Prune Aphid Management

Franz Niederholzer, UCCE Farm Advisor, Colusa and Sutter/Yuba Counties;
Luke Milliron, UCCE Farm Advisor, Butte, Glenn & Tehama Counties

Plum aphids (2 species) are the major pest of prunes. Feeding on leaves and stems of rapidly growing shoots, the mealy plum aphid (MPA) causes curling and stunting of leaves, and also secretes honey dew leading to sooty mold on the fruit surface and an increased risk of end cracking in the summer. Severe, uncontrolled MPA infestations can limit return bloom in prunes, reducing crop load the following year. The leaf curl plum aphid (LCPA) also feeds on growing shoots, severely stunting and contorting leaves and also secreting large amounts of honeydew. Fall or winter are good timings to control aphid. So, with harvest over, it’s a good idea to settle on an aphid control plan to protect next year’s crop.

Leaf plum curl aphid. Photo: UC Statewide IPM Program.

Leaf plum curl aphid (LPCA). Photo: UC Statewide IPM Program.

Both MPA and LCPA move out of most prune orchards to summer hosts once prune shoot growth ceases — usually by June at the latest.  [In highly vigorous, young orchards where shoot growth lasts all season, aphids may remain all season long.] Plum aphids move back into orchards in the fall (late September into October) to feed, mate, and lay eggs that will hatch during bloom the following year.

It is very challenging to effectively monitor plum aphid in California prune orchards before eggs hatch. The fall spur sampling protocol includes aphid eggs, but those eggs are scattered in the orchard and only one egg out of 100 spurs triggers a spray treatment. There is a real risk of missing aphid pressure in a block if you only use the dormant spur test results to determine the need for control. [Still, the dormant spur sampling is vital to scale control, so while looking for scale, keep an eye out for aphid eggs – they are a lot easier to see (when present) compared to scale.]

The black aphid egg is visible at the base of the dormant bud.

The black aphid egg is visible at the base of the dormant bud. Photo: UC Statewide IPM Program.

Since accurate monitoring ahead of aphid infestation is hard to do, growers basically have two choices for plum aphid management:

  1. Assume you have an annual problem and treat between fall and full leaf out. If you have a history of aphid infestation when dormant sprays are skipped or applied with poor coverage (every-other row by ground or aerial spraying), it’s a good bet you have a significant risk of annual aphid infestation.
  2. Wait and watch, treat if aphids show up once shoot growth gets going in the spring. If you haven’t had much or any aphid pressure in the last few years, the ‘wait and see’ approach is a good option. Before you spray, make sure the pesticide sprayed is cleared with your processor/packer.

Both strategies can be effective with the right pesticide materials, spraying and timing. There are advantages and disadvantages to each plan. It’s a grower’s call. Talk with your PCA about options.

The following table shows a range of timings and materials that control aphids, plus options to control other pests commonly controlled with a traditional dormant spray (pesticide plus oil) – scale and peach twig borer (PTB). If you move away from a traditional dormant spray when controlling aphids, make sure to keep those occasional pests under control.

Always read the label & check with your PCA regarding orchard specific rates, materials & timing.

