The effects of host diversity and other management components on epidemicsof potato late blight in the humid highland tropics

A field study at three highland sites near Quito, Ecuador, was conducted to determine whether host-diversity effects on potato late blight would be as important as recently found in studies conducted in temperate areas. We co mpared three potato mixtures and use of mixtures in combination with differ ent planting densities and two fungicide regimes. Treatment comparisons wer e made by absolute and relative measures of host-diversity effects and inco rporating a truncated area under the disease progress curve as a means of s tandardizing comparisons across sites. Potato-faba intercrops consisting of only 10% potato provided an estimate of the effects of dilution of suscept ible host tissue. Host-diversity effects were very different across study s ites, with a large host-diversity effect for reduced disease only at the si te most distant from commercial potato production. Planting density had lit tle influence on host-diversity effects or on late blight in single-genotyp e stands. Fungicide use in combination with potato mixtures enhanced a host -diversity effect for reduced late blight. Potato-faba intercrops produced only a small decrease in potato late blight. Effects of host diversity on y ield were variable, with the greatest increase in yield for mixtures treate d with fungicides at the site most distant from commercial potato productio n. The effects of host diversity on late blight severity may be less consis tent in the tropical highlands than in the temperate zone, but can contribu te to integrated disease management.