|Barberry Situation - Past, Present, Future|
Common barberry (Berberis vulgaris), the alternate host for wheat stem rust, is making a comeback in the north central states after years of extensive Federal and state efforts to eradicate it from cereal growing areas (Fig. 1). Barberry was the primary source of new stem rust races before the eradication program which lasted from 1918 through 1975. Although over 100 million barberry bushes were destroyed in the eradication program, some bushes survived in isolated sites deep in the woods and far removed from cultivated land. In addition, new bushes emerged from seeds that had lain dormant in the soil for years. These bushes are providing the seeds for the current resurgence of barberry.
A few veterans of the barberry eradication campaign in Minnesota and Wisconsin still maintain records of sites where barberry bushes were destroyed. They occasionally visit sites where barberry bushes still survive. Employees of the ARS Cereal Rust Lab visited two such sites in 1995, one is in DaneCountyWisconsin and one is near the junction of Olmstead, Winona, and FillmoreCounties in Minnesota. At the Minnesota site, they found more than 300 barberry bushes ranging from 1 to 15 feet tall. According to Bob Laudon, the site was identified early as a farmstead where settlers had planted a barberry hedge. Barberry bushes were destroyed at the site in the 1920's and again in the 1940's. From then until 1975, the site was checked every 7 years to remove any new barberry plants arising from dormant seed left under the previously destroyed bushes.
According to Bob Laudon, (retired, formerly a field supervisor with the USDA and Minnesota Department of Agriculture) this Minnesota site now has more barberry bushes than were ever found there during the entire barberry eradication campaign. Currently, the bushes only contribute to local stem rust epidemics on quack grass and redtop grass in the adjacent pasture, but it is only a matter of time before barberry spreads into areas where it can pick up stem rust from cultivated crops such as wheat, oat, and barley. Then it will again become a source of new rust races and frustrate the cereal breeders' best efforts to maintain resistance to stem rust in their wheat, oat, and barley varieties.
|The main culprits in the spread of barberry are the birds that feed on the bushes' berries. The seeds can survive passage through the birds' digestive systems and sprout wherever the birds drop them. Now that fruit-laden barberry bushes are showing up in pastures at the margins of woodlots, they are attracting a new set of birds that prefer open farm land and small farm communities rather than the deep woods. These are the birds that will reestablish barberry in the main wheat, oat, and barley growing areas of the north central states.|
According to Bob Laudon, it took 20 years for barberry to move from the deep woods to the woodlot margins after the barberry eradication program was terminated in 1975. He believes that within the next 20 years we will see mature barberry bushes established near grain fields. When that happens, stem rust from the grain fields will spread to the barberry where the fungus produces its sexual stage that generates new pathogenic races.
Stem rust epidemics from barberry bushes will start first in winter wheat, because winter wheat varieties have less resistance to current stem rust races. But the problem will not be restricted to winter wheat for long. Existing races of wheat stem rust that attack winter wheat can hybridize on barberry to produce new races with virulence to overcome the more resistant spring wheat varieties.
Stem rust has been a minor problem in wheat for the last 30 to 40 years, but before 1955, damage from stem rust was often severe. Yield losses caused by wheat stem rust in Minnesota, North Dakota, and South Dakota exceeded 10 million bushes per year in most of the years between 1920 and 1930. In the region's worst epidemic in 1937, more than 100 million bushels of wheat were destroyed by stem rust in these three states. The epidemics of 1953 and 1954 each caused losses of more than 60 million bushels of wheat.
The disease resistance that has protected wheat from stem rust since the mid-1950's may very well be lost if barberries are not kept out of our wheat growing regions. The gravity of the problem can be appreciated by comparing wheat stem rust with oat crown rust. No resistant variety of oats has remained successful for long. Typically, new oat varieties succumb to crown rust epidemics caused by new races within 5 years of their release. The reason is that buckthorn, the alternate host for crown rust, was never eradicated from the north central states. It serves as the breeding ground for new crown rust races in the same way that barberry used to be the breeding ground for new stem rust races.
To protect future wheat, oat, and barley crops, we need a renewed commitment to locate and destroy existing barberry bushes that threaten these crops. As Bob Laudon put it, the barberry eradication campaign was terminated 15 years too soon. Only a few of the barberry eradication campaign veterans are still available for consultation. Their records detailing exact locations of sites where bushes were found and destroyed are extremely valuable, because they show where it is most likely that seedlings may have been reestablished from seeds left by those bushes. Barberry seeds can germinate after laying dormant in the soil for up to 10 years. The records of barberry eradication sites, in some cases, exist now only because the retired barberry eradication workers took it upon themselves to protect the records.
Concurrent with a renewed attack on barberry, we need to strengthen efforts to improve the stem rust resistance of winter wheat varieties. By limiting the amount of stem rust on winter wheat, we can limit the chances that stem rust will move from wheat to barberry, thus delaying the onset of new more virulent stem rust races. If nothing is done, the spring wheat crops of the north central U.S. and the PrairiaProvinces of Canada will once again be subjected to epidemics of stem rust, the most devastating disease known to wheat.