Apple buds are at full bloom to petal in Eastern Ontario and Grey County and at petal fall to 10 mm for Southwestern Ontario.
Growers have started to apply thinners in Southwestern Ontario and it is definitely on the minds of growers in the rest of the province. Most growers have had a fairly heavy bloom.
With the heavy bloom, hot days and warm nights has prompted many conversations about carbohydrate deficits. Carbon deficits occur when the demand from the fruitlets for carbohydrates is greater than what the leaves can produce. According to the Cornell Apple Carbohydrate Thinning Model http://newa.cornell.edu/index.php?page=apple-thin , locations in New York have had enough of a carbon deficit to recommend reducing chemical thinners or not to apply thinners, depending on the day.
Warm temperatures and high humidity have made for ideal conditions for fire blight infection. For most regions, the fire blight risk maps are predicting high to extreme risk of infection for at least the early part of the week. While petal fall is well underway across the province, growers should be aware of flowers still open and monitor closely for secondary, or rat tail blossoms. Removing or protecting these open blossoms from infection will be critical during times of high risk. Antibiotics will break down quickly in high temperatures, likely only providing 24-48 hours of protection before a re-application would be required.
While most regions have over 90% apple scab ascospore maturity, there has been little rain to distribute these spores. This may result in a significant scab infection period during the next wetting event as massive amounts of ascospores could be released. Growers should keep a good protectant program in place if rain is in the forecast.
Now is the time to begin looking for the development of scab lesions from previous infection periods in order to detect and prevent secondary infection from being established. The first lesions are generally found on the lower leaf surface as spores are splashed from the orchard floor during rain events. These start out as velvety brown to olive green with indistinct margins that darken with time. If lesions are detected, a good protectant spray program should stay in place following the primary scab infection period. For resistance management, do not use Group 3, 7, 9 or 11 fungicides if lesions are present.
The dry, hot and humid weather has also been ideal for powdery mildew development and early symptoms have been observed in many orchards across the province. Some key points to remember:
- Unlike scab, mildew thrives in dry weather. So, protectant sprays may still be required during these periods when there is little risk from apple scab.
- Fullback, Nova, Aprovia and Luna Tranquility do not provide good control of fruit scab and should be tank-mixed with a compatible protectant fungicide.
- Vivando is no longer registered for control of powdery mildew on pome fruit.
- Powdery mildew is fairly susceptible to developing fungicide resistance. Rotation amoung fungicide groups is very important.
- Be aware of rotating with pre-mix products that contain multiple fungicide groups, such as Pristine (7+11), Luna Tranquility (7+9) and Inspire Super (3+9).
- Factor in any scab resistance that may be present in the orchard when making fungicide decisions. While scab may not be the spray target at the time, the population will still be pressured if present.
Petal fall insecticides continue to be applied in most areas. The spray window for oriental fruit moth will be over in most early regions by mid-week. Some growers selected insecticides with good efficacy on mullein bug, spring feeding caterpillars, European apple sawfly and/or apple leafcurling midge if monitoring had indicated they had reached threshold or had high pest pressure.
Low numbers of codling moth have been found in traps in most regions across the province, while obliquebanded leafroller has been caught in Essex. San Jose scale has also been trapped in all monitoring orchards in the province. Spray timing for scale crawlers is predicted for the end of June.
Spring feeding caterpillar activity seems to be extended this season likely due to the cooler weather in April slowing things down. Both small and mature caterpillars can still be found in clusters or rolled up in leaves. Significant levels of feeding on blossoms has been observed in some orchards as well as suspected green fruitworm damage to developing fruitlets.
Apple leafcurling midge damage continues to increase across the province. Newly hatched midge larvae can now be found in tightly rolled leaves. In some earlier regions, these larvae are beginning to turn orange, which indicates the later stages of maturity.
Early miticides, such as Apollo, Agri-Mek or Nealta will be applied over the next couple of weeks in orchards with high mite pressure. Refer to Table 3-9. Activity of Miticides Registered on Apples and/or Pear in Ontario in 2016-2017 Publication 360, Guide to Fruit Production for more information on registered miticides.
- Apollo is primarily an ovidicide, which means it targets the egg stage or newly hatched nymphs (typically no later than 14 days after petal fall). Therefore, populations should be monitored to determine the number of eggs present before Apollo is applied.
- Agri-Mek should be applied within 21 days of petal fall. Since oil is required, do not apply Agri-Mek within 14 days of captan or sulphur fungicides.
- Nealta is a miticide that needs to be applied as populations build, so an earlier application is ideal. Include an adjuvant to improve performance.