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...Do not bring May flowers in South Texas, contrary to the popular children's rhyme, as our flowers normally occur from February to April. April is not known as an especially rainy month in South Texas, but intermittent showers persisted through the month of April, further reducing irrigation demand while also increasing reservoir levels. And the so-called Cinco de Mayo rainy spell is yet to come-if it does.
But the wet weather sword cuts two ways-just ask anyone involved in the sugar cane industry. For citrus growers, the rains have been spread out enough in both time and location that there has been little delay in harvest or in most grove operations-but early season rust mite control is proving very difficult to attain in some groves. All I can say is to keep after them, as damage at this stage of fruit development reduces fruit size potential, while also resulting in classic "sharkskin" blemishing.
Before you know it, the rainy weather will disappear, leaving us with the other extreme of South Texas weather-prolonged hot and dry.
Fresh utilization is still running ahead of last season, about 6.7 percent more than season-to-date a year ago. In addition, this crop has already exceeded last season?s final by 2.3 percent. Grapefruit alone has surpassed last season's total cartons shipped by 3.6 percent-despite the continued concerns of adverse interactions with certain medications.
It has been expected that the current season will end in another couple of weeks or so, and one shipper was anticipating a late April end to its operations. While I have not heard of any house closing just yet, the remaining grapefruit and Valencia supply-in relation to the USDA crop estimate-is higher than at the same time last season.
Still, increased direct-to-juice cleanup harvesting of grapefruit, coupled with the relatively low volume of Valencia oranges, supports one of the earliest finishes that we have seen in many years.
A recent article by Ritenour, Stover and DuBois (Proceedings of the Florida State Horticultural Society, 116:219-223. 2003) discusses factors which cause fresh grapefruit eliminations at the packinghouse. In looking at red grapefruit, they show that production has doubled from 15 million boxes in 1981 to over 30 million in 2001, but packouts essentially declined from about 70 percent to barely over 50 percent in the same period. The authors attribute part of the decline to increased marketing into Europe and Japan, both of which are more demanding in terms of external quality (appearance), with Japanese buyers being the most stringent with respect to the quality of fruit they will accept.
Irrespective of the export market influence, however, the authors also examined the causes that eliminate fruit from the fresh market. The top four causes of elimination are windscar, melanose, poor shape (i.e., sheepnosing) and off-size (too little or too big). Other factors include greasy spot, insect injury (rust mite, scale, and others), green color, oleocellosis, mechanical damage (plugging, punctures, hail damage), spray burn, rots and fruit softness-in no particular order.
What is especially interesting when one considers grade-lowering factors is that some are caused by harvesters (plugs, oleocellosis), some are caused by insects and diseases (which are usually controllable by growers) while the majority are caused by nature-windscar, poor shape, small fruit size, green color, hail damage. Fortunately, greening and hail don?t often occur.
Windscar is always problematic, especially when one considers that the damage occurs early during fruit set when our South Texas winds are usually at their worst. I recall seeing extensive crisscrossing of groves in New Zealand and Australia with living windbreaks during the late 70's, but that practice has not caught on in our part of the world.
Sheepnosing is still not fully understood, but we know that our Rio's are prone to this problem. About the best growers can do to attenuate the problem is too fertilize according to crop load so as to avoid excessive vigor when fruit set is low.
Fruit size can be attenuated by grove practices-hedging, topping, nutrition, and irrigation-but some fruit will always be too small, especially in years of a heavy crop set. One often overlooked factor that impacts fruit size is the loss of leaves due to greasy spot disease-this disease most be better controlled in order to retain the leaves for their useful life (usually two years), as the energy required to produce new leaves comes at the expense of the fruit.
One final note about the Florida paper: the authors also reported that grapefruit packouts more or less steadily decline as the season progresses. A small part of the reason for this is attributed to higher export quality demands as the season progresses, but that is unlikely to be the major factor-especially when one considers that the same trend occurs with Texas grapefruit, very little of which is exported.
Certainly, the longer the fruit is on the tree, the sweeter it gets, but it is also more subject to potential blemishes. Too, the fruit becomes softer towards the end of the season, especially after bloom, so it just doesn't hold up as well. Ring picking is also a factor, in that ring picking concentrates on large fruit, so there should be no small fruit eliminations in early season.
Assuming that harvesting and grove operations have been about on schedule to this point, May should be a fairly routine month during which fruit set will be finalized, as will potential fruit size. If fertilization of Rio's was set up for split application, growers should carefully evaluate fruit set over the next couple of weeks to decide how much, if any, additional nitrogen should be applied. A light set means that no additional nitrogen should be applied; a heavy set will require the balance of the annual amount of nitrogen.
Soil moisture levels should be maintained throughout this period, as both fruit set and the cellular potential for size are both established by the end of May. Remember, the growth of the fruit after May is due to cell enlargement, while cell division determines how many cells there will be-and cell division ends about the time final fruit set is achieved. The more cells that the little fruitlet has, the larger it will be at harvest.
Finally, insect and mite populations should be monitored closely, especially citrus rust mites. There are reports that leafhoppers are surging in a few groves across the Valley, and citrus blackfly is still of concern, especially in the western side of the Valley.
It is still a good idea to help yourself with blackfly control by placing 40-50 blackfly-infested leaves in a sealable plastic bag overnight to check for the presence of emerged parasites the next day. If there are parasites, take the bag to another grove or area of the grove with blackfly problems, open it up and hang it in a tree-then go back and collect more leaves to repeat the process.
California red scale (and other scales) will begin to increase over the next month or so. When the young scales (crawlers) are present, they can pretty well be knocked out with commonly available scalicides. However, once the crawlers begin to feed, they lose their legs and secrete a waxy covering-and the standard scalicides are not very effective. Oil is still the best control available for mature scales; common scalicides such as Lorsban are most effective on crawlers-so choose accordingly.
JULIAN W. SAULS, Ph.D.
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