How to Manage Pests

UC Pest Management Guidelines

Prune

Dormant Spur Sample

(Reviewed 6/06, updated 11/11)

In this Guideline

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Dormant spur sampling for prune pests.
This technique can also be used to monitor for these pests in plum and almond.   (View with transcript)

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How to collect dormant spurs in prune.
This technique can also be used to monitor for these pests in plum and almond.   (View with transcript)

Dormant spur sampling is used primarily to determine the need for a dormant treatment to control San Jose scale and European fruit lecanium. If mealy plum aphid and leaf curl plum aphid were not treated in early November, record them in the dormant spur sample as well. If they were treated, eggs in the dormant spur sample may or may not be viable and should not be recorded. European red mite and brown mite are sampled to keep an eye on populations, but treatment is not recommended.

Use the monitoring form (PDF) with detailed treatment threshold information for dormant spur sampling.

HOW TO SAMPLE

(View photos for identification)

  • Take a sample between mid-November and mid-January.
  • Randomly select 35 to 50 trees from each orchard or plot to be sampled.
  • Take 2 to 3 spurs randomly from the inside of each tree's canopy near the main scaffold. (Spurs are the short shoots containing the flower buds.)
  • Clip the spur off at the base, making sure to include some old spur wood along with the past season's growth to detect parasite activities on scales. Continue until you have collected a total of 100 spurs. It is important to choose spurs on older wood because they are much more likely to be infested.
  • Using a hand lens or binocular microscope, examine 20 of the spurs and note the presence or absence of scales and parasitized scales, aphid eggs and mite eggs on the dormant spur monitoring form. It is not necessary to count the number of individual insects or mite eggs present, just identify the pest and record whether it is present or not.
  • A parasitized scale can be distinguished from a live scale by a small hole in the top of the scale covering. Parasitized European fruit lecanium scales turn black. If a large number of scales have been parasitized, minimize the use of insecticides during the growing season, and use those that are not harmful to parasites so that naturally occurring parasite populations will not be destroyed.

TREATMENT THRESHOLDS

If aphid eggs are being recorded because an early November treatment was not made, a treatment is recommended if any aphid eggs are found. Disregard aphid eggs in orchards treated in early November because they are probably dead.

  • If no aphid eggs or scale are found in the initial sample of 20 spurs, no more spurs need to be examined, BUT the absence of aphids eggs in spur samples is not conclusive evidence that aphids will not be a problem. Use past history of aphids in the orchard as an additional guideline.
  • If 1 to 3 spurs are infested with scale, examine the next 20 spurs. If 4 or more spurs are infested with live scale apply a treatment.
  • Continue examining spurs in groups of 20 until a decision is made to treat or not to treat using the treatment guidelines on the monitoring form or the table below.
  • Do not combine totals for the two scale species. Economic thresholds are much higher for European fruit lecanium than they are for San Jose scale.
  • Economic damage is rare for European red mite and brown mite, even at high levels of dormant spur infestation. Treatment thresholds have not been set for brown mite or European red mite, and treatments are not recommended for them.
  • Use the Dormant Treatment Decision Table below to help select an appropriate insecticide.

Choice of pesticides

Oils alone are effective against the white cap and black cap stages of San Jose scale, both of which are present at this time, and will also control low-to-moderate populations of mite eggs and fruittree leafroller eggs. Other pests such as aphids, peach twig borer, and obliquebanded leafrollers will not be controlled by oil alone during the dormant season. Low rates of pesticides applied early or late in the dormant season are very effective against aphid eggs and can be combined with the dormant oil if scale need treatment. Environmentally sound insecticides such as Bacillus thuringiensis, spinosad (Entrust, Success), methoxyfenozide (Intrepid) and diflubenzuron (Dimilin), applied at bloom will control peach twig borer and leafroller caterpillars. The combination of these bloom time treatments along with a dormant oil application for scales, mite eggs, and leafroller eggs and a low-rate application of pesticide for aphid eggs, when needed, is a good IPM strategy for many orchards.

SUMMARY OF TREATMENT THRESHOLDS
  Number of infested spurs
Aphid eggs San Jose scale
Sample no. Don't treat Treat Stop sampling Treat Keep sampling
First 20 Spurs 0 1 0 4+ 1–3
First 40 Spurs 0 1 1 6+ 2–5
First 60 Spurs 0 1 3 8+ 4–7
First 80 Spurs 0 1 5 9+ 6–8
First 100 Spurs 0 1 9 10+

DORMANT TREATMENT DECISION TABLE (% infested spurs)

Pest Threshold Treatment1
aphid eggs2
(mealy plum aphid and leaf curl plum aphid)
1 egg insecticide
San Jose scale below 5%
5–19%
20% and over
no spray
oil at 4–6 gal/acre
oil with insect growth regulator or insecticide
European fruit lecanium below 24%
24% or over
no spray
oil only
overwintering mite eggs3
(brown mite and European red mite)
sprays are typically not needed

1 See individual pest section for recommended insecticides and insect growth regulators.
2 Dormant oil will not control aphid eggs. Research has shown reduced insecticide rates are effective.
3 Oil works best closer to bloom (delayed dormant) or on warmer days when eggs are respiring.

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[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Prune
UC ANR Publication 3464

General Information

C. Pickel, UC IPM Program, Sutter/Yuba counties
F. J. A. Niederholzer, UC Cooperative Extension, Sutter/Yuba counties
W. H. Olson, UC Cooperative Extension, Butte County
F. G. Zalom, Entomology, UC Davis
R. P. Buchner, UC Cooperative Extension, Tehama County
W. H. Krueger, UC Cooperative Extension, Glenn County
Acknowledgment for contributions to Insects and Mites:
W. O. Reil, UC Cooperative Extension Solano/Yolo counties

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