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SPRAYING OR DUSTING OF TOMATOES IN INDIANA
FOR DISEASE CONTROL
By
R. W. Samson

Purdue University Agricultural Extension
Botany and Plant Pathology
Mimeograph No. BP 13	July, 1946.
Late blight and the other important foliage and fruit diseases of tomatoes
in Indiana can be controlled by thorough spraying or dusting with any one of several
fungicides now available. Profitable returns from spraying or dusting will be ob-
tained whenever these diseases are severe enough to cause losses materially greater
than the cost of control. In most Indiana seasons, spraying or dusting of early
planted tomato fields will prove profitable because of the generally higher yield
potential of early planting and the greater losses from disease. Spraying or dust-
ing of late fields may not prove so profitable because of the generally lower yield
potential and lesser disease development.
Tomatoes are difficult to spray or dust satisfactorily. Thorough and com-
plete coverage of plants and fruit with the fungicide is essential to good control
of disease. Repeated applications must be made (1) to cover new growth or expansion
of older leaves and fruit, (2) to replace fungicide weathered away, (3) to build up
a fungicide deposit to protect when weather delays applications, and (4) to counter-
act the mechanical difficulties of obtaining complete fungicidal coverage.

Fungicides for Tomato Disease Control
1. Bordeaux mixture gives excellent control of late blight, fair bo good
control of Septoria and early blight, and only fair control of fruit rots. It is
somewhat injurious to tomatoes. We recommend its use only when severe late blight
conditions occur. The recommended 'formula is 8 pounds of powdered copper sulphate,
4 pounds of hydrated spray lime (not finishing lime) and 100 gallons of water.
Thoroughly dissolve or suspend either the copper sulphate or the lime in almost the
full amount of water and then add the other material with thorough agitation. One
material must be in dilute solution or suspension before the other is added. Add
water to the full amount and use the spray immediately.
2. The so-called fixed copper fungicides have been developed in recent
years and promoted for use on tomatoes, largely because less injurious than Bordeaux.
They are almost equal to Bordeaux for disease control and easier to use. Tribasic
copper sulphate, Copper A Compound, Copper Oxychloride-Sulphate (CQC-S) and Yellow
Cuprocide are all good fixed copper fungicides, and should be used as sprays or dusts
according to the manufacturer’s directions. The different forms vary in copper con-
tent. In making them up as sprays, sufficient quantities are used so that 2 pounds
of actual copper are contained in each 100 gallons of water. This makes them equiv-
alent to Bordeaux mixture.
Most of these fixed coppers are more readily available as ready mixed
dusts, containing about 6 percent of copper.
Dusting, in general, has not given as good disease control as spraying.