Florida Citrus OHS/APS News

A forum to discuss Open Hydroponics and Advanced Production Systems in Citrus

Thanks to everyone for coming!

Click the pictures above, then click the thumbnail to see full size picture.

Back in June, we injected a year’s worth of imidacloprid through the irrigation system in an attempt to achieve systemic control of leafminers and psyllids.  Immediately following the treatment — within a week or so — there was a flush, and it was hammered by leafminers.  We applied a spray application to try and control them, but that of course has limited success when they’re already bad and doesn’t really control anything on subsequent flushes.

Our neighbor on Okeechobee Road, David Robinson, has been working with Dr. Steve Lapointe with USDA on the use of leafminer pheromone that causes mating disruption.  It’s applied in a compound called “Splat” (aptly named in our opinion), and David has built a machine that applied gobs of it on leaves in carefully controlled amounts to evaluate dosage and longevity.  David had a little left over from a recent field application, so he kindly ran over to Rock Bottom and applied a good dose.

The next flush that emerged came out clean.  No leafminer or psyllid damage.  It’s hard to say at this point whether it was the imidacloprid, Splat, or both that had an effect.  I suspect the Splat played a role since we don’t see leafminer in the microjet block, which received an imidacloprid trunk drench instead of an irrigation injection, and usually that has limited success on trees the size of those in Rock Bottom.

We are very interested in using tools such as these to reduce the amount of foliar sprays necessary to grow grapefruit.  Between canker and psyllid control for greening, if we applied a spray every time it appears necessary, the number of applications would be excessive and there wouldn’t be any hope of biological control.  We feel that the imidacloprid injection, because of the root balls and extremely efficient uptake, is a promising tool, and the Splat technology is exciting.

Rock Bottom is being hammered by both canker and HLB.  Our less aggressive program to date has not worked well, so for the moment we would recommend the heavy spray program on commercial acreages.  But, we’re not done yet, and hopefully will find the balance we would need to rely less on spraying and more on less expensive and disruptive measures.

The fertilization and irrigation programs for Open Hydroponics Systems begin their life each year with an “Orchard Information Master”.  It’s basically a collection of the information needed to determine how much fertilizer to apply, the ratio of the different components of the fertilizer, and the basic irrigation program.

Here’s this year’s Orchard Master web page for our Rock Bottom grove: http://www.arapahocitrus.com/files/rockbottom/master

You’ll see that there are a number of items on the download list.  The Orchard Information Master itself is the controlling document, and the other items are necessary to provide the details and general idea of the condition and size of the trees.  We gather and record all this information for each irrigation zone in a grove, then send it to Japie Kruger so he can build the programs.

If you download and open the Orchard Information Master file, you’ll see that it opens to the Metric tab.  To see the same information in pounds, gallons, boxes, acres, etc., just click on the next tab to the left down on the bottom.  When Japie builds the programs, he actually does it in metric units since it’s so much simpler — kilograms and liters are easier to work with than pounds and gallons when building formulas with percentages and ratios.  Not to worry, though — when the programs are finished, we just convert everything back into English units so that the grove managers can set up the Netafim NMC controllers to run the systems.

The Orchard Information Master is broken down by irrigation zones.  The flows, tree characteristics, and leaf, soil, and water analysis are all required to complete the form.  It takes a fair amount of work to pull it all together, but the nice thing is that you only have to do it once a year.

Perhaps the most important, yet most confusing, concept is the “% Canopy Coverage”.  All the programs are first built as if the trees were fully mature and grown to the point where they fill the space allotted to them.  For smaller trees, though, this would result in too much water and fertilizer.  So, the % Canopy Coverage is estimated, and the amounts of water and fertilizer are reduced by that percentage.  For example a block of trees with 70% canopy coverage would receive 70% of the water and fertilizer required for a full size tree.

The Orchard Information Master provides the pieces of the puzzle necessary to build the water and fertilization program for the year.  The program becomes the basic operating schedule for each day of a month.  Then, we fine-tune things as necessary based on the weather conditions and other factors.  You can’t skip steps — the everything has to move through the process the same way every year.

