Apples Diseases Insects Pest Management

Apple Pest Update: April 14, 2023

Bud break is moving quickly in apple orchards across the province -- are you prepared for early spring pest management for fire blight, scab, powdery mildew, scale and mites?

As much as I try to prepare, the growing season always seems to catch me off guard. This year has certainly not been any different with the warm days and nights moving development along quickly. While most regions of the province are seeing signs of green, some of the earliest areas have moved from green tip to nearly tight cluster in only a matter of a few days.

With the season on our doorstep, are you prepared for early pest management? Let’s go through the checklist of things to consider:

Orchard sanitation – your first line of defense

The first line of defense for pest management in an orchard is prevention. There is no silver bullet to eradicate something like disease once it becomes well established. Instead, management is about reducing inoculum and preventing spread to healthy trees or fruit.

  • Prune out dead or diseased limbs, trees or signs of cankers as well as rotten or mummified fruit. These can harbour overwintering pests, such as fire blight, black rot or bitter rot.
  • Get rid of wood or cull piles and stumps that may have been in or near the orchard over the winter. These often provide overwintering sites for insects, such as codling moth and plum curculio.
  • If the ground is dry enough to get the tractor through, flail mow the orchard floor to mulch up leaves, branches and fruit.
  • If you haven’t already done so last fall or earlier this spring, apply 45 kg of agricultural urea per 1,000 L of water/ha to the orchard floor for scab or apple blotch (Marssonina) inoculum reduction.

Dormant copper for fire blight and scab management

Dormant copper such as Copper Spray, Copper 53W, Cueva, Parasol and Kocide can safely be applied up to ¼” green (possibly ½” green) without risk of phytotoxicity. However, the use of a softer copper registered for season-long control such as Cueva could be extended in those early spray timings to ½” green or tight cluster in blocks with low scab inoculum (ie., free of scab last year) to provide some scab protection.

Residual activity typically last about 7-10 days under ideal spring conditions. However, once rainfall exceeds 2” from last copper application, it should be assumed all residue has been washed off. For some copper formulations, using a dormant oil will act as a sticker/spreader as well as provide efficacy on scale, European red mite and suppression of powdery mildew. This is not the case for all registered coppers. Always refer to precautions listed on the product label prior to use.

Dormant oil – the earlier, the better for scale control!

Depending on the target pest, the term “dormant” oil can be rather misleading as sprays can be applied from the true dormant state prior to bud break up until pink. Unfortunately, optimal dormant timing for scale is not necessarily the same for mites.

If monitoring indicates scale is a bigger issue in the orchard, oils need to be applied before or shortly after bud break. This efficacy against scale is significantly reduced with later oil applications for European red mite as they develop a waxy protective layer that impedes the oil from effectively penetrating and preventing respiration.

However, if European red mite populations are the problem, sprays can be delayed. Ideal timing is half-inch green to tight cluster but can be delayed to pink; however, blossoms can be quite sensitive to oil under adverse conditions so consider using a lower rate at this timing.

First cover spray options for primary scab infection

For those regions further along in development, consider the following for the first cover sprays for primary scab infection:

  • Leaves are susceptible to infection as soon as green tissue is present, especially if you had scab in your orchard last year.
  • Green tip to tight cluster is a period of extensive new growth. Keep covered with a good protectant fungicide program (such as captan, folpet and/or mancozeb) and re-apply every 5-7 days during periods conducive to disease development or following heavy (greater than 1”) rain.
    • Protectant fungicides do not provide effective post-infection or anti-sporulant activity.
    • That means if sprays are applied in less-than-ideal conditions, ie., windy, alternate rows, or washed off in rain, the risk of scab infection is increased.
  • Ascospores mature slowly early season and infection takes longer in cooler temperatures, peaking over bloom period so plan to save your systemic scab products (such as Group 3, 7 and 11s) for when infection risk is greatest.
  • During cool, wet springs, protectant fungicides may not be enough. Consider using products such as Syllit, Scala, Inspire Super, Luna Tranquility or Buran which perform better in cooler conditions.
    • These products could help fill potential gaps in early season management and allow mancozeb use to be saved for pink to petal fall timing.

Early season powdery mildew management

High powdery mildew pressure in recent years followed by the mild winter could be an unwelcome mix resulting in an early spring arrival of this disease. Be sure to consider a mildew protectant such as a low rate (3-5 kg/ha) of sulfur in your early season scab program, especially on susceptible cultivars or orchards with a history of powdery mildew. Continue this until tight cluster when more systemic fungicides with mildew activity like the Group 3, 7 and 11s start to be used.

Rain deters powdery mildew development by washing off spores. Instead, mildew thrives in dry weather and high relative humidity. So, protectant sprays may still be required during dry periods when there is little risk from apple scab.

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