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A grower recently brought up the subject of Citrus volkameriana as a potential rootstock in Texas, and wanted to know why it hasn't received more attention. Because he reported current quality of Everhard navel and Rio Red on volkameriana as being comparable to that on sour, it piqued my interest enough to look it up.
Volkameriana is equal to sour in its tolerance to Phytophthora, exocortis and citrus nematode, while it is far superior to sour in its tolerance to tristeza. In addition, volkameriana has better vigor and drought tolerance than sour, and makes a larger tree with higher production.
One down side of volkameriana is that it produces lower solids than sour, being comparable to rough lemon and Rangpur lime in that regard. Because these evaluations were compiled by the USDA-ARS in Florida, solids may or may not be the same as under Texas conditions.
The other problem with volkameriana is its poor cold hardiness-at best, its cold hardiness is comparable to that of rough lemon.
While perusing the ratings of various rootstocks, I recalled that there is some interest in Smooth Flat Seville because of reported tolerance of one selection to tristeza. There are different selections of this rootstock and most selections are no more tolerant than sour. Too, Smooth Flat Seville reportedly has poor cold hardiness and low solids.
No one seems to be interested in sweet orange as a rootstock-probably because of its susceptibility to Phytophthora. Sweet orange is less cold hardy and less drought tolerant than sour orange, but it is more vigorous and makes a larger tree, while producing equivalent yields and solids. The big advantage of sweet orange is its tolerance to tristeza and exocortis. With the availability of the Phytophthora-preventing fungicides Aliette® and Ridomil®, possibly combined with planting on slightly raised tree rows, one wonders about the economics of sustaining sweet orange as a rootstock in Texas citrus.
All of which goes to show that there isn't a perfect rootstock for citrus, regardless of where it is grown.
It is more or less official-the U.S. share of waters in Falcon and Amistad Reservoirs at the start of 1999 is approximately the same as we had at the start of 1998. In other words, district allocations should be equal to or even lower than 1998-which means that we will need either timely rains in the Valley to sustain orchards, additional allocations from rains in the watersheds or wells. At least we know what to expect, since it would be nearly impossible to be any worse than it was during the first eight months of 1998.
There has been considerable interest in a device called Electrostatic Precipitator to reduce the effects of water salinity. A number of units have been installed in citrus and sugar cane within the last year or so. While no independent research has apparently been reported, testimonial results are impressive.
The units, which are made in Port Isabel, apparently utilize electrical charges to render salt ions ineffective when used in irrigation. The salt ions are still in the water-they just don't behave like salt ions.
The most impressive testimony is that of Rio Grande Nursery, which has been using the units for irrigation of tropical foliage plants for a couple of years. Rio Grande has been quite successful in growing a number of salt-sensitive foliage plants without any evidence of typical salt damage.
While Rio Grande's success with the ESP units is impressive, it should be iterated that Rio Grande is a container nursery, i.e., the plants are grown in artificial medium for only a few months and are then shipped out for sale. That is a very different situation from that of crops growing in the field. In other words, the long-term effects of using ESP-treated saline water on a field or orchard over the course of several years is unknown.
Believe it or not, the massive arctic air mass that blanketed most of the U.S. during the Christmas week was being discussed by forecasters at the first of the month. Fortunately for Texas citrus, it was so massive and so spread out that we were not subjected to another Christmas freeze.
Not so parts of California-news reports of several nights of sub-freezing temperatures, most citing the very low 20's over three or four nights, indicate total wipeout of the lemon crop in some counties and extensive damage to oranges in those same counties. If the latter is true, the already short orange crop in the U.S. will become even shorter-and the value of Texas oranges should certainly increase-as the affected area reportedly supplies about 80 percent of all fresh oranges in the U.S.
At the Valley Citrus Conference last month, Richard Hagan of the National Weather Service in Brownsville presented some interesting history about weather extremes in recent years. According to Richard, warming of the Pacific Ocean started in 1976-and such warming cycles normally run 20 to 50 years.
The hottest three summers on record at Brownsville were 1998, 1980 and 1982, respectively. Another of the five hottest summers also occurred since 1976, but Richard didn't give the year. No one can forget that two of the worst ever freezes occurred in 1983 and 1989.
With regard to rainfall, the third most consecutive days without measurable rainfall at Brownsville (65 days) occurred in 1986, while the fourth (55 days) occurred in 1984. Three of the six driest springs at Brownsville occurred in 1995, 1996 and 1998 (sixth, third and fourth, respectively). The driest January through August of record occurred in 1998. If you back down to January through July, 1996 was the driest and 1998 was only the third driest on record.
We asked Richard to compare rainfall patterns in the first six months versus the second six months of the year. Bear in mind that the normal rainfall for those periods in Brownsville is 10.38 inches in January through June and 16.23 inches in July through December. Since 1902, when January-to-June rainfall is less than 75 percent of normal, then July-to-December rainfall is greater than average 76 percent of the time.
When rainfall in the first six months is less than 50 percent of normal, then July-to-December rainfall is greater than average 86 percent of the time. If first half rainfall is between 75 and 125 percent of normal, than the relation to second half rainfall is random. Finally, when first half rainfall exceeds 125 percent of normal, the relation to second half rainfall is somewhat random for the century-but with a tendency to be below normal for the last couple of decades or so.
Considering the current water supply situation, perhaps I should have asked Richard to compare rainfall in the first six months of the year to that of the last six months of the preceding year so we might have at least a historical perspective on what might transpire between now and the end of June when most irrigation districts normally start to feel the crunch.
Through Christmas, we have harvested about a third of estimated grapefruit production and half of the navel/early orange crop. Total fresh shipment for all citrus is up 4.6 percent over last season.
Domestic grapefruit shipments are up 2.9 percent while export grapefruit is up 3.6 percent. Navel shipments are up 1.6 percent while other early oranges are up 14.3 percent.
Eliminations are running about the same for grapefruit as last season, while orange eliminations are nearly 30 percent lower than last season. While not entirely an accurate, assessment, the level of eliminations provides a rough idea of overall quality of the crop.
With reference to the situation in California, it looks as though anticipated higher returns on Texas oranges will be possible for about half of our oranges (plus Valencias), since that's about how much we had left as of the time of the California freeze damage.
JULIAN W. SAULS, Ph.D.
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