More on Orchard Information Masters in later blog posts.


There’s two parts to OHS/APS — “Open Field Hydroponics Systems” (OHS), which is the fertilizer and water management, and ”Advanced Production Systems” (APS), which is the high density planting.  The goal of OHS is to use a drip irrigation system to apply a nutrient solution to clusters of roots under the emitters all day long to create a stress-free environment — unless you want to stress the trees for some reason, in which case the dense roots will dry out the soil under the emitters in less than a day even if there’s good soil moisture around them.

Roots just under the soil surface below drip emitter - click to enlarge

One thing is really backwards from everything we’ve tried to do for years.  You want the roots to be as close to the surface of the soil as possible — no more trying to get them to grow down deep.

The pictures show how shallow the roots are in the soil — we just brushed some soil away under an emitter in the one picture, and then dug out a fistful right where the picture was taken to show how dense the roots become under the emitters. 

Root density management is the single thing that makes OHS different from any other irrigation management system.  Instead of relying on the soil to store and release nutrients and water on demand, OHS serves them directly to these masses of roots under each emitter.  It is a very dynamic system that changes rapidly, which is why we dare plant trees so close — we have control over their growth, fruit production, and fruit quality because of the root clusters that you don’t have when the soil texture and chemistry is dominant, as is the case with microsprinklers and conventional drip.

Density of roots under drip emitter i click to enlarge

This is much higher density than we see under conventional drip systems in Florida.  You can only achieve this kind of root density with high frequency pulses with a nutrient solution — plain water alone won’t do it, and most drip systems have been operated with longer application times than what we’re doing in OHS.

Actually, though, we don’t manage the water to achieve this effect — we manage air.  Each pulse can only be long enough to apply some water with fertilizer without creating an oxygen-deficient environment that would suffocate the roots. 

Closeup of root density - click to enlarge

The length of each pulse, then, is based on how quickly the soil under the emitters becomes saturated during an irrigation application, so we apply for a short period, then wait long enough for air to re-enter the root ball before applying the next pulse.

So, since the soil surface is in direct contact with the air, we want those roots as close to the top as possible to increase aeration — which is why we try to grow the roots up, not down!


The perfect day -- warm weather, and not a cloud in the sky!

Becky Yates, Arapaho’s Irrigation Manager, and I spent the day working out imidacloprid injection in the drip zones at Rock Bottom.  It was a classic “Bluebird Day”, without a cloud in the sky — perfect weather.

Typically, trees 3 years old and up are too large for imidacloprid to work — it’s too diluted in the tissue to control asian citrus psyllids and leafminers.  The South African growers have had success with injecting imidacloprid, so we decided to give it a try with a Florida twist.

The theory is to apply an entire year’s worth of imidacloprid all at once to try and build the level high enough to control psyllids and leafminers on the critical summer flushes that normally get hammered hard.  We planned it out, and then waited for the right moment.

To promote maximum uptake of the imidacloprid, we waited for two days in a row with clear skies and warm temperatures.  These conditions cause the stomates in the leaves to open to the maximum extent, resulting in the highest transpiration rates, and water uptake by the root systems, of the year. June is the month when this is most likely to occur, plus it’s just before the rainy season when the flushes kick off.

Yesterday, we turned off the irrigation in the drip zones.  The root clusters under the drip emitters are incredibly dense right now, and if you turn off the water for even one day, the roots dry out the soil in those clustered areas rapidly, even if the surrounding soil is wet. 

Today, we injected the imidacloprid in 20-minute cycles, followed by 20 minutes of irrigation to get all the material out of the system.  We have been applying six 30-minute pulses each day, so this is much less water than the trees have been receiving on a daily basis, but enough to carry the material down through the root zone, made easier because the roots are clustered right at the soil surface.

We’ll withhold irrigation tomorrow and Sunday.  Usually only one day afterwards should be sufficient, but we’re giving Becky a day off, and want to provide this first attempt the best chance.  The root clusters should suck up every drop of the water we applied today, which will pump as much imidacloprid into the trees as possible within 48 hours.

