Reasons for Decline in Raspberry Crops

New Zealand Journal of Agriculture, Volume 75, Issue 1, 15 July 1947, Page 11

Reasons for Decline in Raspberry Crops

PRODUCTION CAN BE INCREASED BY DISEASE CONTROL AND METHODS OF CULTURE

By

J. H. WATT,

Orchard Instructor, Christchurch.

UNDER-PRODUCTION of raspberries, the most important of the Dominion’s small fruits, is giving concern at present. However, it has been proved that there are ample stocks of good varieties in New Zealand from which it will be possible to supply all the canes necessary to increase production, if adequate disease-control measures and methods of culture are adopted.

The main raspberry-growing areas in the Dominion were recently visited by the author, who found that many growers complained that varieties were “running out.” It was evident from production figures that fruit, both in quality and quantity, was deteriorating, but this, is not necessarily due to the plants “running out.” The methods of culture seem often to be the main cause of crop reduction. In some cases, particularly in old gardens, there -was a high incidence of seedling plants: (rogues) in the plantation. Generally these were of a poor type, giving light crops of inferior fruit, thus reducing the crop average and therefore the total crop from the area. Also there has . been little selection of suckers when new areas have been planted up. Because of the confusion in nomenclature of raspberries in New Zealand, it- is necessary, to start to classify varieties, at least as far as New Zealand is concerned. Then in due course, for it will take some time, it should be possible for a grower to find out what variety of raspberry does best on his soil type and in a particular district, so that he will be able, with confidence, to order more of the variety when required. An identification key form has been devised, and the main varieties grown in each district closely studied, as well as any seedlings or “off-types” which have shown promise. Cropping Trials At the same time varieties and types were selected and tagged for cropping trials shortly to be instituted by the Horticulture Division. More than 70 varieties and types were selected, some of which will no doubt prove to be duplicates, but it is expected to select the strongest types of all promising ■varieties for propagation. - Many growers think that it will be necessary to import new variet-

ies before it will be possible to improve production, but this survey has proved that there are ample stocks of good varieties in • New Zealand from which it will be possible to supply all the canes needed to increase production, if adequate disease-control measures . and methods of culture are adopted. Diseases and Pests In almost every district the incidence of fungous diseases is high, mainly because growers have not learned to recognise the diseases or realised the loss of potential cropping they cause. . Cane wilt (Leptosphaeria coniothyrium) occurs throughout New Zealand and is probably a major cause of crop reduction. Cane wilt can be controlled by the use of Bordeaux sprays, but it should be noted that effective control cannot be achieved unless a definite spray programme is adhered to and efficient equipment used. Most growers do not spray for this disease, while those who do so often use inefficient equipment and so obtain results far from satisfactory. Cane spot (Elsinoe veneta) is generally unrecognised as a disease and so has been little heeded. It is said to be normally of minor importance, but its high incidence in- gardens throughout the areas inspected indicates that it is on the increase and seems to be causing considerable’ crop losses by killing buds. As in dealing with cane wilt, Bordeaux sprays will give control? ■ Septoria spot ( Septoria rubi) is fairly general, but is not regarded as of much importance. When serious infection occurs it often causes premature drying of the . leaf, followed by early leaf drop, which combine to affect the size of fruits and ' also to reduce the vigour of the canes which will carry future crops. Control is

fairly readily obtained by using Bordeaux sprays as for cane spot and cane wilt. ; Silver leaf (Stereum purpureum)' is fairly general, particularly in the Waifarapa, Nelson, and Christchurch districts. Canes are sometimes severely affected and crop loss occurs. The only control measure known is to dig up and destroy all infected stools and to remove all other sources of. infection. Fructifications occur only on dead wood. Good pruning methods and garden hygiene cam do much to stamp out the disease. If precautions are taken from the time when a garden is planted, it should be impossible for the disease to gain a hold. Root rot (Armillaria, mellea) occurs in patches which may spread in all directions. The infection is caused by a fungus which attacks the roots of all plants within the affected area and eventually . kills them. In some areas, particularly the Wairarapa and Christchurch, there have been outbreaks of fairly grave proportions, but generally root rot is not regarded as a serious menace to raspberry production. The spread of the fungus can be controlled by isolating the areas, destroying all the plants within them, and treating the soil with a sterilising agent. Crown gall ( Phytomonas tumefaciens) is fairly widespread, having been found in the Wairarapa, Christchurch, and Roxburgh districts. Its effect on raspberries is not well

