Infection and disease development occur only in the orchard when the fruit is small. Therefore, no spread or contamination of other fruit occurs during processing and storage. Mudcake or sandpaper symptoms of melanose on grapefruit. Tearstaining caused by melanose spores washed down the fruit by dew or rain. Although this disease is primarily a problem on leaves, the fungus also can infect the fruit.
Infection occurs on cells surrounding pores, causing the fruit to become spotted or stippled.
Areas surrounding these spots do not color properly because the cholorphyll present in the cells fails to disappear. If the spots are numerous, the fruit becomes unsightly, resulting in downgrading. The disease derives its name from the small black specks formed on the rind in areas immediately surrounding the oil glands. The fungus that causes this disease prevents infected spots from attaining the typical yellow color of mature citrus fruit. The contrast between green and yellow color lowers fruit grade, even though there is no effect on fruit or juice quality.