General timing, efficacy, and water quality risk for spray practices and material combinations that target key prune insect pests – plum aphid, peach twig borer (PTB) and scale. Efficacy rating assumes excellent spray coverage. “++” = excellent control, “+” = partial control, “--“ = no control or benefit.General timing, efficacy, and water quality risk for spray practices and material combinations that target key prune insect pests – plum aphid, peach twig borer (PTB) and scale. Efficacy rating assumes excellent spray coverage. “++” = excellent control, “+” = partial control, “--“ = no control or benefit.General timing, efficacy, and water quality risk for spray practices and material combinations that target key prune insect pests – plum aphid, peach twig borer (PTB) and scale. Efficacy rating assumes excellent spray coverage. “++” = excellent control, “+” = partial control, “--“ = no control or benefit.General timing, efficacy, and water quality risk for spray practices and material combinations that target key prune insect pests – plum aphid, peach twig borer (PTB) and scale. Efficacy rating assumes excellent spray coverage. “++” = excellent control, “+” = partial control, “--“ = no control or benefit.General timing, efficacy, and water quality risk for spray practices and material combinations that target key prune insect pests – plum aphid, peach twig borer (PTB) and scale. Efficacy rating assumes excellent spray coverage. “++” = excellent control, “+” = partial control, “--“ = no control or benefit.General timing, efficacy, and water quality risk for spray practices and material combinations that target key prune insect pests – plum aphid, peach twig borer (PTB) and scale. Efficacy rating assumes excellent spray coverage. “++” = excellent control, “+” = partial control, “--“ = no control or benefit.General timing, efficacy, and water quality risk for spray practices and material combinations that target key prune insect pests – plum aphid, peach twig borer (PTB) and scale. Efficacy rating assumes excellent spray coverage. “++” = excellent control, “+” = partial control, “--“ = no control or benefit.
General TimingTiming details, materialsAphid (1)PTB (2)Scale (3)Advance BloomWater Quality Risks (4)
Fall (Nov-Dec)Fall spray (pyrethroid only)+++----+
Dormant (Dec-Jan) (5)Lite dormant spray (pyrethroid only)++++----++
Lite dormant spray (3-4 gpa oil + pyrethroid)+++++++++
Dormant spray (3-4 gpa oil + diazinon or Lorsban)++++++++++
Dormant scale spray (3-4 gpa oil + Centaur or Seize----+++++
BloomB.t. with bloom sprays (Dipel, Javelin, etc)--++------
2x 4% 440 oil at bloom (with fungicides) (6)++--?----
Post-BloomAphid spray (late March-April)++--------
PTB "May" spray (timed by Deg Days after biofix) (7)--++------
Scale crawler spray (based on monitoring)----++----
(1) Determine the need to spray for aphid based on: A regular history of some aphid pressure in an orchard may suggest a need for annual treatments; OR No history of aphid infestation suggests “wait and see” strategy could be effective.1. Determine the need to spray for aphid based on:1. Determine the need to spray for aphid based on:1. Determine the need to spray for aphid based on:1. Determine the need to spray for aphid based on:1. Determine the need to spray for aphid based on:1. Determine the need to spray for aphid based on:
(2) PTB feeding on fruit can damage fruit in-season and is an entry point for brown rot. 2. PTB feeding on fruit can damage fruit in-season and is an entry point for brown rot. 2. PTB feeding on fruit can damage fruit in-season and is an entry point for brown rot. 2. PTB feeding on fruit can damage fruit in-season and is an entry point for brown rot. 2. PTB feeding on fruit can damage fruit in-season and is an entry point for brown rot. 2. PTB feeding on fruit can damage fruit in-season and is an entry point for brown rot. 2. PTB feeding on fruit can damage fruit in-season and is an entry point for brown rot.
(3) Scale is not always a problem in prunes, but can be a major problem if not controlled when populations build. Use dormant spur sampling to determine the scale population in your orchard and what treatment is needed.3. Scale is not always a problem in prunes, but can be a major problem if not controlled when populations build. Use dormant spur sampling to determine the scale population in your orchard and what treatment is needed.3. Scale is not always a problem in prunes, but can be a major problem if not controlled when populations build. Use dormant spur sampling to determine the scale population in your orchard and what treatment is needed.3. Scale is not always a problem in prunes, but can be a major problem if not controlled when populations build. Use dormant spur sampling to determine the scale population in your orchard and what treatment is needed.3. Scale is not always a problem in prunes, but can be a major problem if not controlled when populations build. Use dormant spur sampling to determine the scale population in your orchard and what treatment is needed.3. Scale is not always a problem in prunes, but can be a major problem if not controlled when populations build. Use dormant spur sampling to determine the scale population in your orchard and what treatment is needed.3. Scale is not always a problem in prunes, but can be a major problem if not controlled when populations build. Use dormant spur sampling to determine the scale population in your orchard and what treatment is needed.