known, but it is "certainly not good to have it in the ground, as it persists and attacks other important crops. Infected areas should be isolated and no canes taken from them for planting. - . Virus diseases: It is thought that virus infections of raspberries are fairly, widespread in New Zealand, but as yet this has not been determined. It is possible that virus diseases have been a major factor in reducing crop yields, particularly in the Wairarapa and Waimate areas. It will take some time to / determine how detrimental these diseases are and how far they have become disseminated through raspberry plantations. The rogueing of infected plants and the propagation of disease-free or resistant varieties are the only known means of reducing the incidence of virus diseases. Raspberry hud moth (Carposinaadreptella) occurs throughout New Zealand wherever raspberries are grown. It is the most serious pest to the crop' and damages it' by eating out buds during the dormant period, at-, tacking young shoots and foliage during the growing season, and attacking the fruit. Damage to buds has often resulted in extensive seasonal losses; gardens have been seen in which a high proportion of canes were 1 completely denuded of buds through the depredations of the pest. In addition, a much higher percentage of canes had a number of buds destroyed, so that the total damage must have caused a severe reduction of crop. Injury to .young shoots reduces the height of the growing cane and causes axillary buds to break -into growth, often resulting in a many-branched ■cane too low set to be of use for fruiting the following year. Where ' incidence of shoot damage is high there may be a serious reduction in the

number of canes to carry -.fruit in the next season. When the fruit is attacked some of it may be lost and much of the remainder is usually of poor quality because of the presence of caterpillars in the berries. Spraying ' with arsenate of lead, if adequate and timely, will control the bud moth. Investigations are still necessary to find the best methods of control from the pre-harvesting to post-harvesting period. ~ Grass-grub . (Odontria zealandica) causes extensive damage in gardens on the lighter soil types by, eating the feeding roots of the - stools. Arsenate of lead, used as a soil-dressing, should be effective in controlling this pest in districts where it. is liable to cause serious losses. Bronze beetle (Eucolapsis brunnea) occurs in some of the northern areas in sufficient numbers to do considerable damage to foliage, as well as by eating through the fruit stalk. Spraying with arsenate of lead is not a very effective control, but a good spray programme to control bud moth and the carrying out of recommended hygiene, including the destruction of plants such as blackberry on which the bronze

beetle breeds, will do much to reduce this pest. The present use of spray specifics to control diseases and pests leaves much to be desired. The value of spraying to control cane spot, cane wilt, leaf spot, and raspberry bud moth was proved by experiments . carried out by officers of the Plant Diseases Division of the Department of Scientific and Industrial Research at Motueka and Riwaka between 1940 and 1945. The increase in crop yields shown by these trials more than repays - any costs involved. Few raspberry growers have , spraying equipment suitable to their needs. Commercial growers' should have power outfits capable of a reasonable pump delivery at a pressure of about 2501 b. per square inch. Five combination sprays of Bordeaux mixture and lead arsenate should be applied annually until control of the diseases and pests mentioned above ? has been effected, after which it may be possible to reduce the number of applications to three. A great deal of experimental work has z yet to be done with sprays to ascertain the most efficient strengths to use, the most suitable. times for application, and the .minimum number of applications, but the way is already clear for growers to effect a great improvement in health, vigour, and cropping capacity of their plantations by spraying. * ' - It may be possible to obtain a method of control by using dusts in place of normal wet sprays, a case in point being the control of raspberry bud moths during the fruit-harvesting period, when it is not desirable to spray, but when a dust may prove suitable. Hygiene Fungus disease infection could be much reduced if adequate garden hygiene practices were adopted. , The main fault in this respect is inefficient pruning, as stubs of dead cane up tto 9in. . long are prevalent, and on these fructifications of cane wilt, cane spot, and silver leaf fungi abound.