Frost is the traditional enemy of citrus production. Tolerance to cold varies according to variety, e.g. limes are generally the least resistant, kumquats the most. “Frost” in this case is defined by temperature and duration, oranges can survive 24°F for about 4 hours before damage occurs.

Citrus fruit is also susceptible to leaf miner moths, which drill small holes in the fruit. The holes are not generally that damaging, but they open a route for a bacteria called citrus canker, which cause skin lesions and can make the fruit unsellable.

Today the greatest threat to U.S. Citrus production, especially in Florida, is a disease called Huanglongbing (HLB), which is carried by the Asian Citrus Psyllid. In the industry it is called citrus greening. The fruit becomes unsellable, and at some point the infected tree must be destroyed, as there is currently no cure. Production in the U.S. is expected to drop 12-13% in 2021, part of a 20-year decline that overall represents a 2/3 drop in production over that period. Because removed trees are not being replaced, planted acreage has decreased by 40% in the period.

In some parts of Florida, salt stress has begun to impact citrus, especially trees already infected with HLB. Salt stress can lead to less growth, small fruit and smaller yields. It can occur when ground water supplies develop higher salt concentrations either as a result of seawater encroachment or poor flushing. Irrigating repeatedly with higher salinity water can result in salinity buildup in the soil. An occasional increase in irrigation can leech the salts deeper into the soil away from tree roots. Regular diligent soil monitoring is necessary to sustain an irrigation program and avoid over watering.