VOL. 24, NO. 12
IN THIS ISSUE:
My trip to Florida during the first week of November was a good one. I spent the first day in Plantation, Fort Lauderdale, and Homestead with Hilda Gomez of USDA, CHRP, where I took lots of pictures of symptoms of greening on numerous species of citrus—along with citrus scab (on sour orange), citrus canker and citrus black spot (no, black spot isn’t over there, she had fruit in the lab).
The next day was in the company of Pete Spyke of Arapaho Citrus and Tim Gaver (St. Lucie County Extension Citrus Agent) in the Fort Pierce area. More pictures of canker and greening—in commercial groves. We also visited Pete’s Open Hydroponics System of higher density, intensive management, of citrus.
Then to Polk County with Chris Oswalt, Polk County Extension Citrus Agent, who showed me the first and second groves in which greening was detected there. Groves in Polk County generally look pretty good, as greening hasn’t been as widespread quite as long as down south. Still, many orchards had orange flags on the ends of many rows, and even some of the young resets (two or three years old) were showing symptoms of the disease.
Next stop was Felda where I spent the morning with Bruce Sutton learning what it is about a tree that makes a scout look at it more closely for symptoms of greening. By the time he finished with me, I do believe I could have hired on as a scout.
That afternoon was spent at the Southwest Florida Research and Extension Center at Immokalee with Bob Rouse. We were hoping to go to a nearby grove to take pictures of citrus black spot, but the infected trees had just been destroyed by the grower in an effort to get rid of the inoculum, so I settled for pictures that Rouse had taken. Bob has some very exciting research at the center on the Maury Boyd cocktail, and he took me on a tour of the Maury Boyd grove before I headed back to Miami for my return to Texas.
THE MAURY BOYD COCKTAIL
By the time I got to Immokalee, I was already pretty much of the opinion that nutritional sprays would help the appearance of almost any orchard in the shallow soils of south Florida, including those with a high percentage of greening. As I was inspecting the trials that Rouse has underway at the research center there, it began to appear that there was more to the Maury Boyd cocktail than just making the trees look better. The blotchy mottle and raised vein symptoms are still there—not at all hard to find.
Some of Rouse’s work involves measuring root development and phloem transport, as well as other trials to break out different components of the Boyd cocktail. Although the work is still preliminary, there are some measurable differences showing up in the treated trees—and those are generating further investigation at other centers in Florida.
The real excitement, however, came when Rouse took me to the Boyd grove at Felda—about 400 acres of Valencia and Hamlin on Swingle (mostly). This grove tested positive for HLB in early 2006—and apparently counted over 40 percent infection at that time. Boyd began using his nutritional cocktail in the fall of 2006 and has used it spring, summer and fall ever since. He also started a rigid psyllid spray program—initially by standard ground rig, then with the LV rigs, and now by air—every five weeks.
Although psyllid sprays have been applied regularly, the fact is that the grove is now considered over 90 percent infected. I expect you could chalk up the continued increase in infected tree numbers to be due to the long latency period of the disease, i.e., they have been infected for a long time, but just did not express the visible symptoms—without which PCR testing is normally inconclusive or negative.
According to reports, the grove has been producing up in the 500 to 600 box range for the last several years. To put boxes into terms used in Texas, 500 boxes is 22.5 tons, 600 boxes is 27 tons. Frankly, I don’t know an orange grower anywhere who would be unhappy with those yields. The trees were absolutely loaded when I was there—and the fruit was fairly uniform in size, with no obviously smaller fruit, no apparent fruit drop, and no lopsided fruit.
Do the trees have greening symptoms? Yes, indeed—everywhere I looked. Blotchy mottle and raised leaf veins were present on every tree I examined. Even on symptomatic branches, however, there was fruit and that fruit appeared normal in all respects. Too, the tops of some trees look a bit “airy” or not as densely foliated, which is one of the appearance factors that influences a scout to more closely examine a tree. However, obvious stunting and dieback were not apparent (except in a block on Carrizo stock which is suffering from citrus blight).
When you compare the Boyd grove to other groves in the area, you can’t help but be impressed. Bear in mind that Boyd’s approach is contrary to the “official” position of state and federal authorities which advocate a rigid HLB-positive tree removal program, with replanting of clean stock, coupled with good psyllid control. If you think about it, remember that the initial infection rate in this grove was 43 percent—how can a grower remain in business by taking out that many trees? Too, because you can’t kill all the psyllids all the time, the new trees will get infected in time—and I saw greening symptoms on two and three year old replacement trees in other groves.
As you can tell, I can hardly contain my enthusiasm about the Boyd grove. I am working with Dr. Shad Nelson of TAMU-K to see if we can start replicated trials with the Boyd cocktail here in the Valley. We would expect to use lower application rates than in Florida, mainly because of the superior nutritional content of Texas citrus soils, but the actual rate will have to be determined by trial and error.
