Dormant spur or twig sampling is used to determine the need for a dormant treatment to control San Jose scale, European red mite, brown mite, European fruit lecanium, and almond scab, caused by Fusicladium carpophilum (Venturia carpophila). Scale and mites are sampled on spurs; scab is sampled on twigs. Dormant spur and twig samples are taken once a year between mid-November and the end of January.
How to Sample
(View photo pages online for identification)
- Randomly select 35 to 50 trees from each orchard or plot to be sampled.
- Selecting major scaffolds randomly, clip 2 to 3 spurs (scale and mites) or twigs (scab) from the inside of each tree's canopy.
- Clip the spur or twig off at the base. For scales and mites, sample spurs that are at least two years or older. Make sure to include some old spur wood along with the last year's growth to detect parasite activities on scales.
- Using a hand lens or binocular microscope, examine 20 of the spurs for scales, European red mite or brown mite eggs, or one-year-old green twigs for scab lesions.
- Record observations in a sampling form . It is not necessary to count the number of individual insects or mite eggs present, just identify the pest or disease and record whether it is present or not.
- Note how many scales are parasitized. 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 only use those that are not harmful to parasites so that naturally occurring populations will not be destroyed. See RELATIVE TOXICITIES OF PESTICIDES USED IN ALMONDS TO NATURAL ENEMIES AND HONEY BEES for a list of pesticides and their toxicity to parasites.
Treatment Thresholds
Examine each of the 20 spurs or twigs for the presence or absence of scales, European red or brown mite eggs or scab lesions. Do not combine totals for the two scale species. For example, if 3 spurs out of a sample of 20 are infested with San Jose scale and 3 spurs contain European fruit lecanium, neither has exceeded the 20% treatment threshold and sampling should continue.
| Number of Spurs with Scale or Mites Eggs | |||
|---|---|---|---|
| # Spurs sampled |
Do not treat |
Continue sampling |
Treat |
| 20 (scale) | 0 | 1–3 | 4 |
| 20 (mite eggs) | Collect 40 spurs before making a treatment decision | ||
| 40 | 1 | 2–7 | 8 |
| 60 | 3 | 4–11 | 12 |
| 80 | 5 | 6–15 | 16 |
| 100 | 1–19 | — | 20 |
| Number of First Year Green Twigs with Scab | |||
|---|---|---|---|
| # Twigs sampled |
Do not treat |
Continue sampling |
Treat |
| 20 | Collect 40 twigs before making a treatment decision | ||
| 40 | 1 | 2–3 | 4 |
| 60 | 3 | 4–5 | 6 |
| 80 | 5 | 6–7 | 8 |
| 100 | 1–9 | — | 10 |
To determine treatment thresholds use the table below, with detailed treatment threshold information for dormant spur sampling. A dormant spur sampling form is available.
| Pest | Threshold | Treatment |
|---|---|---|
| San Jose Scale | Below 20% 20%–60% Over 60% |
No Spray Oil at 6–8 gals/acre Oil with insect growth regulator2 |
| European Fruit Lecanium | Below 20% 20% and above |
No spray Oil only |
| Overwintering Mite Eggs1 (European red mite or brown mite) | Below 20% 20% and above |
No spray Oil only |
| Scab | Below 10% 10% and above |
No spray Copper + oil or chlorothalonil + oil |
| 1 | Oil works best closer to delayed dormant timing or on warmer days when eggs are respiring. Using dormant oil alone does not provide adequate control for European red mites in Kern County. |
| 2 | See San Jose Scale section for specific insect growth regulators. |