Predicting San Jose scale crawler emergence in apple orchards

As many apple growers have experienced in recent years, San Jose scale (SJS) can cause serious impacts on fruit quality (Figure 1), yield, and if left unmanaged, can result in poor tree vigor or even death of the tree. Not only does the biology of this pest make it difficult to control, but monitoring for an insect so small can sometimes seem like an impossible task in a commercial-sized orchard.

Figure 1. San Jose scale damage often results in small gray patches on apples surrounded by red discolouration around the area.

Figure 1. San Jose scale damage often results in small gray patches on apples surrounded by red discolouration around the area.

Spray timings to target insecticides for SJS require an understanding of crawler emergence or when scale are most vulnerable. In recent years, OMAFRA has been monitoring SJS using pheromone traps and degree-day models to optimize the placement of summer insecticides for SJS control.

This season, the first adult male SJS (Figure 2) was caught at the end of May at the tail-end of bloom or early petal fall. Based on the biology of this pest, crawlers (Figure 3) will begin to emerge a few weeks after petal fall and continue for 4-6 weeks. Similar to last year, the degree-day models are coinciding with this, which puts the predicted timing for 1st generation SJS crawlers beginning June 14-16th in the earliest regions and June 20-25th in the later regions. According to predictions from New York and Michigan, SJS crawler emergence is anticipated in those regions June 12-13th and on. It is important to note, however, degree-day models should be used in addition to visually monitoring infested trees to accurately time insecticide sprays for SJS.

Figure 2. San Jose scale adult male caught on pheromone trap.

Figure 2. San Jose scale adult male caught on pheromone trap. Note the distinct band across the abdomen.

Figure 3. Apple limb speckled with numerous small, yellow San Jose scale crawlers

Figure 3. Apple limb speckled with numerous small, yellow San Jose scale crawlers.

Currently, Movento 240 SC (spirotetramat), Closer SC (sulfoxaflor), TwinGuard (sulfoxaflor + spinetoram) and Sivanto Prime (flupyradifurone) are registered for summer control of SJS. While Closer, TwinGuard and Sivanto are fast-acting and should be applied when crawlers are active, Movento acts as a systemic feeding toxicant and takes some time to move into the plant tissue. Therefore, application needs to be made 1-2 weeks before emergence of crawlers, typically between petal fall and 1st cover and with a penetrating non-ionic surfactant. With any of these products, since crawler emergence can extend over weeks at a time, follow-up 14 days later with a second application.

Successful SJS control starts with prevention. The following are some key points to consider for effective management:

  • Map out localized scale pressure and use harvest assessments to verify. Target sprays to those hot spot areas in the orchard.
  • Once established, SJS can be very difficult to eradicate. Use a targeted SJS control program season-long for several years to achieve effective management.
  • Prune to remove infested branches, open canopy and allow better spray penetration.
  • Dormant oil can be very effective by targeting immature scales before they develop a protective waxy layer. However, complete coverage and timing are essential.
  • Use a DD model with biofix of March 1st or first adult catch (base 10°C) along with visually monitoring infested trees to accurately time control products targeting crawler emergence.

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