Valley Citrus Notes

As tropical storms go, Don was a bust. While the track into the ranch country north of the Valley was pretty well one of the better locations for landfall, the extensive rains that forecasters were calling for simply did not materialize. Very little rain occurred more than a few miles inland from the coast—and even that was not much. As a rule, the south side of such storms is usually the dry side—so Don followed the rules in that regard. The fact of the matter is that Don was simply so disorganized that it basically fell apart at landfall.

It does not appear that Don carried much rain with it towards west Texas, either, so there is little relief for rain-starved ranchland and watersheds. While cotton growers with unharvested fields were scrambling, it appears that much of the unpicked cotton inland was spared serious damage.

In late July, SENASICA announced the finding of citrus leprosis virus in the municipio of Toliman, Queretaro, MX. The find was on sour orange in a dooryard; and Queretaro is not a major state for citrus production. Among the protocols that are underway, the government is removing all infected trees and will treat all trees within 30 meters four times with miticides to control the mite vector.

Leprosis is not new in Mexico, as it was initially detected in eight municipios in southern Chiapas in the summer of 2004. Another seven municipios were added with subsequent surveys in Chiapas. In the winter of 2007-08, officials found the disease in another three municipios, bringing the total municipios in Chiapas to 30.

In April, 2006, it was reported in Tabasco, with another detection following in 2007. Too, one municipio in Vera Cruz on the border with Tabasco was reported with leprosis. The Queretaro detection in 2011 is quite a ways from the earlier infections, so one might conclude that the disease is spreading northward, despite the best efforts to control it.

In the event you aren’t familiar with this disease, we used to call it simply leprosis or nailhead rust, and we really weren’t sure that it was a mite-transmitted viral disease. The common symptoms are chlorotic lesions on leaves, fruit and twigs, mainly on oranges and mandarins. It has been a disease of note in South America for years, and has progressed into Central America and Mexico. Dr. Victor French of the Citrus Center had been sounding the alarm about it for several years before he retired, based in part on the work of his friend and colleague, Dr. Carl Childers of the Citrus Research Center at Lake Alfred.

The virus is transmitted by Brevipalpus species, otherwise known as false spider mites. While not a major mite pest in Texas citrus, false spider mite does occur in the Valley. To date, the disease does not.

A final word—the virus is non-systemic, which means that it doesn’t move within a citrus tree beyond the sites of initial infection from the feeding of the false spider mite vector.

With the failure of TS Don to provide much drought relief, the last significant rains occurred in late June. I was recently questioned as to how quickly the 10-12 inches that occurred in late June, early July was used up in the rather hot, windy conditions of July.

The basic answer is that any rainfall (or irrigation) in excess of the water holding capacity of the soil is pretty much lost to runoff and/or deep percolation. Few Valley soils exceed five inches of water holding capacity in the upper five feet, and because of ongoing irrigation, the soil reservoir wasn’t even close to empty! Thus, the nearly 8.0 inches of rain on June 22-23 was more than enough to fill the soil reservoir, so much of that rain either percolated down to the water table or simply ran off. A week later, nearly 4.0 inches of additional rain exceeded the inch or so of soil moisture that had been depleted, so much of it percolated down or ran off, too.

Essentially, any rainfall in excess of a couple of inches or so is pretty much lost insofar as the soil reservoir and plant growth is concerned—the soil in the root zone doesn’t have the capacity to store the excess, so that water either percolates below the root zone or runs off. If water stands for any time before soaking in, some is lost to evaporation—the quantity depending mostly on wind and temperature, which varies with time of year.

How nice it would have been for that rain to have been spread out at about 1.5 inches a week for the next six to eight weeks… Instead, we were back in irrigation mode soon after the middle of July.

There is nothing new out of Mexico regarding citrus greening—still at four states on the southeast side of the republic and five states on the west coast. In Texas, the surveys by APHIS, TDA and individual growers continue as planned; the numbers of psyllid samples assayed continues to increase, as does the number of plant samples taken from dooryards and groves. It is good to report that there are still no detections in the Valley, where most of the samples are taken, nor at other locations across the state.

It was announced today in a meeting of Weslaco Center personnel that Dr. Michael Gould will be transferring from the position as Center Director to a newly created position at College Station in AgriLife Research. He will continue as Center Director at Dallas and will continue to live there. The Center Director at Corpus Christi, Dr. Juan Landivar, will take over the administration of the Weslaco Center in addition to his duties at Corpus Christi, where he will continue to reside. These changes will be effective September 1.

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

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.