Field Identification Guide for Sweet Orange Scab (Elsinöe australis)

Developed by CPHST in cooperation with MDL and CHRP 10/4/2010

Symptoms on Fruit and Stems

The initial scab will form during the early stages of fruit development, and is slightly raised and pink to light 

brown in color. As the pustule continues to develop it will become warty and cracked and the coloration can 

change to a yellowish brown and eventually to a dark gray. Lesions on orange and grapefruit are sometimes 

flatter and less raised. Scabs are usually dispersed in the same pattern as water being splashed on the fruit. 

Symptoms that occur in a narrow straight line across the fruit are more likely wind damage. Lesions can also 

form on young stems. These symptoms resemble an area of dieback that has scabbed over.

Flatter 

Lesions
Field Identification Guide for Sweet Orange Scab (Elsinöe australis)

Developed by CPHST in cooperation with MDL and CHRP 10/4/2010

Symptoms on Leaves

Lesions begin on leaves as water soaked spots which evolve into pustules that are typically found on the 

underside of the leaf near the mid-vein or the border. Foliar lesions that form on young tissue are typically 

raised, while lesions formed on more mature tissues are typically flatter. Infected leaves can become 

irregularly shaped, stunted or puckered.

Close up of lesions in 

leaves in A, B and C; and 

in fruit in D.

A B

C

D
Field Identification Guide for Sweet Orange Scab (Elsinöe australis)

Developed by CPHST in cooperation with MDL and CHRP 10/4/2010

Multiple types of symptoms can be present on plant tissues

Plant tissues may have a number of symptoms present. This figure illustrates fruit discoloration that may 

result from other causes. In this case, sweet orange scab is also present, and appears to be minor in 

comparison. 

Citrus canker can 

sometimes be confused 

with citrus scab

On young fruit, citrus canker 

lesions will be surrounded by a 

yellow halo. As the lesions age, 

the halo disappears and the 

lesions turn darker brown in 

color (as seen in the 

photograph). 
Field Identification Guide for Sweet Orange Scab (Elsinöe australis)

Developed by CPHST in cooperation with MDL and CHRP 10/4/2010

Injuries and other irregularities can be easily confused with Sweet orange scab symptoms, 

but should nonetheless be examined closely.

Spots appearing similar to scabs can be caused by other pathogens, insects, or environmental injuries. 

Samples submitted to the USDA APHIS that were identified as free of E. australis are illustrated below. If 

symptoms in the field are ever in question, they should be submitted as official samples. 

Insect 

Damage

Environmental 

Damage

Stem Canker Lesion

(Also seen in above 

image)
Field Identification Guide for Sweet Orange Scab (Elsinöe australis)

Developed by CPHST in cooperation with MDL and CHRP 10/4/2010

Common Citrus Scab (Elsinöe fawcetti) symptoms on leaves 

E. fawcettii symptoms are very similar to E. australis, with the exception of the lesions which are typically 

rounder and more raised. The lesions may be grouped singularly or in multiples which may overlap. Any plant 

tissue with citrus scab symptoms should be submitted for testing.

Front and back view 

of the same leaves
Field Identification Guide for Sweet Orange Scab (Elsinöe australis)

Developed by CPHST in cooperation with MDL and CHRP 10/4/2010

Common Citrus Scab (Elsinöe fawcetti) symptoms on fruit