Every day on the farm is a fight to obtain or maintain order against a determination of nature to return things back to the bush. With heavy rain during the winter and intermittent but regular rainy days this month followed by a few sunny days and I am hard pushed to keep the grass in shape much less the weeds under the berries and fruit trees.
We have just about thinned all the stonefruit trees that needed to be thinned. With stonefruit trees it is necessary to thin the fruitlets in order to minimise the potential fro brown rot and ti ensure that the fruit is of reasonable size. We do this for apricots, some plums, peaches and nectarines. Greengage plums usually self thin and prune D’agen we also leave. We do not touch the cherries.
We also thin the nashis but not the European pears (beurre bosse, winter cole and packhams for example ) These have also been done. We haven’t started on the apples yet but will do so within a week. We would be interested in other peoples ideas on thinning- so leave a comment)
But our main and most interesting problem this year has been to explain why we have had so much die-back with the raspberries. The problem has occurred in previous years but never so widespread as we have seen this year.
The symptoms seems to be of two types:
- in the milder cases the top of the canes show a yellowing of the leaves possibly with greenish veins. At one stage I had thought that this might have been due to a nutrient deficiency such as zinc.
- In other areas the buds just don’t emerge after dormancy or die back shortly after starting. The leaves are usually small if they get started at all.
This is a variety in the photo above is called Chillowack. The damage appears to be worst in the middle of the row. As you can see the rows are hilled and heavily mulched which was done just before the onset of winter. I have been researching this for some time and have found a number of sites which have addressed the same problem. A good example is the article Phytophora Root Rot of Raspberry put out by Ohio State University also Integrated Pest Management for raspberries from Washington State University
We had sprayed the rows with a herbicide when the plants were going into dormancy then mulched after some weeding and removal of old canes and topping of the new canes. . And at first I thought that it may have been the combination of much damper conditions and these sprays which had become more systemic than they should have been.
However as this photo shows the problem does not extend the entire length of the row but seems to be confined to what would have been the wetter areas.It could well be that our arrangement does in fact trap the water between the rows where their is no fall to one end or the other of the rows.
So what can we do about it?
I decided to weed and work on one row myself. This row was in fact just above where these pictures were taken. Amongst the weeds were many young plants starting again at one end of the row whilst at the other end the canes were more or less intact. However even the better canes had withered tips indicating staggered growth.
What appears to be happening in these areas is that the water is not draining away from the upper sides of the ridges and that in many cases the mulch is acting as a further deterrent and also keeping the ground too moist. Pefect conditions for growing phytophora.
It would be almost impossible to eliminate phytophora from all of our fields as it seems to be endemic to this area and detroys native trees regularly.
What we have done now as a remedial action is to rotary hoe the sides of the rows where possible thus incorporating the mulch into the soil and allowing it to breathe. We intend to do this twice and go deeper the second time. My observation is that their are no raspberry roots in this zone. After a period of time we will then rehill the rows if they have become too low and put drainage slots in low lying areas.
We are also spraying the canes with Agri Phos ( [potassium salts of phosporous acid) which has been shown to improve the health of live plants. How this chemical provides fungicidal activity is well described in the online guide provided by Oregan State University Extension