Field Mustard

Scientific Name: Brassica rapa L. var. rapa

Field Mustard

General Information
Usda Symbol	BRRAR
Group	Dicot
Life Cycle	AnnualBiennial,
Growth Habits	Forb/herb
Native Locations	BRRAR

Plant Guide

Description

General: Field mustard is an upright winter annual or biennial that is a member of the mustard family (Brassicaceae). Plants exist as basal rosettes until flowering stems develop at maturity, usually in the second year. Plants grow 1 to 3 (or 4) ft tall from a sometimes fleshy, enlarged taproot, with a many-branched stem. The foliage is generally hairless and sometimes covered with a whitish film. Lower leaves can reach 12 inches long, have a large central lobe, and usually one to four pairs of smaller side lobes. Upper leaves are smaller, non-lobed, and have a pointed tip and widened, clasping base. The bright yellow flowers are clustered at stem tops and have four petals that are ¼ to ½ inch long. Plants flower from January to September, depending on climate and latitude, and are insect pollinated and self-incompatible. The fruit is an elongated, two-parted capsule that splits open at the base to release the seeds at maturity. Each half of the pod has a single prominent lengthwise vein that distinguishes it from those of other Brassica species that have 3 to 7 veins. The hairless seed pods are ¾ to 4 inches long, with a narrow beak at the tip, and are born on long, ½- to 1-inch stems that point outward or upward. Seeds are about 1/16 inch wide, nearly round, and reddish-gray to black (DiTomaso and Healy, 2007; Jepson Flora Project, 2012; Pojar and MacKinnon, 1994; Taylor, 1990; Turner and Gustafson, 2006; Warwick, 2010; Whitson et al., 2006). Distribution: This species is native to Eurasia, but has spread all over the world and is now naturalized throughout much of North America. It grows from sea level to 5,000 ft. For current distribution, please consult the Plant Profile page for this species on the PLANTS Web site. Habitat: Field mustard grows in disturbed areas including roadsides, ditches, cultivated fields, orchards, and gardens.

Adaptation

Field mustard is an extremely adaptable plant that grows in sandy to heavy clay soils and tolerates a pH range from 4.8 to 8.5 (Hannaway and Larson, 2004). It grows best in well-drained, moist soil, but may also grow in droughty conditions, moderate heat, and soils with low fertility (Clark, 2007). Although it grows best in full sun, it will grow in moderate shade. Field mustard is hardy through USDA plant hardiness zone 7. Natural Resources Conservation Service Plant Guide Photo by George W. Williams, 2011, courtesy of Wildflowers in Santa Barbara at http://sbwildflowers.wordpress.com.

