How can I address cedar rust disease in my apple trees?
Answer: The fungus that causes this disease moves back and forth between eastern red cedars (actually junipers, not true cedars) and apples, so it can be a major problem where eastern red cedars are endemic. In order to complete its life cycle, this fungus must spend part of its life on eastern red cedar; therefore, it is theoretically possible to eliminate the disease by eliminating the cedars within a given area. However, the spores can be windborne for over one mile, so eradication of the disease in this manner is often impossible or impractical.Nonetheless, if cedars are not too numerous on a given site, their removal around the immediate orchard vicinity can certainly reduce the inoculum reaching the apple foliage. In addition, there are many rust-resistant apple varieties. Only a few varieties, most notably Golden Delicious and its progeny, are susceptible to the point of defoliation.Many fungicides are effective against rust, including the sulfur-and-copper compounds, which are approved for organic production as a last resort in your organic pest-management plan. If you remain observant, you may be able to time sprays to coincide with the springtime appearance of orange gelatinous “horns” on the galls on the cedar. This bizarre-looking structure is actually the fruiting stage of the fungus. The “horns” release the spores that infect the apple trees.To learn more, consult the following ATTRA publications:Apples: Organic ProductionTree Fruits: Organic Production Overview