Well, I must just love writing for you folks! I have some information that I want to share that cannot wait for next week given how quickly growth is progressing. This follow-up newsletter adds additional notes on diseases and insects.
Table of Contents:
- Apple - Scab
- Apple - Fire Blight Prevention
- European Red Mite
- European Fruit Scale
Diseases
Apple – Scab
Beginning at green tip, apple tissues are susceptible to infection from the fungus that causes apple scab, Venturia inaequalis. The environmental conditions for an infection are listed in the Modified Mills Table.- The weather forecast gave us relatively short notice for the rainfall that happened on Wednesday and into Thursday morning. There is plenty of green tissue being reported throughout the Valley that could have been exposed to this wetting event.
- At the average temperature of 6.4°C, it would take 19 hours of leaf wetness for a light infection event to be caused by mature ascospores. Therefore, a light infection event likely occurred as I observed at least 22 hours from Wednesday 12 PM until Thursday 10 AM.
- According to the Gadoury model and using Kentville temperatures, ascospores have matured to 2.3% of the total seasonal load.
- Although we don't encourage post-infection treatment of scab infections, in difficult situations products with kickback activity might be considered: Scala (48-72 hrs) and Manzate (18-24 hrs).
- Remember that there is a new label for Manzate (mancozeb). The product may be applied 4 times/ha/year, the re-treatment interval is 7 days, the REI for hand thinning is 35 days (12 hrs for all other activities), and the PHI is now 77 days.
- If you plan to use oil for European Red Mite control, Captan should be avoided within 7-14 days of an oil application.
Apple – Fire Blight Prevention
The goal of copper application is to cover the bark with copper to reduce the population of bacteria on plant surfaces that arise from bacterial ooze around the pink stage. The copper treatment will reduce the initial inoculum and limit the spread of fire blight bacteria to blossoms or wounded tissue on the tree. This strategy is most effective in blocks that had fire blight cankers in the previous two seasons.Recommendations:
- If possible, apply copper to the entire orchard block including non-susceptible varieties because they can serve as reservoirs of randomly dispersed bacteria. However, if limited by time, prioritize high risk blocks.
- A copper application is recommended when buds have reached green tip. A fixed copper product such as Copper Spray Fungicide (50% copper oxychloride) is recommended because it is resistant to being washed off by rain. If applied later than green tip, residues that persist on fruitlets can cause russetting. Processing varieties where russet is tolerable can be treated later as well as nonbearing trees.
- Copper can be applied as a tank mix with 0.5% by volume (5 L in 1000 L) dormant oil to increase adherence. Apply in a high water volume to cover plant surfaces. Do not use dormant oil within 14 days of Captan or within 48 hours of freezing temperature.
Insects
European Fruit Scale
The best time to target scale is ideally just before the tree breaks dormancy or with a delayed dormant spray of oil by green tip. Scale cannot develop resistance to the smothering action of the dormant oil so the oil can help to slow resistance to insecticides. Also, the spring oil application is more effective than insecticides at reducing the overall scale population.
After green tip, the scale insects start building their waxy coating so the oil does not affect them after they have built their defenses. The scale that are under the waxy coating are the adults that are preparing to give birth to live young. The live young are the active stage known as crawlers.
When the crawlers leave the waxy coating they become susceptible to insecticides. Typically the crawlers are active in July in Nova Scotia but they should be monitored for more specific timing. The traps are made by using black electrical tape (with adhesive side out) around the scaffold limbs of trees, in areas with known infestations. Place bands in trees and replace every two to three weeks throughout the season. Crawlers yellow bodies will be caught on the tape.
When the crawlers are active, using one of the neonicotinoid products (group 4 - Closer, Sivanto Prime, TwinGuard) or Movento (group 23) for insect control of labelled pests would offer the side benefit of affecting crawlers. The insecticides can avoid some fruit damage and potential spread. But few insecticides are registered so there is little opportunity for product rotation and it is a good idea to incorporate the oil in spring into your program to prevent resistance from developing.
***Do not use dormant oil 48 hours before or after freezing temperature. Please note, there are freezing temperatures currently forecast for April 21 and 22.***
Figure 1: A fruit with damage from European fruit scale insects (left). A close up of the scale population on the fruit (right).
European Red Mite
A delayed dormant oil is effective at managing European red mite if monitoring indicates a treatable overwintering egg population. The oil is most effective when applied around egg hatch (typically around tight cluster and before pink) but if practical it may be applied earlier. European red mite eggs overwinter in the cracks on buds and spurs so adequate water volume is needed to reach all of the crevices. The oil treatment is not effective for rust mite or two-spotted spider mite.
For varieties with Delicious parentage (Ambrosia, Gala, Delicious), early applications of oil prior to tight cluster are less likely to result in bark blistering. Oil should not be applied to young trees.
Oil that is applied before freezing temperatures breaks down and adheres to the plant tissues unevenly instead of the target insects. Also if the oil and water mixture freezes before it dries then the green tissue can be injured.
***Do not use dormant oil 48 hours before or after freezing temperature. Please note, there are freezing temperatures currently forecast for April 21 and 22.***
