Any passionate gardener should keep in mind that plants are like any other living organism. They can get diseases if proper care is not shown towards them.
Japanese maple trees can catch some known diseases, but this mostly happens due to some negligence, there is no evidence that suggest that these plants have some track record of genetic ailments. The plant responds back to the any problem either through losing its vibrancy or through other indications. These indicators should not be taken lightly as they are the signs for much bigger trouble ahead.
The most common indication that the plant has caught some ailment is that it starts to wilt and there can be several different reasons behind this symptom ranging from tainted seed, heat stroke, or extra moisturizer in the environment. Most of the time wilting indicates that the water ducts that carry the water to all parts of it have got damaged and as a result the water does not reach to the leaves which then start to lose their vigor. You should not act in a knee jerk fashion to this problem, as sometimes a wrong cure can worsen the whole situation.
Try to analyze where things have gone wrong, what type of negligence you have shown in the past few days.
Knowing where you went wrong solves half of the problem, now after realizing the problem now apply the specific remedy action to fully solve the problem. All the required actions should be taken quickly as unnecessary prolong process can make the situation less likely to cure. After applying the appropriate remedy, try to remove the infected leaves as they can initiate the problem in the future. This can be done in the weekly pruning of the plant to save some time.
Make a habit to provide moisturizers to the plant as clearly many problems arise due to lack of it. You can achieve the required level of moisturizing if you have decided to water the plant on a regular basis.
Pests
There are some known pests that usually feed themselves with the liquid of the plant tissue. As the often camouflage, so it is hard for a naked eye to catch their site. A closer inspection of leaves can reveal their presence on the leaves. This is the reason that the experts suggest closer inspection of the leaves once in a month to avoid such free riders. Once a leaf is infected by these bugs then it usually takes few weeks to show any indication that some alien element is sharing its resources.
Early identification of these bugs can save the leave from total destruction. If the plant is left unnoticed then it is a well known fact that these bugs multiply rapidly and over a very small period of time they will spread across all the leaves of the tree. At that stage they take full control over the resources of the tree and sooner they become a bigger problem for the life of the tree. There are some pesticides available in the market, but they can be useful in the earlier stage of the problem, as statistics reveal that over the period of time it becomes less probable for the tree to sustain. But still if you notice some of them on the leaves then try to analyze complete tree for their presence. If they are present on couple of leaves only then try to remove these leaves immediately.
If you notice that the situation is becoming out of control, then you can ask for professional help that is always available in the nearby nursery. They either will suggest some pesticide or any other appropriate method to solve this problem. As the old golden proverb says, prevention is better than cure, so this is true for this case as well and if you can manage to inspect the leave every once in a while then such encounter with pests can easily be avoided.
