GARDENERS’ QUERIES

Press, Volume CX, Issue 32381, 21 August 1970, Page 8

GARDENERS’ QUERIES

Today I found just these ; \ two new shoots on my Cor- : nubia rhododendron (speci- : mens enclosed) although there is evidence of some crinkling on other leaves. Recently fowl manure was spread over the entire bed in which the rhododendron ■ is growing. Could this have a bad effect? How could Philadelphus be pruned?— E.W. (Chch). The symptoms are those of frost damage which appears ! to have caused considerable and variable damage to numerous rhododendrons and ' camellias. Fresh manure can cause damage particularly to young foliage and seedlings : and for this reason it is always advocated that only decomposed material should , be used.' However, in this case the damage has not ■ ensued from the application <rf manure. Philadelphus or 1 mock orange should be pruned immediately after flowering if required. It will regenerate rapidly and old bushes can therefore be cut back very hard without hesitation. Reason for malformation of rhodendrom leaves. S.W. (Chch). i Frost damage see previ- . ous answer. Enclosed diseased hedge plant and several which I have died at intervals in different parts of a long hedge and about six months later their neighbours start to look sick. ' The rhododendron is one of , several lovely specimens in this old garden. One in par- < ticular, about 12ft high, has died completely in parts and all over the leaves I seem to be turning brown from the tips and dropping. Some of the younger : bushes look like being affected also.—S.P. (Halswell). ! The hedge plant, Olearia poniculata, is prone to this ! sudden die back and it usu-

ally occurs in heavier and wetter soils. There is no means of saving badly affected plants as far as I know. It is more suitable for lighter land and coastal planting. Avoid very deep planting and hoeing too close to the roots. The story attached to the rhododendrons is a different one. Here evidence of scale Infestations has been noted and mites have been present, and some j are still on the leaves; lichens, etc., have eovered parts of the branches and a thin deposit can be noted on the leaves. These things induce ill-thrift in any plant and together their effects can be disastrous. Spray thoroughly with white oil and repeat in about one month. Towards the end of this month apply a fertiliser mixture of 1;2:1 by volume of sulphate of ammonia, superphosphate and sulphate of potash, respectively, of up to 51b for your bigger plants. Straggly plants or those which have grown too large can be safely cut back and they will bush up in a surprisingly short time, although, of course, flowering will be curtailed for two or three years. In my glasshouse last season a lot of my tomatoes never ripened properly. The first two trusses had a lot of green blotches over them.—A.H. (North Beach). It would seem very likely that your problem is one of nutrition, most probably a case of potash deficiency. Glasshouse soils must be replenished if they are to continue to be productive. Soil sterilisation is generally advisable every few years if intensive cropping is maintained. It may be worthwhile having a soil test made.

Enclosed a leaf from a plant in our garden. It appears to grow from a bean-like seed, to about 2ft high.—(Akaroa).' This is acanthus. In recent years I have failed to keep foliage of main crop potatoes (Chippewa) healthy. The tops curl and turn yellow, finally drying off. The early crop does not become affected in the same way. Your advice would be appreciated.— B. (Chch). You do not state at which stages the tops begin to yellow—a natural occurrence once the crop has matured in late summer to early autumn. It could also be virus infection but either more details or preferably a plant would be needed before further comment can be made. Chippewa is usually considered more as a second early rather than a main crop potato. Always use good quality seed. Enclosed lemon leaves from two trees growing side by side. They have had all the recommended sprays and manures. The leaves yellow and fall. What is the remedy?—W.K. (Chch). The leaves individually indicate various problems including spray damage and the presence now, or previously, of aphides or scales from the sooty mould noticeable. Suggestions are: attention to spraying ensuring proper mixing using dilution recommended by the manu-

facturers of the product being used: investigations into whether frost is not causing some harm and also whether the soil around the plant is too dry.

Could you please identify this big seed pod for me? It comes from a climbing plant that we have had growing here for sometime.—N.T. (Christchurch). The fruit comes from a Brazilian native evergreen vine, Araujia sericofera, once :alled Physianthus albens. It

is also known as the cruel plant: or moth plant as it traps moths. Flowers are white and the fruit is uncommonly large. Could you please tell me the cause and remedy for walnuts turning black and falling before maturing? The trees are over 30 years old. “Walnuts.” (Blenheim).

Your walnuts are almost jertainly suffering from ittack of bacterial blight which can manifest itself on rt>ung and old walnut trees

alike. Effective control of large trees is almost impossible but the smaller ones can be dealt with providing one has a really good spraying unit. A mixture of Bordeaux and winter oil is used: Bozs copper sulphate to 3}ozs hydrated lime plus 21 fluid ounces white oil mixed in 10 gallons of water. The disease is carried over on infected

buds and trees which have been severely affected in previous years should be sprayed thrice: When about half the terminal buds are open: Just before most of the female flowers are fully open; When the young nuts are about the size of moth balls.

Could you please advise what is causing leaves of my rhododendrons to turn brown at the edges? Even the new shoots at the top of the plant have started to discolour.—G.A. (Chch). Your specimens were too poor for me to diagnose the trouble with certainty. It is possible that your plants are in too exposed a position and also are dry at the roots. No amount of fertilisers will be of any benefit in such circumstances.

Enclosed samples of hydrangeas. The disease showed up in early summer last year and is now spreading to other hydrangeas. C.A. (Chch).

This is not a disease but a pest problem, one of which is very prevalent indeed. Hydrangeas are susceptible to scale insect attacks, in this case the cottony cushion scale, control for which is white oil. If not controlled these pests can kill the plants and where infestation is really heavy the worst should be cut out and buriit.