(4) Indicates relative risk of runoff from orchards to surface water and harm to aquatic life (fish and their food chain). “++” = significant risk, “+” = relatively less risk, and “–“ indicates relatively little to no risk.4. Indicates relative risk of runoff from orchards to surface water and harm to aquatic life (fish and their food chain). “++” = significant risk, “+” = relatively less risk, and “–“ indicates relatively little to no risk.4. Indicates relative risk of runoff from orchards to surface water and harm to aquatic life (fish and their food chain). “++” = significant risk, “+” = relatively less risk, and “–“ indicates relatively little to no risk.4. Indicates relative risk of runoff from orchards to surface water and harm to aquatic life (fish and their food chain). “++” = significant risk, “+” = relatively less risk, and “–“ indicates relatively little to no risk.4. Indicates relative risk of runoff from orchards to surface water and harm to aquatic life (fish and their food chain). “++” = significant risk, “+” = relatively less risk, and “–“ indicates relatively little to no risk.4. Indicates relative risk of runoff from orchards to surface water and harm to aquatic life (fish and their food chain). “++” = significant risk, “+” = relatively less risk, and “–“ indicates relatively little to no risk.4. Indicates relative risk of runoff from orchards to surface water and harm to aquatic life (fish and their food chain). “++” = significant risk, “+” = relatively less risk, and “–“ indicates relatively little to no risk.
(5) This spray mix is very effective on indicated pests in late dormant or delayed dormant (Feb. 1 to pre-bloom), but does not move bloom date and/or must be reported to Ag Commissioner’s office to avoid bee kills after Jan31. 5. This spray mix is very effective on indicated pests in late dormant or delayed dormant (Feb. 1 to pre-bloom), but does not move bloom date and/or must be reported to Ag Commissioner’s office to avoid bee kills after Jan31. 5. This spray mix is very effective on indicated pests in late dormant or delayed dormant (Feb. 1 to pre-bloom), but does not move bloom date and/or must be reported to Ag Commissioner’s office to avoid bee kills after Jan31. 5. This spray mix is very effective on indicated pests in late dormant or delayed dormant (Feb. 1 to pre-bloom), but does not move bloom date and/or must be reported to Ag Commissioner’s office to avoid bee kills after Jan31. 5. This spray mix is very effective on indicated pests in late dormant or delayed dormant (Feb. 1 to pre-bloom), but does not move bloom date and/or must be reported to Ag Commissioner’s office to avoid bee kills after Jan31. 5. This spray mix is very effective on indicated pests in late dormant or delayed dormant (Feb. 1 to pre-bloom), but does not move bloom date and/or must be reported to Ag Commissioner’s office to avoid bee kills after Jan31. 5. This spray mix is very effective on indicated pests in late dormant or delayed dormant (Feb. 1 to pre-bloom), but does not move bloom date and/or must be reported to Ag Commissioner’s office to avoid bee kills after Jan31.
(6) Cannot be tank-mixed with captan or chlorothalonil (Bravo®, etc.) fungicides.6. Cannot be tank-mixed with captan or chlorothalonil (Bravo®, etc.) fungicides.6. Cannot be tank-mixed with captan or chlorothalonil (Bravo®, etc.) fungicides.6. Cannot be tank-mixed with captan or chlorothalonil (Bravo®, etc.) fungicides.6. Cannot be tank-mixed with captan or chlorothalonil (Bravo®, etc.) fungicides.6. Cannot be tank-mixed with captan or chlorothalonil (Bravo®, etc.) fungicides.6. Cannot be tank-mixed with captan or chlorothalonil (Bravo®, etc.) fungicides.
(7) Check with your packer to make sure anything sprayed is on their “OK to spray” list.7. Check with your packer to make sure anything sprayed is on their “OK to spray” list.7. Check with your packer to make sure anything sprayed is on their “OK to spray” list.7. Check with your packer to make sure anything sprayed is on their “OK to spray” list.7. Check with your packer to make sure anything sprayed is on their “OK to spray” list.7. Check with your packer to make sure anything sprayed is on their “OK to spray” list.7. Check with your packer to make sure anything sprayed is on their “OK to spray” list.

More information on prune pest control:

Dormant aphid control
San Jose Scale control
Peach twig borer control

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