Plum trees may be infested with the San Jose or by the European fruit scale. The treatment for them is the same as recommended for scale on apples. (Page 149.)
JUST BEFORE THE BUDS SWELL, spray with the dilute lime sulphur (or
the Bordeaux mixture) and arsenate of lead, 2½ to 3 lbs. to a barrel. This is to prevent leaf-spot, fruit rot, black knot and curculio.
Arsenate of lead is preferable to Paris green on all stone fruits, owing to tenderness of foliage in such fruits.
IMMEDIATELY AFTER THE BLOSSOMS FALL, it is very essential to make another spraying using the dilute lime-sulphur or Bordeaux mixture or self-boiled lime-sulphur, and two pounds of arsenate of lead to every 50 gallons. (For the Japanese varieties use the self-boiled lime-sulphur or dilute the Bordeaux one-half.) This spraying is to prevent the leaf diseases, fruit rot and curculio. Be sure it is made immediately after blossoms fall. Our experiments last year showed that dilute lime-sulphur was very satisfactory on plums and it is easier to prepare and spray than Bordeaux or self-boiled lime-sulphur.
TEN DAYS OR Two WEEKS LATER, it will pay to repeat the previous spraying, especially if the weather is wet or the curculio is serious. This spraying should be repeated every ten days or two weeks until there is danger of staining the fruit; stopping at least a month before picking time.
On varieties especially susceptible to rot, an application of weak copper sulphate may be made about two weeks before ripening. One pound of copper sulphate to 150-200 gallons of water. No poison need be used.
BLACK KNOT. Early in the spring a careful inspection should be made of every tree, and all “black knots” cut out and destroyed. Cut back several inches below the knot. Disinfecting cuts as for pear blight is not necessary. Wild cherry trees harbor the disease and if diseased ones are near plum or cherry orchards, they should be destroyed, if possible.