Laurus nobilis 'MonRik'

Summary

South Coast Research & Extension Center (South Coast REC/SCREC) is located in Irvine California, this site has a sandy loam soil and plants are irrigated with reclaimed water. UC Davis is located in Davis, California, this site has a silty clay loam soil and plants are irrigated with potable water. More information about the field sites is located in the Nuts & Bolts section.

Little Ragu^® is a compact form of sweet bay with deep green, aromatic leaves. Results for this cultivar were compromised in Davis by foliar necrosis symptoms and stunted growth. As the season progressed, some plants grew partially out of these symptoms but never enough to attain an average of acceptable appearance for any treatment. At the end of the trial, plants were excavated and roots sent off for analysis by Dr. Johanna Del Castillo Munera. Pathogens were found on all samples. Phytophthora cinnamomi was observed on samples from the high and medium treatments, and interestingly Phytopythium littorale was recovered from the low treatment. As a result, further plants were excavated with findings of Phytophthora capsici, P. mengi, and P. tropicalis. This case was the first report of P. mengi on Laurus. It is believed that these pathogens arrived with the plants. Since the disease triangle consists of a susceptible plant, a pathogen, and the right conditions for the pathogen to attack a plant, it is possible the different irrigation treatments created conditions favoring different Phytophthora species, although further investigation would be needed to confirm. The presence of these pathogenic organisms is consistent with recent studies finding high incidence of pathogens in nursery production¹. These pathogens may go unnoticed or detected because species are not susceptible. However, because of these disease susceptibility issues, Little Ragu did not reach its potential in Davis.

In Irvine, plants did not appear to be affected by the reclaimed water treatments, though disease resistance scores declined as the deficit season progressed. Unfortunately, plants grown at South Coast REC were not submitted to test for pathogens. After analyzing the data collected, Little Ragu is assigned a low water recommendation for WUCOLS regions 2 and 3.

1.S. Rooney-Latham et al.(2019). Phytophthora Species Are Common on Nursery Stock Grown for Restoration and Revegetation Purposes in California, The American Phytopathological Society, Vol. 103, No. 3, March. https://doi.org/10.1094/PDIS-01-18-0167-RE 

Growth and Quality Data

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