Dormant shoot sampling is used to determine the need for a dormant treatment for the control of San Jose scale, European fruit lecanium, and mite eggs (brown mite and European red mite).
How to Sample
(View photos for identification)
- Take a sample between late November and mid-January.
- Randomly select 20 trees from each varietal block in the orchard.
- Choose 5 shoots randomly from the inside of each tree's canopy near the main scaffolds for a total of 100 shoots.
- Clip off a 3-inch section from the basal portion of the shoot that contains both 1- and 2-year old wood.
- Using a hand lens or binocular microscope, examine the section of the shoot and note the presence or absence of scales and parasitized scales and mite eggs on a 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.
- Note if scales have been parasitized. A parasitized scale can be distinguished from a live scale by a small hole in the tops 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.
- Use the Dormant Treatment Decision Table below to determine if treatment is required and what to spray.
Dormant Treatment Decision Table (% Infested Shoots)
| 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 | ||
| San Jose scale | Harvested before June 15 | Harvested after June 15 | |
| Below 20% | Below 5% | No treatment | |
| 20-60% | 5-10% | Oil at 6 gal/acre | |
| Over 60% | Over 10% | Oil at 2-6 gal/acre plus insect growth regulator1 | |
| 1 Using oil at the 4-6 gal rate will help prevent development of resistance to the IGR. If oil is used at the 2 gal rate, do not use the IGR in consecutive years to prevent resistance development. |
Choice of Pesticides
Choice of pesticide depends on which pests are present at damaging levels and when treatment is being applied. During the dormant season, 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 populations of mite eggs and provide moderate control of fruittree leafroller eggs. Only the highest levels of San Jose scale will require addition of an insect growth regulator. Other pests such as peach twig borer and obliquebanded leafrollers will not be controlled by oil during the dormant season. Environmentally sound insecticides such as Bacillus thuringiensis, chlorantraniliprole (Altacor), diflubenzuron (Dimilin), and methoxyfenozide (Intrepid), however, applied at bloom will control peach twig borer and leafrolling caterpillars. Combining these bloomtime 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, are no more effective than reduced risk products, and should be avoided. Never spray before an expected rainfall. If you wish to treat peach twig borer during the dormant season, consider an environmentally sound insecticide such as spinosad, spinetoram, or diflubenzuron. See the peach twig borer guideline.