Spring/Summer Monitoring for Aphids

Monitor mealy plum aphid and leaf curl plum aphid in spring. This practice is especially important if a dormant or delayed-dormant insecticide spray (does not include oil sprays) was not applied or if aphids have been a recurrent problem in the orchard. Begin monitoring weekly at petal fall until a treatment is applied or until July 15. After treatment, monitor every other week through July 15. If aphid numbers 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 (PDF) with detailed treatment threshold information.

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, particularly cattails and reed grass in the case of mealy plum aphid.

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, time yourself on each tree. 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.
   1. Look for signs of aphid presence, such as curled leaves, honeydew, waxy- or silvery-looking leaves, and the presence of bees, ants, and natural enemies that prey on aphids.
   2. If any of these signs or 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 half of the tree has live aphids, determine whether the aphid population is significant. A population is significant if aphids (of either species) occupy 10% or more of the tree’s leaf surface as determined by a visual search.
   1. Determine whether they are mealy plum aphids or leaf curl plum aphids.
   2. If one or both halves of the whole tree has significant aphid populations, record the tree on the monitoring form (PDF) as having a significant aphid population.
   3. After looking at 10 whole trees, move to a slightly different part of the orchard and repeat the procedure. Continue monitoring until 10 minutes have passed or 40 whole trees have been examined.
3. After you have sampled 40 whole trees in this manner, decide to treat, continue sampling, or stop sampling.

Monitoring result	Action
More than 12 trees have significant aphid populations.	Stop the search and treat. See Mealy Plum Aphid or Leaf Curl Plum Aphid 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:

Monitoring result	Action
More than 16 trees from both searches have significant aphid populations.	Stop the search and treat. See Mealy Plum Aphid or Leaf Curl Plum Aphid 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 from both searches have a significant population of aphids.	Do one additional 5-minute search (see step 5).

5. If a second 5-minute search (20 new trees) is required:

Monitoring result	Action
More than 16 trees from all three searches have significant aphid populations.	Stop the search and treat. See Mealy Plum Aphid or Leaf Curl Plum 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 population of aphids.	Do one additional 5-minute search using the same thresholds (spray if more than 16 trees from all 4 searches with significant aphids and stop if less than 8 trees from all searches have significant aphid populations.