Springtime in the Orchard: Organic Strategies for Apple Pest Management

With the temperature gradually increasing, buds are swelling and green tip is just around the corner in many of the early apple growing regions of the province. Spring is a great time to get a head start on pest control in the orchard, before insect populations or disease inoculum build, and actively growing tissue and dense foliage makes management a little trickier. If you haven't already, now is the time to begin thinking about IPM strategies that can be done over the next few weeks that will help reduce the likelihood of chasing certain pests later in the season.

Dormant Oil

While a dormant or delayed dormant oil spray can be an excellent management tool, timing and thorough coverage are critical to achieve good control. Understanding how oil works, as well as the biology of the pests will help to optimize control applications and avoid tissue damage.

Oil can work by suffocation, interfering with egg development, and/or prevent settling of scale crawlers. If applied properly, the use of dormant or delayed dormant oil can sufficiently reduce the scale or mite populations respectively that could develop later in the season. Once these pests have become established, they can be very difficult to eradicate. Early season oil sprays also fit well into organic programs because the product is applied before predatory mites and other beneficial insects are present.

There are several species of scale insects affecting apples; San Jose scale is the most common in Ontario orchards. This insect overwinters as an immature scale on the bark until tree sap starts moving in the spring (Figure 1). Dormant oil is the best timing for control of this pest while there is little foliage preventing sprays from reaching the trunk and branches. The use of summer oil has shown to have effective, long-lasting control over scale in some Ontario orchards, but is often difficult to time and may not be as reliable as a dormant spray.

Figure 1. Overwintering San Jose scale on apple twig.

Figure 1. Overwintering San Jose scale on apple twig.

European red mites overwinter as eggs (Figure 2) on roughened bark around the bases of buds and spurs, or in the inner parts of the tree close to the main trunk and branches. Oil sprays should be applied before egg hatch, which often occurs around half-inch green or tight cluster. Some growers in Ontario, who have used dormant oil with sufficient water volumes and good coverage, have achieved excellent mite control with few summer escapes. Delayed dormant oils may also kill overwintering aphid eggs, if the timing coincides with hatching.

Figure 2. Overwintering European red mite eggs on apple spur

Figure 2. Overwintering European red mite eggs on apple spur.

Unfortunately, optimal timing for scale is not necessarily the same for mites. If harvest assessments last year indicated scale is a bigger issue in the orchard, oil needs to be applied before bud break. This efficacy against scale is significantly reduced with later oil applications timed for mites. Be mindful that a tree carrying a few infested fruit last season can result in large scale populations this year if not properly managed.

Although most horticultural oils have become quite refined, with sulphur impurities removed, even "summer" oils may still cause crop injury when applied:

  • with or too close to products containing sulphur; do not apply oil within 14 days before or after these products.
  • within 48 hours of freezing weather.
  • above label rate; use 2% solution (20L/1,000L) for dormant sprays and 1% solution (10L/1,000L) for summer sprays in high water volumes.
  • to trees under moisture stress.
  • during temperatures above 25¢XC.
  • to sensitive cultivars, such as Red Delicious, Empire or Mutsu/Crispin.

Monitoring Tools

Spring can also be a time to assess your inventory of the monitoring tools that will be used this season, including pheromone traps and weather monitoring equipment.

Degree day models often make use of these tools to accurately predict the life stages of many apple pests, including codling moth, oriental fruit moth and oblique banded leafroller. For example, egg hatch for first generation codling moth occurs around 139 DDC (base 10C) after sustained moth catch. This could be a difference of one or two weeks depending on the temperature from one year to the next.

Check out the guidelines for using insect pheromone and visual traps on the apple module of Ontario cropIPM. There you will find information on appropriate trap type, number to use, placement in the orchard and when to deploy for each pest.

Visit the OMAF website to find a list of IPM suppliers of pest monitoring equipment. To extend the life of pheromone lures, remember to store them in the fridge or freezer until you are ready to use them.

Dormant Copper

The efficacy of copper sprays this time of year to reduce the spread of fire blight inoculum from overwintering cankers has often been debated. Its effectiveness really comes down to how it is applied and post-application weather. Copper provides an unfriendly environment over the bark and bud surfaces of the tree, preventing bacteria from getting established or spreading to blossoms through rain splash or insects. Thus, it must be applied as a high volume spray to ensure sufficient coverage.

David Rosenberger from Cornell University recommends that copper sprays should be applied at ¼ to ½" green only since later sprays can result in severe fruit russetting. As well, in order for copper sprays to work effectively, it is recommended they be applied to all of the trees in the block. Untreated trees, even non-susceptible varieties, provide a safe haven for the bacteria and insect vectors can move the bacteria around easily.

Copper sprays applied to green tissue may also provide some protection against apple scab when applied before spores are released. Follow a dormant copper spray with an early-season sulphur program for scab and powdery mildew, beginning at green tip, at 7-10 day intervals through primary scab season, especially during wet periods. The use of scab resistant varieties will greatly reduce the need for early-season fungicide use.

Orchard Sanitation

One of the most important aspects of a successful organic program (or any IPM program) is eliminating or reducing sources of infestation and disease inoculum from the orchard. If your fall clean-up program missed any of the following, consider them this spring to help lower pest pressures for the upcoming season. Good sanitation practices should include:

  • Remove sources of inoculum, including dead or diseased trees, infected branches, cankers, and rotten or mummified fruit. This is a primary control strategy for management of summer rots, such as black rot (Figure 3), but can also be effective against powdery mildew (Figure 4) and fire blight.
  • Remove wood piles, fruit bins, stumps and loose bark that could provide overwintering sites for insects, such as codling moth. Shred leaves with a flail mower to stimulate leaf decomposition. This may also disorientates leaf pieces so they eject ascospores toward the soil, instead of up into the tree canopy, reducing primary scab infection. Rake or blow leaves from under trees into the middle of the row, or off-set the mower to reach them.
  • Prune to increase air flow and promote faster drying time.

Figure 3. Apple branch infected with black rot (right) acts as inoculum source, causing frog-eye leaf spot on developing foliage (left) the following season

Figure 3. Apple branch infected with black rot (right) acts as inoculum source, causing frog-eye leaf spot on developing foliage (left) the following season.

Figure 4. Dormant apple shoots infected with powdery mildew (Photo: Chris Duyvelshoff, Perennia)

Figure 4. Dormant apple shoots infected with powdery mildew (Photo: Chris Duyvelshoff, Perennia)

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