Types of Mustard
There are two types of mustard being used in the Columbia Basin: white mustard (Sinapis alba, also called Brassica hirta or yellow mustard) and oriental mustard (Brassica juncea, also called Indian or brown mustard). See Figures 1 and 2. Commercial varieties are used to produce table mustard, oil, and spices. Blends of the two types of mustard, most with a high proportion of oriental mustard, are often planted for green manuring.
Farmers are using mustard green manures, mainly before potatoes, to:
Suppress soilborne diseases and nematodes. When used as a green manure, researchers (Larkin and Griffin 2007, Ochiai et al. 2008) have found that mustards can suppress some diseases such as Verticillium dahliae and Aphanomyces euteiches (common root rot). Mustard green manures have also been found to suppress Columbia root-knot nematodes and may be effective against other types of nematodes (Mojtahedi et al. 1993; Fourie et al. 2016). However, because even low levels of some nematodes puts potato crops at risk of being rejected by processors, mustard cover crops should be used to enhance, not eliminate, chemical control of nematodes. Fall incorporation works best for control of nematodes and soilborne diseases and, oriental mustard may be better for this use than white mustard for disease suppression (Lazzeri and Manici 2001). Research is ongoing.
Suppress weeds. Weed control using mustard green manures has been variable (Haramoto and Gallandt 2004). The level of suppression seems to depend on the combination of mustard type and weed species and on the management of the green manure crop.
Biofumigation. Reductions in the numbers of nematodes, disease problems, and weeds are thought to be due in part to the presence of glucosinolates in mustards (Matthiessen and Kirkegaard 2006).