Gardeners’ queries

Press, 14 February 1986, Page 14

Gardeners’ queries

We have increasingly large areas of dead lawn; these appear on the high spot in a basically flat lawn. Is it possible to distinguish between grass grub attack and viral infection and what are the appropriate treatments, please? G.B. (Chch).

It is suspected that this problem is not one of either pest or disease, but dryness. However, it is impossible to be sure without inspection. A common occurrence with uneven lawns is that they tend to develop hard dry areas around the high spots. This is caused predominantly by the mower constantly removing more grass in such places, packing down the soil and thus inducing moisture run-off instead of penetration. Coring and levelling off should alleviate this problem. Evidence of the presence of grassgrub is indicated by the presence of holes in the ground, soil casts, and particularly loose grass which can almost be rolled up like a mat. Disease in grasses is almost invariably displayed by off-colour plants.

I have this silver birch tree which for the past two years has had aphids on IL

They drop a sticky substance and there is also a black substance to be found on the lower branches, and leaves. In the autumn, the leaves turn brown instead of the usual gold before dropping off. What can be done about all this? F.F. (Chch).

Aphids are a common pest of silver birches, sometimes seeming to smother one tree while leaving others almost entirely alone. They exude honey dew, the sticky substance which sometimes almost splashes off trees that are heavily infested by these insects. The blackening of foliage and limbs is caused by a mould fungus which thrives on the sticky exudation. Control of large trees in the home garden is a virtual impossibility but small ones could be sprayed witih maldison.

I am a keen gardener in great sorrow over an area of very sick plants in rank soil. Time and again I have replanted and renewed the soil with good compost Just when they show signs of progressing, the same old situation develops again. I have tried to persuade my neighbour, an avid user of

all sprays, to keep away from my garden. Is there anything I can do? J.S. (Chch).

Examination of the plant samples enclosed has failed to indicate that their appearance is due to contamination by herbicides. The plants certainly do not suggest that they are flourishing but there is no clear indication of what the cause may be. Virus, thrips, aphids, mites, poor drainage, and impoverished soil are some of the most likely leads to follow up. It is another of those cases where a site inspection may provide the clue(s) and answer. I have recently developed blisters on my hands which are of some concern. Mention has been made to me that working amongst parsnips can cause this problem. I have never heard or read of any warning in this direction and would be pleased if you would comment J.H. (Chch). It is not uncommon for blisters of a seemingly innocuous nature to develop on the skin of some people who are much in contact with parsnip leaves, it can also apply to some other plants

belonging to the same family. This bullous dermatitis only develops if the skin is subsequently exposed to sunlight. It does not appear to be regarded as a serious problem. If you are allergic it would seem that contact should either be avoided or the skin covered. , Identification of this plant and its use would be appreciated. It grows wild and is now seen as a crop. “Curious” (Rangiora). 1 The plant appears to be dill, a herb which is very similar to fennel. The latter is a perennial whereas the former is an annual. Dill is used for flavouring sauces and soups, as an accompaniment to fish, in pickling cucumbers, with salads, and in a number of other ways. Please find enclosed a sample of tree which is close to the end of its flowering now. It is scented and about April the fluted section below the blossom becomes red and fleshy with a dark blue collar. Most spectacular. Could you name it, please? J.P. (Chch). The specimen is from Clerodendron fargesii.