Attached GMAT SC question from Kaplan test suggests that - "Use of Present perfect tense is required and use of "did" implies that the wine growers have stopped harvesting.

Use of "still" already indicates that wine growers are harvesting, isn't it?

Please explain.

Thanks,
Swapnil.

The simple past tense implies that something happened in the past but did not continue into present or future. Therefore, choice E is contradictory, because you cannot still do something that you stopped doing in the past. You could have done something in the past, then stopped doing it, and now could have picked it up again. However, this sequence of events cannot use the word still because there was a clear interruption of the activity in the past.