assumption

Hi guys,

I want to play, too.

A certain experimental fungicide causes no harm to garden plants if it is diluted at least to ten parts water to one part fungicide. Moreover, this fungicide is known to be so effective against powdery mildew that it has the capacity to eliminate it completely from rose plants. Thus this fungicide, as long as it is sufficiently diluted, provides a means of eliminating powdery mildew from rose plants, without entailing any risk of harm to the other garden plants.

Which of the following is an assumption on which the argument depends? This is a tricky question. If you just showed me the paragraph and asked me to list some of the writer's assumptions, I might think of things like these.

At least some roses have powdery mildew.

Roses, other garden plants, the fungicde and powdery mildew all exist. (Yes, a bit philosophical, but still an assumption.)

Powdery mildew is caused by a fungus. (This one might be worth a bit of serious consideration.)              

Readers of this paragraph will all speak English. (Well, the writer obviously assumed his readers would understand him. )

 I'm not actually sure I would even call items A to E 'assumptions on which the argument depends', so I'm just going to look at each in terms of whether it is true or false.

A. There is no alternative method to application of fungicide for eliminating powdery mildew from rose plants without harming other garden plants.

To me, this is not a well-written sentence, and thus is not a good beginning for a logic problem. I have trouble grasping this sentence clearly. I assume it means this.

Other than the application of fungicide, there is no alternative method for eliminating powdery mildew from rose plants without harming other garden plants.

The paragraph does not mean that A is true.

When I looked later at this problem as stated on some other links, I found at least one case where this option A was phrased differently. That makes me wonder whether there are any other differences and or inaccuracies in the problem we are looking at here. 

B. When the fungicide is sufficiently diluted, it does not pose any harm to people, animals, or beneficial garden insects.

The paragraph does not mean that B is true. B also seems irrelevant.

C. Powdery mildew is the only fungal infection affecting rose plants.

The paragraph does not mean that C is true.

D. There are no antidotes available if the fungicide is not sufficiently diluted inadvertently.
The paragraph does not mean that D is true.

E. The effectiveness of the fungicide on powdery mildew does not depend on its concentration levels being (just a typo?) greater than one part in ten parts of water.

Best wishes, Clive