Apple Update: June 7, 2016

Crop Stages

Apple fruitlets range in size between 10-20 mm with the largest fruitlets in South Western Ontario and the smallest fruitlets in Eastern Ontario and around Georgian Bay

Production

Up until this past weekend, the weather has been very dry, especially in Eastern Ontario. Most growers across the province have applied their first thinning application and will be making the decision whether a second or third application is needed. Depending on when the first applications of Apogee were applied and the vigour of the tree, growers will be making a second application of Apogee 14-21 days after their first application.

Diseases

The risk of blossom blight has passed in most orchards. However, particularly in the later regions of the province, growers should still be on the lookout for rat tail bloom. If ideal conditions continue and secondary bloom is not removed or protected, the bacteria can easily wash into the blossom initiating infection.

Fire blight strikes can now be found across the province and growers have begun pruning these out, especially in young plantings. See a previous ONfruit post, Fire Blight: Are You Out of the Woods? for tips on removing strikes.

Apogee has been applied for management of shoot blight. It should be noted this product has no impact on blossom blight or fire blight bacteria, but rather reduces the vegetative growth, making the tree less susceptible to shoot infection. Accurate timing is critical, ideally when shoots are 2.5-5.5 cm long and again 14-21 days later.

Scab lesions have been observed in some orchards. These would have been as a result of infection periods that occurred in May. Many areas experienced a massive infection period over the weekend and into Monday. While the warm weather in recent weeks pushed ascospore maturity along, the dry days have kept these spores from being released. Most areas have been sitting at nearly 100% ascospore maturity based on degree days, but little to no infection periods. Growers that did not have orchards adequately covered should consider applying a material with good kickback activity as soon as possible since maximum post-infection activity is calculated from the start of the infection period. See Table 3-13. Characteristics of Apple Scab Fungicides in the 2016-2017 Publication 360, Guide to Fruit Production for more information. Keep in mind, Scala should be used prebloom only. As well, Group 3, 7 and 11 fungicides are weak on fruit scab and should be tank-mixed with a protectant.

There is a very good chance that with this precipitation, the majority of ascospores were released, signalling the end of the primary scab infection period. However, it is recommended to continue a protectant spray program for at least 3 weeks while monitoring for signs of scab lesions. If nothing develops, a relaxed program can continue for the remainder of the season.

At the Durham study group last week, there was a discussion around how long mature ascospores will stay if the moisture just has not been there for an infection period. These spores are maturing in scab-infected leaves on the orchard floor from last season. So long as these leaves have not broken down, the spores can be discharged during any wetting event (eg., rain, heavy dew, overhead irrigation). Dry weather tends to slow leaf decomposition down, which means the primary scab period can be quite extended if there has been little to no precipitation.

The hot, dry weather has favoured powdery mildew development. This disease can be found in many orchards that have a history with mildew pressure. Mildew does not invade mature leaf tissue, so spread ceases when trees stop producing new terminal leaves.

Frog-eye leaf spot (Fig. 1) and cedar apple rust (Fig. 2) have also been observed in some orchards. Most scab products will provide control of these diseases. See Table 3-14. Activity of Fungicides on Apple Diseases in 2016-2017 Publication 360, Guide to Fruit Production for efficacy ratings of registered fungicides for rust and rot management.

Fig 1. Frog-eye leaf spot

Fig 2. Cedar apple rust

Insects

Most areas are at the tail end of oriental fruit moth egg hatch. Ideal spray timing would have been at petal fall/calyx, when most growers select a product effective against fruit moth. The next internal lepidopteran pest on growers’ radar is the codling moth. Egg hatch is quickly approaching over the next few days in some of the earlier regions. Timing is very important as the larvae often tunnel into the fruitlets within 24 hours of hatch. It is too late for insect growth regulators, such as Rimon (petal fall timing) or Intrepid (83-111 DDC) as they need to be on early to interrupt regular development. Contact or ingestion larvicides are applied typically around 138 DDC. This timing may also help with early obliquebanded leafroller hatch, too.

Mullein bug tap counts have been exceptionally high in many places this year. Not all common petal fall insecticides have efficacy on this pest. See Table 3-8. Activity of Petal Fall Insecticides Against Orchard Pests in 2016-2017 Publication 360, Guide to Fruit Production. If a grower suspects there may be inadequate protection with what was used and numbers have reached threshold (7-9 nymphs per 25 taps), a targeted spray may be required, particularly on susceptible varieties, such as Red Delicious, Spartan, Spy, Empire, Cortland, Gala, Jonagold and Golden Delicious.. The critical time for damage (Fig. 3) from this pest is generally from dime- to quarter-sized fruit. Several weeks after petal fall, nymphs become predaceous and begin feeding on European red mites and aphids. The presence of nymphs with red bellies is an indication that feeding on mites has started, after which management is no longer needed.

Woolly apple aphid colonies have been observed in some regions. Their characteristic cottony covering can be quite obvious along shoots (Fig. 4). There are no thresholds for woolly apple aphid but management is often better when nymphs are young and colonies are just starting to form. If using Movento, the earlier the application, the better as control may not be apparent for 2-3 weeks. As this product should be used with an adjuvant, do not use captan or sulphur-based fungicides at that time. Early season control and good orchard management also allows for important natural enemy populations to build later in the summer, which growers should encourage for woolly apple aphid control.

Fig 3. Mullein bug damage causes small, raised bumps on fruit.

Fig 4. Young shoot infested with woolly apple aphid colonies.

Apple leafcurling midge adult catch has declined. Leafcurl can be easily found in many orchards. Larvae within the rolled leaves are beginning to turn orange in early regions, which is a sign of late instar stages just prior to pupating. Second generation adult emergence has typically occurred in mid-June to early July in previous years.

European apple sawfly flight has finished and some damage has been reported. This was to be expected given that activity occurs over bloom. The extended prebloom conditions made things more difficult even for growers that did apply a prebloom spray as any residuals likely did not stay on long enough to cover activity until a petal fall spray could be applied. Damaged fruit will likely abort at June drop. Those fruitlets that hold on will develop the characteristic ribbon-like scar (Fig. 5).

San Jose scale adults have been trapped since mid-May in all monitoring orchards in the province. Based on degree days, 1^st generation crawler emergence is predicted around the weeks of June 13 and 20. Depending on the weather, activity (ie., movement to new shoots and developing fruit, Fig. 6) will continue for 4-6 weeks. Registered products, including Movento, Closer, TwinGuard and Sivanto Prime should be applied at the beginning of crawler activity and reapplied 10-14 days later due to the extended generation.

Leafhopper and mite activity is increasing.

Fig 5. European apple sawfly damage causes a ribbon-like scar on fruit.

Fig 6. San Jose scale on apple causes grey patch surrounded by a red halo. Yellow crawlers can be seen in this picture.