Dormant spur sampling for prunes.
This technique can also be used to monitor for these pests in plum and almond. (View with transcript)
Dormant spur sampling is used to determine the need for a dormant treatment to control San Jose scale, European fruit lecanium, European red mite, and brown mite. If mealy plum aphid and leaf curl plum aphid were not treated in early November, also record the presence of aphid eggs in the dormant spur sample. Spurs are the short shoots containing the flower buds. Dormant spur samples are taken once a year between mid-November and the end of January.
Use the sampling 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.
- Select 2 to 3 spurs randomly from the inside of each tree's canopy near the main scaffold. 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.
- 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.
- Using a hand lens or binocular microscope, examine the spurs and note the presence or absence of scales and parasitized scales, aphid eggs and mite eggs on the sampling 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.
Dormant Treatment Decision Table (% Infested Spurs)
| Pest | Treatment threshold | Treatment | |
|---|---|---|---|
| European fruit lecanium | 24% and below | No spray | |
| Over 24% | Oil only | ||
| Overwintering mite
eggs (brown mite and European red) |
Below 20% | No spray | |
| 20% and over | Oil only | ||
| Overwintering aphid eggs (mealy plum aphid or leaf curl plum aphid) |
If any | See aphid PMGs for materials | |
| Harvested before June 15 | Harvested after June 15 | ||
| San Jose scale | Below 20% | Below 5% | No treatment |
| 20-60% | 5-10% | Oil at 6 gal/acre | |
| Over 60% | Over 10% | Oil at 6 gal/acre plus insect growth regulator1 | |
| 1 See the San Jose scale section for more information about treatment choices according to infestation levels. |
Choice of Insecticides
Oils alone are effective against the white cap and black cap stages of San Jose scale, 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 peach twig borer and obliquebanded leafrollers will not be controlled by oil alone during the dormant season. Environmentally sound insecticides such as Bacillus thuringiensis, spinosad (Entrust, Success), methoxyfenozide (Intrepid) and diflubenzuron (Dimilin), however, 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 is a good IPM strategy for many orchards.
Organophosphates applied during the dormant season for peach twig borer are particularly vulnerable to run-off into waterways and should be avoided.