I had initially planned on writing about something else today, UNTIL......this came across my E-Mail: New Citrus Disease Confirmed In Texas And Louisiana. I won't reuse the exact words I said when I saw this, but "Oh Crap" will suffice. I could not imagine what they had discovered now. The word "New" is what scared me. I knew Citrus Greening was already present here in the states, but what could be new?
This is where the title is a little hint. They discovered Sweet Orange Scab (SOS).
This is the first detection in the U.S. of the fungal pathogen, Elsinoe australis. The infected citrus trees were found on residential properties in Harris and Orange counties in Texas, and in Orleans parish, LA.
Luckily, it has not been found in Florida yet. They have enough problems with: Alternaria brown spot, Blight, Citrus Canker, Greening, Greasy Spot, Melanose, Phytophthora-induced diseases (foot and root rot, brown rot), Postbloom fruit drop, tristeza and common Scab. Yes, you read that correctly, common Scab. Common Citrus scab is serious on many tangerines and tangerine hybrids such as Temple, as well as grapefruit and lemons, but rarely causes lesions on sweet orange. In contrast, Sweet Orange Scab can cause significant damage on all sweet oranges as well as tangerines and their hybrids.
The damage produced is superficial and does not affect internal fruit quality or taste. Infected fruit are more likely to drop prematurely. It poses no harm to human health.
Sweet Orange Scab is common in humid citrus growing areas of South America such as Argentina, Bolivia, Brazil, Ecuador, Paraguay, and Uruguay. It had not been seen here in the U.S. until this past July. Surveys completed in Texas, within a 1 square mile of the initial detection has resulted in 6 additional detections on citrus trees located on 4 separate residential properties; all in close proximity to the initial Harris County detection. The detection in Orange County, Texas, which was on some Satsuma trees is located about 100 miles east of the initial find. In August, the find of the Sweet Orange Scab was discovered in the Louisiana site on a Lime tree. Incidentally, this disease was discovered while on a routine check for Citrus Greening disease.
The causal agent of Sweet Orange Scab is the fungus Elsinoe australis, which is quite similar to Elsinoe fawcetti, the cause of common citrus scab, but clearly a distinct species. In contrast to Common Citrus Scab, The sweet scab does not form lesions on leaves or twigs. The symptoms are corky, wart-like pustules on the fruit that are tan to gray in color. These lesions are flatter than those produced by the common citrus scab.
The Sweet Scab pathogen requires moisture for production of spores and for infection to occur. The fungus attacks only young fruit. Fruit are susceptible for 6 to 8 weeks after the flower petals fall off. Fungus spores are primarily distributed by rain or irrigation being splashed between trees, and can also be spread short distances by air. The common Citrus scab pathogen survives in unfavorable conditions in old leaves and stem lesions. Long distance spread is due to the movement of infected fruit by humans. How this outbreak occurred and spread is still being investigated.
As with Common Citrus Scab, Sweet Orange Scab can be controlled by properly timed fungicide applications. Sweet Orange Scab must be controlled and confined to where it already is, even though it primarily only affects fruit for the fresh market. Why you ask? Given that the climatic conditions in Florida are suitable for establishment of the pathogen, it would increase production costs of fresh market citrus if it were introduced into that state. That Orange you take to work for lunch could suddenly skyrocket in price.
This leads me back to a theme that I have launched into numerous times on my blog. PLEASE, do not bring any exotic fruit, twig, leaf, stem or plant from another country into the United States. Just one infected plant could cause millions and millions of dollars in damage and losses. THIS disease does not look like it will be as major as Greening disease is, but it sure is going to cause a lot of headaches for the already stressed Citrus producer.
Please, I know this is probably getting old to some of you, stop the illegal importation of plant material. If you are traveling abroad, take lots of pictures, leave the cuttings and plants there. There is a lot of money at stake, and entire industries that could be in jeopardy...the plants you save, might even be ours!