Gardeners’ queries

Press, 15 May 1981, Page 10

Gardeners’ queries

Could you please tell me what is wrong with the enclosed geraniums? I keep them in an unheated glasshouse. Some of the plants have developed a black- fungus on the stems and leaves which is more noticeable on the fancy leaved ones. I have tried spraying with Zineb and Captan to no avail. J.F. (Chch). The blackish coating of the stems and the discolouration of the leaves has been caused by the presence of "honey dew” exuded by certain insects such as aphids which are feeding on the foliage. The sooty mould lives on this exudation. Elimination of the insects will completely control the situation, and an application of Acephate is suggested for this purpose.

I enclose two shrub samples for identification. 1) This one is about ten feet tall at present and has blueish flowers. The leaves are rather a pale greyish-green and apart from wishing to know its name, I wonder whether it has something the matter with it? 2) A nice little conifer with rather flatfish leaves. Could you also please give some information about how high they grow and if they need attention such as pruning? H.N. (Chch). l)The plant with the greyish leaves and lavender coloured flowers is called Abutilon vitifol-

iuni; variation in flower colour exists, and there is also a white form. This species can grow into a small tree exceeding 4.5 m tall, but, like all abutilon, it is responsive to hard annual pruning which will help to keep it bushy. The foliage is naturally downy and the colour is tj’pical of this shrub. 2) The conifer is Thujopsis dolobrata "Nana,” which requires no attention and has an ultimate height of around 1 to 1.25 m, with a spread of similar dimensions; it is slow growing.

Could you please identify the enclosed weed from my lawn and x suggest a suitable spray to get rid of it? "Interested.” (Chch). The weed is hydrocotyl which has become exceedingly invasive in local lawns. Unfortunately, means of control without also damaging if not destroying the lawn in the process are at present very limited, the only herbicide having shown reasonable effectiveness being Picloram. Picloram, which is available as a combination containing either 2,4,5-T or- 2,4,D, is currently only sold in large containers. Any comments on the state of the black mulberry leaves, enclosed? Tbe disease is not new and is less prominent than in some seasons. The tree fruits abundantly, but half the crop or more falls prematurely. P 5. (Chch).

The trouble prevailing on this mulberry is a leaf spotting fungus. This disease can at times cause complete defoliation but is usually only prominent under very wet seasons. Suggested control is the application of copper based material at bud movement and again a fortnight later; in very wet seasons, a third spray at weaker strength should be applied after fruit set. Where the disease has been evident fallen leaves should be gathered up and disposed of. Mulberry trees do not like exposure to wind’s, particularly cold ones, and it is possible that fruit drop is associated with this factor; dryness at the roots could also be a contributory factor.

Is there any treatment I can give this weed, which bas appeared in the lawn? It has a little yellow flower, and bas quite a long root. If necessary I am prepared to use Glyphosate to eradicate it. W.D. (Chch). The weed in vour lawn Is Oxalis corniculata, another of those weeds which is not the easiest-to get rid of once established in a fine lawn. Picloram has been successful when used in the course of treating Hydrocotyl, and the combination of MCPA and MCPP has’been quite good when repeated. Weeds in lawns can be kept .well under control by good management, which includes regular feeding and

attention to mowing procedure. Glyphosate is particularly recommended for grass control of all kinds, and if you were to apply this to the lawn the end result would be an area of bare ground. Please could you tell me what is wrong with this bean plant? It has had every care and attention, but there has .been only one crop off the whole row. P.W. (St Andrews). The crop residue was too dried up to be able to make more than a guess as to the cause of the trouble which has afflicted this bean crop. It is important when growing dwarf beans to ensure that adequate air circulation is possible particularly in heavy or poorly drained soil. Double rows, 150 mm apart with 10 to 150 mm between plants, and not less than 450 mm between the double rows provides a good basis to work on. All beans are sensitive to wind and dryness. Diseased plants should not be put on the compost heap. Enclosed is a specimen of my Daphne which bas grown and flowered well for the last ten or more years. It now appears to be dying or is already dead from some cause. I ahi anxious to save another bushi which is growing about four feet away and would like to know what to do. A.G. (Amberley). There is still life in the Daphne bush, and it is worth persevering

with it for a little longer. Cut the plant fairly hard back leaving, at least three to four 'buds on each stem. Stems more than 10mm in diameter should have their ‘ cut ends covered with a suitable sealant. Spray the whole plant with copper Oxychloride on completion of pruning. Spring time will give you indication whether or not to retain the shrub.

Please find enclosed some samples of a standard rose which was transplanted to its present position two years ago. In its previous position it suffered from lack of water. It has performed very poorly against a healthy rose six feet away, planted at the same time. Is there anything that I can do to bring it right? W.B. (Chch).

Die-back caused by the bacterial disease known as blast is responsible for the dead wood and sickly colour of much of the foliage. Treatment should consist of cutting well back all dead, diseased and spindly wood, and following this up with a very thorough application of Bordeaux mixture or copper Oxychloride. It ’ was noticeable that previous pruning , was made well short of bud or leaf - junctions; treatment of this nature tends to promote die-back to which all roses are prone, to some very muchmore so than others. Pruning cuts should be made to just above a biid.