CUCUMBER DISEASE

New Zealand Herald, Volume LXXI, Issue 21698, 13 January 1934, Page 8 (Supplement)

CUCUMBER DISEASE

METHODS OF TREATMENT The wilting and dying of cucumber plants, as recently reported from the Whangarei district, may be caused by two species of fungi, both of which, to the writer's personal knowledge, were present in the Whangarei district five years ago. In seasons of normal temperature, with plenty of heat, the disease has not caused much trouble, but with a season like the present, with continued low temperatures and excessive moisture, it can become very' virulent. The two species of fungi are Verticillium albo-atrum and Fusarium vasinfectum. The external symptoms of these two diseases are the same—namely, wilting, yellowing and drying up of the lower leaves, followed by the same effects on successively higher leaves, until the whole plant withers and dies. If the stem is cut across the wood is seen to be yellowish brown, where verticillium is present, and reddish brown in plants attacked by fusarium, the two diseases being equally common.

As these fungoid diseases are propagated by spores, all diseased plant tissue should he burned. Burying it by digging or ploughing only provides a source of infection for the next crop. The spores can persist through the winter on rotten ,wood, and it is important that everything used for the next crop is sterilised. All debris should be rerfoved and burned, and boxes and frames sterilised with emulsified cresvlic acid. This is made by pouring one gallon of cresylic acid into a benzine tin, adding eight pounds of soft soap. The soap is dissolved by heating the tin over a fire, the process taking about ten minutes. The strong emulsion is diluted at the rate of one pint in six gallons of water. Rubber gloves should be worn, a3 the liquid is very caustic. Boxes may be dipped in this mixture and frames sprayed.

THE NEED FOB CARE The verticillium wilt can be controlled by earthing up the bases of the plants with clean soil and reducing watering to a minimum. Any infected leaves should be picked off and burned and the slants sprayed with liver of sulphur at weekly intervals. These measures will not cure fnsarinm wilt, for which at present no cure is known. The diseased plants should be removed and the soil soaked with a solution of formalin (1 in 100), before replanting in the same position. When an area is badly infected it is a work of some magnitude to clean it. But if care is. taken in the disposal of infected plant tissue and prompt disinfecting is undertaken on the first appearance in the following season, control can be moderately successful. Some growers are still inclined to look upon sprays as cures, instead of ivhafc they really are " preventatives." Spraying should be looked upon as an insurance policy against loss of crop, especially as disease has been experienced before. As fungoid diseases are propagated by spores, conditions for their growth are favourable in spring. The spores float around in the wind, alight on a leaf or stem, and thpn germinate much in the same way as a seed. Tt is obvious that once the fungus is safely inside the plant tissue, no amount of spraying will control the disease effectively, but if those leaver, and stems were already coated with a fungicide when the spores alighted the spores are immediately killed and so prevented from perpetuating the disease.

OYSTER SHELL SCALE

METHODS OF CONTROL Oyster shell scale sometimes appears in large numbers on plum, apple, pear, apricot, nectarine, and peach trees and currants. Trees are very much weakened, and sometimes killed, by this pest. It does not appear to spread rapidly from one tree to another, but once a tree is affected it increases quickly and soon causes serious harm. The small scale is rather like an oyster shell in miniature. The small, circular, black spot is to be found near the centre. The scales are flattened, and often pressed closely to the bark. Winged males, which are yellowish in

colour and have a single pair of wings, appear in October and November, and fertilise the females. Eggs arc laid, which hatch in December into minute, active larvae. This is the most vulnerable stage for control purposes. By autumn, they have formed scales over themselves. The egg stage is not like mussel scale, found in winter. During the winter, the oyster-shell scale is found in its miniature stages. Severely-affected trees are best cut down and burned. Spraying with oil sprays in winter will give a good control. but spraying during the period when the young larvae are active, with a dilute kerosene emulsion or oil spray, will prove more effective, but care should be taken to apply at such a strength that the foliage" will not be damaged.