Uses

Cover crop: Field mustard is used as a winter annual or rotational cover crop in vegetable and specialty crops as well as row crop production. It has the potential to prevent erosion, suppress weeds and soil-borne pests, alleviate soil compaction, and scavenge nutrients (Clark, 2007). It has rapid fall growth, high biomass production, and nutrient scavenging ability following high input cash crops. Field mustard can be grown as a cover crop alone or in a mix with other brassicas, small grains, or legumes. In the Northeast, Mid-Atlantic, and Great Lakes bioregions, it appears to be a good tool as a biofumigant cover crop for control of nematodes, soil-borne diseases including the fungal pathogen (Rhizoctonia) responsible for damping-off, weeds, and other pests. When biomass is incorporated into the soil, soil microbes break down sulfur compounds in the plant into isothiocyanide, which can act as a fumigant and weed suppressant (Olmstead, 2006). Field mustard produces 2,000 to 5,000 pounds of dry matter per acre per year and biomass contains 40 to 160 lb/acre total N (Clark, 2007). Intercropping: Intercropping can increase cropping system diversity and profitability by producing two simultaneous crops on the same land. In New Mexico, forage turnip was interseeded between rows of chili peppers and sweet corn without affecting yields of the cash crop when the turnip seeding was timed correctly (Gulden et al., 1997a, 1997b). Forage: Cultivars with larger roots, commonly called forage turnip, have been a popular forage crop for livestock in Europe and Asia for at least 600 years (Undersander et al., 1991). Forage turnip is a useful crop for extending the fall grazing season for dairy cows and other livestock (Thomet and Kohler, 2003; UMass Extension, 2012). Forage turnip was largely replaced with corn silage in the early 1900s because it required less labor. The use of forage turnip increased again in the 1970s with the development of new cultivars that could be seeded directly into pastures. Aboveground vegetation contains 20 to 25% crude protein, 65 to 80% in vitro digestible dry matter (IVDDM), about 20% neutral detergent fiber (NDF), and about 23% acid detergent fiber (ADF). The roots contain 10 to 14% crude protein, and 80 to 85% IVDDM (Undersander et al., 1991). Caution: The roots, leaves, and especially seeds of Brassica rapa and related species contain sulfur compounds (glucosinolates) that can irritate the digestive tracts or create thyroid problems in livestock if consumed in large quantities over time (DiTomaso and Healy, 2007). Toxicity in livestock, particularly horses, can create symptoms such as colic, diarrhea, anorexia, excessive salivation, and thyroid enlargement (DiTomaso and Healy, 2007; Ahmann Hanson, 2008). Problems arise when livestock eat large quantities of seed or are confined to pastures composed primarily of mustards. Nitrate nitrogen toxicity can also be a problem for ruminants if field mustard is grazed when immature or if soil N levels are high (Undersander et al., 1991). Vegetable crop: Brassica rapa has been cultivated in Europe as a vegetable for human consumption for more than 4,000 years (Duke, 1983). Turnip roots are the product of horticultural cultivars of this species. The leaves, known as “turnip greens” or “turnip tops”, are also eaten raw or cooked and have a slightly spicy flavor similar to mustard greens. Rapini, or broccoli raab, is another vegetable derived from a cultivar of this species. Seed: Canola is a cultivar of either Brassica rapa or B. napus. Seed was developed with lower levels of erucic acid and glucosinolates to make the oil safer for human consumption (Canola Council of Canada, 2012). The name canola comes from Canadian oil, low acid; rapeseed oil must contain less than 2% erucic acid to qualify as canola. Canola and rapeseed oils are used as cooking oil, industrial lubricants, lamp oil, in soap making, biodiesel production, and the meal is used as a protein source in animal feed (Canola Council of Canada, 2012; Plants for a Future, 2012).

Ethnobotany

Field mustard roots and leaves were used as food by many Native American tribes following introduction of the plant by white settlers (Moerman, 2012). Various parts of the plant have been used as a folk remedy for different types of cancer, either by boiling the mashed stems and leaves, powdering the seeds, or making a salve from the flowers (Duke, 1983; Plants for a Future, 2012).

Status

This plant may become weedy or invasive, primarily in cultivated fields and disturbed or waste areas, and may displace desirable vegetation if not properly managed. Brassica rapa is listed as an invasive weed in Weeds of the West and Weeds of the United States and Canada (SWSS, 1998; Burrill et al., 2006). Brassica spp. are state-listed restricted noxious weed seeds in Arizona and prohibited noxious weed seeds in Michigan (MDA, 2011; Parker, 1972). Please consult with your local NRCS Field Office, Cooperative Extension Service office, state natural resource, or state agriculture department regarding its Volunteer field mustard cover crop in a California vineyard. Photo by Gerald and Buff Corsi © California Academy of Sciences. status and use. Please consult the PLANTS Web site (http://plants.usda.gov/) and your state’s Department of Natural Resources for this plant’s current status (e.g., threatened or endangered species, state noxious status, and wetland indicator values).

Planting Guidelines

Drill seed in the spring, late summer, or fall at a rate of 1.5 to 10 lb/acre and a depth of ½ to ¾ inch in rows 4 to 12 inches apart; alternately, broadcast at 8 to 14 lb/acre followed by cultipacking (Clark, 2007; Hannaway and Larson, 2004; Knodel and Olson, 2002). Field mustard has approximately 150,000 to 200,000 seeds per pound, so a seeding rate of one pound per acre will result in approximately 3 to 5 seeds per square foot. The target spacing for a pure stand is 5 to 6 plants per square foot (Undersander et al., 1991). Some ecotypes have seed that requires a cold, moist period to break dormancy and stimulate germination (DiTomaso and Healy, 2007). Winter cover crops should be established as early as possible, or at least four weeks before the average date of the first hard freeze (Clark, 2007). Soil temperatures for planting should be between 45–85°F. In northern climates, spring-planted crops generally produce less aboveground biomass and root growth, and are less reliable due to cool soil temperatures.

