Non-native, invasive species can be very threatening and harmful to an ecosystem. The Texas Hill Country is facing one of these threats from a plant called the annual bastard-cabbage. This non-native, invasive plant could potentially kill off the Texas state flower, the bluebonnet.
The annual bastard cabbage has many common names; such as,
turnip-weed,
wild turnip, tall mustard-weed, ball mustard, common giant mustard, and
wild rape. (Enyedy1, 2002). It’s scientific name is Rapistrum
rugosum
(L.) All. The full classification is:
Kingdom
Plantae – Plants
Subkingdom
Tracheobionta – Vascular plants
Superdivision
Spermatophyta – Seed plants
Division
Magnoliophyta – Flowering plants
Class
Magnoliopsida – Dicotyledons
Subclass
Dilleniidae
Order
Capparales
Family
Brassicaceae – Mustard family
Genus
Rapistrum Crantz– bastardcabbage
Species Rapistrum rugosum (L.)
All.–
annual bastardcabbage
(USDA, 2002)
The annual bastard cabbage has little yellow flower clusters, which makes it look very similar to the flowers of broccoli and cabbage. The leaves are wrinkled and dark green although they can sometimes have a red color to them. It can grow anywhere from 1 – 5 feet high with a broad and full bunch on leaves on multiple branches. This multi-branched plant flowers from early spring to summer and has a large taproot system. It can also be identified by it’s tiny, dark brown, oval shaped, seeds that are kept in a two-segmented seed capsule. It grows mainly on recently cultivated land in open areas. (Enyedy1, 2002).
Due to it’s preference for disturbed soils and open areas the annual bastard cabbage tends to grow along roadsides, agricultural fields, preserved natural areas, along streams, and construction sites. In 1999 there seemed to be a sudden increase of this bastard cabbage along the Texas roadsides, especially the highways. One thought is that it came from the annual spreading of wildflower seeds by the Texas transportation department. TxDot spreads these seeds along the highways as part of a beautification project. It is difficult to weed-screen this seed out of the wildflower seed mixture because it is the same size as other grass seeds, such as rye and wheat. This bastard seed is also suspected of contaminated other seed mixtures used in landscaping and stream stabilization. The reason it is so successful competing with Texas wildflowers along roadsides is because these areas have recent soil cultivation or disturbance thus leaving it an early successional habitat. It germinates early in the growing season, as do bluebonnets and Indian paint brushes. The problem is that it tends to grow first and cover the entire ground with young seedlings blocking the sunlight and moisture from the other native plant seeds. By doing this it creates a monoculture and decreases plant biodiversity. (Enyedy2, 2002).
It is not well documented of how the annual bastard cabbage arrived in Texas and research is still being conducted. One legend says that it could have been planted along wagon trails by the early colonizers to help separate and distinguish the trail from someone’s land and maybe so they could find their way back. There isn’t actual record of the bastard cabbage until 1946 in McLennan County where it was recorded as growing along the highway and suspected of spreading from nearby cultivated fields. It is again recorded in Kaufman County in 1949, Navarro County in 1953, Bell, Ellis, Gonzales, Hill, and Wharton counties in 1955. It was also spotted growing in agricultural fields north of Dallas in 1988. But it wasn’t until the first scientific paper about the bastard cabbage was written in 1991 that we heard it was spreading into the Edwards Plateau and east-central Texas where we see it today. (Enyedy2, 2002). It is documented in 16 other states, as well, and introduced to all of them. (USDA, 2002). It is said to be native to Central Europe, the Mediterranean, northern Africa, and western, temperate Asia. (Enyedy1, 2002).
