Valley Citrus Notes

As you may know, trucks began rolling from Valley shippers to California markets on December 22 after seven weeks of a self-imposed moratorium on fresh fruit shipments to California. While the fruit did not make it to consumers there in time for Christmas, at least they will be able to get our delicious grapefruit and oranges again.

Several things happened about the same time—APHIS-PPQ imposed a quarantine on Texas, Louisiana and Mississippi (and Mexico) for sweet orange scab. However, they also conducted a substantive risk assessment that concluded 1) that asymptomatic fruit poses no risk of introducing SOS into other citrus-producing states and 2) that symptomatic fruit which has been subjected to standard packinghouse procedures also poses no risk of transmitting SOS (those procedures are clearly spelled out in the order or related documents).

Each shipper signed a compliance agreement that assures that any non-organic fruit being shipped to another citrus-producing state will be subjected to a sanitizing wash treatment, treated with a fungicide and waxed. There are inspections involved at the shipping point and documents that must accompany the fruit. Fruit that is not subjected to these protocols and any plant materials are not allowed to be shipped into a citrus-producing state.

For organically-produced citrus, only asymptomatic fruit can be shipped into other citrus-producing states, while symptomatic fruit is limited to non-citrus producing states. Both must still be washed and disinfested, and there are a couple of other requirements for packers.

Meanwhile, researchers will continue to work on culturing the causal organism for later studies on the disease. Unsubstantiated reports are that the samples that CFDA submitted to Beltsville were PCR negative for SOS. I reiterate that it was suggested that CDFA was looking for tissues that exhibit symptoms that are characteristic of the disease rather than the uncharacteristic symptoms that we are finding, i.e., late-season windscar. Too, there are also unsubstantiated reports that there has been a PCR positive sample in Florida.

To date, there have been no apparent issues with fruit on arrival in California. About the only problem that has occurred is getting enough trucks to haul the fruit.

According to reports from Texas Citrus Mutual, approximately 84 percent of all Valley groves were sprayed for Asian citrus psyllids during the November targeted spray program. Another spray is being planned for later this month into February and TCM is hosting a couple of meetings on the matter for Thursday, January 6.

Both meetings will be held at the Citrus Center in Weslaco—the first at 10:30 to noon, the second at 1:30 to 3:00. A complimentary lunch for both meetings will be served at noon, but you will need to call 956/584-1772 or email nora@valleyag.org to confirm that you will be there for lunch.

An update for organic growers will be held at the conclusion of the afternoon session.

Dr. Shad Nelson of TAMUK in Kingsville, Dr. Juan Enciso of AgriLife Extension in Weslaco, and Mac Young of AgriLife Extension in Corpus Christi had an interesting article on the placement of drip lines in mature citrus in the last issue of the Citrus Center Newsletter (Vol. 28, No. 6, December, 2010)—you can access it at http://kcc-weslaco.tamu.edu.

Basically, they analyzed the wetted pattern and absorptive root distribution under drip irrigation lines and concluded that a double line system is essential to provide adequate moisture distribution (and root distribution) for mature citrus trees in Texas. I have been preaching this for decades, so it is gratifying that these researchers have sustained the message.

With all the concentration on SOS, little has been heard about greening in the last couple of months. However, the most recent news out of Mexico, according to the SAGARPA/SENASICA website, is increased detections of the disease in trees and “hot” psyllids in the seven states where HLB has previously been confirmed.

On the Pacific side of the Republic, the state of Sinaloa has confirmed HLB in trees in two separate locations, with “hot” psyllids in a third location nearer the northern border of Sinaloa with Sonora. In addition, the state of Michoacan now has confirmed HLB in trees in one location and “hot” psyllids in two locations.

Thus, Mexico now counts eight states with HLB in trees and “hot” psyllids—Quintana Roo, Yucatan and Campeche in the east, with Michoacan, Colima, Jalisco, Nayarit and Sinaloa in the west.

