Contribution of a winter wheat cover crop to the maintenance of root lesion nematode populations in the red raspberry production system

Authors: RUDOLPH, RACHEL - Washington State University; WALTERS, TOM - Walters Ag Research; DEVETTER, LISA - Washington State University; Zasada, Inga

Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/5/2018
Publication Date: 4/1/2018
Citation: Rudolph, R.E., Walters, T.W., Devetter, L.W., Zasada, I.A. 2018. Contribution of a winter wheat cover crop to the maintenance of root lesion nematode populations in the red raspberry production system. HortTechnology. 28(2):182-188. https://doi.org/10.21273/HORTTECH03971-18.
DOI: https://doi.org/10.21273/HORTTECH03971-18

Interpretive Summary: Cover crops are plants that are grown with, before, or after a cash crop with the intention of benefiting the cash crop and surrounding soil by lessening soil erosion, increasing water infiltration, and promoting pest management. In the he northern part of the United States where most of the U.S. processed raspberries are produced, a wheat cover crop is grown before a new raspberry planting is established. This research was conducted to evaluate the role that a wheat cover crop plays in maintaining the root lesion nematode, a microscopic worm that damages the roots of raspberry. Additionally, nematode management methods were applied to the wheat cover crop to attempt to reduce the numbers of root lesion nematodes in commercial raspberry fields. Results indicate that wheat is a host for root lesion nematode and maintains the nematode until raspberry is planted. Methods used to try to reduce the number of root lesion nematodes in wheat were not successful. While a wheat cover crop is a host for root lesion nematode, the benefits of winter cover cropping, primarily by lessening soil erosion, out-weigh the minimal contribution that wheat makes to maintaining the root lesion nematode population. This research will be used by scientists and farms to further the adoption of cover crops in the raspberry production system.

Technical Abstract: One of the primary production challenges red raspberry growers in the Pacific Northwest confront is root lesion nematode (RLN; Pratylenchus penetrans). In this perennial production system, raspberry serves as a sustained host for RLN. When a raspberry planting is slated for removal in the fall, a new raspberry planting quickly follows in the same field the following spring. The primary crop that occurs in rotation with raspberry is a winter wheat cover crop to provide soil coverage and protection during the winter. The objectives of this research were to determine if winter wheat provides a green bridge for RLN in continuous raspberry production systems, and to determine if modified winter cover cropping practices can be used to reduce population densities of RLN prior to replanting raspberry. Four trials were established in fields being replanted to raspberry and the following modified winter cover cropping practices were considered: cover crop planting date (at fumigation or two weeks after fumigation), termination date (cover crop kill with herbicide two or six weeks prior to incorporation compared to the industry standard of incorporation immediately prior to planting), and the additional application of methomyl. The winter wheat cultivars ‘Rosalyn’ and ‘Bobtail’ planted as cover crops in these trials were demonstrated to be maintenance hosts for RLN (ranging from 10 to 947 RLN/g wheat root across trials) allowing them to be a green bridge for RLN to infect the following raspberry crop. Altering wheat cover crop planting date, termination date with herbicide, or methomyl application did not affect RLN population densities in the subsequent raspberry crop. Although planting a maintenance host may be of concern to growers, the advantages of reduced soil erosion and nitrate leaching associated with cover cropping outweigh the perceived risk to the subsequent raspberry crop.