Yellow Mignonette (Reseda lutea)

Jerry D. Harris, Edward S. Dams, and David M. Wichman

INTRODUCTION

Yellow mignonette (Reseda lutea (L.) is a broadleaf perennial weed that is native to the Mediterranean Basin and Asia Minor. It has been spread around the world and is widely recognized in Australia as a trouble­some noxious weed in croplands (4). It is a problem in cropland and pastures because of its high seed output, extensive reproductive root system, ability to thrive under disturbed conditions, and high nitrate levels (2, 4). While nitrate levels of 2.5 to 3.1 % have been detected in plants during the rosette to early flower growth stages, when yellow mignonette is most palatable (2), no livestock in­juryor deaths have been reported. Yellow mignonette was first reported in Montana in 1958 but was not recognized as a weed problem until 1990 (10). Since 1988 it has invaded several hundred hectares of small grains and alfalfa (Medicago saliva L.)-grass pastures in Central Montana and is spreading rapidly along gravel road shoulders.

DESCRIPTION

Yellow mignonette is a glabrous biennial or short-lived perennial 30 to 70 cm tall, usually diffusely branched. The basal leaves are mostly three lobed while the cauline leaves are three to seven lobed with rather narrow segments on the upper 1/2 to 2/3 of their length. The lowest pair of segments is often again lobed, narrowly and minutely callous denticulate as are the pedicels and the five to seven (usually six) linear sepals. There are five, sometimes six, yellowish petals approximately 5 mm long, nearly equal and the appendage is usually divided to the base into three segments. The lateral lobes are 2 to 4 times as broad as the narrowly linear and usually shorter middle one. There are 15 to 25 stamens, the anthers are about 1.5 mm long, and the capsule is oblong, 6 to 8 mm in length. The seeds are pyriform, black, smooth, and shining.

BIOLOGY

Yellow mignonette reproduces by seed and vegetative rootbuds. The seeds are contained within capsules that produce an average of 14 seeds and as many as 24. Average seed production was 14,000 per plant although up to 220,000 seeds per plant were reported. Seed germi­nation and seedling establishment occur readily in disturbed sites such as roadsides, fallow ground, and gravel piles. Seeds germinate in early spring with some germination in the fall. Flowering occurs from June through September. Mature seeds remain in capsules until dispersed by physical disturbance.

Vegetative buds are numerous on the crown and primary and secondary roots. Severed crowns and root sections in fallow fields reestablish following tillage. Greenhouse studies showed that 10 cm sections of roots excavated at 0 to 50cm depths have equal regenerative potential. Likewise, lateral roots and roots from one-year-old plants produce numerous shoots if they are severed and replanted. In Australia, the tap root of a yellow mignonette plant grew to a depth of 4 m.

Yellow mignonette initiates growth from crown and root tissue early in the spring and continues growth late into the fall. Leaves, stems, and seed capsules turn orange-red as the plant begins to senesce and when subjected to stress such as drought or herbicide injury.

DISTRIBUTION

Yellow mignonette is native to the Mediterranean region. It is well adapted to the arid and semi-arid regions of Iran where it occurs at elevations ranging from 300 to 1900 m and in annual precipitation zones ranging from 100 to 400 mm. It survives temperatures ranging from 50 to 25 C. In England and Scotland, yellow mignonette is a weed problem in carrot and potato fields and is abundant in the chalk grassland regions of the United Kingdom. Yellow mignonette is a principal weed in Australia and South Africa, a common weed in Iran, Lebanon, Portugal, the former Soviet Union, and Spain, and present in Chile, Morocco, New Zealand, Turkey, United States, Afghanistan, and Israel.

In the United States, yellow mignonette is found from Montana to the east coast. It was first reported in the Great Plains in a disturbed prairie in Nebraska in 1974. The first infestations recorded in Montana were in the central part of the state in Judith Basin County near Stanford in 1958, in Park County in 1970 and in Fergus County in 1984. The largest infestation of yellow mignonette in Montana occurs in the Judith River drainage of Judith Basin County. This infestation most likely started in a hay field in the 1950s. Today, several hundred hectares of cropland in the surrounding area are heavily infested with yellow mignonette.

CONTROL OF YELLOW MIGNONETTE

Cultivation enhances the spread of yellow mignonette. Root segments and crown tissue detached from parent plants and relocated by tillage implements readily form new roots and shoots. The remaining intact root regenerates numerous shoots near the cut end in response to tillage giving a witchbroom appearance to the newly emerged plant. The effect of intensive tillage on depletion of yellow mignonette root reserves has not been determined; how­ever, the plant flourishes along roadsides where top growth is continually removed by grading.

Hand pulling or digging is effective only if the entire root is removed. The large primary root tends to break when pulled rather than remaining intact. The remaining root system has sufficient nutrient reserves to support regenerative shoot growth from considerable depths. When the root system in the top 40 cm of soil was removed, the remaining root system regenerated plants within a year.

Metsulfuron has shown excellent selective activity against yellow mignonette in wheat and barley and has been used successfully as a spot treatment along roadsides. Metsulfuron at 17 g ai/ha in combination with 1000 g/ha 2,4-D , showed 96% control when evaluated 10 months after a fall application to yellow mignonette in barley stubble. Dicamba, glyphosate, and pi­cloram at 1000, 600, and 300 g/ha, respectively, in combina­tion with 1000 g/ha 2,4-D showed less then 15% control.

DETECTION AND AWARENESS IN MONTANA

Support by the Montana Noxious Weed Trust Fund is being used to study the biology and control of yellow mignonette as well as initiate a project to restrict the spread of this weed to other parts of the state. Extensive mapping of yellow mignonette in Judith Basin and Fergus counties was completed and will be used to monitor its spread and the success of the control project. Field tours, news releases, "Weed Watch" posters, and seminars are being used to increase the public awareness of the weed and the threat it poses to the state.

Control of yellow mignonette along roadways is a major focus of the project. Metsulfuron at 14 g/ha plus 2,4-D at 1000 g/ha are being applied by backpack sprayers to areas that are inaccessible to boom sprayers. Herbicides and technical support were supplied to the county weed district, the USDA Forest Service, personnel at Malmstrom Air Force Base, and area landowners to help control infestations.

This intensive control project will continue for two years at which time area weed districts will provide control along roadsides. It is imperative that the awareness program be continued throughout the state and into the neigh­boring Great Plains States so that early detection and elimination of new infestations will prevent this weed from becoming established in other areas.

If you would like more information, email MWCA at acamm@montana.edu with your questions. A weed control expert will be happy to answer your questions.