DISEASES AND PESTS OF PLANTS. 25 



which the dodder-plant depends entirely for its nourishment. It is therefore a total 

 parasite, and on this account causes serious injury to, and ultimately the death of, 

 its host. The pest is always introduced by its seed being present in the seed of the 

 clover or alfalfa sown. The seeds germinate, and the seedling attaches itself to a 

 near-by clover-plant. Once established, the dodder-vine branches profusely and 

 spreads over neighbouring plants until a whole patch is infested. In the earlier 

 stages of infestation the pest is generally distributed over the field in such patches 

 which are visible at a distance from their yellowish colour, due to the mass of 

 yellow dodder-vines, and the death or debility of the otherwise green clover. Large 

 numbers of clusters of small pinkish blossoms are produced, each forming one to 

 four seeds. In the case of clover grown for seed, these are finally threshed out and 

 mixed with the clover-seed. If left until ripe they fall to the ground and germinate 

 next year, giving rise to a new Infestation. Clover-dodder is usually an annual, 

 although it has been shown to be perennial in certain cases. 



Control. Infection comes through sowing impure seed ; every care, therefore, 

 should be taken to avoid such seed. Seed should be purchased under a guarantee 

 of freedom from dodder, and a sample should be sent to the Seed Branch, Dominion 

 Department of Agriculture, Ottawa, or to the Western Office of this Branch at 

 Calgary. An examination will be made and a report furnished free of charge. 



Where infestation has occurred, treatment will depend on its extent. If it 

 occurs in patches, these should be cut close, and well beyond the edge of the patch, 

 the material mixed with straw or saturated with coal-oil and burned on the spot. 

 Where the infestation is general, the field should be ploughed up and not seeded 

 again to clover or alfalfa for two or three years. 



CORN. 



SMUT (Ustilago z&e). 



This occurs in the Coast and Island sections, but the writer has not seen it in 

 the Interior. Any part of the plant above ground may be attacked, and infection 

 may take place at any time if the tissues are still sufficiently tender. Infection 

 results in the formation of a tumour, varying in size according to the part attacked, 

 but often as big as a man's fist. Inside this enormous numbers of black spores are 

 produced. The tumour is at first covered with a shining -white membrane, which 

 later breaks, allowing the spores to be scattered. 



Control. Cut out and burn the tumours before they break and scatter the 

 spores. Do not in any case throw them where they will find their way on to the 

 manure-pile, as this gives the spores an opportunity to multiply further. Seed- 

 treatment as used against smuts of oats and wheat is useless against this disease. 



GOOSEBERRY. 



POWDERY MILDEW (Sphatrotlieca mors-uvce). 



This is the most serious disease of the gooseberry. Many varieties of English 

 gooseberries are so susceptible that they cannot be grown profitably where conditions 

 favour the disease. The fungus is a typical powdery mildew, in that it is of super- 

 ficial habit, and reproduces in the usual way, but it is more resistant to spraying 

 and more difficult to control than most powdery mildews. It first appears on the 

 leaves as greyish-white patches of mycelium, and later on the fruit. Spores are 

 produced in large numbers from this mycelium, and new infections take place until 

 the young shoots and berries may become entirely enveloped in mycelium. As this 

 gets older it changes from white or grey to yellowish and finally brown. The 

 growth of the shoot is stunted and the leaves remain small. The fruit may be 

 directly injured, becoming malformed or cracked, but the chief damage is due to 

 the unsightly appearance of attacked berries which renders them unsaleable. Small 

 black fruiting-bodies ultimately appear in the mycelium, and these produce another 

 form of spore and carry the fungus over the winter. 



