TOMATO DISEASES. 
173 
In one case 68 per cent, of the plants in a nursery were 
showing symptoms of wilt before the above methods were enforced, 
but a fortnight after only 10 per cent, remained wilted. In view of 
the fact that low spring temperatures are favourable to infection by 
Verticillium some advantage might be gained by planting later than 
normally, so that the higher summer temperatures may arrive by 
the time the plants have reached a suitable stage for infection. 
Perhaps the most familiar disease of the tomato is that commonly 
termed " Mildew," which is caused by Cladosporium fulvutn Cke. 
The term is an unfortunate one, as the fungal growth on the leaves 
is typically brown in colour, while the " Mildews " are typically 
white. The disease first, appears as a pale grey mould in isolated 
spots on the under side of the leaf, but it soon turns brown, spreads 
over the leaf, and causes desiccation and death. Spores are pro- 
duced in abundance, and under favourable conditions the disease 
spreads with alarming rapidity. The fungus usually attacks the 
old leaves first, but in bad cases even the young leaves are attacked. 
High temperatures and a saturated atmosphere favour the disease ; 
and, therefore, a most important factor is ventilation. In most 
glasshouses the amount of ventilation given is not sufficient to stop 
the spread of the disease, and strong measures have to be taken. As 
soon as the fruit has been removed from the bottom four trusses, 
the leaves up to the fourth truss must be removed to allow the air 
to move freely through the plants, and as the tops develop they must 
be kept well pruned for the same purpose. Full ventilation should 
be given when the disease appears, and in bad cases it is frequently 
necessary to leave the doors open if possible. Dusting or vaporizing 
with sulphur is of considerable value in checking the disease. 
Spraying with liver of sulphur has also proved valuable, where 
spraying is possible, but under normal commercial conditions it is 
not possible to spray the plants after they have reached a height of 
4 feet or so. 
A fungus of considerable economic importance is Botrytis cinerea, 
which produces a stem rot and a fruit rot. The damage which it does 
to the stems is largely assisted by the carelessness of the practical 
man. The fungus grows as a saprophyte upon dying, badly pruned 
leaf-bases, and thus gains entrance to the main stem through which 
it ramifies. 1 The stem tissues are destroyed, causing the death of the 
plant above this point. By carefully cutting away with a sharp 
knife the unwanted leaves, a clean flat wound close to the main stem 
is made, which rapidly heals and offers no foothold for Botrytis spores. 
The removal of the leaves from the lower portions of the plant is also 
necessary, for this prevents a stagnant moist atmosphere from accumu- 
lating round the wounds and so assisting spore germination. Once 
the fungus has entered the plant, the latter may be saved only by 
cutting out the tissue containing the fungus. In the case of Botrytis 
the browning of the plant tissue occurs ahead of the fungus, and hence 
by removing the brown portions of the stem the entire fungal growth 
