The plum has certain characteristic enemies, both fungi and insects. One fungus begins to attack the plant soon after its bloom is shed.
The young fruit soon develops a “plum pocket,” which is bladder-like or pouch-like in appearance. It is hollow and usually about 1″ to 2″ inches long.
The fruit continues to develop, but the walls become thickened, and there is no pit.
If the fungus also attacks the leaves and stems, they become bloated and distorted in appearance.
Most Common Plum Insect Enemies
One of the most common insect enemies of the plum is the curculio, a small, rough, grayish-black beetle only about one-fifth of an inch long.
The female slits the skin of the developing fruit and deposits an egg in the slit. Then she cuts a crescent-shaped second slit in front of the other one.
This causes the plum to wither and prevents the wound from healing around the egg. The fruit provides the first food for the young larva when it hatches.
Eventually, the diseased plum falls to the ground. The larva now leaves the fruit and burrows into the ground, undergoing a metamorphosis and transforming into a pupa or cocoon stage.
It remains in the pupa stage until the next flowering season for the plum tree. Then, when the tree begins to bud, the adult insect emerges.
During this stage, it feeds on the tree’s twigs and buds. Then, when the new fruit begins to form, the female lays eggs just as the female did the year before, and the life cycle starts over again.
Spraying Program For Insect Enemy And Fungus Control
An adequate spraying program can control the plum’s fungus and insect enemies. For fungus, ferbam, captain, or lime sulfur sprays are helpful.
Captain “General Purpose Spray”
The Captain is also a helpful general-purpose spray for fungus control and an effective weapon against curculio and other orchard insect pests, such as the codling moth, which attacks apples. Incidentally, the curculio also causes damage to apples.
As a general-purpose spray, Captain is effective for any orchard fruit, plum, and apple. It can be obtained at drug stores, gardens, or farm supply stores.
Ask for a “50% wettable powder.” This term refers to the strength or concentration of particular ingredients.
For one or two trees, as most homeowners have, five gallons of the spray should be adequate to prepare for each application.
The following formula should be mixed with five gallons of water:
- 3/4 cup of Captain (50% wettable powder)
- 3/4 cup of methoxychlor (50% wettable powder)
- 3/4 cup of malathion (25% wettable powder)
All measurements should be level. (16 level tablespoons equal one cup; 3 level teaspoons equal one level tablespoon.) Niethoxychlor and malathion can be obtained from the same sources as the Captain.
Spray regularly in the spring before the trees start to bud out, again at budding, and again when the petals fall. Then, about 10 days to 2 weeks after the petals fall, spray again and continue spraying at two-week intervals.
In areas where plums mature toward the end of July, the spraying program should be discontinued about the middle of July.
A corresponding time allowance should be made for localities where plums mature at a different date.
(If captan is used on apples that mature in the late summer or early fall, the spraying program should be conducted the same way as for plums, but spraying should be continued until about the end of July.)
There are ready-prepared commercial general-purpose sprays on the market, but the captain spray usually is more effective.
Commercial preparations cost less for a large number of trees than the captain spray, but for a few trees, such as most homeowners have, the cost of captan and the commercial general purpose sprays will be about equal.
Wettable Dieldrin Powder
Plum curculio is also effectively controlled by adding 50% dieldrin wettable powder, eight tablespoons, to 25 gallons of water. This should be used for petal fall, and the first cover sprays only.
Never use dieldrin on any, but the first cover spray for plums, except on late maturing varieties (those ripening later than ‘Wealthy.)
On late varieties, dieldrin may safely be used in the second cover spray, but never beyond the second cover spraying, and then is recommended only in case curculio is severe. “Cover sprays” are put on after the petals have dropped.
Proper Care For Chemicals
Never leave chemicals where children or pets can get into them. A locked cabinet is best, or instead of that, a high shelf well beyond the reach of children.
A tin container, such as a covered coffee can or a glass jar with a screw-on top, will preserve chemicals from possible water damage or attack by mice.
For your protection, never store chemicals without labels, and by all means, never use unlabeled chemicals. If the brands come off, don’t take a chance that you will know which chemical is which.
It is wiser – and safer – to dispose of them and buy new materials. And, of course, you should always read the directions and other information given on package labels.
Observe all precautions provided on the label. Never store leftover spray. Discard it in a safe place and rinse out the sprayer with clear water.
Remember that effective control of fungus and insect enemies of the plum depends upon the thoroughness of your spraying program and how carefully you time the various sprayings. Care and thoroughness on your part will pay dividends in a fine crop.
44659 by Roberta F. Caldwell