GARDENERS’ QUERIES

Press, Volume CXII, Issue 33100, 15 December 1972, Page 13

GARDENERS’ QUERIES

The soil here does not lack lime but my gerberas do not look healthy, with yellowing of the leaves. The plot has good drainage. They do not lack water and good compost—they flower fairly well. Are gerberas lime lovers and are tea leaves of any benefit to them or in fact to any flowers? — “Keen Gardener” (Amberley). Gerberas prefer a more acid medium than many of the similar types of plants but can be grown satisfactorily in most soils. “Yellowing of the leaves” can mean one of various problems and therefore it is not possible to give you explicit advice without seeing the plants in question. Lack of nitrogen, which is not usually a major requirement of gerberas, or chlorosis induced by excessive soil alkalinity' are the most likely causes. Tea leaves should not be used in excess — rather add to the compost | heap. Enclosed some leaves I

from (1) Black currants. The colouring of the leaves is now turning into pale green and the edges curling downwards. (2) This leaf is from an apple tree, a whole branch is dying off although the remainder is still looking healthy. (3) This leaf is from another apple tree and this tree is not bearing any fruit. Our rhubarb plant is showing large purple spots on the leaves. Could you help me with your valuable information and advice?—J.J. (Christchurch). The black currants display the debilitating effects of the sap - sucking white fly. Aphides will cause a similar distortion to the foliage. Control can be achieved by spraying with maldison. The spotting on the rhubarb leaves is probably due to a leaf spot fungus which is usually of minor significance. If it becomes really prolific a copper-based spray could be used for treatment. The enclosed daphne cut-

ting is typical of my new bush. Can you diagnose the problem? The Bellis were purchased from a nursery | some months ago. A week ago I noticed three plants were affected. Now all the plants are suffering, and one has already died. I should be sorry to lose them.—J.O. (Christchurch). | Bellis are fairly commonly affected by a rust disease which can be very destructive. Badly infected plants should be pulled up promptly and burnt; all others should be sprayed with zineb. The die back on the daphne appears to be a leaf-spot disease. Copper-based sprays are sometimes effective in control. Enclosed is a branch from one of several shelter trees growing on our property. Recently it has been noticed that spots, greyish in appearance, have been developing all over the leaves and this has now given cause for concern as they seem to be completely covering each tree, with no signs of disappearing. It would be appreciated if you could detail cause and cure, and at the same time advise of the name of the trees. — “Farmer” (R.D., Christchurch). . The specimen belongs to the conifer species, Cupressus arizonica. The “spots” need not cause any alarm as they are a natural occurrence and are resin glands. The sample of tree appears perfectly healthy. I am enclosing for your inspection cuttings of a weed which appears most obstinately in my flower garden every year. It is spreading a little further every time in reappears in the spring, but does not develop any more than the cuttings show. The average height of the plant is about IBin to 2ft. As it has been

coming up in the garden for 20 years or more I should very much like to know its origin and designation.—N.S. (Chch). The plant is broomrape, a parasite, for which there is no other control at present | than diligent application to (the task of digging out completely each one. Initially, plants develop from seed just as the average plant does. The roots then seek out a host—it may be clover, Isenecia or perhaps dandelion ( —to which they become attached.. Thereafter the (young broomrape lives a j totally parasitic existence. An enormous number of seeds are liberated by individual plants so it is essential to be methodically painstaking if it is desired to get rid of them. Would it be possible for . you to publish one of your I lucid articles on summer ( pruning of cordon-trained | fruit trees. I have recently . bought a small property I which has a cordon fence of apples, and one of Omega plum, and I cannot find any information on summer pruning in the numerous gardening books j here.—G.R. (Chch). The average gardening (publication does not deal' specifically with fruit grow-, i ing, but covers everything in I a general way. For your purpose a book such as “The; Home Orchard,”, Bulletin 349, published by the Department of Agriculture and | Fisheries, is recommended, j Summer pruning should be I carried out on most dwarf .apple trees, cordon, espalier,

and similarly trained trees, and could well be applied to stone fruit, particularly apricots. Where the intention is to foster fruit bud initiation it must be done in spring time. Summer pruning as carried out in January is done primarily to restrict vigorous growth. It also helps to reduce the tendency of tip bearing on apple varieties prone to this, such as Irish Peach and Granny Smith, and promotes feathering of shoots. It may be possible to deal with this aspect of pruning on this page of “The Press” early next year. Summer pruning does not mean that as a consequence winter pruning can be dispensed with. The area round our fruit trees is full of twitch. We would like to make it into a lawn. Can you please advise on the steps to eradicate the twitch in preparation for lawn. How close is it safe to use a rotary hoe? E.C. (Ch.ch.) The methods used in the control of twitch are dependant on the intensity of the infestation, the area in which it is located (e.g. waste ground ornamentals, etc.) and the subsequent use to which the ground is to be put. In the above case dalapon and amitrole T could be used but recommendations are that they should be applied either before fruit set or after harvest; it is also advisable not to make such applications in the vicinity of trees which have been established for less than three years. In both cases one should avoid spraying foliage and trunks of the trees. Providing that the trees are well established rotary hoeing can be as close as the operator can safely handle the machine. However, irrespective of how well anchored the trees may appear to be it is preferable to pass them at a shallow cut and it may even be preferable to skim the surrounding surface with a spade particularly when there are low overhanging branches to contend with. Three years ago I purchased a Morrison Seedless and a Wheeny grapefruit, both on trifoliata graft. The Morrison Seedless bears fruit but none from the Wheeny. Should I persevere with this one?— “Gore Bay” (Cheviot). I cannot really suggest a reason why your Wheeny grapefruit does not bear fruit in the prevailing circumstances. Sometimes one comes across a plant which will not flower due to a genetical fault. Give it another year or two. Incidentally, citrus are usually budded and not grafted; a Morrison Seedless fruit will loose its characteristic if or when the Wheeny flowers as they cross pollinate very readily. A well balanced fertiliser application and moisture help to promote good fruiting of citrus. A Stauntonia hexa

phylla planted four years ago has flowered profuselyproducing, as far as I can tell, only female flowers although reference books state that both male and female flowers are borne on the same plant. What do you suggest is the reason for the lack of female flowers and could anything be done to encourage fruiting? The article on mint was interesting but not nearly long enough.—H.M. (Christchurch). Male and female flowers' 1 are borne on the same plant on Stauntonia hexaphylla. I This plant sometimes takes a; few years before it produces fruit. It does best in good, moist soil, with roots in par-! tial shade and not too exposed to wind. It is doubtful i whether the specific culture! of mint would be of special interest to more than a few people for which reason the! article was thought to be: sufficiently detailed enough. ;