Here's a bit on citrus scab:
Your Florida Dooryard Citrus Guide - Common Pests, Diseases, and Disorders of Dooryard Citrus
Citrus Scab
Scab is undoubtedly the ugliest disease of citrus, appearing as a rash of scabs or warts on leaves, twigs, and fruit ( Figure 4 ). Since new generations of inoculum (infectious material) can be produced within five days, scab is a "compound-interest" disease that can spread rapidly, given the right conditions, from overwintering infections on leaves and stems. Compared with the greasy spot fungus, the scab organism is an aggressive pathogen, with the first seasonal infection usually occurring with early spring cold fronts accompanied by rain during March and April. Water from rain, overhead irrigation and dew is, in fact, the most important factor affecting disease development.
Early stages of scab infection include well-defined, conical growths on one side of the leaf with a corresponding conical depression on the opposite side. These lesions may occur singly or be grouped irregularly ( Figure 4 ). The crests of these wart-like growths usually become covered with a scabby tissue ranging in color from pale to dark. Infected spots often run together and cover large areas with a corky, scab-like growth. Badly infected leaves and twigs become distorted and stunted. When fruit is infected when very young, it can become misshapen, with warty growths or projections, especially on Temples ( Figure 5 ). However, interior fruit quality is usually not affected. The lighter coloring of the lesions usually distinguishes citrus scab from melanose, which may also distort young leaves.
Susceptible cultivars include Temple oranges, lemons, Minneola tangelos, Murcotts, and Page oranges. Other cultivars like satsuma tangerines, Orlando tangelos, Tahiti limes, and grapefruit are less susceptible. The best scab management strategy is to remove and destroy the source (infected leaves, twigs, and fruit) of inoculum, controlling the disease before it develops momentum.
Since scab also occurs on some rootstocks (sour orange, rough lemon, Rangpur lime, trifoliate orange, and Carrizo citrange), this disease is commonly introduced into the home landscape on already infected nursery trees.
When buying a nursery tree, carefully examine the leaves for disease lesions and evidence of insect damage and eggs. It may be worth your while to remove all infected leaves, twigs and fruit, if possible. In this way you can avoid introducing the pathogen or pest into your dooryard.
Avoid overhead irrigation that spreads scab. Install drip or micro- sprinkler irrigation. Copper sprays also can be applied 2-3 weeks after petal fall, and again 2-3 weeks later to control scab.
Figure 4. Scab: cone-like distortions on leaves.
Figure 5. Scabs or warts on leaves, twigs and fruit.
The Figure 5 photo is awful because it gives the appearance the fruit and leaves have turned black which is not the case at all. Warty and scarred looking, yes, but still the normal green looking. I hadn't noticed the leaf growths until I started looking more closely after wondering what the heck had happened to my fruit!
It's way past petal fall now so I'm wondering if maybe regular copper applications will suffice to eliminate the scab if I first eliminate the affected fruit and leaves?
.....Alan.
