I posted this on the HOS forum; am now adding it to the General. Thank you for the responses. I have a major outdoor ant infestation. I have ants swarming over the leaves, one by one of my European plum tree. They have brought bugs about 1/4" long - pale green, almost translucent, oval with two long slender antennae. I was told they were aphids. The leaves were first curling and now are dying; there were many tiny fruits that are now gone. I released ladybugs about 3 weeks ago; only 2 stayed around, and to no effect. Any way to get rid of the ants from the yard/garden in addition to the tree? I live in the Pacific NW.
I use a product called Tanglefoot, it's available from most garden centers in squeeze tubes or tubs; I've even found it in a calking gun sized tubes. If your tree is free standing and does not touch a fence, post, tall grass or weeds, I'd smear a line of this ultra-sticky stuff around it's trunk.
It will last for about a year and is amazingly sickly. The ants I've watched usually have a nest beyond the tree and will stop (filled with aphid juice I suspect) on the upside - while the empty ants are stuck below. The top ones can likely jump 
but no replacements can get beyond the line of Tanglefoot.
Just watch that it doesn't need a new coating or that anything else touches the tree above that line!
MANAGEMENT OPTIONS FOR COMMERCIAL AND HOME USE
In all cases, follow the instructions on the pesticide label. The PNW Insect Management Handbook has no legal status, whereas the pesticide label is a legal document. Read the product label before making any pesticide applications.
The following management information provides a suggested amount of each formulation per acre when applied to mature trees. The size of trees, amount of foliage, type of equipment used, and other factors are important in determining the amount of spray to use per acre. Read carefully the entire label of each material to be used.
Note : Products are not listed in order of preference or superiority of pest control.
Protect pollinators —see “How to Reduce Bee Poisoning from Pesticides,” in the Bee Protection section of this handbook.
For mite identification —see “Field characteristics of PNW fruit-tree attacking spider mites” at the beginning of the Tree Fruit Crops section of this handbook.
Plum and Prune—Aphid
(Hop aphid) (Phorodon humuli) ID photos: Adult Immature
Leaf curl plum aphid (Anuraphis helichrysi)
(Thistle aphid) (Brachycaudus cardui)
Pest description and crop damage Several aphid species attack plums and prunes, including the leaf curl plum aphid, hop aphid, and thistle aphid. Aphids feed initially on the shoot tips, which on young trees can cause stunting and malformation of the tips. On older trees, fruit set may be reduced in subsequent years if populations are high; honeydew production can cause sooty mold problems on fruit.
Biology and life history Aphids overwinter as eggs in crevices and twigs. The eggs hatch near budbreak and the nymphs feed on unopened buds and the undersides of the leaves. The leaves curl and protect the aphids as they feed. After two to three generations, winged forms are produced that migrate to summer hosts which include weeds, ornamental plants, and vegetables, or plants of the mustard family in the case of black cherry aphid. After several more generations, the winged forms migrate back in the fall to the fruit tree to mate and lay the overwintering eggs.
Scouting and thresholds Begin observing shoots prior to budbreak, as management is best undertaken early while the aphids are small.
Management—biological control
Aphids have many natural enemies, which include ladybeetles, syrphid fly larvae, and green lacewings. Avoid broad-spectrum insecticide applications that would disrupt these controls.
Management—cultural control
Home orchardists: Wash aphids from plants with a strong stream of water or by hand-wiping. Aphid populations tend to be higher in plants that are fertilized liberally with nitrogen. Avoid excessive watering which, together with nitrogen applications, produces flushes of succulent growth.
Management—chemical control: HOME USE
Dormant-season spray
Apply only during dormant or delayed-dormant period. Apply with enough water to cover the entire tree thoroughly.
1. superior-type oil
Growing-season spray
Apply when overwintering eggs hatch during prebloom or petal fall. Summer applications should be before leaves curl.
1 acetamiprid.
2. azadirachtin (neem extract)
3. carbaryl
4. gamma-cyhalothrin
5. esfenvalerate
6. imidacloprid
7. insecticidal soap—May require several applications.
8. pyrethrins
Management—chemical control: COMMERCIAL USE
Apply when overwintering eggs hatch during pre-bloom or petal fall. In summer, apply before leaves curl for best control. Fall sprays can provide excellent aphid control the next growing season.
(Dormant spray)
1. horticultural mineral oil at 2 gal/100 gal water (8 gal/a). Use oil sprays during dormant or delayed-dormant period. EC formulation is preferred when label says to mix with oil.
2. horticultural mineral oil at 1 gal/100 gal water (4 gal/a) + an organophosphate insecticide such as Diazinon 50W at 1 lb/100 gal water (4 lb/a) .
Spring and summer spray
1. diazinon (Diazinon 50W) at 1 lb/100 gal water (4 lb/a). Do not exceed one application per growing season. PHI 21 days. REI 4 days.
2. imidacloprid (Provado 1.6F) at 2 fl oz/100 gal water (4 to 8 fl oz/a). PHI 7 days. REI 12 hr. Generic labels for chlorpyrifos are also available. Warning: Toxic to bees. Do not use until pollination is complete and bees have left the orchard. Generic formulations of imidacloprid are available.
3. spirotetramat (Movento, Ultor) at 6 to 9 fl oz. PHI 7 days. Do not apply after petal fall. 4. thiamethoxam/chlorantraniliprole (Voliam Flexi) at 0.1 to 0.175 lb ai/a. Do not apply exceed 0.35 lb ai of Voliam Flexi per season. Do not apply by air. Minimum interval between applications is 10 days. PHI 14 days.
(Postharvest spray)
1. diazinon (Diazinon 50W) at 1 lb/100 gal water (4 lb/a). REI 4 days. Do not exceed one application per growing season.
2. phosmet (Imidan 70W) at 1 lb/100 gal water (4 lb/a). REI 12 hr. Extremely toxic to fish; avoid spray drift and runoff to surface waters.
Randy
Yamhill County Master Gardener
For cheap, lazy, safe, quick help........you could use water and masking tape. First, blast all the tree with your garden hose to 'start over'. Second, use 3/4" or 1" wide sticky masking tape to make a couple separated, wrap-around rings on the trunk with the sticky side facing outward. Just overlap the ends a couple inches so they adhere to each side as you tightly pull the tape snug to a round, smooth section of the trunk. Crawling things will usually get stuck in place. I would check the tape rings regularly, so that if any small lizard got caught you could gently set it free. It is easier to free them from narrower tape than 2" wide tape.When the tape is either full of bugs or no longer sticky, remove and replace. One morning I found about 30 or so small black ants had just arrived, and each one was carrying a live, green aphid.
I have cured my aphid problem. Look on Google images and see the ants sucking the sweet juices from the aphids butts. The ants herd the aphids to the very ends of the branches last leaves and prevent them from traveling back up the branch. They then 'milk' the aphids. Come fall they carry the aphids down into the ground and keep them there until spring, whereupon the cycle repeats when they bring them back up into the tree. My cure is to wrap a nylon stocking around the base of the tree and secure it with a safety pin. Every spring, I renew coatings of sticky Tanglefoot on the stocking and the ants get trapped. They will even build grass blade bridges over the sticky stuff to cross over and get the aphids back working. Go out on a warm night and watch the ants working.
When you take a sweet cherry that is infested with aphids at the ends of its branches, and install a stocking -Tanglefoot barrier, in a matter of days it comes back to life. You can see its new vigor! Be careful, the ants will find ways to climb up between bark furrows and valleys. They will even climb neighboring trees and cross over to the protected tree! Don't apply much Tanglefoot directly on the bark except in places the stocking does not reach like deep valleys. 
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