There has been a steady change from the European varieties to the Californian. The Californian hop was brought to the district about 40 years ago and is the only one now grown commercially. New varieties bred by the Hop Research Station are now being released and may replace some of the Californian. The new varieties resist root rot (Phytophthora cactorum), are heavy cropping, and are of high alpharesin content. All hops grown are seeded. The area has been steadily decreasing (750 acres in 1948 to 530 in 1963) as export markets for seeded hops become increasingly difficult to find. The yield per acre has been decreasing lately and is now approximately 1,250 lb of dried hops, with a total yield of approximately 660,000 lb.