Transactions of RHASS Volume 1940 - Page 058
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| Year | 1940 |
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104 INSECT AND OTHER PESTS OF 1939. Among insect parasites there is a fly (Buccn‘lcs geniculata) the maggot of which has been recovered from Leather Jackets in various localities. Although the parasite appears to be fairly common it is not possible with the information available to assess its efficiency as a control agent of the grub. Taking all the facts into consideration it is probably not overstating the case to say that continuous dry Weather in autumn has a greater controlling effect on Leather Jackets than any other natural agency. TOMATO SICKNEss ( H etcrodera schachtii). In last year’s ‘Transactions’ I recorded a case of severe damage to tomato transplants by the Root Knot Eelworm (Hetcrodera mario'ni) in a nursery in Roxburghshire. In 1939 my attention was drawn by Mr J. Bruce, Department of Horticulture, East of Scotland College of Agriculture, to an infestation of tomatoes by the related Potato Eelw0rm (H. sehachtii) at a nursery in Midlothian which has been in operation for the past nine years. Altogether there is about half an acre under glass, and all of the ground is planted to tomatoes. Every second year the soil is steam sterilised, and in intervening years is treated with formalin. The year 1939 happened to be one in which the soil received the. formalin treatment. The history of the nursery showed that there had been no previous occurrence of a schachtii infestation. During the whole of the nursery’s existence the soil had not been once changed, so that there was no possibility of the eelworm having been introduced with infested potato soil from outside. Previous Records.-—-Thirty-two cases of tomato sickness in Yorkshire due to H. schachtii were recorded during the period 1928-1936 by Johnson and Thompson,1 who also refer to a single case recorded by Miles in Lancashire in 1935. Symptoms—Tomato plants attacked by the eelworm are affected in the same manner as potatoes. Growth is retarded, so that the plants rarely surpass a height of about four feet and wilting is severe. Infested roots turn brown and decay as a result of the larval invasion and, to make good the damage, the plant sends out a mass Of fibrous roots above the first ones. At intervals along the attacked rootlets cysts of a white or brown colour, according to their age, project into the soil and are readily detached. Some of the flowers remain unopened and drop prematurely without setting. The result is an appreciable reduction in the yield of fruit. 1 Johnson, L. R., and Thompson, E. “K, 1936. “ Tomato Sickness in York- shire.” Jour. Min. Agric., Vol. XLIII., No. 1, pp. 48-54. INsECT AND OTHER PEsTs OF 1939. 105 Life-hi8’1‘()i”]/.—Til(‘ mature female eelworms are oval in shape and are just visible to the naked eye. They are attached to the roots of diseased plants, where they are found and fertilised by the minute, active males. After pairing, the males die, but the female continues its attachment to the host whilst its skin changes from white to dark brown. At the same time the skin becomes hard and tough and serves as a protective coat for the eggs which fill the whole of the internal cavity. Finally, they drop from the rootlets into the soil and remain dormant during the winter. The cysts may remain viable for a period of at least nine years. During this time a few eggs appear to hatch each year, but hatching is greatly speeded 111) by the stimulating effect of the root excretions of those plants on which the eelworm can feed and breed. Thus when a susceptible crop such as tomatoes is planted, numerous eggs hatch to liberate larvae which burrow into and destroy the tissues of the young roots. As an offset, the plant sends out additional roots. Source of Infestation—A tomato crop is liable to infestation in one or other of two ways. The eelworm may be introduced into a glass house with cyst-infested soil or it may be brought in with farm manure. Under Yorkshire conditions infestation is attributed to the importation of cyst-infested soil, for in the East Riding particularly there are large tracts of land that are heavily infested with eelworm from potato crops. In some cases growers have set down a Dutch type of cold glass house on a piece of arable land, and the light of later ex- perience has frequently shown that the enclosed piece of ground must have been infested from the start. In the Midlothian nursery there had been no change of soil in the glass houses since their erection nine years previously. The grower, however, remembered that the farmyard manure which was used as fertiliser in 1939 had contained some refuse potatoes. It is possible that these potatoes had come from an infested crop and had been inadvertently cast on the manure heap. Control—(1) Steam Sterilisation.—This is the best method of controlling the eelworm, since it destroys the infective cysts with their contained eggs and thus renders them innocuous. (2) Layering the Plants—This remedial method is applicable to infestations which occur in small patches. The soil around and beneath the affected plants is dug out and replaced by fresh eelworm-free soil, into which the plants are layered. As a result the plants are induced to send out new roots which help them to make a substantial growth. VOL. LII. H |
| Title | Transactions of RHASS Volume 1940 - Page 058 |
