Gardeners’ queries

Press, 25 February 1977, Page 10

Gardeners’ queries

What can we do to prevent rust from destroying our broad beans? They finished up with black spots on the leaves and then these dropped off leaving only the beans and stalks. Also could you name this weed which we have coming up in many places?—A.D. (Christchurch). There are two fairly common diseases of broad beans which may appear similar and which have similar symptoms in the advanced stage—namely, that infected plants may shed their leaves. The diseases, both fungoid, are rust and chocolate spot. It is not possibly to rely on the description to decide which of the two is prevalent. In both cases crop refuse should be gathered up and burnt and spraying should begin before the disease becomes evident. For chocolate spot treatment should commence in winter applying benlate or thiram at two to three weekly intervals. Zineb is recommended for rust control and this should be applied prior to flowering at the intervals mentioned for chocolate spot. The weed is a young specimen of Euphorbia.

I have a 10ft Viburnum burkwoodii in too confined a space. Would it be possible to shift it, and if so, how would I go about wrenching it?— M.P. (Christchurch).

Viburnnums can be shifted without great trouble. Wrenching should be done now. Size of root ball retained will depend on soil, root development and manpower available. It is always sound policy to retain the maximum amount of soil and roots on any subject which is being moved to another site. For a shrub of the size and type mentioned a minimum of ,45m radius of soil and ,55m depth should be retained if possible. Cut straight down right around and beneath. the plant severing the extending roots cleanly: replace the soil and water well. Some pruning back may be desirable to reduce moisture loss through the foliage. I have seed of a miniature calla which I would like to grow. Could you advise when and where to sow, etc? Also where they grow best? I also have seed of a red Kaka Beak; can I get a shrub by sowing seed and will the seed from my African violets germinate? — S.G. (Christchurch).

Kaka Beak, Ciianthus puniceus, can be grown from seed or from cuttings taken now. Seed is best soaked in warm water over night to hasten germination. Another way of promoting this is to chip the seed coat. Cuttings should be 15;20cm long. Callas like a rich soil and do best in a sunny position. Soil aciditv has some influence on intensity of colour. Variations in colour are likely from seed saved from garden plants but this can be overcome by annual selectivity. The seed can be sown in the open ground or in boxes if desired. No special treatment is neces-

sary. African violets grown ,in the house generally require hand pollination to obtain seed as this job is usually done by insects. Viable named seed can be bought and plants can be alternatively raised from cuttings.

Tomatoes in my glasshouse are covered in a small white flying insect which rises in a cloud when the plant is disturbed. The leaves and fruit are also covered in a black powdery dust. I have used Tomato Dust, Bordeaux, fly spray, and a mild solution of Jeyes fluid and none of these appear to have any effect. Could you identify the pest and give me some advice on the eradication of it?— A.M. (Hokitika). The insect is white fly, a pest which has become a major problem now in glasshouses throughout the country; in fact, it has been described as having reached epidemic proportions. Apart from their sap sucking mode of feeding, these insects also secrete honeydew which attracts sooty mould — the “black dust” referred to in the query. None of the substances mentioned will give the slightest control. Further, it is not recommended that tomatoes be subjected to experimentation in this way as some materials of doubtful value can be most damaging to these (and other) sensitive plants. At the present time a number of controls are being further evaluated in an endeavour to obtain more fully satisfactory results. The use of lannate has given reasonable control, but as with all other materials that have been recommended until now, repeated applications are necessary. Maldison is the only other material available for home garden use, and although resistance is suspected, at least three sprays at threeday intervals can give at least some control; good coverage is essential. It is proposed to include a detailed article on white fly in the near future.

Samples enclosed are typical of the leaves and fruit of our pear trees. The leaves started showing signs of distortion early in December. Now, as the fruit comes to maturity every pear is affected. The trees have been sprayed only with malathion and winter oil.—B.C. (Christchurch).

Definite existence of pear slug and leaf roller caterpillar account for the furrowed lines and dark “mottling” of the fruit and leaves, respectively. There is also a suggestion of fireblight by virtue of blackened leaves and rotted fruit, but this requires further evidence to substantiate it. Control for the insect pests consists of spraying with carbaryl at fortnightly intervals from about late November until February. Sprays applied were too early in the season to have any influence on problems current. Fireblight necessitates cutting back of shoots to at least 15cm below visible signs of disease, a task which should be undertaken now.