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How to Manage Pests

UC Pest Management Guidelines


Plum

Spring/Summer Monitoring for Aphids

(Reviewed 5/06, updated 5/06)

In this Guideline:


Monitor mealy plum aphid and leaf curl plum aphid in spring if a dormant spray was not applied or if only oil was applied during dormancy. Begin monitoring weekly at petal fall and continue until a treatment is applied. After treatment, monitor every other week through July 15. If aphid populations remain low during the first 8 weeks of weekly monitoring, monitoring can be reduced to every other week until a treatment is applied or until July 15.

Use sampling form with detailed treatment threshold information. (100KB, PDF)

WHERE TO MONITOR

Monitor trees at the outside edge of the orchard or in known or potential "aphid hot spots." Potential hot spots for aphid infestation are areas of the orchard that have windbreaks or adjacent areas of natural vegetation.

HOW TO MONITOR (View photos for identification.)

Each sample begins with a search of 40 whole trees. Spend 10 minutes (about 15 seconds per tree) on this search, using a stopwatch or kitchen timer to time yourself. Look for the presence or absence of aphids and rate the population as significant or not.

1. Walk down a tree row and visually examine the half of the tree on your right and half of the tree on your left. These two halves constitute one whole tree for the purposes of this sample.

  • Look for signs of aphid presence, such as curled leaves, honeydew, waxy- or silvery-looking leaves, and the presence of bees, ants, and beneficial insects that prey on aphids.
  • If any of these symptoms are observed, closely examine branches and leaves for the presence of live, damaging aphids. (Damaging aphids are the young wingless aphids.) If leaves are curled, uncurl the leaf and examine up to 5 leaves per tree to verify the presence of live leaf curl plum aphids.

2. If either tree-half has live aphids, determine whether the aphid population is SIGNIFICANT.

  • Determine whether they are mealy plum aphids or leaf curl plum aphids.
  • If aphids (either species) occupy 10% or more of the tree's leaf surface as determined by a visual search, the population is SIGNIFICANT. Whether one or both halves of the whole tree has significant aphid populations, record the tree on the monitoring form as having a significant aphid population.

3. After you have sampled 40 whole trees in this manner, make a decision. The results of the sample will lead to a decision to treat, continue sampling, or stop sampling.

If you find Take action
More than 12 trees have significant aphid populations, Stop the search and treat. See the mealy plum or leaf curl aphid sections for treatment choices.
Less than 4 trees with a significant aphid population, Stop the search. Monitoring is over for the week and no treatment is needed.
Less than 12 but more than 4 whole trees have a significant population of aphids, Do an additional 5-minute search (see step 4 below).

4. If you could not come to a final decision in step 3 above, conduct an additional 5-minute search that surveys 20 new trees. Up to two additional 5-minute searches may be required to reach a decision. Record results on the monitoring form.

After the first 5-minute search of 20 additional whole trees,

If you find Take action
More than 16 trees from both searches have significant aphid populations, Stop the search and treat. See the mealy plum or leaf curl aphid sections for treatment choices.
Less than 8 trees from both searches have significant aphid populations, Stop the search. Monitoring is over for the week and no treatment is needed.
Less than 16 but more than 8 whole trees have a significant populations of aphids, Do one additional 5-minute search (see step 5).

5. If you did not come to a final decision in step 4, a second 5-minute search is required,

If you find Take action
More than 16 trees from all three searches have significant aphid populations, Stop the search and treat. See the mealy plum or leaf curl aphid sections for treatment choices.
Less than 8 trees from both searches have significant aphid populations, Stop the search. Monitoring is over for the week and no treatment is needed.
Less than 16 but more than 8 whole trees have a significant populations of aphids, Do one additional 5-minute search.

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Plum
UC ANR Publication 3462
General Information

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Statewide IPM Program, Agriculture and Natural Resources, University of California
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