One of the most impressive examples of a horticultural chart must be this calendar issued by the firm of Walter Voss & Co. Ltd., of Millwall in east London. The firm was founded in 1904, and flourished until its works were damaged in the Blitz; the chart probably dates from the 1920s.
In the outer ring are the names of pests and diseases (with numbers that relate to further diagrams). The central ring lists the treatments, all of them no doubt available from Voss, and several of them proprietary products - Vossoline, Voss Standard Lime Sulphur, Voss Safety Cyanide Packages. The inner ring gives the months of the year.
So to find out how to treat a given infestation, you follow the red line (if an insect; green line if a fungus) to the recommended treatment, and then follow it further to learn in which month to administer it; when treatment is likely to be protracted, the lines change direction and circle the centre for the appropriate number of weeks or months. A note at bottom right indicates that pests marked with asterisks “return to Fruit Sept-Oct when a further spraying… would be advantageous”.
That’s right: fruit. The entire calendar is geared to the spraying of fruit, and another note helpfully alerts the reader: “Do not pick fruit within six weeks of use of Arsenate of Lead”. Presumably once you’ve used the Safety Cyanide Package you could eat the fruit with less delay.
Now: for a modern comparison, go to the UK Pesticide Guide for 2014, and start making your way through its 753 pages…
Pesticides for home gardeners RHS Advice leaflet (333kB pdf)
Chemicals: using them in gardens