San Jose Scale: Past, Present & Predictions

For the past few years OMAFRA specialists have been monitoring San Jose scale (SJS), a pest in Ontario apple orchards. We have been monitoring the lifecycle and population trends of this insect to determine optimal spray timings, as there is a small window to effectively apply insecticides.

San Jose scale is very difficult to eradicate once it has become established in an orchard. This pest was not an issue in Ontario for a number of years, but perhaps with an increase in warmer weather and a changing IPM program, scale is once again a pest to be reckoned with in Ontario orchards. We have begun to monitor for this insect and investigate any effective models that predict emergence and lead to better management.

Female scales spend their lives immobile and protected under a waxy scale, which is very effective at protecting them from predators, desiccation, and pesticides. Male scales are small flying insects. Young scales emerge from underneath the female's scale as crawlers, and will be active for up to a day before finding a suitable place on bark or fruit to feed (Figure 1). The crawler will settle in this spot, building a protective, waxy, scale covering. Because of the short time that the crawlers are active there is a small window when crawlers are unprotected and insecticides will be effective. It is therefore vital to know when crawlers have emerged. Since this pest is so small, monitoring and scouting for this pest can be difficult and time consuming. Using degree day models to predict crawler emergence is an attractive alternative to constant scouting for these tiny insects.

Figure 1. San Jose scale damage on developing fruit.

Figure 1. San Jose scale damage on developing fruit.

We have been comparing two different models that predict SJS emergence against our own observations to assess how effective these models can be in Ontario. Using the data that we have collected in previous years and this year's data, we can compare our monitoring results to the predictions and determine how accurate these models are at predicting crawler emergence.

Cornell DD model

  • Biofix: March 1st
  • Base temperature: 10°C
  • 1st generation crawler emergence: 278 DD, or approx. 29 ± 12.5 days from McIntosh petal fall
  • 2nd generation crawler emergence: 806 DD, or approx. mid-July

Washington DD model

  • Biofix: first adult male catch
  • Base temperature: 10.5°C
  • 1st generation crawler emergence: 222-249 DD, or approx. 1st generation codling moth (CM) biofix
  • 2nd generation crawler emergence: n/a

Table 1. 2014 degree day results.

Region

Predicted emergence
(NY model)
1st generation

Predicted emergence
(NY model)
2nd generation

Predicted emergence
(WA model)
1st generation

Predicted emergence
(WA model)
2nd generation

Observed emergence

1st generation

Observed emergence

2nd generation

Middlesex
June 16-17
Aug 10-11
No biofix
n/a
Not observed
Aug 14
Norfolk
June 19-20
Aug 19-20
June 22-24
n/a
June 25
Aug 18
Georgian Bay
June 26-27
Aug 25-26
June 29-30
n/a
June 27
Aug 27

Table 2. 2015 Degree day results.

Region

Predicted emergence
(NY model)
1st generation

Predicted emergence
(NY model)
2nd generation

Predicted emergence
(WA model)
1st generation

Predicted emergence
(WA model)
2nd generation

Observed emergence

1st generation

Observed emergence

2nd generation

Middlesex June 13-15 Aug 9-10 No biofix n/a Not observed Aug 21
Norfolk June 10-12 Aug 3-5 June 22-24 n/a June 22 Aug 28
Georgian Bay June 20-22 Aug 18-20 No biofix n/a Not observed Aug 21

To monitor for the adult male scales, pheromone traps were placed in orchards in mid-May, and monitored through the apple season. Monitoring for crawlers was more difficult, as they are very small and difficult to see on the tree limbs. We found using black electrical tape to monitor for the presence of crawlers to be effective this past summer (Figure 2). Crawlers are small and yellow, and can easily be seen on black tape (Figure 3).

Figure 2. Black electrical tape wrapped around the trunk for crawler monitoring.

Figure 2. Black electrical tape wrapped around the trunk for crawler monitoring.

Figure 3. San Jose scale crawler trapped on black electrical tape.

Figure 3. San Jose scale crawler trapped on black electrical tape.

Table 1 & 2 summarize the findings using both the New York (NY) and Washington State (WA) models. The WA has generally been more accurate at predicting first generation crawler emergence. This model uses first adult catch as a biofix, which tends to be more accurate than using March 1st as a biofix as this is not specific to orchards and may not accurately reflect the actual development of scale in that location year to year.

There are two full generations of scale each year, and monitoring indicates that these generations overlap, as we consistently found crawlers on black electrical tape throughout the summer. However, using tape is time consuming and is not always effective; having alternative methods to determine optimal spray timing would be beneficial. Using these degree day models in addition to intensive scouting will help accurately time insecticides and control this pest.

I would like to thank Victoria Blake, OMAFRA summer student, for her help in conducting the monitoring throughout the summer.


For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca