It is 'possible' that it is natural decline but does not appear so when compared to natural cotyledon decline in the many plants I'm familiar with (never grown this one). It is also 'possible' that it is leaf scorch from the lights as it has that appearance but usually shows on true leaves, not just cotyledons. But the most probable IMO is pest damage. Aphids will do this but so will spider mites and fungus gnats. As to a fungus disease - assuming you are not keeping the soil too wet or the humidity way too high, the odds are quite slim. Especially given it is inside and the true leaves would also show symptoms. Soil fungus develops inside but leaf fungus is rare. Can't see the true leaves in the pics but if it were my plant and IF the true leaves do not have these symptoms I would removed the cotyledons and dispose of them carefully. They are no longer needed by the plant anyway. Then monitor for pests very carefully and treat accordingly. Hope this helps. Dave

I have a lot of willows, and they're entwining. Just had a huge thunderstorm, almost tornado, blast through here yesterday, so everything's tangled. What a mess. What I'm finding is that one must monitor the branches carefully because if they cross or touch they will rub each other and make wounds which hurt the trees and invite insects and fungus. I like the look of mixed foliage but it's more work. I use a binoculars and tall pruners. Had to cram lots of trees in here to suck up a swamp water problem. Willows like sunshine and will get leggy competing with each other. Had I had enough land would have planted them far apart to be specimen trees to shine in their individual glory. Look into the Prairie Cascade, imho the most beautiful of all willows, very fast growing and strong and hardy with bright golden branches in winter and large glossy dark green leaves in summer.

Not much to show on a pic... When I take my fingers and gently rub the surface of these new leaves (does not affect the mature leaves) fine sticky rust colored powdery stuff becomes evident. I don't know, maybe it is normal. I just never noticed anything like this before. I'll let it go for a while & see if it disappears as the leaves mature. Thanks anyway.

Yellowing of leaves falls into the following categories. Yellowing of a leaf between darl green veins is called chlorosis. Many conditions can be responsible. Poor drainage, planting too deeply, heavy soil with poor aeration, insect or fungus damage in the root zone and lack of moisture all induce chlorosis. After these conditions are eliminated as possible causes, soil testing is in order. Chlorosis can be caused by malnutrition caused by alkalinity of the soil, potassium deficiency, calcium deficiency, iron deficiency or magnesium deficiency. A combination of acidification with sulfur and iron supplements such as chelated iron or iron sulfate will usually treat this problem. Chlorosis can also be caused by nitrogen toxicity (usually caused by nitrate fertilizers) or other conditions that damage the roots such as root rot, severe cutting of the roots, root weevils or root death caused by extreme amounts of fertilizer. Yellowing of leaves sufaces, often with brownish burned areas, occuring on leave that are more exposed to sun, is caused by more sun exposure than the plant is able to tolerate. Yellowing and dropping of leaves is normal toward the end of the second summer on the small-leaved lepidote rhododendrons. These should have dense enough habit that this doesn't matter. Uniformly yellowish-green leaves is often just the need for more nitrogen. This will be more noticeable in the full sun. Some less sun tolerant varieties will always be light green in full sun. Yellowing of leaf edges has been noted in gardens where sandy soil conditions or root competition with other plants caused insufficient soil moisture and nutrients. See the link below for more information. Here is a link that might be useful: Yellowing of rhododendron leaves