Landscape gardening- diseases


This week’s sojourn into the world of horticulture and design begins with a response I sent to a couple regarding their cherry trees. As you will know, cherries are truly magical in Spain. The sweetness un-matched. Therefore, I am going to introduce a few common diseases and treatments. In order to assist your fun in the sunHere is an extract of the question
Hi, two cherry trees planted five years. This year first fruit on one, other one flowered but no fruit. Four weeks after flowering leaves started to go brown and fall, now sticky goo has started to leak out of trunk, hope you can help .Stan.
Well, firstly, as usual there are several answers. It is at first appearance not uncommon to see trees leaking a little sap from the bark. This is often caused by a little stress in the growing conditions. Too much or too little water will cause the tree, of whatever variety, to crack. The tree then protects itself by producing, leaking more sap, which dries, and helps heal the tree. Tree sap, mainly in pines but also some other species is mildly antiseptic, (thanks Ray Mears) and this excess production helps keep the tree safe from external attack. PICTURE A
The remedy is to standardise the watering regime. A regular and expected watering regime is a principal requirement for even and healthy growth. Too much water causes the ring layer to expand quicker than the bark layer, causing the cracking. Add to this a regular feeding regime and you will grow a healthy tree that will fight many air and insect born diseases on its own.
My own alarm bells went off though, because of the description ‘sticky goo’ as opposed to ‘clear sap’. To me this describes something altogether more serious. Cherries are prone to bacterial canker. Bacterial spores enter through small cracks and fissures in the bark – caused by the irregular growth pattern as described above. Poor air circulation compounds the problem within a garden environment. With higher humidity in late spring / early summer, the bacteria multiply uncontrolled. Their by-product is the sticky goo described in the question. PICTURE B and C
Combined with the browning of leaves and no fruit I have suggested the following answer, which firstly attacks the disease, then the tree and then the environment. PICTURE D
The following regime is equally appropriate for very many disease and ailments caused by both environmental factures and bacterial/ viral infection.
Firstly, remove and burn all infected material. It is important to burn the twigs and leaves, bacterial and fungal spores need to be destroyed by fire in order to stop them spreading. If you suspect canker (PICTURE E) or worse, fire blight in apples, cut the branches behind the visible areas of infection. If the heartwood is clear, whitish then that is fine. If you can see very much darker heartwood in twigs and branches, you must keep cutting back until this has disappeared altogether. This dark staining is caused by the infection; it is how the infection travels through the tree and you must remove it. If you get back to the main trunk, you may need to consider removing the whole tree.
This is quite a drastic solution, and I would recommend using someone who knows his or her plant diseases. You would not want to lose a whole tree, to discover that that particular variety always has dark heartwood anyway. Therefore, some expertise is required. Prune cleanly with a smooth cut at the collar of the branch. This picture is an example of how badly it can be done, condemning the tree to firewood. PICTURE F
Next, you need to spray the cuts and the bark of the tree with a copper-based fungicide/ bactericide. If you have some fruit on the tree, this will be best not eaten; you will get the runs! Nevertheless, you are saving the tree.
Follow this by cleaning, with bleach the tools you have used to do the work. Some plant diseases are highly infectious within the variety of their intended victim and it would be a shame to help it infect others.
Prune back other trees and shrubs around it if you think it is affecting the airflow around you tree and water the tree for about ten minutes. Allow this water to penetrate for half an hour or so and then apply a good fertilizer either soluble or granular and water that in, for two lots of ten minutes each. This soaking and drying allows the water to penetrate where it is needed.
The fertilizer needs to be higher in potassium than nitrogen and phosphorous in order to promote good root growth. This will help prevent reoccurrence in future years. Too much nitrogen, which is what most people do, forces the young shoots to grow too quickly. They do not get a chance to bake and harden in the sun and will be more prone to damage. Some of you may know these as water shoots. It is best to remove these and alter the feeding regime so that this is avoided
The healthier the tree, the better it is at dealing with these disease itself. Now arrange to stabilise the watering of young trees in particular.
This applies to almost all trees in your garden. Always be aware that a stressed tree is more prone to diseases. You can grow resistant varieties. Cherries in particular prefer neutral soils so in Spain an amount of pH altering is necessary for the benefit of the tree. Of course having said all that, it may just have been a bit of drought damage or too much water. Fickle, trees. Moreover, all this done without a picture!
More commonly grown fruit trees, orange and lemons, are not prone to much. There have been attempts by the wonderful and sometimes overprotective authorities to restrict the imports of fruit trees from those countries where bacterial and fungal infections are rife. There is usually an import label and licence attached to new trees available at the garden centres. A blue or white plastic tag with a number on it. In fact, do not buy one without it. This has helped no end, but they are obviously prone to the above bark splitting from the aforementioned reasons.
Added to this, some older trees are susceptible to more difficult viral infections. Root rots, ring rots and fruit rots, some mould and fungal infections. They are too much for this article because they all need a different treatment, but if requested, I will write further on this later on, but watch out for bits of bark falling off and whole branches dying back. 
However, it is not all plain sailing. Insects love them as much as you do. They are sweet and tasty after all. Aphid attack and scale insects are very common. In some cases, you may see a black residue taking over the plant. PICTURE G This is not fungus, as it looks, but the honeydew, or aphid juice! A good indication of an aphid attack is the amount of ants around. Ants farm the aphids and whilst they do not damage the tree themselves, they are very good at keeping the aphids eating your tree. PICTURE H, and I
I would rather try cultural methods first. Available in the post are ladybird larvae and little ladybird hotels. Have not seen them in Spain yet, but I dare say your local Garden centre could get them in for you. PICTURE J
 I personally think there are too many chemicals in use, but with a serious bought of aphids or scale insect and woolly aphid, a systemic insecticide is the answer. Spray at first sight of the things- leaf curling or pale spots on the leaves. This should control aphids and spider mites. PICTURE K. Follow manufacturers’ instructions as always, and bear in mind, these are poisonous to all sorts of other things as well.
Sometimes, and only if you have inherited trees that are too close together, mildew will attack. PICTURE L This is usually due to poor air circulation and you should consider thinning them out to one every four or so meters if not further apart. Nevertheless, if you have it, spray with a fungicide and treat as all the other fungus and bacterial attacks. Remove foliage and burn it. If you have pruned back main branches, as is sometimes necessary, paint with a fungicide to prevent disease entering the wound.
All fruit trees need water and fertilizer for production of fruit, but my advice is to read labels on fertilizers. On the back is an NPK ratio. This is the amount of N-Nitrogen, P-Phosphorous, and K-Potassium. Nitrogen is for leaf and growth; phosphorous is for fruit and balance and, Potassium is for root growth and overall health. Your trees need all of them but at different rates in the growing season. As they set flower and produce fruit, they need slightly higher Phosphorous. The rest of the year slightly higher potassium and nitrogen and, as they enter the end of the growing season, much less nitrogen so they establish strong roots over winter. Increase the health and therefore reduce the disease.
In addition, check out the other ingredients, the trace elements, metals, and calcium. These are all important and the tree will soon tell you if it is running low in iron, magnesium, or molybdenum by the different colouration of the leaves. Calcium is very important in fruit production so you will need at least two types of balanced fertiliser for a growing season and not rely too much on the bags of blue nitrogen sold at the Agricola.
Well, that will about do for now. Lots to know out there! If you have any plant pathology questions, please forward them to my email, with a picture if possible; although not impossible without. And of course any other enquiries and observations.
Cheers for now
This email address is being protected from spambots. You need JavaScript enabled to view it.

Additional information