Diseases and pests
This page provide information in relation to diseases and pests that can affect Strawberry Production.
Diseases of major importance
Botrytis or grey mould is a widespread and damaging disease of strawberries. It causes rotting of the green and ripening fruits, quickly reducing them to a soft mass covered with grey dusty spores of fungus.
Botrytis is an inhabitant of dead plant tissue so old strawberry leaves and leaf stalks provide extra material for the fungus to live on and to produce spores. Infection starts during the flowering period although the disease remains inactive until the fruit begins to develop. Infected fruit is a source of secondary infection.
Good control of botrytis can only be achieved thorough protectant cover of fungicide during the blossoming period. Because of the long flowering period apply up to four sprays beginning at first open flower and continuing through until petal fall.
Commence spraying early in the flowering period, even in dry weather as additional later sprays after blossom will not compensate for omission of early sprays, particularly if weather conditions favour development of the fungus.
Thorough wetting of all plant parts, especially the flowers, is required to give disease control. The use of a ruffler bar to aid penetration of the spray into the crown of the plant is recommended.
Powdery mildew thrives under hot dry conditions and is likely to be a problem in the late summer. The leaves of attacked plants show characteristic dark red coloured blotches while the margins curl inwards to expose the underside which can become covered with a white powdery mildew. The infected plants often appear to be suffering from drought. The fungus can also cover flowers and fruit in a white powdery mildew.
The variety Elsanta is very prone to mildew and preventive sprays should be applied frequently.
Red core is a serious disease of strawberries. The fungus lives in the soil and attacks the roots of strawberry plants causing them to rot.
The effects of the disease are normally first noticed in late spring or early summer when diseased plants look as though they are suffering from drought. The plants are dwarfed and they will die in dry weather. The leaves are often dull bluish-green and older leaves are sometimes tinged with red.
If the roots of an infected plant are examined in spring it will be found that the white feeding tips have rotted away. Main white roots may be brown and rotten for various distances from their tips. If these roots are cut lengthways a red discolouration of the centre tissue will be seen. This is the 'red core' from which the disease takes its name.
The disease can be spread on infected runners or by infected soil on implements carried from one field to another. Where drainage is poor or there has been a high winter rainfall, the fungus readily invades strawberries. The fungal spores are carried in drainage water so causing spread of the disease.
Before planting make sure that drainage is good. Growing plants in beds or ridges will help in heavy ground.
Some modern varieties, for example, Elsanta are particularly prone to crown rot. Symptoms of this disease are seen when the youngest leaves wilt and often turn bluish-green. This wilt spreads quickly to the entire plant which collapses normally within a few days. When diseased plants are lifted they often break at the upper end of the crown leaving the main part of the crown and the roots behind in the soil. If the crown is cut open lengthways, browning of the tissue will be seen. It appears that cold stored runners are susceptible to infection by the causal fungus.
Pests of major importance
Several species of aphids (greenfly) can occur on strawberries.
Aphids may cause severe damage especially after mild winters when high populations produce leaf distortion and stunting of plants. In addition, the flowers can be malformed and little fruit develops. Some species of aphids are carriers of virus diseases which can give various symptoms from marginal yellowing of the leaves, reduced leaf size, stunting of the plant, leaves crinkled and distorted, yield and vigour appreciably reduced.
There are a number of approved aphicides for use in strawberries and sprays are normally required in the spring after some growth has taken place but before flowering commences.
Red spider mite
Adult female mites overwinter and become active in early spring. The mites feed on the underside of the leaves causing mottled yellowing. If plants are heavily infested growth becomes poor and stunted with the whole plant appearing bronzed and covered with webbing.
Control can be difficult. Different chemicals act differently on certain stages of mite so it is important to examine the leaves to determine what stages of mite are present.
Where mites are detected, spray programmes should be commenced early in the year to eliminate populations before they have time to build up. A further spray may be required after harvest and this can reduce the risk of serious infestations in the following spring.
Vine weevil is a serious pest of strawberries. The creamy-white legless grubs feed on the roots in the winter and spring, finally excavating deep tunnels in the base of the crown and so causing complete collapse of the plant.
The adult vine weevil feeds on foliage at night during June causing a distinctive marginal notching. Although leaf damage is unlikely to be important, it indicates that damage by grubs may occur later.
Control of this pest is difficult. Adult weevils feed only at night and sprays intended to control adults have to be applied during the hours of darkness. In addition, not all adults feed every night so one spray will only eliminate a proportion of the adults.
Baits can be used to attract adults and these can then be trapped using a sticky base or a funnel trap.
Plants which are especially attractive to adults can be planted around the edge of the crop to encourage adults to feed. These plants can then be sprayed and adults killed.
Chemical or biological control measures may be used depending on conditions and timing.