People are still trying to determine the best way to remove or destroy the annual bastard cabbage. A major problem for the spread along the highways is that there is not enough manpower or funds available to test the seed mixtures used by the transportation department. It is also not feasible to remove it by hand along all the highways. Another problem with the highway is that when they are mowed it enables the seeds to spread and can extend its growing season. (Enyedy2, 2002). One research project that the Lady Bird Johnson Wildflower Center is conducting is “to determine if oversowing with native grasses and herbaceous groundcovers is effective in controlling annual bastard-cabbage.” (Enyedy1, 2002). The Austin American-Statesman newspaper printed an article on the invasive plant stating that Indian paintbrushes may inhibit or overcome the growth of the bastard cabbage. The article stated that with Wildflower Center ecologist did a small experiment of overseeding an area with Indian paint brushes and noticed a reduction of the annual bastard cabbage, which in turns makes it easier to control a smaller percentage of the invasive plant. (Bullnettle, 2002). Time will tell whether there will be any negative impact with this experiment. There are certain pesticides one can use on the annual bastard cabbage, but may not be completely effective. Annual bastard cabbage tends to have the ability to resist herbicides, particularly to Atrazine. There is a new herbicide called Bothal that might be effective in crop areas, but requires tilling, while most farmers do not practice tilling. (Windhager, 1999). A study in Australia, who also has a problem with annual bastard cabbage, stated that is also builds up a resistance to the herbicide chlorsulfuron, but it is developed over a period of 3-10 years. (WeedScience, 2000). Another problem with using herbicides in the Texas hill country is the possibility of the chemicals getting into the watershed and the Edwards Aquifer. Extensive research is badly needed in order to control this weed before it kills off all the native flowers and without affecting our current natural resources.
The big question now is how do we control this bastard cabbage currently while research is being conducted. Unfortunately this is not an easy question to answer due to the negative consequences with most of the before mentioned management approaches. In smaller, privately owned landscaping areas I would suggest manual removal by pulling it early in the growing season before it has a chance to create its taproot. When removing a plant it is always best to pull it from the base of the plant as close to the ground as you can. This will help in pulling out the entire root system. It is also easiest to do this when the ground is slightly wet. (Enyedy2, 2002). If you do not catch it at the beginning of the growing season, then make sure when you pull it to pull the taproot as well and you must get rid of the seeds right away. In the larger areas, such as the roadsides, I would suggest using the experimental management approach of sowing more Indian paintbrushes. Indian paintbrushes usually come up first and are a sign that the bluebonnets are almost here. The Indian paintbrushes will battle for control of the sunlight and moisture with the bastard cabbage. It is thought that the Indian paintbrushes are stronger, so hopefully they will overcome the annual bastard cabbage. These are probably the best management approaches we have for controlling the annual bastard cabbage here in the Texas hill country and we eagerly await any new promising research results.
References
Bullnettle. 2002. Battling Garlic Mustard – a possible
response. GardenWeb Forum chat room. GardenWeb
on-line.
http://forums.gardenweb.com/forums/load/woodland/msg031408473316.html
Enyedy1, Karen. 2002. Annual Bastard-Cabbage. The National Park System online. http://www.nps.gov/plants/alien/fact/raru1.htm
Enyedy2, Karen. 2002. Rapistrum rugosum (Annual Bastardcabbage) in Central Texas. Lady Bird Johnson Wildflower Center online. http://www.wildflower.org/?nd=res_popular&view=full&key=4
Simmons, Mark. 2002. Plant Photographs. Lady Bird Johnson Wildflower Center photographer. Austin, TX. http://www.nps.gov/plants/alien/fact/raru1.htm
USDA, NRCS. 2002. The PLANTS On-Line Database, Version 3.5 (http://plants.usda.gov). National Plant Data Center, Baton Rouge, LA.
WeedScience. 2000. Herbicide Resistant Weeds. WeedScience on-line. http://www.weedscience.org/Case/Reference.asp?ReferenceID=11
Windhager, Steve. 1999. Rapistrum rugosum. WWW
Archives
of the Aliens-L List. The World Conservation Union on-line
message
board.
http://indaba.iucn.org/archives/aliens-l/wwwmsgs/July98-April99/00000543.htm