigenes des prairies sablonneuses ont ete evaluees pour leur susceptibilite au nematode des lesions. Onze especes appartenant a quatre familles (Asclepiadaceae, Asteraceae, Poaceae et Fabaceae) ont ete identifiees commes des hotes faibles. Les populations tres faibles de P. penetrans sur ces especes indiquent qu'elles pourraient avantageusement servir comme cultures recouvrantes.