Root crop diseases

Press, Volume CXIII, Issue 33252, 15 June 1973, Page 11

Root crop diseases

Carrots and parsnips form ' the bulk of root crops which • are generally carried over l ;through autumn and winter ! in the vegetable garden. ' These vegetables are hardy •land under normal circum- ■ stances can survive the “heaviest frosts with little ■ apparent ill-effect. ■ . The flavour of parsnips is , said to improve after a • number of hard frosts, though Jit is not as marked as one : might expect from the • frequency with which this 11 contention is upheld in some 'quarters. t Although these vegetables - can safely remain in the soil for a long time without attention they are susceptible to a number of serious diseases. SOFT ROT Bacterial soft rot can often cause severe losses to carrot crops and parsnips are not immune to attack either. The disease usually gains entry as a secondary infection, [through damage caused by careless cultivation, or it can i be promoted by unfavourable weather. ![ Symptoms of the disease I are a rapid breakdown of the j root into a soft and slimy [structure, the disintegration [of which is speeded up by iwet weather, especially if the [soil is not particularly well drained. There is no control once the disease has gained entry.; The only thing that can and should be done is to dig up the affected roots and use the sound portions that remain. Diseased roots should I be gathered up and burnt and I not dug in or left lying ! around. PARSNIP CANKER There would be few growers of parsnips who have not encountered parsnip canker. This is a fungus disease which is usually first seen around the shoulders or crown of the parsnip. Conspicuous and characterised by its rusty brown colour, it [causes a rough or dry decay [of the root tissue which can sometimes be invaded by a [secondary infection. ! It is precipitated by alternating frosty and wet con-

ditions, can affect the foliage! in severe cases and can in [time cause a total loss of the ‘root. Ways of reducing the incidence of parsnip canker in- , elude the provision for crop rotation, good drainage, regular liming, avoiding excessive use of nitrogenous fertilisers and not sowing too early. Moulding up of the crop as it develops is also a help. MILDEW Powdery mildew has become a more prevalent disease of parsnips than it once was. The incidence and persistence of this disease 'is ; largely dictated by the weather—dry conditions increasing its prevalence. In the first instance it is recognisable by the mealy appearance imparted to the foliage. In severe cases it affects the roots, which remain small. Although powdery mildew in parsnips is not a really serious problem, control can be obtained by spraying with colloidal sulphur under warm conditions or with benlate or karathane. Carrots are particularly susceptible to attacks from aphids, which are at their worst in spring. Apart from having a severe debilitating effect on the plant through their sap sucking, which in major infestations can lead to complete crop losses, they can also carry virus infection. Motley dwarf is a common such virus, recognisable by the eventual discolouration of the foliage and loot top to a reddish purple colour. Control consists of delayed planting and timely spraying with such materials as menazon or maldison.