Anthracnose can be a problem in semi-arid climates (and probably arid ones), too. It mostly seems to be a foliar issue (and a fruit storage problem, too), however. The foliage problem seems kind of mysterious due to the dry air until you realize that anthracnose appears to be what often causes fallen apples to rot after they get too old to eat (apples fall a lot when it's dry), and spider mites (which love dry areas), love infesting apple trees. They are probably all over the rotting apples on the ground, too. I hypothesize that they afterward go on to other things like watermelon to spread anthracnose to at least the foliage of the watermelon. I've found that showering the watermelon plants and such tends to keep the spider mites (and foliar anthracnose) at bay the first half of the season or so (and the showering helps the plants grow faster). So, yeah, pick up your apples that fall (don't let them rot).
The combination of spider mites an anthracnose in my semi-arid area seems to tend to cause speckling of the leaves at first (they look stonewashed); you don't see large or dark cirlces, usually. It can cause the same thing on watermelon rinds, too, without rotting the fruits (the stonewashed look). Anthracnose-resistant watermelons still get the foliar anthracnose just as bad as regular watermelons in my experience (but the fruits don't seem to get the stonewashed look). For breeding foliar resistance, I recommend saving your seeds from exposed plants every year to help acclimatize them to the pests/diseases (if they occur every year). However, I zap my seeds with three frequencies of a Z4EX to hopefully remove any anthracnose pathogens (because if the infection is still there at germination time, you might not see a benefit to saving seeds, and it may spread the disease to other plants). The results of my saving and zapping seeds seem to be positive, so far (especially with my Ledmon watermelons), but more years of doing this are needed.
It should be noted that the combination of foliar anthracnose and spider mites can stunt and/or kill plants. Watermelons that get the problem usually die after a while (Red-seeded Citron is probably the most resistant variety I've grown). Muskmelons seem more resistant than watermelons (on a foliar level).
Anthracnose can be a problem in semi-arid climates (and probably arid ones), too. It mostly seems to be a foliar issue (and a fruit storage problem, too), however. The foliage problem seems kind of mysterious due to the dry air until you realize that anthracnose appears to be what often causes fallen apples to rot after they get too old to eat (apples fall a lot when it's dry), and spider mites (which love dry areas), love infesting apple trees. They are probably all over the rotting apples on the ground, too. I hypothesize that they afterward go on to other things like watermelon to spread anthracnose to at least the foliage of the watermelon. I've found that showering the watermelon plants and such tends to keep the spider mites (and foliar anthracnose) at bay the first half of the season or so (and the showering helps the plants grow faster). So, yeah, pick up your apples that fall (don't let them rot).
The combination of spider mites an anthracnose in my semi-arid area seems to tend to cause speckling of the leaves at first (they look stonewashed); you don't see large or dark cirlces, usually. It can cause the same thing on watermelon rinds, too, without rotting the fruits (the stonewashed look). Anthracnose-resistant watermelons still get the foliar anthracnose just as bad as regular watermelons in my experience (but the fruits don't seem to get the stonewashed look). For breeding foliar resistance, I recommend saving your seeds from exposed plants every year to help acclimatize them to the pests/diseases (if they occur every year). However, I zap my seeds with three frequencies of a Z4EX to hopefully remove any anthracnose pathogens (because if the infection is still there at germination time, you might not see a benefit to saving seeds, and it may spread the disease to other plants). The results of my saving and zapping seeds seem to be positive, so far (especially with my Ledmon watermelons), but more years of doing this are needed.
It should be noted that the combination of foliar anthracnose and spider mites can stunt and/or kill plants. Watermelons that get the problem usually die after a while (Red-seeded Citron is probably the most resistant variety I've grown). Muskmelons seem more resistant than watermelons (on a foliar level).