Plant diseases - lettuce mosaic - Digital Library

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Journal of the Department of Agriculture, Journal of the Department of Agriculture, Western Australia, Series 3 Western Australia, Series 3

Volume 1

Number 5 September-October, 1952 Article 18

9-1952

Plant diseases - lettuce mosaic Plant diseases - lettuce mosaic

H L. Harvey

Department of Agriculture

Follow this and additional works at: https://library.dpird.wa.gov.au/journal_agriculture3 Part of the Biosecurity Commons

Recommended Citation Recommended Citation

Harvey, H L. (1952) "Plant diseases - lettuce mosaic," Journal of the Department of Agriculture, Western Australia, Series 3: Vol. 1: No. 5, Article 18.

Available at: https://library.dpird.wa.gov.au/journal_agriculture3/vol1/iss5/18

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LETTUCE MOSAIC

By H. L. HARVEY, B.Sc. (Agric), Senior Plant Pathologist.

P

RELIMINARY surveys of metropolitan market gardens during July and August showed that the virus disease known as lettuce mosaic was present in amounts varying from one to 90 per cent. If not checked it is likely to hecome one of the most serious diseases of local winter lettuce crops.

The spread of lettuce mosaic may occur by means of infected seed or by aphides which carry the virus from diseased to healthy plants. Other re- corded hosts are peas, sweet peas and weeds such as groundsel and prickly sow thistle.

Symptoms.—The most obvious symp- tom is a mottling of leaves on which the normal green colour is interspersed with areas which are white to yellow in colour especially along the veins (see Figure 1). The effect may be one of green blisters on a pale background and is seen more readily when viewed against the light. This mottling may be very noticeable or just barely perceptible on affected plants. In addition, wrinkling of the leaves tends to be more pronounced than in healthy plants. Mosaic- infected plants may be completely dwarfed if early infection occurs, or partially stunted if infection occurs at later growth stages. Poor development of hearts is often a result of mosaic

infection. The loss to the growers is therefore that much of the crop is either unsaleable or can only be sold as low grade lettuce.

Control.—On a basis of observations made to date under local conditions and on general principles, the following control measures are recommended:—

(1) As seed saved from mosaic- infected plants may carry the disease, growers intending to raise their own seed should select mosaic-free lettuce for the

purpose. Cases are known where seed has been saved by growers from plants showing mild symptoms because they were consid- ered attractive.

(2) Where transplanting is practised, seedlings should be dipped in a nicotine sulphate solution to destroy aphides just prior to transplanting. (loz. nicotine sulphate, 2£oz. soft soap, 5 gal- lons water.)

667

Journal of agriculture Vol. 1 1952

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Left.—Mosaic-Infected lettuce leaf showing pronounced vein-clearing and the presence of green blister—like areas between the pale-coloured veins. Leaf wrinkling may become very exaggerated and affected plants may fall to form compact hearts or may remain partially or completely

stunted. Right.—Healthy lettuce leaf

(3) Frequent applications of aphis- controlling insecticides to the crop, especially during the early stages of growth will help to prevent infection. (See article on aphides in this issue.) (4) Remove and destroy mosaic-

infected seedlings or plants as soon as the symptoms are noticed.

(5) Weeds in the vicinity of lettuce beds should be kept down to re-

duce the aphis population and destroy possible weed hosts of the disease.

(6) Where successional plantings are practised, the new planting should be made as far away as possible from the older ones, so as to reduce the chances of spread of the disease by aphides from one planting to the next.

For the same reason old beds should be ploughed in as soon as cutting is finished.

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