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SCREENING COVER CROPS TO REDUCE SOYBEAN CYST NEMATODE IN INFESTED FIELD
EXECUTIVE SUMMARY

NORTH DAKOTA SOYBEAN COUNCIL
June 2017

Dr. Guiping Yan, Principal Investigator, Dept. Plant Pathology, NDSU
Co-investigators: Dr. Marisol Berti, Dept. Plant Science, NDSU
Dr. Samuel Markell, Dept. Plant Pathology, NDSU

Soybean cyst nematode (SCN), Heterodera glycines, is one of the major pests of soybean production in North Dakota. This nematode not only infects soybean, but also invades other leguminous crops and weed species which help in the survival and increase of the nematode populations in the fields. Host resistance and crop rotation are commonly used practice to manage SCN, but limited sources of resistance have been used for developing resistant soybean cultivar, so an integrated management strategy, including cover crops, could be a best approach for SCN management. In addition to improving soil quality and ecosystem, cover crops are considered to have the ability to reduce plant-parasitic nematode populations in infested fields.

Our objectives were to evaluate the ability of cover crops for SCN host and population reduction in infested soils by performing greenhouse and microplot experiments using naturally infested soils from Cass and Richland counties of North Dakota.

Twenty-one cover crops and two susceptible soybean cultivars were planted in cone-tainers each containing 100 cm3 of infested soil and kept in a growth chamber at 27 oC for 35 days (Figure 1). SCN white females (cysts) were extracted from root and soil then counted under a microscope for evaluating SCN reproduction in each cover crop. Out of twenty-one cover crops evaluated in the greenhouse conditions, annual ryegrass, camelina, carinata, ethiopian cabbage, faba bean, foxtail millet, radish, rape dwarf essex, red clover, sweet clover, triticale, and winter rye did not support SCN reproduction. Cowpea, crimson clover and turnips showed very low reproduction (white females: 1 to 13), but Austrian winter pea, field pea, forage pea, and hairy vetch showed some levels of reproduction (white females: 13 to 173) compared to the susceptible soybean cultivars Barnes and Sheyenne (white females: 827 to 1,251).

Among 21 cover crops screened in the greenhouse, ten cover crops such as annual ryegrass, Austrian winter pea, carinata, faba bean, foxtail millet, radish, red clover, sweet clover, turnip, and winter rye were further selected for a microplot study. Cover crops were planted in pots, each containing 5 kg of soil from each of two naturally infested fields under natural conditions (Figure 2). After 75 days of growth, soil samples were collected from each pot. SCN eggs were extracted from 100 cm3 of soil and counted under the microscope then compared with the initial population density to evaluate the ability of each cover crop for population reduction.

In both field soils, all the tested cover crops except Austrian winter pea reduced the SCN populations compared to the non-planted control and susceptible soybean. Among those crops, radish and annual ryegrass were more effective than others on reducing SCN populations. Our preliminary results suggest that cover crops could be an alternative means of managing SCN in soybean fields, but screening of more cover crops, conducting field trials, and understanding the mechanisms of population reduction are necessary to make recommendations to grower for planting cover crops for managing soybean cyst nematode.