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CITRUS IN MEXICO
OTHER ITEMS OF INTEREST
CTV AND GRAPEFRUIT
CITRUS IN MEXICO-
I had the opportunity to address the Simposio Internacional "La Citricultura en el Siglo XXI" in Cd. Victoria, Tamps. during mid-June. Since I had not visited that area in many years, it was interesting to note the changes that have transpired during the last decade or so. The most notable was tree spacing in younger orchards-mostly about 13x26, as compared to 26x26 for the stuff older than 12-15 or so years.
The area north and west of Cd. Victoria is hurting for lack of rainfall-those orchards without irrigation being wilted and drying up. With the heat and drouth, insect pressure is very light. In contrast, nearer the coast towards Tampico, the climate is much wetter-and pests were easy to find. Surprising, I saw a number of orchards (Valencia) which had not been harvested yet, and there was some question as to whether or not they would be.
Depending on the speaker, as they didn't agree and no one knows for sure, Mexico's citrus industry is in the area of 1.2 to 1.3 million planted acres producing some 4.5 to 5.5 million metic tons annually. For a variety of reasons, production levels are rather low-averaging around five tons per acre.
The current industry is comprised of 4 or 5 percent grapefruit, a like acreage of mandarins, about 19 percent lemons and limes, and the balance in oranges-mostly Valencia. There are an estimated 57,000 producers, about 150 packers and about 18 processors.
Unlike the rest of the world, juice consumption in Mexico is increasing rapidly-about 10-15 percent annually in the last few years-probably as a reflection of the growing economy. Fresh squeezed is the major source of juice, but the non-refrigerated, aseptic Bric pack is very popular there. Still, it is a global economy and both growers and processors complain of low returns during the season just ending.
A couple of individuals contend that they have seen the Diaprepes root weevil, but its presence has not been officially verified. Brown citrus aphid is present in the Yucatan region. Citrus tristeza virus is a major concern because of the preponderance of sour orange rootstock, but most people seem to believe they have no major CTV infections. Nonetheless, officials are strongly pushing the use of certified plant materials throughout the republic.
To that end, the "Comite para el Fomento e Investigacion Citricola del Estado de Tamaulipas" has the Campo Citricola Experimental "Gral. Francisco Villa" which is producing virus-free budwood and plants of a large number of varieties, including Rio and Star, lemons, limes, numerous mandarins, several Valencias and some other oranges. Available rootstocks include Carrizo, Troyer, Swingle, Volkameriana, Cleo and rough lemon. It is my understanding that the program was started with certified budwood imported from the California Citrus Clonal Protection program, much as we have done with the non-commercial varieties in our program.
OTHER ITEMS OF INTEREST-
Because I traveled with several entomologists from Florida and Mexico, I picked up a little information that would be interest to Texas growers. One entomologist, J.P. Michaud, reported that Asian citrus psyllid, a major vector of citrus greening disease (which isn't present in Florida) is under good biological control in Florida. The psyllid does attack the newly emerging flush, resulting in some leaf distortion, which damage would appear comparable to that from aphids or leafminers. Interestingly, the psyllid's honeydew is stringy and non-sticky, so it does not support sooty mold. Apparently, brown citrus aphid does not seem to be as damaging and widespread as feared in Florida, primarily because of some pretty good biological controls.
Dr. Carl Childers reported on mites-primarily rust mites. I learned from him that there are two different rust mites which affect Florida citrus, and both are undoubtedly in Mexico. In addition, to the citrus rust mite that we all know so well, there is also a pink citrus rust mite which he described in the Proceedings of the Florida State Horticultural Society in 1999 (112:79-87). From our discussions and his published work, the pink CRM causes damage to fruit somewhat earlier than does CRM. It will also feed within the sunspot (the sun-exposed surface of the fruit) which CRM avoids.
The reason Dr. Childers thinks that pink CRM is present in Mexico is that we saw an enlarged, poster-sized exhibit in which he could identify both mites. No one, however, could tell him exactly where the picture was taken-only that it was within Mexico.
