Update on the effect and extent of nematode suppression with cover crops

Root lesion (Pratylenchus penetrans) and northern root knot nematodes (Meloidogyne hapla) can cause significant damage to many crops and have a wide host range including many weeds native to Ontario. Strawberries are particularly sensitive to damage cause by these nematodes. Nematodes can also provide infection sites for disease-causing fungi which further reduce yields. Planting cover crops such as marigolds, pearl millet, and certain hot mustard cultivars has been shown to reduce plant parasitic nematode soil populations below economic thresholds without affecting beneficial soil-borne organisms or the environment. Although these cover crops reduce nematode populations, some are difficult to seed, manage and the reduction in nematode populations may not last over the period a perennial crop such as strawberries is grown.

An on-farm trial funded by Horticulture Crops Ontario was initiated in 2006 to evaluate the effectiveness and extent of nematode reduction in strawberries following Oriental Mustard cv. Cutlass, Marigold cv. Crackerjack and Canadian Forage Pearl Millet 101 compared to the nematicide Vapam and an untreated fallow plot. The marigolds, oriental mustard and Canadian Forage Pearl Millet 101 were planted in separate replicated plots, during 2006. Fallow plots and plots fumigated with Vapam were established for comparison. Strawberry cv. Mira was transplanted across all treatments in the spring of 2007.

Nematode populations were monitored in each plot throughout 2006 when the cover crops were growing and again in 2007 after strawberries were transplanted. Fallow and all cover crops suppressed root lesion nematode populations during the year the cover crops were grown. Root lesion soil populations continued to be suppressed in strawberries throughout 2007 following Marigold, and Oriental mustard. Although fallow and Pearl Millet suppressed root lesion nematodes during 2006, the soil populations increased in these plots throughout 2007. Fumigation with Vapam in the fall 2006 provided complete control of root lesion soil populations throughout 2007.

Root knot nematode soil populations were suppressed during 2006 in plots planted with marigolds, oriental mustard or left fallow. Fumigation with Vapam in the fall 2006 provided complete control of root knot soil populations which was also observed in the spring 2007. Root knot nematode soil populations increased most slowly in plots following either Canadian Forage Pearl Millet 101 or oriental mustard. By the end of the 2007 season, root knot nematode soil populations increased significantly in all plots regardless of the previous cover crop or treatment applied in 2006. Populations particularly increased in plots that were fumigated the previous fall with Vapam. The reason for the significant increase in root knot nematode populations in strawberries after fumigation is not known. However, it is likely that fumigation not only eliminated root knot nematodes from soil in the fall of 2006 but may have also eliminated natural microbial competitors and antagonists. The natural microbial competitors and antagonists may not have been affected as much by the cover crops and kept the root knot populations in check when strawberries were transplanted the following year.

Nematode populations will continue to be monitored throughout 2008 and strawberry yields will also be assessed to determine the effect and extent the cover crops have suppressing nematodes.

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