The flower of the rhubarb plant shoud be removed immediatly

...and it will probably keep on trying, so keep on removing them!

If you let the flower try to produce seeds, it will use too much energy on that, and you will get much less rhubarb. The sooner you can remove the flower stem after it forms, the better--if possible, pinch them off before they show above the leaves!

If you allow the flower to stay it ill make the rhubarb taste bitter as it takes all of the goodness from the plant. Remove it as soon as it appears.