Gardeners’ queries

Press, 8 February 1985, Page 13

Gardeners’ queries

GARDENING

by

M.Lusty

For some years my runner beans have been failure because of the disease which is apparent on the enclosed leaves. Also enclosed are leaves from pepino and apple which show similar symptoms. Other plants are affected — boysenberries, parsnips and peaches — but not to the same extent. I have sprayed with copper oxychloride but it is not effective. Diagnosis and treatment would be appreciated. “Wondering” (Chch).

The very mottled appearance of these runner bean leaves is caused by a very severe infestation of mites, which are also responsible for the speckled appearance of the pepino and the dry, brownish discolouration of the apple leaves. The boysenberries could be similarly affected. The parnsip is probably suffering from powdery mildew. It is not possible to comment on the peach trees without seeing affected parts. Mites can be controlled by spraying with a miticide, such as dicofol or tetradifon. During spells of dry weather it also helps if the foliage is wetted from time to time with a misty spray of water. Powdery mildew can be controlled by the application of dinocap. Copper oxychloride is a fungicide suitable for the control of certain diseases such as blights and leaf spots, but is ineffective against powdery mildew and will not control any insects.

This year my tomatoes are the best I have ever grown, the plants being big and healthy and with a very heavy crop of good fruit. However, in the last few days, three of them suddenly wilted and died, and on examination I found that the stem on each of them at, or just above, the ground had gone • brown and withered. In the bag attached to this letter I enclose a portion sfcm.

Would you please tell me what caused it and what I can do to avoid it happening to any others? “Puriri” (Chch).

These tomato plants are suffering from two problems — root rot and grey mould. Both have reached the stage at which the infected plants should be pulled up and destroyed. The grey mould may be regarded as secondary to the root rot, entry having been gained as a result of the injuries cause by the latter. Carry-over in the soil of the root rot is likely and sterilisation is suggested at the end of cropping. Regular spraying with benomyl or equivalent is recommended. The cause of the initial disease symptoms is generally attributable to over watering or poor drainage or both, so it would , pay to check these factors.

After growing tomatoes successfully in our glasshouse for two seasons we decided to sterilise the soil. We did this with Basamid in March, and afterwards we fertilised with horse manure

and some untreated sawdust. The soil was then dug over. Tomatoes were planted in early September. After the plants had grown well for a couple of weeks, distorted growth started to appear. We dug out the tomatoes, and in November planted grafted tomatoes. After a few weeks, the same symptoms appeared. We thought we had perhaps not watered the ground well enough after sterilising, so we flooded the glasshouse and also gave a dressing of trace elements. We then planted potatoes, which grew well initially but then started to show the same symptoms as the tomatoes. It has been suggested that the damage has been caused by a hormone spray. If this is so where would it have come from? Would removing the soil to a depth of half a metre ensure the disappearance of our problem? N.B. (Chch).

The distorted foliage apparent on the potato and tomato plants has been caused by residues of Basamid in the soil. Both these plants belong to the same family and are sensi-

five to the presence of various chemicals. Basamid is a very good soil sterilant with a very wide spectrum of control over soil-borne problems, but it must be applied strictly to proprietary recommendations to avoid residues in the soil. There is very little lateral movement of Basamid granules in the soil. For this reason it is not only essential to apply it evenly but to ensure that the soil is adequately moist at the time of application and to fully aerate it before any planting or sowing is contemplated. Thorough forking over, or the use of a rotary hoe, is advocated to assist in the process of aeration and a trial planting with an indicator plant such as beans will provide an indication of the presence or otherwise of chemical residue. There should be no need to remove the soil if the above precautions are carefully followed through.