OCTOBER, 2010      

VOL. 24, NO. 10                                                                             

IN THIS ISSUE:

EFFECTS OF GREENING ON ORANGE FRUIT
THE TROPICS AND OUR AREA
AREA-WIDE PSYLLID CONTROL MEETINGS
ULV SPRAYER CALIBRATION
OTHER GREENING NEWS
CROP ESTIMATES
MORE SWEET ORANGE SCAB REPORTED

EFFECTS OF GREENING ON ORANGE FRUIT

We all know that among the effects of citrus greening is reduced fruit size and reduced fruit quality, but the extent of these reductions has not been widely reported.  We simply continue to state that fruit size is smaller, fruit often becomes misshapen and flavor becomes acrid or bitter.  T. M. Spann and M. D. Danyluk at the University of Florida—IFAS CREC at Lake Alfred have recently published some of the results of their findings in oranges over the last couple of seasons. 

They studied Hamlin and Valencia varieties in three different groves in Florida during 2008-09 and 2009-10.  Without getting into the finer details, they essentially compared fruit of each variety from trees that were visibly symptomatic of citrus greening and trees which were free of symptoms (the latter trees have not tested positive for the disease).  Several significant differences were noted.

Symptomatic trees yielded approximately one box (90 pounds) less per tree across groves and varieties in 2008-09.  In 2009-10, Hamlins dropped to almost two boxes less per tree, but Valencia was unchanged. The caveat is that the production of both varieties was down substantially in the 2009-10 season, possibly because of the effects of frost during bloom in 2009. 

In addition, the symptomatic trees were of smaller average fruit size than asymptomatic trees, with a substantially greater number of small fruit (2.25 to 2.5 inches, which is equivalent to size 162 in Texas).  Though the article in Citrus Industry (September, 2010) did not report data for each size, the accompanying photographs generally showed greater numbers of fruit in the two smallest sizes that they recorded.

Finally, fruit quality differences were pretty much limited to the smaller, symptomatic fruit from infected trees.  The differences were usually manifest as lower Brix, higher acid and lower ratio (i.e., very much comparable to immature fruit); juice color was sometimes—but not always—poorer.  The authors report that other juice analysis studies haven’t shown new flavor compounds in the juice of symptomatic fruit; instead, the lower ratios and altered content of normally occurring flavor compounds is apparently what causes the different tastes that are reported.

In sum, citrus greening reduces average fruit size, it reduces overall fruit numbers, and it lowers Brix, acids and ratios in oranges.  The degree of yield reduction seems to be related to the relative percentage of the tree canopy that shows greening symptoms.

It should go without iteration that these results on oranges may or may not be the same as what might occur on grapefruit.

THE TROPICS AND OUR AREA

It has been a busy storm season so far, with named systems all the way to Nicole—and there’s still a few weeks to go.   While the river and the floodway water levels finally went back to normal, weather systems affecting the Valley and/or the Rio Grande Watersheds in Northern Mexico during the last half of September resulted in the IBWC deciding to release additional waters from upriver storage.  Naturally, some areas along the River were again flooded, though not so badly as earlier in the summer, and diversions into the floodway were again made.  While diversions started September 24, water has not reached the floodway crossing at Mercedes as of September 30.

AREA-WIDE PSYLLID CONTROL MEETINGS

With the fall area-wide psyllid control period coming up (the first three weeks of November), Texas Citrus Mutual has scheduled a series of grower meetings across the Valley to inform growers of the need for concerted action to control psyllids at that time and to encourage grower participation in the program. 

The schedule of the meetings is as follows:

October 4 @ 10:00 am    Holiday Inn Express         1921 S. 10th, McAllen
October 4 @ 02:00 pm    Holiday Inn Express         1921 S. 10th, McAllen

October 6 @ 10:00 am    CC Irrigation District 2     1301 FM 510, San Benito
October 6 @ 02:00 pm    Citrus Center                  Weslaco

October 8 @ 10:00 am    Citrus Center                  Weslaco
October 8 @ 02:00 pm    Citrus Center                  Weslaco
               
Catch-Up Meeting--October 11 @ 5:30 pm   Citrus Center        Weslaco
               
For Organic Growers--October 14 @ 1:30 pm   Citrus Center        Weslaco

Given the number of locations, dates and times, every grower should be able to attend one of these meetings.

ULV SPRAYER CALIBRATION

Reports are that there are 10 of the ULV or LV sprayers in the Valley.  With that number and the hope that all will be in use in both rounds of the area-wide psyllid control effort, a sprayer calibration clinic is being scheduled for October 27 at the Citrus Center.  The calibrations will be carried out by USDA personnel from College Station.  More details will be available later, but insofar as I know, the calibration is free—all that is necessary is to bring the rigs to the Citrus Center for the testing and calibration.

OTHER GREENING NEWS

There have been no confirmed new detections in Mexico, but between the flooding in southern states and the drug-related violence along the border, authorities have not been able to do as much survey and scouting for the disease as would have been possible otherwise. 

On the control front, there are some sketchy reports that there has been some success in suppressing the disease with certain antibiotics—but I have not located any published work as of yet.  There is also progress being made In earlier diagnostic tests for the disease in tissue, but I have not been able locate any published work on that either.  Hopefully, I will have something more to add on both subjects in the next newsletter.

CROP ESTIMATES

The official crop estimates for the 2010-11 season are due to be released by USDA, National Agricultural Statistics Service, on Friday, October 8.  

MORE SWEET ORANGE SCAB REPORTED

USDA-APHIS has reported additional discoveries of sweet orange scab (Elsinoe australis) in Texas and in several parishes in Louisiana.  The most recent detections of local interest are that 11 of 12 samples collected from dooryard trees in Hidalgo County have tested positive for the disease.  Because of this detection, additional efforts are underway to look for other cases of this disease in South Texas, particularly in Cameron and Willacy counties.

Along those lines, it is strongly believed that sweet orange scab has been around a lot longer than we previously thought.  Dr. Mani Skaria at the Citrus Center confirms that better diagnostic and identification techniques indicate that a lot of what we previously thought was simply sour orange scab is, in fact, sweet orange scab.  I have pictures of “scab” in East Texas that I took back in the 1980s and the late 1990s, assuming that it was standard sour orange scab.  It may well be that I was actually photographing sweet orange scab at that time.

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