Early Signs of Green Tip in Apples

Growers in some of the southwest regions of the province have reported green tip in early varieties like Ginger Gold this week. If dormant applications have not gone on yet, now is the time to get those trees covered for early season pest management.

Fight fire blight with dormant copper

• Apply copper from silver tip to 1/4″ green to protect against any bacteria oozing from overwintering fire blight cankers that may have been missed during pruning.
• This dormant application may have an impact on any early apple scab activity if overwintering inoculum is present. However, this should not replace your first scab cover, especially if you were chasing scab last year.
• If you have LOW scab pressure in your orchard and are using a copper registered for season-long use (e.g., Cueva), you could consider extending the number of applications into 1/2″ green to tight cluster while the number of mature ascospores still remains relatively low. Refer to the label for appropriate rates at specific growth stages.
• If fire blight was a problem in your orchard OR IN YOUR NEIGHBOURHOOD, consider applying copper to all your blocks, including young trees. Getting on top of management early will save you from any surprises later.
• Depending on the copper product, the later into the season you make an application, the greater the risk of phytotoxicity and fruit russeting.
• Residual activity typically last about 7-10 days under ideal spring conditions. However, once rainfall exceeds 3” from last copper application, it should be assumed all residue has been washed off.

Avoid summer rescue sprays with dormant / delayed – dormant oil

• If scale damage was found at harvest last year, management is critical to prevent even higher losses this year. Dormant oil is the first line of defense.
• While the optimal timing for scale control is before bud break, a delayed-dormant oil application from green tip to tight cluster will still have some efficacy while also targeting European red mites.
• Since oil works by suffocation of immature scale and mite eggs, getting this spray on as soon as you can and with thorough coverage (to point of drip) will maximize efficacy.
• Delayed dormant oil may also provide some suppression of powdery mildew which overwinters in the buds.
• There are often concerns of bark damage caused by the use of oil. Like many other products, there is a possibility of damage if used improperly. Be sure to avoid the following situations to reduce the risk of injury:
  • Do not apply oil if frost is forecast 48 hour before or after planned application.
  • Allow at least 10-14 days between oil and the use of captan or sulphur products. Oil can enhance penetrant activity of these products, resulting in phytotoxicity.
  • Do not apply oil during periods of slow drying conditions that may lead to burning of sensitive tissues.
  • Red Delicious, Empire, Mutsu and Ambrosia can be particularly sensitive to bark damage if applied in conditions listed above.

Reduce scab inoculum before primary infection

• Both Pennsylvania and New York have reported detection of first mature ascospores on March 19 and 20, respectively (see Penn State Extension Disease Update and Acimovic Lab’s blog post), which means Ontario is not far behind.
• If you were chasing scab in your orchard and did not do any sanitation practices (urea, flail mowing) in the fall, the inoculum levels are likely high enough that mature spores could be released with early wetting events.
• A good way to reduce the scab pressure you’re starting out with in the orchard this season is to apply urea fertilizer at 45 kg/ha (mixed with 1,000 L water/ha) and/or shred fallen leaves with a flail mower. Both practices facilitate the breakdown of leaf litter.

Keep green tissue protected from scab

• Leaves are susceptible to infection as soon as green tissue is present.
• Green tip to tight cluster is a period of extensive new growth. Keep covered with a good protectant fungicide program and re-apply every 5-7 days during periods conducive to disease development or following heavy (greater than 1”) rain.
  • Protectant fungicides such as captan, mancozeb or metiram 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, peaking over bloom period so plan to save your systemic scab products for when infection risk is greatest.
• During cool, wet springs, protectant fungicides may not be enough. Consider tank-mixing with post-infection products such as Syllit, Scala, Inspire Super, Luna Tranquility or Buran.
• If powdery mildew has been a problem, include 3-5 kg/ha sulphur (Microthiol Disperss, Microscopic Sulphur, Kumulus, Cosavet DF Edge) with your protectant sprays until tight cluster when more effective mildew products will be used.