"Plant down" isn't a commonly used term in botany or horticulture. It's possible there's a misunderstanding or a specific context where this phrase is used.

Here's what could be meant by "plant down":

* Downy mildew: This is a fungal disease that affects many types of plants, leaving a powdery, downy substance on the leaves. This is the most likely interpretation if "plant down" is meant to describe a plant disease.

* Downy feathers: Some plant parts might be described as being "downy" due to their soft, feathery texture. This might be used to describe a plant's seedpods, for example.

* Plant debris: In some cases, "plant down" could refer to fallen leaves, branches, or other plant material on the ground, especially in a forest or other natural setting.

To understand what "plant down" means, more context is needed. Could you please provide more information? For example:

* Where did you encounter this term?

* What was the context of the conversation?

* Was there any specific plant or situation being discussed?

With more information, I can help you understand the meaning of "plant down" more accurately.