Watch out for the crops.
The owner of a field has sown a field of wheat and and “enemy” has sown seeds of weed in the field of the wheat crop. “Enemy” is I think perhaps too strong a term. I suggest that business rival, or competitor might be nearer to a correct description.
What is not explicitly stated in the passage in the NIV UK Bible, is that the particular weed sown amongst the good wheat was Darnel, which may also be called Tare. This particular weed looks similar to wheat until it is fully grown. So similar that in some places it is called false wheat.
Darnel is mildly poisonous. It is highly unlikely to kill you if you consume it, but you will feel ill for quite a while.
From the rival farmer’s perspective, that sowed the bad seed, the benefit continues after the season in which the good farmer’s crop is blighted. If the good farmer’s crop mildly poisons someone because of the Darnel, people will be more wary of purchasing from that farmer for a number of years.
When the farmer’s workers discover that the weed Darnel has been sewn with the crop, they ask if they should pull it out. The farmer says no, it is too young to be able to separate it from the good plants. They must wait until it is fully grown to separate the good from the bad.
Jesus explains to his disciples that at the end of the age, when the weeds and crop have grown together, it is possible to separate the good from the bad, the good people from the bad. The bad crop or weeds to be burned.
While not explicitly stated, it seems to me that there is a secondary lesson in that parable. It is found in the action of the farmer letting the crop and weed grow together. By acting too soon the farmer would lose much more of the crop than by waiting, letting the weeds grow amongst it. Patience was needed to know which to keep and which to discard.
God has infinate patience, unlike humankind, who want everything now.
As a minor point of interest to end, I do not think that parable could be applied today, because of the mechanised farming methods. Farm machinery could not, as far as I know, separate the wheat from the darnel.