Former GDR
From 1984 to 1990, cultivar mixtures comprised a substantial percentage (up to 92%) of the barley acreage of the former German Democratic Republic (East Germany). This country is the most remarkable example of large-scale use of this disease control strategy in industrialized agriculture (more...).

China
A varietal diversification program was tested in the Yunnan province to control rice blast. Involving 812 ha in the first year and 3342 ha in the second year, mixtures of susceptible and resistant cultivars reduced the average rice blast severity on the susceptible varieties from 1% to 20% (Zhu et al. 2000). This experiment was unique in both its scale and experimental design.

USA
Wheat cultivar mixtures are increasingly popular in northeastern Oregon and southeastern Washington (Mundt 1994) for the objectives of stripe rust suppression and stabilization of yields. In 1998, 10% of soft white winter wheat and 76% of club wheat fields in this region were sown to cultivar mixtures. In Kansas, wheat variety blends occupied 7% of fields in 2000, with yield stabilization viewed as the most significant benefit received from mixture deployment (Bowden et al. 2001).

Switzerland
In 1992, a financial support program for cereal production ('Extenso') was introduced. Under ‘Extenso’ guidelines, applications of fungicides, insecticides and growth regulators are prohibited. As a consequence, the importance of cultivar mixtures for disease suppression has increased (Mertz and Valenghi 1997).

Denmark
In 1979, seed companies were allowed for the first time to produce and sell cultivar mixtures of spring barley. Winter barley mixtures with powdery mildew resistance were released in the mid-1980s. In 1996, 62,000 ha of barley (9.7% of the total) were sown to variety mixtures (Munck 1997). For the 1997 growing season, 49 different mixtures were marketed, involving 20 different varieties from six resistance groups to powdery mildew.

Poland
Use of barley cultivar mixtures for disease suppression was initiated in the early 1990’s and has now reached about 90,000 ha per year (Gacek 1997). The main emphasis has been on spring-sown feed barley (eight mixtures recommended), but two spring-sown malting mixtures and three winter barley mixtures also have been recommended. The mixtures are designed for control of powdery mildew, but more general recommendations for their use are given to farmers. Before introduction into commercial production, candidate mixtures and their variety components are grown in field trials for three years at three or four sites. The best performing mixtures are selected for multiplication (initially as pure varieties with the final year as a mixture).

Colombia
Mixtures of coffee genotypes have been planted on a large scale in an effort to proactively reduce anticipated infection by Hemileia vastatrix in Colombia (Moreno Ruiz and Castillo Zapata, 1990).

Uredinia of Hemileia vastatrix, causal agent of coffee rust. (Used by permission from J.R. Baker) Click image to enlarge.