RHODODENDRON PESTS

New Zealand Herald, Volume LXXI, Issue 21763, 31 March 1934, Page 8 (Supplement)

RHODODENDRON PESTS

RAVAGES OF BUGS The rhododendron bug (Septobyrsa rhododendri) lives on the underside of the leaves, and causes brown spots to appear, a pale freckling appearing on the upper surface. In severe attacks death of the plants may occur. Most types of rhododendrons are attacked, but the newer hybrids are the most susceptible. The adult bugs arc small, being only one-eighth inch in length. The wings are very prominent, and form a covering to the body, which is black, and seldom visible. The general colour of the rest of the bug is light grey. The fully-matured bugs may be found on the undersides of tho leaves in January. The eggs are laid inside tho tissues of tho mid rib of the leaves, slits being made for their reception. The shape of the egg is somewhat liko that of the capsid bugs. The adult bugs die at the beginning of autumn, tho winter being passed in the egg stage. The eggs hatch during the early summer of the following season. The young bugs are at first very small dark grey insects, like other bugs, casting their skins several times, increasing in size, acquiring wings, and then maturing.

The best measures of control are spraying the affected bushes with ordinary soap solution at a strength of one pound of soap to 10 gallons of water. The first spraying should be made about the end of December. A second spraying is given two weeks later. In order to avoid any damage to the leaves the operation should be carried out during dull weather or in the evening. In the case of slight attacks hand collection of the affected leaves is übually sufficient to prevent further increase. Removal and destruction of all the leaves during the winter would account for all the and this is one way of tackling the pest. Fungi do little serious damage and flourish as a rule only when the shrubs are growing in unsuitable situations. A number of fungi may attack the leaves, and scorched and spotted rhododendron leaves are frequent. The most common species is Glocosporum rhododendri and several species of phyllosticta. They can all be readily controlled by removing and burning badly attacked leaves, and spraying at intervals of three weeks with Bordeaux mixture, to which a sticker has been added; this is necessary to make the spray adhere to the leaves. Spraying has little effect on the rust caused by chrysomvxa, and this can only be controlled by the constant removal of diseased leaves as they are seen.

THALICTRUMS SUCCESSFUL NEW VARIETY Thalictrums have long been popular border flowers, but the introduction from Western China of Thalictrnm dipterocarpum immediately captured the interest of gardeners, tor lightness and elegance there was not an herbaceous plant to equal it. It had one disappointing feature. When cut, the daintv tussels of yellow stamens which contribute largely to the beauty of the pale lilac sepals, fell very quickly. It was soon apparent that it was not going to be as useful a cut flower as had at first seemed probable, and its use was more or less confined to the garden. At the Chelsea Show last year a now variety was introduced which overcame many of the disadvantages of the original type as a cut flower. This is Hewitts' Double. Each bloom is a perfect pompon, as full and rounded as the best forms of double gypspphila paniculata, yet, like the gypsophila, it has lost none of its grace through the increase in number of sepals. It has the same wiry-branching habit, and the same maiden-hair foliage. In colour it is a little deeper and more purple than the common form. One drawback of the newcomer is that the flowers are so fully doubled that they never give any seed, and the plant must be propagrated by vegetative means. Increase must necessarily be slow. VALUE OF WOOD ASHES Wood ashes are a valuable manure, containing potash and soda beside other inorganic elements of plant food. They are well adapted for mixing with guano and are also excellent by themeslves. A bushel of wood ashes will weigh about •501b. and will contain potash and soda to the extent of 4.61b. and small quantities of other elements. An excellent substitute for wood ashes may be made by mixing muriate of potash (01b.), phosphate of lime (61b.) and slaked lime (351b.). , The roots of plants, weeds, etc., arc frequently burned and the ashes applied to the soil, but as all the organic matter and nitrogen is lost by this means, it s more economical to form them into a compost with earth and quicklime or other substances which destroy their vitality. Thoroughly decomposed to a state of vegetable mould they make an excellent substance for horticultural purposes.