Reversion
Post categories: pests and diseases
| 07:00 UK time, Thursday, 9 June 2011
‘Big buds’ on blackcurrant shoots caused by the Blackcurrant Gall Mite
We gardeners are the worlds worst for using the same name for different things. The classic, which I come back to 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, re-cycling organic matter that we use to re-vitalise our soils.
'' is another one. We have the Reversion that can affect blackcurrant bushes - a virus transmitted by otherwise known as 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 'oak leaf' stage. Long before the condition gets to that point, you will have had ample confirmation and advance warning when the disease is likely to be present by looking at your bushes in the dormant period, paying particular attention to the buds at the top of the young stems. 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. The mites are very small but can be seen using a hand lens. 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 which, by the way, has taken an awful hammering from the winter weather in our part of the country. It happens regularly to variegated forms of Euonymus. The plant will suddenly produce some leaves or even a whole shoot without variegation, in other word it has reverted to the plain green colour of it's parentage. This is about the time of year when you will first notice the problem.
Reversion on a variegated Euonymus
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 eventual 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. They have to be made to feel special!
This kind of reversion is not to be confused with , 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.
Jim McColl presents 91Èȱ¬ Scotland's .
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