Illness and plants

Solution 1:

Can I use the word "illness" when it comes to plants? Yes it appears so.

A study shows the efficiency of composts of agro-industrial waste to reduce **illnesses of the plants** Horticulture 2012

and

American Journal of Pharmacy 1923 google books

... has discovered that many illnesses of plants, similarly to those of people, are due to these microscopic animal parasites.

Management and Applications of Complex Systems - Page 143 google books 2019!

The content of the knowledge base includes the following: types of soils, sorts of wheat, classes of machines and mechanisms, illnesses of plants, insects, pesticides, fertilizers, etc.

Plant diseases is more common but plants can have illnesses too.