Apple Update: May 16, 2017

Crop Stages

• In all locations bloom stages are pretty spread out, depending on variety and proximity to water.
• In Essex, Kent Middlesex, Lambton, apple blossoms are at bloom to petal fall.
• In Elgin, Middlesex, Norfolk, Brant and Niagara, apple blossoms are at early pink to king bloom petal fall.
• In Grey, apple blossoms are at pink
• In Durham and Northumberland apples blossoms are at pink to king bloom.
• Further along the St. Lawrence and into the Ottawa Valley, apples are at early pink to pink.

Production

Poor bloom return is being reported in many parts of the province, particularly on Golden Delicious, Honeycrisp, Ambrosia, Gala, Mutsu, Cortland, Empire and Northern Spy. This is more pronounced on non-irrigated land that had very little rainfall during the summer. There are also reports of weak king buds within a cluster that are either slow in development or appear dried up.

As bloom progresses, this is the time to think about Apogee application. The label application timing is at 2.5 cm to 7.5 cm of growth, but many experts are recommending to apply earlier at king bloom petal fall.

Thinning applications are starting in areas of the province that are past full bloom. Temperatures will be rising up into ideal ranges of plus 20˚C for thinning this week on Wednesday, Thursday and Sunday in some areas.  For specific phenological application timing and ideal temperatures for application, refer to the 2016-2017 Publication 360, Guide to Fruit Production.

Diseases

Cool temperatures kept the risk of fire blight infection low last week. However, the forecasted weather has most areas across the province with orchards in bloom at high to extreme infection risk from May 17-21 based on the fire blight prediction maps. Management will be critical during this time.

Frequent applications of antibiotics (Streptomycin, Kasumin) may be required during periods of high infection risk for the following reasons:

• Fire blight bacteria multiply rapidly in a very short period of time when temperatures are above 18⁰C.
• Bacteria can be transferred to new blooms by rain, wind or insects. Bees are very active in the orchard right now and can easily spread the bacteria around.
• Antibiotics degrade rapidly in sunlight so are only active for 2-3 days MAXIMUM. Apply these products as close to a wetting event as possible.
• Streptomycin will provide kickback following an infection, but only within the first 24 hours from the start of infection.
• New blossoms are opening daily and will not be protected by sprays made while these blooms were closed.
• ALL blossoms are at risk of infection including secondary (rattail) bloom or delayed bloom on newly planted trees.
• Any wetting event, including rain, dew and even your sprayer will wash bacteria into the floral cup and initiate infection.

For resistance management, it is important to rotate between Streptomycin and Kasumin. Kasumin has been found to kill Streptomycin-resistant bacteria. While these are both antibiotics, there is no risk of cross-resistance. With bloom spread out between varieties, there may be an extended infection risk period. Incorporating Kasumin (maximum 5 applications per year) between Streptomycin (maximum 3 applications per year) sprays will provide a significantly larger management window.

Most areas are still within – though nearing the end of – the peak scab ascospore maturation period. Orchards have had a few rain-free days to help dry things up. However, that means there will be a significant build-up of mature ascospores ready to be released during the next rainfall. The length of leaf wetness required for infection will also be greatly reduced with temperatures above 20⁰C. Refer to the Revised Mills Table for more information.

Scab lesions (Fig. 1) have been found in some orchards, likely as a result of late April infection events. Long infection periods and heavy rains had many growers scrambling during the rain to maintain good fungicide coverage. With lesions developing, secondary scab management will be essential to prevent spread throughout the season.

Powdery mildew (Fig. 2) has also been found in some orchards despite the wet weather. Most systemic fungicides from Group 3, 7 and 11 applied at this time for scab have good efficacy on powdery mildew. See Table 3-14. Activity of Fungicides on Apple Diseases in the 2016-2017 Publication 360, Guide to Fruit Production for efficacy ratings for most registered powdery mildew products. Management of this disease will be required until terminal bud set.

Figure 1. Initial apple scab lesions often appear as olive-brown velvety patches on the underside of leaves.

Figure 2. Powdery mildew often appears initially as white, felt-like patches of fungal growth on the underside of leaves.

Some orchards that experienced Sudden Apple Decline (SAD) last year are beginning to see similar symptoms again. Seemingly healthy young trees that have broken bud and growing normally, then suddenly have terminal wilt or even tree collapse. In most cases, the leaves have a pale yellow hue, and then rapidly turn purplish or reddish just before the tree collapses. Cause for this collapse has yet to be determined. For more details on SAD, refer to Apple tree collapse: What we know (and don’t know) in the December 2016 Orchard Network Newsletter.

One to 2 bloom sprays of Pristine are being applied for control of black rot in some orchards with a history of this disease. Pristine is a pre-mix product belonging to Groups 7 and 11 so should not be rotated with Fontelis, Aprovia, Sercadis, Kenja 400SC, Luna Tranquility, Flint or Sovran.

Insects

Insect activity is starting to kick off in many regions. The cooler weather has delayed activity for some pests, but not others.

Some growers in the later regions still at tight cluster to pink are considering a prebloom insecticide, particularly those with historical issues with plant bug, European apple sawfly, spring feeding caterpillar and/or leafcurling midge.  A number of growers in the earlier regions were disappointed to see their prebloom application washed off in the heavy rains.

Oriental fruit moth biofix has been set for early May in some regions. Degree-days are now being accumulated to determine the appropriate spray timing window. Other traps up include codling moth, European apple sawfly, apple leafcurling midge and San Jose scale.

Apple leafcurling midge eggs (Fig. 3) have been observed on the newest growth of leaf terminals in high pressure blocks. These shiny, orange eggs can be found in clusters near leaf folds or margins of the youngest unfurled leaves of shoot tips. With warmer temperatures, egg hatch can occur in less than 1 week so leaf curling is expected shortly. Movento 240SC was recently registered for suppression of leafcurling midge. Other petal fall insecticides may also have some efficacy on this pest. Refer to Table 3-10. Activity of Insecticides and Miticides on Apple Pests in the 2016-2017 Publication 360, Guide to Fruit Production.

Shiny, orange and elliptical- or bullet-shaped apple leafcurling midge eggs.

Figure 3b. Scouting for apple leafcurling midge includes detecting presence of eggs in folds of newest leaves of terminal.

European red mite hatch continues, though relatively slow. Activity will likely increase with the warmer temperatures that are predicted.

Mullein bug nymphs, tarnished plant bug, green and rosy apple aphid, and spring feeding caterpillar can be found on new growth and blossoms. At the same time, beneficial insect activity has also been increasing including lacewing, minute pirate bug and lady beetle.