It's hard to say whether or not a fungal infection is the underlying cause of the lesion (probably not), or, if there is a colony of fungi simply taking advantage of an opportunity. Fungal spores are ubiquitous, so any time conditions are favorable enough to support germination of spores and there is a host susceptible to the infection, it occurs.

The most likely cause would be natural senescence (aging), mechanical damage (like a bruise), or over-watering. Lesions do occur as a matter of course when leaves are in the process of being shed, and nutritional deficiencies are a very common cause of the shedding of older leaves. Reason: Some nutrients are considered to be mobile in the plant (nitrogen, phosphorous, potassium, magnesium, sulfur). That is to say plants can borrow nutrients from older leaves and use those nutrients as building blocks from which new growth is formed. The result of scavenging older foliage for nutrients used in new foliage results in the shedding of older leaves; and as noted, it is very common for leaves being shed to show signs of fungal activity.

That it occurs on a single leaf and an older leaf at that, should be seen as heartening. I would snip through the petiole (leaf stem) to remove the leaf. This will leave a strem which will fall off within a week or two after the leaf is removed. Don't pull it off as that can damage latent buds that reside in the leaf's axil, located immediately above the leaf's attachment point. It's not uncommon for these suppressed buds to be conspicuous in F altissima.

If you aren't fertilizing regularly, let's talk about that. It's an important part of any care regimen for plants in containers. Conventional container culture is much different than growing in the ground/garden. One of the differences that calls for attention from the grower is the fact that when growing almost all herbaceous houseplants, the grow medium cannot be counted on as the sole source of nutrients. It's almost always essential that the grower has a working plan to provide an adequate supply of nutrients. Also, what fertilizer you choose is pretty important. Some will be very close to perfect and others will be very problematic.

Thoughts or questions?

Al

Wow. And wow. And THANK YOU!!! This is so incredibly helpful and informative. I’m going to lean on the side of it not being fungal and, yes, I’m going to remove that leaf.

As for fertilizing, I just brought the tree inside for the winter (zone 4 a Minnesota) and I was told to cut back on fertilizing. I was using some old water-soluble, generic-use Miracle Grow. I’m open to suggestions.

This tree, and my Ficus Audrey are the plants that my family is instructed to save if the house is on fire.😂. I love them!

Thank you, sincerely!
Rani

Thank you for the kind words, Rani.

I'm a bonsai practitioner and have many Ficus in my collection, covering about a dozen species. Of course, most have much smaller leaves than those you mentioned.

Fertilizing is literally monkey-easy if the grower is using a grow medium that allows a planting to be watered to well beyond the point of saturation (so the entire soil column is saturated and at least 20% of the total volume of water applied exits the drain hole) without the need to worry that the grow medium will remain too wet for an extended period, and in doing so, limiting root's ability to function normally/ efficiently, or worse, wrecking root health. If you can water that way, you can tie the frequency of fertilizer applications to the number of times you water. E.g., in summer, drop a marble in the pot when you water. When the 3rd or 4th marble is about to be added, fertigate (water + fertilize) instead and remove the marbles. It's a perfect way to easily determine who needs fertilizer and who doesn't. In winter, change the frequency to every 4th or 5th time you water. It makes MUCH more sense than arbitrarily fertilizing according to the calendar.

I use Foliage-Pro 9-3-6 for all plants I grow in pots. It has a lot more going for it than any of the Miragle-Gro products. It has ALL nutrients plants acquire by the root pathway (MG products usually lack calcium, magnesium, and some micronutrients), it has a RATIO of nutrients that mimics the rate at which the average plant actually uses the nutrients, it derives none of it's nitrogen from urea (MG products do - urea promotes coarse growth and long internodes), and more than 2/3 of its nitrogen is in nitrate form (easier on plants).

Al

i know its getting close to halloween.. but are you really scared of it??/

never fert a houseplant in winter .. im sure you have fert'd enough for the next year or two ..

i give my houseplants one single sip of very diluted water sol fert.. when i take them outside in spring .. like 25% of recommended .. i spend my money on more plants.. not enriching the fert dudes ....

they are plants.. they are not children.. they do not need to be constantly feed.. nor clothed.. nor educated .. treat them like plants .... and you should have them for decades ...

also. too much fert can lead to salt accumulation in the pot.. and that can end up being worse than never fert'g it ..

have fun with your plant.. but dont love it to death ..

ken

Plants need a full complement of nutrients in the soil/ soil solution and available for uptake at all times if they are to grow and function normally. The parroted advice to 'stop fertilizing in the winter' is based on 2 assumptions: 1) the plant will be in a water-retentive grow medium, and 2) therefore the grower will be forced to water in sips (instead of flushing the medium) to avoid extended periods of saturated soil and the negative effects that has on root function/ health.

