The Press and Journal (Aberdeen and Aberdeenshire)
GARDENING NOTES WITH JIM McCOLL
Just finished my soft fruit pruning the other day, such has been the weather to date.
I finished the job pruning my gooseberries. Turned out to be a quicker job than usual because the buds have come alive as little green dots which made it easier to select the pruning points.
Shaped like apple trees and redcurrants, the gooseberries have a short stem then the main branches radiate to form a balanced bush. All the side shoots sprouting from the main branches are simply pruned back to about 2-3cm from the main stem.
Next to the gooseberries are my blackcurrant bushes which have also just started into growth so I gave them a quick examination to check that all the buds have burst.
My reason for doing so was to check for the presence of a pest known as Big Bud Mite. An attack by these mites, which you can see using a lens, causes the bud to become twice the normal size so they are easily spotted. If you see any, pick off and burn.
In themselves these mites are not killers but they carry a much more deadly organism that leads to a slow death of the plant. The condition is referred to as reversion.
We gardeners are the world’s worst for using the same name for different things. The classic, which I come back to again and again, is compost. I would love to find a handier name for the compost that is growing medium and leave the word compost solely for the heap of decaying, recycling organic matter that we use to revitalise our soils.
“Reversion” is another one. We have the reversion that can affect blackcurrant bushes – a virus transmitted by the blackcurrant gall mite.
Like many plant viruses, reversion will slowly debilitate the blackcurrant bush. You may notice that the leaves are getting smaller and some are turning yellowish, making the bush less fruitful over time. You may indeed conclude that the plant is in need of a nitrogenous pick-me-up.
The clincher and the symptom, which gives it its name, is a regression of the leaf structure as it reverts to a simpler form (fewer major lobes to each leaf ). One of the later stages of the progression is referred to as the self-explanatory “oak leaf ” stage.
Long before the condition becomes serious you will have had ample confirmation and advance warning by the appearance of these big buds. When they stick out like a sore thumb several times bigger than normal buds, it indicates that they have been colonised by the mite, which transmits the virus.
Early control by nipping off these buds will slow down the progress of the disease significantly. To my knowledge, there is no pesticide available that will kill the mites.
The other use for the word reversion relates to a variegated plant producing plain green leaves, quite common in several popular garden shrubs.
The classic example is Golden Privet, a much-favoured choice for hedging. It happens regularly to variegated forms of Euonymus and Lonicera.
The plant will suddenly produce some leaves, or even a whole shoot, without variegation. In other words, it has reverted to the plain green colour of its parentage.
The simple message is – whilst you ponder why, be aware that green leaves are more efficient than variegated ones in converting solar energy, they are stronger and will eventually take over.
Forget the pondering bit for now, cut out the wholly green shoots immediately if you wish to save your variegated plant. You may not have done anything wrong, some of these variegated cultivars by their very nature can be slightly unstable and are certainly not so robust.
This kind of reversion is not to be confused with mutation, the natural “sporting” tendency of some plants.
Chrysanthemums are a classic example. A single plant in a uniform group may suddenly throw up a shoot with a flower on top that is quite different in colour from all the others in the group. If it is sufficiently different, if it is appealing – propagate from that one shoot and you have a new variety on your hands.