Gardeners’ queries

Press, 17 February 1978, Page 8

Gardeners’ queries

Please find enclosed a sample of my three-year-old citrus tree which seems to be curling up although otherwise healthy looking. As with this year, the two preceding years have shown plenty of flowers but no fruit has finally eventuated. It Is in a sunny area and It is sheltered and has been protected from the frost. Your analysis of what is wrong would be appreciated. Whilst writing would you tell me the best time to re-position my three-year-old hydrangeas and azaleas. Also could you give me a cure for the discoloured roses enclosed.—W.T. (Chch). The citrus is suffering from both scale insects and mites. These pests are quite common on these trees and periodic spraying is fully recommended to keep them under control. Apply summer oil or one of the alternative "all seasons” oils together with kelthane. As there were numerous pests and diseases on the rose leaves, one of the proprietary rose sprays should be applied. Such preparations contain a variety of chemicals which control the usual problems associated with roses. Autumn is the best time to transplant both shrubs. Wrench them about two months prior to shifting them. Failure of flowers to develop into fruit is generally caused by lack of pollination. This can be attributed to a number of reasons including insufficient nutrients, lack of moisture and unfavourable site conditions. Citrus trees cannot tolerate cold, exposed situations and as this may be one of the more obvious causes for failure to set fruit it would be advisable to check them out.

Enclosed are two pear* from our Bon Ch retian tree. The tree has appeared very healthy, has made good growth and for the first time has a good crop. Suddenly it changed as per sample. It was sprayed with Captan, and Pyrox for slugs. The other pear tree is showing signs of infection also.—M.A. (Diamond Harbour).

Fire blight is the predominating affliction of your pear tree but symptoms of black spot were also apparent on the fruit. Fire blight is a bacterial disease and the major form of control, as far as home garden trees are concerned, is to remove the source of infection. This involves cutting out all infected shoots and cankers at least 200 mm below the last visible signs of infection. Tools used in the operation should be sterilised In 1:50 formalin solution to avoid transferring the disease to healthy growth and all pruning cuts should be covered with a suitable sealant. Excessive pruning in the Winter should be avoided. Captan is ineffective against fire blight but a weak Bordeaux mixture applied at five-day intervals during blossoming is of some value. Pears are somewhat slower to come in to full cropping than apples and it is essential to provide a suitable pollinator close by. Cross pol-

llnators for William’s Bon Chretlan include Beurre Bose, Conference and Winter Nelis.

Could you please tell mo what is wrong with my pot plants? The little leaf is from a hanging plant which is in full bloom now. Could I still save the plants? Also all the plants in a big bottle died. They have done very well for a year, but once a month I gave It rain water. Would this have been the cause of the sickness? When I put the plants in I did It In sterilised soil. I still have some pot plants (healthy) left, so hope to save them. I bought house plant Insect spray (Yates) but does not seem to help.—L.M. (S R.D., Chch).

Your pot plants are suffering from the effects of a severe infestation of mites while some scale insects were also noticeable on the Aralia. A combination spray of summer oil and Kelthane Is recommended and should be repeated within three weeks. The rain water would prove most beneficial to the plants in the bottle. The use of sterilised soil as a rooting medium is a good Idea as it would be weed free. It is possible that the plants may have been over-watered.

The enclosed apple* are from a Cox's Orange. They are badly cracked and are all falling off. The crop was very poor and now looks as if if will be nil.—C.L. (Chch).

The symptoms displayed by the fruit of this Cox’s Orange are typical of a disease which is generally known as blister disease and also apple cracking. It predominates on trees growing in poor soil and those which lack vigour. The only cure is to boost development through Increased feeding and ensure that the tree receives plenty of water during the drier months. There is considerable varietal susceptibility. Cox’s Orange being one of those which is more prone to the problem than others.

We would appreciate identification of tho enclosed specimen. It i* a climbing vine which was found In a patch of bush high up on Banks Peninsula. A very prolific splash of colour, very dense flowers.—R.J. (Chch). The climber is Tropaeolum speclosum, commonly known as Flame Nasturtium or Scotch Flame Creeper. It is not a native but comes from Chile. This plant must be regarded as a “garden escape” and is not uncommon on the Peninsula. It is a very attractive climber which can be grown from seed.

Ceuld vou tell me what Is wrong with this tree. It seems to be dying. It has been very healthy. Almost two months ago I was advised to sprinkle Prefix around the orass at th* roe* of * H ls shrub to stop the latter from growing. What ean be done to brine the shrub back to normal.—M.S. (Chch).

It is possible that the action of Prefix was responsible for the current condition of your hebe. The samples examined were either dead or dying but there was no evidence to suggest that the use of the weedkiller was responsible. Prefix can be applied quite safely around most trees, shrubs, fruiting stock and even roses by means of careful application. It Is not recommended that it be used in the immediate vicinity of either shallow rooted or other than established plants. You could try cutting the hebe hard back but if the rest of the plant has wood tissue similar to what was forwarded there is not much hope of revitalising it.

I have a blue eedar In my front garden, and am now find. Ing that It is growing too large. Could you tell me If this could bo pruned drastically to about half its size, if this could be done by a layman or If l should obtain expert attention for It?—G.P. (Christchurch). You do not say what height your tree is, but if the job is done with care, there should be no great problem pruning it. The job can be done In early autumn or late spring and can be attempted by anyone, with a little care. Shape and balancp are of considerable importance in conifers.

My literature on pests and disease* of potatoes doe* not appear to describe the symptoms that each year show up in some part of my crop. Sometimes, most of a row is affected, sometimes individual plants in a row, and some, times a healthy plant persists in a row of affected plants. The first sign of trouble is the progressive curling of the leaves; then loss of colour, and finally the underside edges become purple and then brown. Can you please diagnose the trouble and indicate cause and cure. A second problem occurs every season when first one segment of a tomato leaf loses colour. Progressively the colour becomes more yellow and the disease extends to whole leaves and then moves upwards throughout the plants. I keep on removing affected leaves. The crop itself Is not significantly affected. I spray both potatoes and tomatoes regularly and thoroughly with Dlthane 7» or Zineb.—D.D. (Christchurch). It is possible that virus is Infecting your potato crop, but before commenting further I must see more and larger samples. The same applies in the case of the tomato plant, where the disease, spotted wilt, is the suspected pathogen. Many pests and diseases are

common to many plants; symptoms can be similar or variable, and unless fully representative samples are sent with tho details of the problem the task of providing a helpful answer is an onerous one.

We have a 30-year-old weeping elm, planted when our home was built. It now has terrible suckers coming up everywhere. We would hate to lose the tree, but wonder what measures there are to combat these suckers. Can we put on a weedkiller where they con. stantly pop up, or is a trench the answer, cutting off all roots? The suckers are coming up for 30 yards radius Weeping for Help (Scargill).

There is unfortunately no practical way of stopping a suckering tree from doing so. Suckers can be controlled, but not with a weedkiller. While it is possible to kill the suckers with a herbicide it is likely that the tree will also suffer from the effects. Suckers should be removed at the point of origin, not simply grubbed where they appear. If left these growths will soon form thickets and in close proximity to buildings or paths they can cause damage.