Huanglongbing (HLB) is a major disease of citrus that has caused catastrophic damage to citrus trees worldwide. The disease causes reduced fruit quality and yield, tree decline, and eventual tree death.
Symptoms are variable and can resemble several disorders of citrus. Typical symptoms include:
- yellow shoots with pale green and yellow flushes;
- non-symmetrical mottled leaves (shades of yellow and green on either side of the mid-rib);
- thickened, leathery leaves;
- enlarged, corky mid-ribs of leaves; and
- leaves with zinc deficiency symptoms that include upright leaves in relation to the shoot (acute shoot-leaf angles).
Defoliation, fruit drop, and shoot dieback occurs in more advanced stages. Young trees may die soon after infection; whereas older trees may die in seven to nine years after infection.
Fruit symptoms include small, misshaped fruit that are lopsided or asymmetrical and exhibit color inversion from yellow to orange to green on the peduncle side while remaining green on the stylar end. The vascular tissue is brownish at the peduncle side of fruit. Seeds of affected fruit are small, brown, and aborted.