Gardeners’ queries

Press, 27 April 1984, Page 9

Gardeners’ queries

GARDENING

by

M. Lusty

Eaclosed are samples of Cliffs Kidney potatoes and also grubs that are apparently responsible for the damage. We have had this problem for more than 10 years. I have tried diazinon repeatedly, using it at different times of the season but these creatures persist, more so on the late potatoes. The last two years the onions have also been affected, the roots destroyed starting about mid-January

This Liriodendron tulipifera “Aureomarginaturn,” is a fine young specimen of the variegated form of the Tulip Tree growing in a local garden. The species grows into a beautiful big tree of considerable proportions under suitable conditions. A mature specimen is growing in the Christchurch Botanic Gardens, opposite the entrance to the Robert McDougall Art Gallery. The variegated form does not grow nearly as large as the species. It tends to display some variability in the intensity of the yellow colouring of the leaf margins. Although very hardy these trees do best in a sheltered position and in good soil. With the exception of the fastigiated form, they are not the best choice for small sections, despite their interesting leaf form, flowers, and autumn foliage.

and becoming more obvious as the year goes on. — I.C. (Chch). The potatoes appear to have been eaten by slugs as suggested by the’ holes in them. Tuber moth caterpillar have also left their trade mark to a lesser degree. The grubs are millipedes which probably got into the tubers to feed through the inititial inroads made by other pests. Millipedes are not so easily controlled but the old tried and proven method of trapping them in a buried tin full of potato peelings is still worth using. These creatures do feed on the root systems of a large variety of plants and could therefore be responsible for the damage to your onions. There are proprietary slug baits available, and tuber moth can be controlled by spraying with orthene; attention should also be paid to the thoroughness of earthing up or moulding the potato plants.

Could you please advise me what is wrong with my walnuts? Both this year and last year they have been like this. There would have been less than 75 per cent any good. — J.R. (Chch).

A similar query was answered recently with the suggestion that the damage could have been caused by codling moth. However, alternative possibilities have been forthcoming and various aspects of the condition of the nuts has aroused wider interest about the origin of the trouble. It would be most appreciated if you could send in further samples together with such information as to when the damage was first noticed and whether the fruit was gathered from the ground in the state in which they are sent.

I have been recommended to use benlate for remedies for the bugs on my plants, which are enclosed. Perhaps I should have continued with regular weekly doses, and maybe you have the answer to the problems? — E.D. (Ashburton No. 4 RD.). It has not been possible to identify either the buds or the problem associated with them. However,- the gerbera leaves

displayed very advanced symptoms of white rust, a disease which is not easy to control once it has become well established. There are several views on the best form of control including the destruction of badly infested plants. Alternative’ treatment is to strip off the old leaves and to maintain persistent control by spraying. The best fungicides are triforine, maneb, and zineb. If either of the latter two are used they should be applied at double the recommended strength. Enclosed herewith a cutting of Rhododendron ‘Cornubia.’ The plant is several years old, flowered beautifully the first year and poorly since. About Five years ago a lot of branches died, and other rhododendrons have behaved similarly to the sample, yet camellias thrive. — V.L. (Rangiora). The only inference that it has been possible to draw from the specimen of rhododendron is that it is from a very sick plant, probably with a dying root system. Although rhododendrons and camellias thrive under similar general conditions the former appear to be far more sensitive to less than adequate situations, perhaps because of their symbiotic relationship with mycorrhizal fungi. Poor drainage, too-alka-line soil, too dry at the roots, and over exposure to sun and wind, together with too deen

planting are common faults which have resulted in the loss of many garden rhododendrons.

Tbe enclosed leaves are from a magnolia tree which was badly hit by frost two years ago when in full bloom. It did not flower last year. As it is a young tree I do not want to prune any branches off it as it is a good size and a nice shape. — E.H. (Chch).

Apart from the presence of leaf spot, not uncommon on some magnolias, it appears as though some insect with a rasping feeding habit was prevalent on the foliage at some time. While the infloresence of late winter and early spring flowering plants is susceptible to frost damage, the plants themselves are generally hardy enough not to suffer other than perhaps superficial damage from which they soon recover. Triforine or zineb could be used for leaf spot control and the likes of acephate for insects. Magnolias are responsive to judicious pruning and can be trained and shaped if necessary.

Gardeners’ Queries should be sent directly to Mr M. Lusty, From May 6 the address will be 56 Wayside Avenue, Christchurch 5. Samples should be well wrapped, contained in a plastic bag with air holes. Wrap them separately, and provide representative, good-sized samples.