SHEEPNOSE POTENTIAL
TOPWORKING DEMONSTRATION
RAIN AND WATER
NEW EXPORT MARKET
STILL GOING
MICROIRRIGATION

SHEEPNOSE POTENTIAL-

I have previously indicated that I would anticipate sheepnosing problems to be common in the 1999-2000 Rio Red crop because of erratic and/or delayed bloom. Indeed, I have noted many fruit to be rather pyriform (pear-shaped) in late May, which shape should be the forerunner to sheepnosing.

The maximum, minimum and mean daily temperatures at Weslaco since the first of January are all running substantially above normal. As you may recall, I believe that warmer than normal temperatures during flowering and early fruit development result in sheepnosed grapefruit, especially for those fruit and varieties which are susceptible to sheepnosing.

Obviously, time will tell-but fruit shape indicators don't look very encouraging at this time.

TOPWORKING DEMONSTRATION-

More growers are expressing interest in some form of topworking to change existing Ruby-Sweet trees into something with better potential returns. In response to this interest, Dr. Mani Skaria and I are planning to conduct a demonstration of topworking-I'll do the grafting, he'll cover pathological aspects.

The plan is to start at 9:00 am on Wednesday, June 23 in an orchard at the intersection of FM 2556 and FM 506 about 3.0 miles north of Santa Rosa. This is a Rio Red orchard, about 7 years old, in which a number of Henderson trees were identified during the 1998-99 harvest.

To present a better idea of topworking, I have already inlay-bark grafted the stumps of a number of those Henderson trees and will do a few more in a couple of weeks. Thus, you'll be able to see the actual grafting during the demonstration, plus you can see what they look like two and four weeks after grafting. For those really interested, we can then travel south a few miles to see a couple of trees that I topworked two year ago.

RAIN AND WATER-

Most citrus areas received welcomed amounts of rainfall during May-although the area northwest of La Feria received less than half an inch as compared to the 1.0 to 3.0 inches reported for most of the Valley. Those rains have been a blessing, but more rainfall is needed.

Overall, irrigation supplies should be better than last year, as the total U.S. supply is about 35.6 percent of capacity as compared to only 26.1 percent at the end of May, 1998. Too, the winter/spring vegetable crops are finished, as is sorghum and much of the corn crop. With few exceptions, that leaves cotton, cane and citrus needing irrigation. With a couple of timely rains over the next couple of months, the overall water supply should end the summer in much better volume than last year.

The situation is somewhat more variable with individual irrigation districts, however, as their remaining supplies depend on the amount allocated, efficiency of delivery and usage, relative rainfall and crop mix within the district. In other words, districts with high proportions of cotton, cane and citrus will have higher usage in the next couple of months as compared to districts which have higher proportions of those winter and spring crops that have pretty much finished already.

NEW EXPORT MARKET-

China has recently agreed to open its markets to US citrus, which could be a boon for citrus exporters. The initial exports from Florida should occur in the coming season from a handful of south Florida counties, with several other counties being allowed to ship in 2000-2001. Remaining Florida counties will be added the following year if they are not under medfly quarantine.

The announcement from the U.S. Trade Representative's office was not available to me, so I don't know when or if Texas citrus will be allowed into China.

STILL GOING-

A couple of packinghouse are still shipping grapefruit, but not for long. The grapefruit harvest to date is some 238,640 tons-a whopping 27.3 percent above the 1997-98 season. Fresh utilization of grapefruit is up only 16.7 percent over last season, however.

Production of all early and midseason oranges was down 8.0 percent and Valencias were off 4.0 percent from last season, but fresh utilization of oranges was down only about 2.2 percent from 1997-98.

MICROIRRIGATION-

I was a guest at the Grove Managers Association meeting in Mission this week-the topic was microirrigation and fertigation, sponsored by Netafim and Terra. The information presented was timely and interesting-and I even agreed with most of it, despite the fact that drip irrigation was the main topic.

Citrus growers using microirrigation, some drip but mostly microsprayers, are apparently having doubts about how much water they should be applying (and maybe how often). We covered that is depth several years ago in this newsletter-but it is worth repeating.

For June, July and August, citrus should receive an amount of water equal to 75 percent of Class A pan evaporation for the interval since the previous irrigation-in the absence of any significant rainfall. It doesn't matter whether you are running the system every couple of days or weekly-just add up the daily pan evaporations since the previous irrigation and multiply by 0.75. The result will be in inches, so multiply that by 27,154 to get total gallons needed per acre. Then multiply by the number of acres being irrigated to obtain the total gallons you need to pump. Divide that by pumping rate (gallons per minute X 60 = gallons per hour) to determine how many hours you should run the system.

Irrigation frequency is another matter. Most microirrigators run about weekly, partly because of convenience and partly because of scheduling water delivery from the irrigation district. For microsprayers, weekly irrigation is fine-but drip systems really should be operated daily or at most every other day. Why? The limited capacity of drip systems is designed for daily operation to replenish only the water used that day. To operate drip systems less frequently requires much longer operation times to replenish the water used. The problem with long irrigation runs is really two fold. First, long runs result in a lot of water percolating downward (not outward!) beyond the absorptive root zone. In effect, that water is lost insofar as the tree is concerned. Second, long run times result in a saturated wetted zone, i.e. all air is forced out of the wetted zone, causing intense root stress and even death of the absorptive root hairs for lack of oxygen.

Saturation of the wetted zone occurs in about 10-12 hours in heavier soils, much less in sandy soils. After the saturation point is reached, there is no air left for the roots and any additional water moves below the root zone. So, yes, you can run for 18 to 24 hours or longer- from an engineering standpoint, but not from the standpoint of tree health.

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