According to Florida Department of Citrus economist Mark Brown, in a presentation at the Indian River Citrus Seminar as reported in Citrus Industry (May, 2001), tristeza could potentially kill enough grapefruit trees to reduce production to around 36 million boxes by the 2005-06 season, but the production could recover to near current levels in about five years. The basis for such projections is that about 70 percent of Florida grapefruit is in the Indian River District, with over half of that acreage being on sour orange rootstock, most of which was planted in the 1980's or earlier.
If CTV does take out most of the sour-rooted grapefruit (and oranges) in Florida, it should start to do so gradually, then accelerate over time-assuming that the process follows the same pattern as occurred in South America. Obviously, such pattern may not repeat because of efforts to manage both the brown citrus aphid and CTV. Given the current grapefruit oversupply and marketing dilemma, such a reduction in production, even for a few years, would certainly help make the remaining grapefruit acreage profitable for a few years.
Donald Warnecke called last week about an anomaly that he is seeing in a number of orchards that he scouts for the Citrus IPM program. In both grapefruit and oranges, there are darker green, irregular areas on the rind. The affected areas are slightly raised to obviously ridged or pimpled.
As I examined fruit in several orchards, I noted that those areas with substantially raised ridges or pimples are usually capped by the tannish-colored cortical tissue characteristic of wind scar. The seemingly flat, darker green-colored areas show no evidence of scarring-indeed, it appears that the epidermal tissue around the oil glands is just greener and only slightly raised in contrast to surrounding tissue.
Dr. Vic French, showed me some fruit with similar symptoms that were initially suspected to have been caused by spray oil. However, the transient oil damage with which I am familiar is usually somewhat round, occasionally streaked, "water soaked" areas on the rind-and the "watersoaked" areas disappear within a couple of weeks.
Meanwhile, my opinion is that the problem resulted from windscarring. As you well recall, winds were extremely strong during the post-bloom period this spring-much more so than normal. Too, most of the fruit I have examined is from groves which have not been sprayed with oil. The existing tan cortical tissue damage is permanent, the darker green areas may or may not disappear as the fruit enlarges.
June brought some unexpectedly good rains across much of the Valley-area farmers had to cut the borders to drain fields, but I didn't see any borders being cut in citrus groves. With the rains, growers should be especially vigilant for pest outbreaks-late June to July commonly bring the need for summer sprays to control rust mites, greasy spot, California red scale, chaff scale and other pests before they cause economic damage.
June also brought the long-awaited close of the 2000-01 season. While there was still-unharvested grapefruit, in many cases the packouts just weren't sufficient to provide a positive return to growers. Also, much of the packable fruit was simply too soft to hold up to the rigors of getting it to market. It was not a good season for growers-but it was a boat in which we had lots of company from other citrus-producing states and countries.
Production for the new season is already set-it's just a matter of keeping the crop irrigated and free from economic pest damage levels as the fruit enlarges and matures. It's a little hard to believe that packinghouses will start opening again in a little over two months. The final data are not in yet, but Texas growers had record production and record shipments. Returns may have set records, also, just the wrong way.
In the Citrus Center Newsletter for June (Vol. 19, No. 3), Drs. Skaria and French reported on new labels for citrus. First, Ridomil Gold® EC (Ciba-Geigy) received a Section 24(c) Special Local Need Label for use against the root weevil/Phytophthora complex. For the weevil side of the complex, both Admire 2®F and Provado 1.6®F (both from Bayer) received Section 3 federal labels for citrus. In addition to root weevils, both insecticides are highly effective against aphids, citrus leafminer, leafhoppers, mealybug, armored and soft scales, blackfly and whitefly. Provado is for foliar spray application, while Admire is applied to the soil, either as a banded spray, basal trunk drench or through a microsprayer system.
JULIAN W. SAULS, Ph.D.
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