Gardeners’ Queries...

Press, Volume C, Issue 29679, 24 November 1961, Page 10

Gardeners’ Queries...

What is the matter with my rhododendron? All the leaves are going brown and scorched around the edge, like the sample enclosed. The plant flowered last year, and has many buds this year, but I am afraid they are not very healthy looking. '(“Gardener,” Waimate.) Tills type of damage may result from several causes. One of the commonest is exposure to draughty conditions, but it is difficult to be certain without knowing more about the conditions under which the plant grows. Leaf scorch may also result when surface-rooting plants nearby compete for moisture with your rhododendron. I do not think the trouble is caused by fungus attack; it is almost certainly physiological in origin. Ensure that the plants are sheltered and obtain adequate moisture. Plant and disease for identification. (Mrs G.M., Tinwald.) Please send me an adequate example to examine. Your specimen was too small and incomplete. I have two cherry trees 12 to 15 years old, and 10 to 15 feet tall. They blossom freely each year, but when the fruit is about as large as my little finger nail it all falls off. I am told that the flowers have not been fertilised, but can a flower which is not fertilised form any fruit at all? I’m afraid that 1 cannot name the variety—and 1 think both trees are the same. (“Fruitless,” Christchurch; also T.J.R., Dromore.) This trouble is definitely due to lack of fertilisation. Cherries are rather tricky in their fertilisation requirements. No cherry will self-pollinate, and cherries of the same variety will not cross-pollinate each other. The various varieties are divided into 12 groups, and a cherry which belongs to one group will only set fruit when pollinated by a variety belonging to another. However, there are a few varieties known as “universal donors,” which will cross-poliinate any other cherry. In your case, when the variety is not known, it would be best to plant one of these as a pollinator. Noir de Guben is one which is not too difficult to obtain

The fruit which drops is only the unfertilised ovary and receptacle, which is always formed ready for pollination to occur. Some plants do set fruit without fertilisation. The cucumber is a good example, for it is normal in this plant. I enclose a leaf from my Magnolia gran difl or a. It was only planted this season, but the leaves are all becoming spotty, and falling off. It gets the sun after midday, and receives a good soak about once a. week with the rest of the garden. New leaves which develop soon turn as the specimen. (Mrs A., Fendalton.) Magnolia grandiflora frequently develops these symptoms in the young stage when exposed to conditions which are hot and dry. At the Lincoln College nursery we have found it necessary to grow this plant in the shade house until two or three years, old to overcome leaf drop. Provide your plant with shelter from sun atnd wind, and make sure that it does not dry out at the root. Your query about polyanthus was answered for another correspondent on this page last week. My garden and surrounds Is all sand, and 1 wish to get rid of a healthy crop of flowering ice-plant. The remedy perplexes me. The

strip to remove is fast encroaching over the lawn. (F.H.A., New Brighton.) There should be no difficulty in controlling ice-plant with a hoe. Lf you cut the plant at the limit at which you wish it to go, and then run the hoe under the plant at ground level you will be able to remove it in a sheet. Although I have not heard of hormones being recommended for the control of this plant, I have no doubt that 2.4. D or M.C.P.A.. the weedkillers for use on lawns, would control ice-plant. This would enable you to kill off the plant without harming your lawn. I sprayed my peach and nectarine trees for peach leaf curl this year, but unfortunately they seem to be as badly attacked as ever. To add insult to injury, one large branch of peach has decided to die. Why should a part only do this? I enclose a sprig from the dying part for examination. (E.S.C., Hills road.) The sample you sent was infected by a different trouble—stone fruit blast. The typical symptoms of this disease are dying back of the shoots—often quite large—accompanied by discolouration of the attacked wood The characteristic attack is usually a branch at a time, rather than the whole tree. Unfortunately there is no control once the tree has become infected. It may be possible to prune out the infected part. Cuts should be at least six inches below the discoloured tissue. I have been growing tulips for several years, and each year they are getting gradually worse. The trouble is apparent when they are flowering. Dry spots appear and some blooms take on a transparent look, resulting in the blooms lasting only a short time. I have dug the bulbs each year and planted them deep (Bin), but the trouble still persists. The bulbs appear clean and healthy-looking, and the leaves also, the trouble being only associated with the flowers. (1.8., Blenheim.) In some respects this trouble sounds like tulip “fire,” but in other respects it does not. The petal damage you describe could be due to this fungus, but the leaf and bulb are usually attacked, too. It may be necessary to remove the skin on the bulb to see the diseased areas. Deep planting is usually a good preventative for ‘•fire,” since diseased bulbs rot away before they emerge through the ground, but if bulbs are replanted on infected ground infection is still liable despite this precaution. Although I suspect “fire” as the trouble, I cannot be sure without exam-, ining specimens. Repeated sprays of Dithane at 10-day intervals from late August or September onwards is the standard spray control for this disease. I have two Black Hamburg grapevines in a glasshouse which have borne well. Last year and this they have produced tremendous growth in the laterals. How can I check this? (D.E.* To tar a road, Riccarton.) The normal method of stopping laterals at two leaves past the bunch is a method of checking vigour. This stopping will,, of course, induce the formation of side growths on the laterals and these should be stopped at the first leaf. It is too late to carry out this procedure this year, but you should bear it in mind for next. Have your vines any access to rich soil? This may be giving rise to the unbalanced growth.