Washingtonia Horror

[Canuck]

Greetings. We have a group of Washingtonia in one corner of the yard; all planted around three years ago (transplanted from pots); they were growing slowly, but steadily, consistently putting out new fronds. The irrigation water here is very briny which I think affects the growth rate (and I'm probably not fertilizing them enough), although Washingotia are very salt tolerant and hardy. All was well until about a month ago when something peculiar happened. One palm stopped growing; back this up....about six months previous to this, I removed some loose fibres at the base of the palm, they were mushy and black on the ends - obvious fungus invasion of some kind. At that point I modified watering schedule and removed soil away from the base so water wouldn't collect there during irrigation as much. Efforts proved futile, one by one the remaining palm fronds withered and browned until it stopped growing altogether, taking on a dried out appearance.

Fast forward to the other day, I noticed a nasty smell emanating from the general area.... I touched the centre and it pulled right out!; the smell suddenly became worse...like rotting meat. Inside was a nasty surprise.

 

Questions; Any idea what these are? Obviously an insect found a home inside the dying palm, or were they the cause? The remaining palms appear OK.

With much effort, I ripped the palm out of the ground, the roots in the middle area had dark mushy parts, outer roots were white and healthy - there were a lot of roots, the palm was very established.

Is it safe to plant a replacement palm in the same spot? Is it necessary to sterilize the area, such as removing the sand and put in fresh stuff? Or would it be safer to cut losses and dig a new hole nearby?

Several issues going on; most plants here are originally started in pots at a nursery, the soil commonly used is clay-like (you can see this in the picture of the roots; the soil in the center from the original planting pot is black and rich) retaining moisture, whereas they are planted in the native sand in the ground. Most desert plants adapt well and become established, but there definitely appears to be an issue where some plants retain too much moisture in the centre of their root ball, succumbing to fungus or other infection (particularly succulents). I've had a few trees die of odd fungal infections; they do well, then all of a sudden dieback; lose all their leaves, quit growing, and die. There are also root mealy bugs everywhere here, an invasive species that weakens and attacks plants and flowers - some trees/shrubs/flowers can withstand them, others obviously cannot. Date palms fare better, perhaps because their roots are shorn off when they're transplanted and they regrow them entirely. I'm also still figuring out optimal watering schedule for the various trees/palms/succulents/shrubs - we're experimenting with watering twice a week now that it's 'winter' here, instead of every second day - some plants appear healthier with the change. The succulents/cactus garden is on a separate drip line, they only receive water once a week or less - I've changed to watering them manually with filtered water. There are hundreds of washingtonia and date palms all over the neighbourhood; they're mostly bulletproof (even with rampant nutrient deficiencies and fungus); maybe I just got back luck with this one.

The survivors:

Edited November 22, 2021 by Canuck

[Fallen Munk]

Maggots.  AKA fly larvae.  They like rotting stuff so they didn't kill it, the flies laid eggs in the rotting meristem. 

If you removed that much soil from around the base and exposed that much roots, you killed it because those roots would air harden and no longer take up water or nutrients.

Sorry for your loss.

Edited November 23, 2021 by Fallen Munk
added more info

[UK_Palms]

Where in Egypt are you? Alexandria? Cairo? That's a hot, dry desert climate. Even with near constant irrigation I find it hard to believe they would rot like that. Have you got a close up of the larvae as they may be Red Palm Weevil larvae if they have a red bit on the front of them. It could even be a Paysandisia attack as those grubs look similar to Paysandisia larva. Both are massive problems in the Mediterranean basin. I don't think it is an irrigation problem as much as it is a pest problem. You appear to have an infestation of something. Close ups of the larva would help.