We are hoping to achieve psyllid control even with relatively large trees.  For comparison, we applied the same amount of material to the trees in the microjet zone as a trunk drench last week.

We’ll keep you posted.


Nice looking young grapefruit trees on sour orange. Microjet irrigation with intensive fertigation.

A number of people are going back to Sour Orange as a rootstock choice.  The rationale is that Sour is the most adaptable rootstock for our area, and that psyllid control programs will also control brown citrus aphid and other tristeza vectors.   There’s a lot of truth there, and it just might work.

There is a note of caution, though — beware of Diaprepes!  Most of the trees on Sour that we’ve  lost lately were due to Diaprepes rather than Tristeza.  Sour is resistant to the regular strain of Phytophthora, but is very sensitive to the one that invades Diaprepes feeding sites on the roots — Phytophthora Palmivora.  That strain really works on Sour Orange hard, and where Diaprepes has become established, trees on Sour declined dramatically, and most of them died.  Drainage, soil type, and other factors have some bearing on this, of course, but as a general rule Sour gets hit harder than trees on other rootstocks.  So, if Sour Orange is under consideration, one of the decision points may be whether Diaprepes is established in the area.

When we first planted Rock Bottom and the trees started really growing fast, the Diaprepes exploded.  There were adults on every new shoot.  We’ve knocked them down by injecting nematodes through the drip system, but when we pull up a tree there’s always some Diaprepes damage visible on the roots.  We don’t have Sour in the planting, so I can’t say how it would react compared to the other rootstocks.

The point is, when you plant new trees and start growing them fast, if there are any Diaprepes in the area, they’re going to come to the grove.  If that’s the case, rootstocks such as Cleo, X639, or US897 — all good performers where Diaprepes is present — or even other rootstocks may be better choices than Sour.   X639 and US897 both look good in Rock Bottom under OHS, so they’re viable alternatives.  Pete

Dr. Arnold Schumann, from the CREC in Lake Alfred, established an OHS planting at a grove near the Center. It has microjet, which will be used for cold protection, and Arnold added the drip system. He’s using two plug-in emitters per tree, and he’ll add more as the trees grow larger. I don’t know if he has plans to eventually add a second drip line.

There is an area in the block where the trees don’t have drip — they’re on microjets operated by the grower. It appears that Arnold’s trees are larger, and the trunks are nice and small. Thin diameter trunks indicates that the trees are nearly stress-free – something I’ve noticed in every OHS system. Skinny trunks, then, are a good indicator of the way that water and fertilizer are managed.

From the looks of it, Arnold is growing off the trees very nicely. It’ll be interesting to follow this planting since he is monitoring salinity and soil moisture along with different water and fertilizer treatments.  Arnold has a web site with more details on the project:


Arapaho just finished planting an Advanced Production System block in an existing grove that originally had 58-ft double beds. We designed and installed microjet manifolds that tied into the original two submain connections and provided 3 connections for poly lines to convert each bed to 3 tree rows. Richard Chandler’s Arapaho tree planting crew helped lay out each bed to accommodate differences in shape, mostly about 18′ between the tree rows on the tops with wider spacing across the relatively deep water furrows, then planted the trees at 8′ in the row. That’s roughly equal to 281 trees/acre. It looks really good, and saved a lot of money over re-doing the beds and irrigation system!

The basic premise of Advanced Production is to increase the tree count to minimize production losses as trees are removed for HLB management.  By increasing the number of trees per acre, the grove care costs per tree are lower because you’re still mowing the same acre but passing more trees.  As they begin to produce, then, the cost per box is also lower than with conventional spacing, which means higher profits.

It’s the anticipation of higher profits that offsets the greening risk.  So, increasing tree density is a good way to do that in the early years of the planting because we don’t know how long the groves will hang in there on the back end.  We still have a lot to learn about growing high-density groves — what Bill Castle has dubbed “Advanced Production Systems” — so exchange of ideas and experience is an important part our learning experiences.