Defect and tolerance
Alternaria black rot, and the navel it enters by
It goes in where the fruit gets its name. On navel oranges the infection sits at the stylar end, and the cultivars that suffer it are the ones whose navels are poorly formed. The rot then runs into the core, which means it is found by cutting fruit open and never by looking at it.
The figures
| The fungus | Alternaria citri in the Californian guideline, Alternaria alternata in the Spanish manual |
|---|---|
| Which fruit it affects | Mainly navel oranges and lemons |
| Where it enters on a navel | The stylar end, generally on cultivars with poorly formed navels |
| How it is found | By cutting the fruit in half, where the rot is seen extending into the core |
| What the outside shows | Dark brown to black firm spots at the stylar end or in the navel, once it shows at all |
| When it develops | Infection occurs in the grove, development follows harvest, and most damage happens during storage |
| The counterintuitive sign | Affected fruit can carry more intense colour than sound fruit |
| Post-harvest fungicides | Imazalil, azoxystrobin, fludioxonil or mixtures of them give partial control |
What it changes on an order
You cut fruit at goods in
This is the defect that pays for the knife. Nothing on the outside of a package or a pallet leads you to it, and a sample assessed whole will pass a load that a sample assessed cut would not.
You hold navels for several weeks before selling
Storage is where the damage happens rather than where it starts, so your holding time is the exposure. Fruit that moves in days and fruit that sits for a month carry different risk from the same grove.
Your sorters work by colour
Affected fruit can be the deeper coloured fruit, which means a colour led sort can quietly select for it. Anyone grading on appearance should know that this one runs the wrong way.
What this note does not settle
- The two reference sources disagree on species and on common name. The Californian guideline files it as Alternaria rot and black rot on navels, the Spanish manual as brown spot, and it names susceptible mandarins rather than navels.
- Cutting finds it only in the fruit you cut. We know of no citable method for finding it in fruit left whole, which puts a hard limit on any inspection at goods in.
- The fungicides named give partial control and not control. Treating their presence on a specification as an answer to this particular rot reads more into them than the guidance offers.
- We have no post-harvest fungicide confirmed and no storage regime agreed, so we cannot tell you what a load of ours would have carried or how long it would hold.
Source: UC IPM Pest Management Guidelines, Alternaria rot on citrus, IRTA, Manual descriptivo de podredumbres y fisiopatías en naranjas y mandarinas
The inspection that cannot find it
Everything a goods-in check does well is defeated here. You look at the outside of packages and the rot is in the core. You count fruit and the affected ones sit in your sample looking better than the rest, since colour on infected fruit can run deeper than colour on sound fruit. Only the knife works, and the knife only works on what it cuts.
That changes what a clean inspection means. On most defects a properly drawn sample coming back clean is real evidence about the lot behind it. Here it is evidence about the fruit you cut, and the honest position afterwards is that the rest is unknown. Anybody holding navels for weeks needs that distinction more than anybody moving them in days.
Why the navel is the door
The stylar end of a navel orange is a structure rather than a smooth surface, and the cultivars that suffer this rot are the ones whose navels came out poorly formed. What makes the fruit recognisable on a shelf is also what lets the fungus in. The infection happens out in the grove, months before anybody packs anything, and then it waits.
Storage is where it lands on the bill. Most of the damage happens there, so your own holding time is part of the exposure rather than a neutral gap in the middle. Ask what would be applied after harvest and how long a lot would have sat before it reached you. Neither is settled on our side, and saying so is the only accurate answer available today.
Talk to the grower
Tell us the variety, the sizes and the delivery week you need. You get a delivered price and what we can commit to in writing, from the person who picks the fruit.
The grower handles enquiries. Response times are still to be confirmed.