Black Powder? on Rhubarb Leaves
 

Hi all

I have noticed what looks like black powder on the underside of my rhubarb
leaves.
It is probably some very small bug-type-thingy. Does anyone know what?

Also on the subject of rhubarb.........

For a few weeks, the stems produced were a good size, maybe 1-1/2" across.
Lately they are far more puny - between 3/4 and 1" across.
Is this usual as the growing season progresses and the large sticks get
pulled?
(I have never drastically reduced the numbe of stems in one hit, if that
makes a difference).

Phil

Depending exactly where you live, you may well have experienced some extended warm and dry weather recently. Since rhubarb likes it cool and damp, this is likely to have affected output. Also it will have used up nutrients in the soil. In general the oxalate content of the stalks goes up later in the season too, and the plant needs some energy for next year, so usually people stop pulling in high summer to give the plant chance to recover, and not eat too much oxalate.

Black powdery stuff sounds like mould. Rhubarb stalks that are not pulled will go rotten after a few weeks. Be more worried if this is occuring on fresh stalks.