DECEMBER, 2009       

VOL. 23, NO. 12                                                                             

IN THIS ISSUE:

HLB/ZC CONFERENCE
HLB SESSIONS
TEXAS GREENING WEB
WEATHER AND HARVEST
AREA WIDE PSYLLID CONTROL PROPOSAL

HLB/ZC CONFERENCE

This was a first of a kind conference regarding the several species of Liberibacter bacteria which cause the various forms of citrus greening and zebra chip disease of potato (and other nightshade plants) and the psyllid vectors of those diseases.  I believe I was told that some 290 scientists, regulatory personnel, industry personnel, growers and others attended this event in McAllen last month. 

I did not participate in any of the separate sessions of the zebra chip group, confining my efforts to the citrus greening sessions.  What I can relate about the zebra chip disease is that it has spread from initial discovery in Mexico into South Texas and across many of the western states where potatoes are grown.  While some plant death does occur, the main problem comes post-harvest with the development of the zebra chip blackening of chips, fries and whole potatoes, thus resulting in tremendous losses to growers as such tubers are turned away at processing facilities.  In addition, tomato, eggplant and other solaneceous plants are affected by the bacterium to some degree.  The potato psyllid appears to be widespread on solanaceous plants across the west, including some common weeds such as nightshade. 

HLB SESSIONS

As for the HLB sessions, I didn’t miss a single presentation, even though some of the talks were clearly over my head—especially those dealing with genomes.  However, one of the highlights for me was the presentations of the status of HLB/ACP in various areas of the western hemisphere. 

I think I have previously reported on the occurrence of HLB in Louisiana, Georgia, South Carolina, Florida, Belize, Cuba, Jamaica, Mexico and other countries.  However, the Mexico situation was especially revealing, in that from only a handful of “hot” psyllids and infected trees reported in the Yucatan Peninsula during the summer, nearly 60 discoveries were reported at the conference—about half and half “hot” psyllids and infected trees, with the “hot” psyllids getting ever closer to Merida.  To date, there have not been any reports in commercial citrus to the south-southwest of the affected areas.  Mexico is monitoring a series of sentinel trees along the coast from Yucatan to Tamaulipas.

Another highlight was the various expressions of the symptomology in different species of citrus and related genera.   We have all heard that blotchy mottling of the leaves is the most consistent symptom across species, but that it may be a bit different in some species.  Indeed, from what Hilda Gomez, USDA-APHIS, showed at the conference and from the images she had previously provided to me for inclusion in our Texas Greening website, some species exhibit larger, more angular blotches than one would consider as “mottling”, i.e., more “blotch” than “mottle”. 

Another very important distinction for the blotchy mottle symptom in relation to alternative causes of similar symptoms in citrus is that the individual blotches can and do cross the lateral veins in the leaf but do not cross the midrib.

TEXAS GREENING WEB

It is still not online, but I turned over brief descriptions and 80 some odd images regarding symptomology.  Because some of us see suspicious chlorosis patterns in citrus, growers wanted a comprehensive collection of chlorosis patterns that are caused by something other than greening, i.e., insects, other diseases, nutritional problems, et cetera.  Hopefully, the way I organized it for the greening web will satisfy grower needs and help distinguish those common symptoms that we commonly see from those that may be caused by HLB.

I hope that as soon as the site goes online, we will begin trying to offer it in Spanish.  To that end, Hilda Gomez was very generous is providing me with Spanish translations of the various symptoms that we can quickly incorporate into the symptomology section.

WEATHER AND HARVEST

As a rule, harvesters take a little break at Thanksgiving, in part for the holiday but also because the market seems to take a break.  While I don’t know how much fruit was harvested or how much is in the pipeline in the various packinghouses, this was not the time we would have liked for it to rain as much and as widespread as it has since the end of the Thanksgiving weekend.

From a few phone calls this morning, it appears that anywhere from an inch and a half to nearly three inches of rain had fallen across the citrus area since early Monday morning.  While it may be a few days before significant harvesting can resume, this amount of rain coupled with overnight temperatures in the 40s will do wonders to increase natural de-greening in the field and should further aid in fruit sizing.

AREA WIDE PSYLLID CONTROL PROPOSAL

As if we haven’t been to enough meetings in the last few months, we had another last week to try to work out the logistics for a Valley-wide citrus psyllid spray effort for sometime in January. The consensus is to combine aircraft, traditional ground rigs and non-traditional low volume applications to all of the commercial acreage during a two to three week period in January—if it all comes together.  Some growers have access to the LV applicators while others have speed sprayers that can be run a little faster to get over a lot more acreage in the limited time.  However, there are some operations that are simply too large to cover by available means, so it is hoped that something can be worked out to use airplanes to help get over those acres.

There are some logistics still being worked on—the actual timing, who will spray their own, who will resort to aircraft, what to do near organic groves, what to do about apparently abandoned groves, what to do about dooryard citrus and so on.  In addition, there remains the issue of trying to get appropriate label changes to permit the use of LV applications—either by aircraft or by the special LV rigs that are available.

Even if we can’t resolve the dooryard and abandoned grove issues or even get all of the commercial acreage sprayed in the targeted timeframe, we should not be dissuaded from trying to accomplish a valley-wide application.  After all, the more overwintering adults we can knock out in January, the fewer there will be to re-infest groves with the emergence of the spring flush.

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