Garden queries

Press, 23 September 1988, Page 10

Garden queries

Could you please tell me what the grey substance is on the enclosed cauliflower, what the orange marks are on the silver beet, and how to control both. I have noticed similar orange on my newly-sown lawn which is not doing too well. Also, could you tell me how to collect the seeds of carrots and lettuce? T. M. (Chch). Cabbage aphids are infesting the cauliflower. The meally, greyish, powdery substance which surrounds these pests can create the impression that the problem is perhaps disease-related. There are several materials which will give good control of aphids, including piriphosmethyl I permethrin, acephate and maldison. The orange spotting on

the silver beet leaves is rust fungi, a not uncommon disease of this plant which can render it unfit for consumption unless it is checked. Badly damaged leaves should be entirely removed and remaining plants should be promptly sprayed with zineb. Following such aplication requires a 14 day waiting period. Only the very best plants should be selected if seed is to be saved, health being of paramount importance. As the seed heads begin to mature they should be enclosed in a polythene bag which will prevent the seed from dropping. It can then be dried, the chaff removed and the seed packeted, labelled and held until required. Grass species are also suscept-

ible to rust infection, but this could well be mistaken for one or two other fungal diseases of turf. It would be necessary to see the infected grass before commenting further. In the meantime it would be worth while feeding the area with an appropriate fertiliser mix at the rate of 30g per square metre.

Could you please identify the cause of the black spotting the leaves of my hoya? About half of the leaves are affected and these I have removed. Apart from that the plant looks healthy. Is there a preventative or cure for this complaint? R. L. (Chch). The exact cause of the spotting of the leaves is not known but you should consider the cultural attention given to your plant. Although direct sunlight is not necessary for these plants, a well lit position is desirable. During active growth do not allow it to become dry. This also applies at other times when, however, considerably less water is needed. Periodic feeding throughout the growing season can be beneficial. It is not considered necessary to remove the leaves which could be detrimental to the vigour of the plant.

A lot of the wood of my apple trees, most of which are pretty old have these orange pimples on them like the samples. The trees seem to look all right when they are in leaf, although I did notice some of the leaves did not look just right in their green colour, and a few shoots seem to peel their bark. Is this something to be concerned about? “Doubtful” (Chch). The pinkish, fruitifica-

tions noted on the branches of this apple tree belong to a fungus known as coral spot. This canker producing disease attacks a wide range of plants and is locally very prevalent on red currant bushes. All affected wood should be cut well back to healthy parts and the exposed areas sealed. Prunings should be promptly burned, and not left lying around. This disease, although not regarded as serious, is classed as a wound parasite and as such can cause wilting and die-back.

I am worried about one of my 30-year-old camellias. The leaves are as healthy as can be, but the flowers get a bluish edging which later turns black. With all the other camellias here the frost leaves brown stains on the flowers so I fee! that this one has got a blight. “Camellia” (Chch). Examination of the camellia flower suggests that very close and numerous petals may be conducive to the problem of petal blight occurring on this particular one. Camellias vary considerably in their resistance to climatic variability, and are often more vulnerable when under stress such as suffering from a lack of moisture. Spraying with captan, could prove helpful. All affected flowers should be gathered and destroyed. Gardeners’ Queries should be sent directly to Mr Mike Lusty, 56 Wayside Avenue, Christchurch 5. Samples should be separately wrapped in a plastic bag with air holes. Provide representative, good-sized samples, and your name and address. A nom-de-plume can be used for publication.