GARDENERS’ QUERIES

Press, Volume CIX, Issue 32274, 17 April 1970, Page 10

GARDENERS’ QUERIES

Enclosed some very unhealthy rose leaves. I hope you can tell me the cause of the white edging round each one. This peculiarity has shown up on three old varieties of polyanthus for the last two or three seasons. However now the trouble is. appearing on several other roses as well.

Al) the usual sprays have been applied?—“Lace Edging” (Christchurch). It has not been possible to determine the nature of the white edging on the leaves but considerable numbers of mites were present on the underside. However I do not consider them to be the cause of the marginal discolouration.

I have an Azalea mollis which has become straggly and is growing over the path. Could I prune it and when would be the correct time? A.C. (Christchurch).

Azaleas can be rejuvenated by cutting them back quite severely if neces-ary although of course flowering is suspended for a year or two. Winter time should be chosen for pruning them.

Enclosed rhododendron leaves with some sort of pest which is eating the leaves: I have sprayed twice with arsenate of lead but It still persists. Could you please tell me how to combat this pest which is a complete stranger to me?— “Fed Up” (Christchurch)

1 am not familiar with the pest which you have described. If you have covered all the leaves with arsenate of lead it ought to give control over any caterpillars. The leaves do not provide a specific clue to the pest. As an alternative to shifting a cabbage tree established three years in the area being developed for a swimming pool would the ringing of the plot with rubber tyres prior to concreting be successful?— R.B. (Christchurch).

If by ringing the tree with rubber tyres you mean to suppress or confine the roots its would not be a success. When large, Cordyline australis sheds considerable amounts of leaves. Apart from this I do not think it is a good idea to have a large ; growing tree in such close ! oroximity to pool construc- [ tion.

Would It be possible to use the ash residue from incinerated carcases, as diesel oil is used to burn them? Would plants thrive on thio ash and which plants' would not tolerate it? “Inquirer” (Geraldine). The ash should be safe to use but should not be applied to acid loving plants such as heaths, rhododendrons and azaleas. As rain rapidly leaches the constituents from it ashes should not be stored in the open. Applications made to the soil should be

fully incorporated, not just: spread over the surface.

On the Illustrated cover of a book I am reading la a large spike of blue perennial about 2ft to 3ft high (“My Wilderness Blossomed”). Inside the book are references as to this perennial as Pride of Maderia, colour bluish purple. What plant is being referred to? K.M. (Blenheim).

The plsnt is Echium condicans.

Enclosed please find a potato—coultf you please tell me what is causing the trouble on it? We sprayed most of our vegetable garden with Jeyea fluid tn August, including some of the potatoes. Other potatoes were sprayed with malathion but all seem to have this trouble. It seems to be on the ones near the surface. —Amateur (Islington) Before answering your query I would like to draw attention to a mistaken conception about sprays of which you and many other gardeners may not be aware. Apart from knowing what pests and diseases must be controlled at a certain time of the year and selecting the appropriate pesticide(s) to control, them, it must be

realised that the residual properties of these materials last only for a certain time. The majority of them are persistent for less than three weeks, and it is therefore necessary to repeat most spraying every fortnight or so at times when pests are very prevalent, or perhaps until good control has been achieved. One spraying during the season will give control for a short time only and cannot be expected to give protection for the rest of the season however much this may be desirable. Your potato has been attacked by the potato tuber moth lavae which has been particularly • prevalent this season. The

moth usually lays eggs from November onwards and potatoes near the surface are particularly vulnerable. Malathion can give some control but probably the best method of preventing inroads of this pest into the tuber is by adequate moulding of the plants.

Enclosed leaves from Albany Surprise grape. This is only Its third year and it hasn’t yet fruited. Leaves appeared normal previously but exhibited these peculiarities quite early last spring. Some tomatoes and beans growing within 10 feet of the grape display similar symptoms. At first I thought some hormone spray may have drifted from somewhere though I had not used any.— P.S. (Christchurch.)

Your Initial inference was correct. The trouble has been caused by hormone spray. Grapes, tomatoes and beans are amongst the most susceptible of all crops and the lightest drift can affect them. Where drift has come in contact with desirable plants they should be swabbed with water immediately. Hormone sprays should not be used when there is the slightest chance of drift. Slightly affected plants will grow out of it in time. It is better for the plant to become well established rather than rushing it into fruiting.

Could you. answer the following. 1. Apple—an intereating type, crisp, Juicy, tart, mellowing with age, umbrella shaped tree, over 40 years old. Could you name the variety? 2. Weed —our name is parsnip weed because the well-grown root is not unlike a parsnip root Some leaves are rounder than enclosed; flowers are mauve (Bluebell shaped) and on long stalks; the roots can grow 10 inches long and thicker than a man’s tliumb. Name please. 3. Control for this weed and oxalis which is growing in open ground within the drip line of trees and shruhs and are entwined with shrub roots. R.H. (Barfield).

Thank you for your precise notes and the good specimens sent—this sort of assistance is most helpful in providing satisfactory answers. The apple is almost certainly a Ribston pippin, a seedling which gave us the now more familiar Cox’s Orange Pippin. The socalled weed eould be called a garden escape; it is Campanula rapunculoides. There is no safe control for oxalis growing in the vicinity of trees and shrubs. You would have to experiment for the control of the campanula.