Why look into it now, since we don’t have the disease? Perhaps use of a reduced rate of the cocktail will result in increased yields. Perhaps trees under the cocktail program will be better able to withstand initial infection. Perhaps trees under the cocktail program will experience a longer latency period for the disease. At worst, if the program works in Texas as it appears to do in Florida, doing the research now will provide local growers a leg up on living with the disease should we be so unfortunate as to get it. Basically, it’s being proactive and proactive is what we are when we started on area-wide psyllid control efforts in early 2010.
SWEET ORANGE SCAB
As is widely known, the Texas industry initiated a self-imposed moratorium on shipments to California that started the first of November—that moratorium is still in effect, which is having an adverse impact on harvest, on shipments and, unfortunately, on fruit prices. You may not know that about a fourth or more of our fresh shipments goes to California, so that really forces shippers to try to move some of that volume into other markets and those markets are already at or near capacity, thus forcing prices down.
How bad is it? Well, suffice to say that the post-Thanksgiving movement historically doubles the pre-holiday volume—but apparently the orders are not there and movement is estimated to be down substantially from historic levels.
The voluntary moratorium is expected to give way to a federal quarantine in the very near future, as we are expecting to receive a draft quarantine proposal later this week, prior to a meeting next Monday of CHRP, APHIS, PPQ, TDA, the industry and others to discuss the situation. In addition, the industry has contracted with Dr. Pete Timmer, retired plant pathologist at Lake Alfred (and formerly of the Citrus Center) to come to Texas to work on the issue.
Okay, so what does this beast look like? I keep hearing that scab-infected fruit looks like windscar. Problem is, there are two kinds of windscar—typical windscar occurs when the fruit is quite small, and the blemish is as smooth as a baby’s cheeks. But, late season windscar is rough to the touch, as the damage is typically raised about the surface of the rind. And, so are the lesions that are testing positive for sweet orange scab (as well as those lesions that test negative).
After spending a morning in Dr. Mani Skaria’s lab looking at confirmed positive samples, looking at confirmed negative samples (the two don’t look any different to me, but I am not a pathologist) and looking at fruit that he was screening (collected by APHIS surveyors), I went out and saw the same symptoms just about everywhere I looked. It wasn’t hard to find, as I have been seeing these same symptoms on grapefruit and oranges for years—like everybody else, I always assumed that it was late season windscar.
The disease has been detected on fruit imported from Mexico, specifically on Tahiti limes bought at a market in Fort Worth, TX, by Dr. Skaria. That finding is mostly irrelevant, as there is no way to verify that the subject fruit actually came from Mexico. There are no confirmed, official, reports of assays on other fruit from Mexico or from California, so rumors to that effect are just that—rumors—and will remain so until official confirmation occurs, if ever.
The possible options at this point are somewhere between not so good and really bad. To wit, the best case scenario is that the disease is confirmed in Mexico, California, and/or Florida, rather than just in Texas, Louisiana, and Mississippi. That would perhaps prompt the feds to deregulate the disease as being too widespread to be of further concern. Politically, that is a rather sensitive issue, so I won’t be holding my breath.
The second scenario is a long-term risk assessment of the possibility that this disease cannot be spread via fruit that has gone through the standard packinghouse practice of washing, waxing and fungicide treatment—much like the Gottwald work where he showed that there is essentially no risk of canker lesions on fruit being capable of transmitting canker. The latter took years to complete, but it resulted in fruit being allowed from Florida into Texas and other citrus-producing states.
A third scenario might involve a complete re-examination of the PCR process that identifies the disease to assure that the process is valid for this particular species of Elsinoe. While unlikely, it is difficult to reconcile negative results on fruit that exhibits virtually identical symptoms as fruit that results in positive results.
The first option would obviously be the most desirable from the Texas standpoint, as the industry is certainly hurting right now. The only way that becomes possible, however, is through increased testing in California and Florida and of fruit originating from Mexico, presuming, of course, that the rumors are true that the disease does indeed exist in those other areas. If not, we had better develop alternative citrus markets quickly, or figure out some use for our fruit other than as intact, whole fruit.
Just so you’ll understand what the preceding article was describing, I include a couple of pictures. First is the classic, smooth, early season wind scar. Indeed, if you look at the upper right portion of this picture, you will note some late scarring that is presumed to be late season wind scar, but which may be sweet orange scab.
The second picture is what I have always considered to be late season wind scar, but it now appears to have about a 50-50 chance of being sweet orange scab.
Classic early season wind scar.
Late season windscar (or sweet orange scab?).
THE AREA-WIDE PSYLLID SPRAY
Because of rather windy conditions during the latter part of the targeted spray period, a decision was made to extend the period through the end of November to allow completion. Dr. Mamoudou Setamou indicated this morning that he and TCM are expecting a bit over 80 percent of the commercial acreage to have been sprayed during this event.
JULIAN W. SAULS, Ph.D.
THE INFORMATION GIVEN HEREIN IS FOR EDUCATIONAL PURPOSES ONLY. REFERENCE TO COMMERCIAL PRODUCTS OR TRADE NAMES IS MADE WITH THE UNDERSTANDING THAT NO DISCRIMINATION IS INTENDED AND NO ENDORSEMENT BY THE COOPERATIVE EXTENSION IS IMPLIED.
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