CITRUS RUST MITES
RAINFALL-AT LAST
WATER METERS
MILESTONE® HERBICIDE
WATER SUPPLY
HOPE ON THE HORIZON (VOLCANO)
CURRENT SITUATION

CITRUS RUST MITES-

If your grove is not experiencing citrus rust mite control problems this season, there are a lot of growers who are keenly interested in what you are doing. I know some growers who have already sprayed three times, others who have sprayed once or even twice behind Temik®. The situation is seemingly more common in groves which experienced a January-February infestation that damaged a lot of fruit.

That such late and widespread citrus rust mite damage was generally unexpected and undetected until the damage became obvious was bad enough, but even cleanup sprays followed by Temik® or other sprays just haven't been as effective as expected. I don't know what is going on-but it is not just an isolated caretaker or orchard that is having the problem.

Monitor-monitor-monitor and spray when necessary-just don't ask me what to use, as I've heard of less-than-normal control with practically all of the more common materials-whether applied in 125 gallons or in 250 gallons.

RAINFALL-AT LAST-

Probably no one got too much rain and not too many got enough, but apparently everybody has received at least some rain since the morning of May 20. From what I hear, there is still some chance of rain in the forecast-although as spotty thunderstorms rather than as general rains across the Valley. If it comes, may it fall where you need it.

WATER METERS-

While metering of irrigation water has become more common in the last couple of years, there's still more needed. For years, the standard meter has been Micrometer, with a specific size meter and pipe saddle to be clamped onto the appropriate plastic pipe. Typically, the size of the propeller is based on the size of pipe into which it is to be installed.

Waterman has a new meter that consists of two parts-a sensor unit and pipe saddle for a specific pipe size and a detachable electronic totalizer for any pipe size. The sensor unit consists of a two-blade propeller that is standard for all size pipes-one simply calibrates (electronically) the totalizer for the particular size pipe being metered. The two-blade propeller also means that the insertion hole into the pipe is only 2.5 inches in diameter.

Given the smaller propeller blade number and size, this meter should better avoid clogging from grass or plastic bags in the supply canals. A truly neat feature is that if clogging occurs and stops the meter, its electronics kick in to record the elapsed time since clogging, thereby allowing easy calculation of total water use.

Everybody I know who has seen this Waterman meter is impressed. As I understand it, the electronic control head (totalizer) easily detaches and can be used on a different sensor unit on another line (not at the same time, obviously). This feature could be economically advantageous to both water districts and growers alike, in that a grower could buy and install the sensors only, while the water district could provide the totalizers for use during the actual irrigation. The ditch rider could install, calibrate and recover the totalizer for each irrigation, thereby recording total water use for each block, field or orchard.

Pricewise, the complete Waterman system is competitive with other meters-more so where a single totalizer is used for several sensors.

MILESTONE® HERBICIDE-

In the world of citrus herbicides, there have been very few new materials registered in the last couple of decades. The latest in the short list is Milestone®, a pre-emergent, broad-spectrum material from DuPont.

This product binds very tightly to the soil, so it doesn't percolate into groundwater and it doesn't run off. It can lay on the ground for 3-4 weeks in the absence of rainfall or irrigation without degrading, and only 0.5 inch of rain is needed for activation. It is intended for bearing and non-bearing citrus, tank mixes well, can be injected into irrigation, has a 12-hour pre-harvest interval and comes in water soluble bags of 10 ounces per packet.

The application rate is 20 ounces per acre, which should provide 10 months of control. The anticipated price is supposed to be comparable to other materials on a per-treated-acre basis.

Unfortunately, it hasn't cleared the registration process yet. DuPont anticipates availability about two months after full registration is granted by EPA...maybe by fall. We'll keep you posted.

WATER SUPPLY-

The total water in the reservoir systems was about 1.4 million acre feet as of May 20, which is about 24% of capacity. The U.S. share is nearly 1.2 million acre feet, representing about 36.07% of our capacity. If you have been following the situation, you will realize that the supply has not dropped nearly so much as one would expect during the first five months of the year.

The reason that our supply has dropped slowly is not that we haven't been irrigating. Rather, it is because Mexico has transferred ownership of almost 165,000 acre feet of water in partial repayment of the treaty deficit.

Transfer of ownership involves water that was either already in the reservoirs or from the so-called 50:50 waters. The later is water that comes into the reservoirs from sources other than those treaty-designated tributaries, which also includes rain directly on the reservoirs. In other words, the 165,000 acre feet is not water that was released from storage impoundments on the six named tributaries in Mexico.

According to some numbers I have seen, some eight reservoirs in Mexico currently contain about 27.3% of capacity, or about 1.6 million acre feet of water. Given those levels, there's barely enough water in the Mexico system to fully repay the current deficit, let alone to also provide for water use in that part of the country.

What we need is timely rains in all irrigation areas coupled with storms in the reservoir watersheds, the first to preclude the need for irrigation and the latter to refill all of the reservoirs. Since that isn't very likely, all irrigation users in both Mexico and Texas must become more conserving of our water through better soil moisture/crop need monitoring and better delivery systems.

HOPE ON THE HORIZON (VOLCANO)-

As many growers in sandier soils are aware, leafcutter ants can be devastating to citrus orchard management, not only from their leaf cutting activity, but also from the mounding of soil around the trunks (potentially resulting in foot rot)-to say nothing of uneven ground from mounds or from mound collapses in drive middles. Most products and treatments just haven't been effective-at least until now.

Griffin has a product called Volcano Leafcutter Ant bait that is supposed to knock them out completely. Presently, it is labeled only for use in pine forests in Texas, but Dr. Vic French is testing it in local orchards at present, so we'll know more about its effectiveness when his tests are complete. The bait contains 0.5% N-ethyl Perfluorooctanesulfonamide.

I called some folks over in East Texas who have been using it in pines, particularly in newly planted pine tree seedlings in reforestation efforts. They swear that it works as the label says, i.e., that excavation and foraging decreases within 1-4 weeks of application and continues to decrease gradually until the colony dies out within 4-8 weeks. Who could ask for anything more?

CURRENT SITUATION-

While some rainfall has occurred in the last couple of weeks, few orchards received enough rain to last more than a couple of weeks. Unless more rain is forthcoming, irrigation will continue to be of high priority in most orchards.

Final fruit drop has occurred, so what you see is pretty close to what you should have at harvest (except for navels, which will continue to drop into September). Unfortunately, some groves have bloomed a second (in some cases, a third) time in late May. Hopefully, most of this late bloom won't set, as the resulting fruit is usually coarse, thick-skinned, of poor quality and late in maturing-and, if it is grapefruit, it is also sheepnosed.

Keep on top of rust mites, as they have been problematic and current conditions are favorable to rapid population increases. Generally, California red scale crawlers should be developing soon, if not already, so if you need to spray anyway, don't overlook red scale potential. Too often, growers have relied on scalicides that kill crawlers, but will not kill adults which have already taken up residence under their waxy, armored covering.

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