To the best of my understanding of Spanish, Mexico has been destroying an awful lot of trees in an attempt to stem the spread of the disease, but I didn’t pay a lot of attention to what they are doing to control the psyllid. Despite their best efforts to date, the disease continues to stay ahead of them, particularly in the west.

Meanwhile, the APHIS-PPQ Residential Survey for HLB in the Valley continues to collect and screen plant samples for the disease, and they continue to pull psyllid samples for testing—the total number of samples tested continues to increase monthly, and all are PCR negative for the bacterium, both in plant samples and in the pysllids.

(NOTE: This article is a preliminary draft of how we in Texas should approach the question of how to scout for greening. It is presented here in hopes of getting some feedback from Florida colleagues and others who read this newsletter and who have been dealing with the problem for the last several years.)

During a trip to Florida to learn more about the symptoms of citrus greening, I had the opportunity to see the disease in areas where it has been around for years as well as in areas where it is relatively new. That difference is important as we try to figure out what we should be looking for in Texas trees and orchards.

In the southern part of Florida where the disease has been present for several years, greening is pretty easy to detect, as any number of “eye-catching” symptoms almost jump out at you as you walk or ride through a grove—yellowed shoots, dieback and decline, leggy growth in the tops of trees, and an ‘airy’ or open appearance to the tree tops. During fall and winter, excessive fruit drop and early color intensification of some fruits on a tree are obvious symptoms that can be spotted from a distance.

Further north, however, the disease has not been present as long and the “eye-catching” symptoms are not as intensive or well-developed. There, the existence of yellowed shoots is perhaps the most common symptom that stands out, though the others can be present—particularly in trees that aren’t old enough to have been topped as yet. In these trees, too, the presence of a lot of off-bloom flowers and/or off-bloom fruit can be a dead giveaway.

“Eye-catchers”. In Texas, we should concentrate our efforts on those “eye-catching” symptoms that would cause us to look more closely at a particular tree. Obviously, any bearing tree that is showing a lot of chlorosis, twig/limb dieback or tree decline should be inspected closely to try to rule out other common causes for such symptoms—foot rot, nutritional problems, suboptimal care, freeze damage, damage caused by excessive soil moisture or damage caused by insects or other diseases. Even if these problems cannot be ruled out, the inspection should include close examination for even the faintest blotchy mottle and raised midrib and lateral veins on leaves, as these symptoms will be present if greening is responsible for the tree’s appearance.

Looking at a mature, apparently healthy grove can be intimidating and seem pointless, as routine hedging/topping practices commonly eliminate much of the leggy top growth and/or “airy” appearance of the tree tops—but you should still look for them, especially in non-topped groves. The presence of yellowed shoots should get your attention, but don’t overlook the presence of a lot of off-bloom flowers or off-bloom fruit, especially in the summer and fall. Closely examine such trees for the faintest indications of blotchy mottle and raised midrib and lateral veins.

Blotchy mottle. It should be noted that the earliest appearance of blotchy mottle and raised veins often occurs along the scaffold limbs inside the tree rather than on the exterior canopy, so be sure to include the interior of the tree in your inspection. If the mottling is faint, compare the patterns on opposite sides of the midrib of a leaf.

An easy way to do this is to scribe a circle (using a pen and a small coin) on each side of the midrib and check for symmetry inside each circle. Greening-induced mottle will be asymmetrical in the two circles, while that caused by nutritional problems will be fairly symmetrical. Mottling patterns caused by insects and fungal diseases such as greasy spot may also be asymmetrical across the midrib, but they will appear more like irregularly shaped spots rather than like angular blotches, so try to eliminate these as you examine the leaves. Too, the blotchy mottle patterns cross lateral veins but do not cross the midrib.

Finally, if you are not absolutely sure about greening, the suspect area should be marked with flagging tape and a sample should be submitted for screening by experts for possible PCR testing.

This discussion, along with illustrative pictures, will be posted on www.texascitrusgreening.org in the near future.

JULIAN W. SAULS, Ph.D.
Professor & Extension Horticulturist
2401 East Highway 83
Weslaco TX 78596

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