Many tree leaves can get various molds and mildews and most cause few problems for the trees. If the leaves become covered over more than 50 percent of the leaf surface that could inhibit photosynthesis enough that the tree will drop the leaves. Whether what you have is something of concern probably is best addresses at your local office of your state universities Cooperative Extension Service.

Willows - Salix species - are prone to a host of fungal and insect issues but few that bother foliage enough to be a concern. Too often folks freak out about leaf spotting or minor insect issues and rush to spray something........usually unnecessarily. Plants get problems and blemishes - pretty much a fact of life and the natural course of events. At this time of year, as ken notes, there is nothing you need or should do other than clean up fallen leaves and discard.

Okay, I have further observations on these two plants. The plant whose leaves are flat has no leaves beneath the canopy. Basically, the leaves have fallen off the stems of the plant, except for the top canopy. But the leaves in that canopy look very healthy. The plant with the curled leaves has leaves underneath its canopy. So it has retained most of its leaves all along the stem, but the leaves look a little less healthy because they have this curled-in feature. I am not sure what to make of this. I am testing two different soil mixtures, and I am not seeing a clear winner. Each plant seems to have its own issues that make me think neither is optimal.

I have a good idea what's occurring, but I can't be sure w/o all the information asked for. You're almost certainly over-watering. If a pot is 10" deep, the bottom 6" of grow medium could easily remain 100% saturated when the top inch or two of the medium is dry. I suggest you skip the finger test and start using a "tell" to "tell" you when it's time to water. (see 'Using a Tell' below. Over-watering makes uptake of Ca(lcium) difficult. Without enough Ca in the nutrient stream (and it must be present in adequate amounts at all times, cells/tissue cannot form normally. This leads to poor root growth, misshapen strap leaves, malformed leaves, clawed leaf tips (like your tree), and other less conspicuous symptoms. W/o the needed information, I'll have to guess that whatever type of light you're using is too close to the affected leaves. Photosaturation is the point where the plant has absorbed all the light it can handle. Additional light beyond that point results in photoinhibition (a slowdown of photosynthesis). Duration and intensity of the light the plant is exposed to act conjointly to determine when enough (light) is enough. To some degree the excess energy associated with photo loads beyond the saturation point is turned to heat before being lost to the surrounding air - a safety mechanism, but in home environments where air is usually comparatively still, the boundary layer of air surrounding leaves acts as an insulator. Abnormally wavy leaf margins is a built-in defense mechanism which reduces the angle of incidence of the light hitting the leaf. Light is most intense when it strikes the leaf when the light source is 90* to the leaf surface. Wavy margins forces much of the light to strike leaf surfaces at angles other than 90*, which has the effect of reducing photo load. I ask again: What kind of light is the plant under, and are the leaves closest to the light the ones with the rippled/ wavy foliage? Also, how close is the light to the affected foliage? Using a 'tell' Over-watering saps vitality and is one of the most common plant assassins, so learning to avoid it is worth the small effort. Plants make and store their own energy source – photosynthate - (sugar/glucose). Functioning roots need energy to drive their metabolic processes, and in order to get it, they use oxygen to burn (oxidize) their food. From this, we can see that terrestrial plants need plenty of air (oxygen) in the soil to drive root function. Many off-the-shelf soils hold too much water and not enough air to support the kind of root health most growers would like to see; and, a healthy root system is a prerequisite to a healthy plant. Watering in small sips leads to avoid over-watering leads to a residual build-up of dissolved solids (salts) in the soil from tapwater and fertilizer solutions, which limits a plant's ability to absorb water – so watering in sips simply moves us to the other horn of a dilemma. It creates another problem that requires resolution. Better, would be to simply adopt a soil that drains well enough to allow watering to beyond the saturation point, so we're flushing the soil of accumulating dissolved solids whenever we water; this, w/o the plant being forced to pay a tax in the form of reduced vitality, due to prolong periods of soil saturation. Sometimes, though, that's not a course we can immediately steer, which makes controlling how often we water a very important factor. In many cases, we can judge whether or not a planting needs watering by hefting the pot. This is especially true if the pot is made from light material, like plastic, but doesn't work (as) well when the pot is made from heavier material, like clay, or when the size/weight of the pot precludes grabbing it with one hand to judge its weight and gauge the need for water. Fingers stuck an inch or two into the soil work ok for shallow pots, but not for deep pots. Deep pots might have 3 or more inches of soil that feels totally dry, while the lower several inches of the soil is 100% saturated. Obviously, the lack of oxygen in the root zone situation can wreak havoc with root health and cause the loss of a very notable measure of your plant's potential. Inexpensive watering meters don't even measure moisture levels, they measure electrical conductivity. Clean the tip and insert it into a cup of distilled water and witness the fact it reads 'DRY'. One of the most reliable methods of checking a planting's need for water is using a 'tell'. You can use a bamboo skewer in a pinch, but a wooden dowel rod of about 5/16” (75-85mm) would work better. They usually come 48” (120cm) long and can usually be cut in half and serve as a pair. Sharpen all 4 ends in a pencil sharpener and slightly blunt the tip so it's about the diameter of the head on a straight pin. Push the wooden tell deep into the soil. Don't worry, it won't harm the root system. If the plant is quite root-bound, you might need to try several places until you find one where you can push it all the way to the pot's bottom. Leave it a few seconds, then withdraw it and inspect the tip for moisture. For most plantings, withhold water until the tell comes out dry or nearly so. If you see signs of wilting, adjust the interval between waterings so drought stress isn't a recurring issue. Al