A diagnostic visit when a grower swears the gel did nothing

The call comes in July, four months after planting. The grower has a number ready before you get out of the truck: 31 dead trees out of 2,400, a drip line that has run six hours a week since March, and 240 kg of polymer on the planting invoice. That works out at 100 g per tree, close to double what the block should have needed. His conclusion is that he paid for expensive sand.

Then he walks you to the corner where 19 of the 31 are standing dead in a row. Eight more are within ten metres of a gate where a trailer has sat all season. That pattern is the whole case. A diagnostic visit is not a defence of the product and it is not a sales call with a shovel in it. It is a search for the one physical fact that explains why the deaths cluster, and that fact is almost always between 20 and 40 cm below the surface.

Ask for the paperwork before you ask for a spade

Four things decide how the rest of the visit goes, and none of them require leaving the ute.

• Planting date and the dose written on the crew sheet, not the dose on the purchase order. They are often different numbers.
• How it went in: mixed through the backfill, banded under the root ball, poured into the auger hole, or broadcast and rotary-hoed. Each one fails in a different place.
• Water applied since planting, in millimetres or litres per tree per week, including any rain the block actually received rather than the district average.
• The lot number and the bag size. Not because the lot is usually at fault, but because it rules the material out in about four minutes instead of four weeks.

If the grower cannot answer the second item, stop there. Half the visits I have made ended at that question.

The pit: one face, good light, 40 cm deep

Dig beside a dead tree, not under it. You want a vertical face that cuts through the original planting hole and into undisturbed soil, so you can see the boundary. Take the loose soil off in 10 cm layers and lay each one on a board in order. Then look for three things: swollen beads that still hold water, flattened empty shells that swelled once and collapsed, and a clean absence of both.

Where they sit matters more than how many you find. Beads 15 cm below the root plate are doing nothing for a tree whose feeder roots are in the top 20 cm. Beads concentrated on one side of the hole tell you the mixing was done with a shovel from one direction. Beads in a horizontal line at a single depth tell you it was banded, and the band may or may not be where the roots went.

The failure I keep meeting: gel in the wrong horizon

Last season’s version of this visit was a 6 ha block of young walnuts on a sandy loam. The crew had done everything the label asked for, at the label rate, on the label date. They opened a furrow, dribbled the granules in, dropped the tree, and then bedded soil up over the row to close the furrow. The bedding pass lifted the effective planting depth by 20 cm. When I opened a pit, the gel was in a neat band 28 cm down, and the root plate was at 11 cm. The granules had swelled and shrunk three times by August, and not one root had reached them.

The grower’s 100 g per tree was real. The 100 g that mattered was closer to 20 g, because only the fraction inside the root zone was ever in contact with roots. That is the counterintuitive part of these visits: the dose on the invoice can be correct and the dose in the ground can still be wrong, and no amount of extra product fixes a placement problem. Adding more gel to a badly placed block usually buys a second wrong band.

Write it up on one page, with a date on it

The report that gets acted on has three findings, two fixes and a follow-up date. Findings: where the material is, what state it is in, what the roots are doing. Fixes: what changes at the next planting, and what changes in irrigation this season. Date: when someone goes back to the same three trees to check.

Keep the tone flat. A grower who has just lost 31 trees does not need a lecture on polymer chemistry, and he does not need to hear that the product is fine. He needs to know that his placement put the material out of reach, that the corner with the trailer failed for a different reason, and that the remaining 2,350 trees are probably fine. If you want the standard placement diagrams to attach to that page, the application guide has them at field scale.

If you are standing in a block like this one right now, send me the planting date, the dose per tree, the application method, and two photos of a spade-depth profile with a tape measure in frame. That is enough to tell you whether you have a placement problem or a water problem, and those two need opposite responses.