Watering in sips ENSURES a build-up of dissolved solids (salts) in the grow medium, which can severely limit water/ nutrient uptake, so it is posited the only way to avoid an excessively high level of dissolved solids in the soil is to stop fertilizing. Pure hokum. Has anyone seen Mother Nature running around at a dizzying pace pulling nutrients out of the soil in winter? How is it that I fertilize all my indoor plants at low doses every time I water - all winter long, yet they remain perfectly healthy?

Al

I agree. This has been my experience. Growing in pots is so unnatural and plants outside continue to have access to nutrients, but take them up more slowly during the slow growing season, right? These ficus are not going into a full dormancy - at least I don’t think so.

I am very intrigued by the thought of my type of soil being a potential problem. I like to water thoroughly when I do water, like you said, but I have several shallow rooted plants that take forever for the base of soil to dry out. Looks like I will be mixing some new soil and repotting some plants.

Thank you! This is like taking a class at the university!

i suggested cutting fert during winter because the OPs history suggests they fert'd plenty enough all summer long ...

fert is salts.. and excessive fert leads to salt buildup in pots.. when you have a ring of salt in your pot.. your are ferting too much ...

bottom line.. its your plant.. do whatever you want to it ... period ...

ken

"..... excessive fert leads to salt buildup in pots." The key word here is 'excessive'. Of course it CAN lead to a high level of salts if the grower doesn't flush the soil regularly, but that is also true in the summer; so, should we never fertilize in summer either? It's not appropriate to make the assumption the grower is going to use fertilizer to excess, then base the adamant advice to "never fert a houseplant in winter" on that assumption.

Too, deposits of dissolved solids on the grow medium or pot cannot be taken as indication the level of dissolved solids in the soil solution are too high or even have at some point been too high. It will occur naturally whenever the grower doesn't habitually water the top of the soil evenly when watering. Rings occur on pots, inside or outside, because pots have a capillary pull - most prevalent in clay or other porous pots. The soil solution rises above the level of the soil. As it evaporates, the dissolved solids from tapwater and fertilizer solutions are left behind. Those solids are not in the soil or the soil solution, and because they are insoluble (or largely so) they are not returned to the soil solution when irrigation water flows over the deposits. These deposits will occur even if the grower never fertilized because they consist primarily of CaCO3 and or MgCO3 (calcium and magnesium carbonates, respectively).

"..... the OPs history suggests they fert'd plenty enough all summer long ...". No, it doesn't, Ken.Rani said the plants had been fertilized with a water soluble MG product. Applications of soluble synthetic fertilizers are effective for about 3-4 waterings if the grower is watering correctly. After that, the level of fertilizer would be much too low, even if the beginning level of fertility was at luxury levels. How often a plant was fertilized in the summer has no bearing on a winter fertilizing strategy. When it comes to deciding when to fertilize, even when the plant was last fertilized is far less important than how many times the plant has been watered since the last application.

The only reason we might advise someone NOT to fertilize houseplants in winter would be because we know the grower is using a grow medium so water-retentive it precludes the ability to flush the soil appropriately when watering. This puts the grower on the horns of a dilemma - Do I fertilize and subsequently flush the soil appropriately, even though I know it will affect root function and root health, or, do I withhold fertilizer and water in sips, thereby subjecting the plant to the consequences of low fertility or the skewed nutrient ratios that are a part of watering in sips for intervals measured in months? The best answer is NEITHER. Ideally the grower would work toward getting to a place where the grow medium can be flushed regularly without valid concern about root health/ function, and fertilize at an appropriately reduced rate during winter.

I use FP 9-3-6 weekly at higher than production rates when the plants are outdoors for summer vacation. When they are indoors, I fertilize EVERY time I water from Oct to about Memorial Day at maintenance rates, and make sure the grow medium is appropriate flushed every time I fertigate (fertilize + irrigate).

Nutrients represent more than the building blocks for growth. They are an essential to the plant keeping it's systems orderly and for metabolic processes. Withholding nutrients in winter can cause imbalances. When plant systems become unbalanced it's a bit like an unbalanced spinning top. As the wobble increases, all balance is lost and systems can spin out of control, resulting in loss of viability. People experience similar issues when their systems are out of balance, and imbalance is usually what our Drs are looking for when they order bloodwork.

Al

I am pretty careful when fertilizing in the summer. So far, no salt build up and nice healthy plants with awesome growth (Audrey and Altissima sure do love hot, humid, sunny days).

My guess is that the older leaf is being sacrificed, as suggested and it has been removed! Let’s hope that’s the end of that!

And thanks again!!