I have 5 beaucarneas. All very small considering that they are about 5 years old, but at least they have been healthy until now (although for several months last year I had to devastate the mealybugs with insecticidal soap at intervals) This summer I decided to put them outside in a somewhat shady spot. When I brought them in at the end of the summer I saw that two of them had "leaves" with brown spots about 5" out from their start. The oldest leaves were not affected, nor were the newest, but the middle aged ones were in bad shape. The other three plants had no or just a few such spots. Actually they are brown-edged white spots. And they are not really "spots" at all, rather they are more like long ovals. As they age, they expand and eventually the leaf disintegrates at that point. At first I though it had to be a fungus or virus, and quarantined the two worst plants. But reflection tells me that they are likely the result of some insect. But an internet search of Beaucarea problems just turns up countless sites all saying - "No pests ever bug this plant!" So I turn to the collected wisdom of the UBC website community for aid. If I have done it right, there should be four pictures attached. Best I could do...
I have seen this. In my experience, the damage occurs as the new foliage begins to emerge from the crown. A short-term case of root rot from overwatering is usually the cause of this spotting. As new leaves begin to emerge, they will often stick together, if overwatering and/or root rot is present, damage will occur here. That is why the spots are in the middle of the foliage and apparently no where else. Sometimes, if the plant is outdoors and receiving too much rain in the early Spring before the plant is actively growing, this will occur. I am guessing the plants appear otherwise healthy right now? This does not appear to be insect damage, bacterial, or a systemic fungus. I am going to predict that the plants will do just fine if you leave them alone. Another tip...if you start seeing growth spurt with a lot of very light green foliage, beware of root rot in the near future. Excess water triggers initial growth, but the roots cannot tolerate being wet for long and the plant suffers, then the new growth can die off, be deformed,... or spotted, like yours.