Management

Fertilization: Soils should be tested prior to planting to determine fertilizer and lime requirements. When planted as a fall catch crop following a cash crop that has been well fertilized, additional fertilizer may not be needed (Duke, 1983). Lime should be added to correct pH to 5.5 to 6.8. Fertilizer applications, if required, should be banded at least 2 inches to the side and below the seed. Forage: Forage turnips reach their maximum yields 70 to 100 days after planting. Turnip tops can be grazed up to four times at four week intervals to a 5-inch stubble. Animals can be allowed to graze plants to ground level including the roots on the final grazing (Undersander et al., 1991). Forage crops should not be allowed to go to seed and should be fed in combination with other forages to avoid problems with toxicity (see caution note above in Uses section). Cover crop termination: Field mustard usually survives early frost, but temperatures below 25°F will likely kill stands. However, some winter-type cultivars can withstand temperatures as low as 10°F (Clark, 2007). Winterkilled mustard decomposes quickly, leaving a seedbed that is easy to plant into the following spring. If the crop does not winterkill, it can be terminated with herbicide, by flail mowing (good for no-till systems), or tillage (especially for biofumigation) before the plants have reached full flower. They can also be killed with a roller-crimper when they are in flower. Some Brassica rapa cultivars have become resistant to glyphosate treatments (Clark, 2007), so another termination method may be needed for complete kill. Cover crop termination should occur before or at full bloom to avoid seed set and volunteers in subsequent crops.

Pests and Potential Problems

Field mustard is susceptible to a number of viruses, including Arabis mosaic nepovirus, broad bean wilt fabavirus, and cauliflower mosaic caulimovirus (Hannaway and Larson, 2004). It is also susceptible to turnip mosaic virus, which is transmitted by many species of aphids. Pest problems are best avoided by planting resistant cultivars and/or using crop rotations to break disease cycles (Black, 2001). Clubroot and black rot are the most serious diseases of turnips, while turnip aphid, root maggot, and flea beetles are the most damaging insect pests (Duke, 1983). In order to avoid disease problems, Brassicas should not be grown on the same field for more than two consecutive years. A six year rotation should be used in areas with clubroot (Undersander et al., 1991). Flea beetles can also cause extensive damage in canola, and are best avoided by planting on wider row spacing (12 inches) from April to mid-May, with a no-till planter in fall, or by treating seed with a systemic insecticide (Knodel and Olson, 2002). Wild mustards, including field mustard, can also harbor pests and diseases that attack closely related crops in the mustard family (DiTomaso and Healy, 2007).

Environmental Concerns

Concerns

Concerns

It has been reported that field mustard seeds can survive for fifty years or more if they are deeply buried, but seeds closer to the soil surface are not as persistent (DiTomaso and Healy, 2007). Modern cover crop cultivars do not have hard seed, but may have a small percentage of “latent seed” that fails to germinate immediately when planted if adequate growing conditions such as light and moisture are lacking (S. Davidson, AgriSeed Testing, G. Weaver, Weaver Seed, and D. Wirth, Saddle Butte Ag, personal communication, 2017). If left to mature in unmanaged areas, weedy mustards also may become a fire hazard when they dry at the end of the growing season (UC IPM, 2011).

Control

Unwanted plants can be mowed or manually removed before seeds mature to deplete the seedbank (DiTomaso and Healy, 2007), Managing stands with fire or other physical disturbance is not recommended for mustard species as this can increase populations, Use soil moisture sensors to measure the soil moisture of Field Mustard., Please contact your local agricultural extension specialist or county weed specialist to learn what works best in your area and how to use it safely, Always read label and safety instructions for each control method,