This section is from the book "The Gardener V2", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
I have never found much difficulty in preventing red-spider from gaining much of a footing on Peaches. Cleanliness in connection with the wood-work, glass, and everything else, the dressing recommended for the trees after they are pruned, and the syringing recommended throughout the forcing season, are the best preventives. When spider does make its appearance, attack it vigorously with clean tepid water from the syringe or engine. After the fruit are gathered a handful of flower of sulphur may be mixed with the water. Peach foliage seems to thrive under the influence of sulphur applied in this way. This insect is easily driven off the smooth surface of the Peach-leaf, and vigorous syringings I have always found sufficient to master it when it did appear.
Green-fly is very easily destroyed by fumigating with tobacco, and its very first appearance, in however small numbers, should be the signal for exterminating it. I have known it destroy a crop very much when it got a footing when the fruit were setting. The trees should be dry the evening of fumigation, and the tobacco should never be allowed to burst into flame. The fumigation should not take place when the trees are in bloom.
I never had to deal with this insect on Peach-trees but once. The trees were syringed after they dropped their leaves with water at 145°, and though the wood was coated with the insect, I never saw more of it after the syringing.
This is a troublesome enemy to Peaches when it attacks them. It cannot be said that the Peach is subject to thrips; but when plants infested with them are placed in Peach-houses - which never should be, but often is, - they spread rapidly on the Peach foliage. Fumigation with tobacco, on which some Cayenne pepper has been dusted, for a few successive nights, destroys it. Engine the trees freely after the fumigations to wash the insects and the smell away. When the fruit are gathered, thrips can be conquered by syringing two or three times with tobacco-liquor, made by boiling at the rate of 3 oz. of tobacco to a gallon of water. This should be applied late in the evening, and the house kept close for the night, so that the liquor may hang longer about the foliage.
The Peach and Nectarine are singularly free from disease under glass in a good border, unless it be mildew at times on some varieties; they are rarely attacked with those diseases, such as curl and canker, which are so troublesome on the open walls. Gumming occasionally causes the death of a branch, and is often the result of a bruise or a tie that has been too tight and cut into the branch. When it appears to any extent, the best plan is to remove the affected branch at once. Mildew is the effect of over-dryness, and also of too much wet. Whenever it appears, dust the affected parts with sulphur, and if the border is dry, water it sufficiently to moisten the soil. If the cause is traceable to bad drainage it should be rectified. D. T.