Apple Update: May 9, 2017

Crop Stages

• In Essex and Kent, apple blossoms are at king bloom to king bloom petal fall.
• For the rest of Southwestern Ontario including Elgin, Middlesex, Norfolk, Brant and Niagara, apple blossoms are at pink to full bloom.
• In Grey, apple blossoms are at pink.
• In Durham and Northumberland, apples blossoms are at tight cluster to first pink.
• Further along the St. Lawrence and into the Ottawa Valley, apples are at tight cluster.

Production

Currently the province is going through a period of frosty nights. We have had a risk of frost on Monday and Tuesday morning and are expecting a risk on Wednesday morning. On Monday morning, temperatures did go below zero in areas of Norfolk, Elgin, Niagara, Kent, Essex, Brant and Niagara.  However, temperatures were above the critical temperature for 10% damage at -2.2˚C but some low areas of orchards could have reached this temperature. The coldest area was around Leamington where temperatures reached  -2˚C. On Tuesday morning, the coldest areas in the province were around Lambton Shores, Woodstock and Simcoe touching down to -2 or -3˚C.  Other areas with temperatures below zero, but not quite hitting critical temperatures were Middlesex, Waterloo, Oxford, Elgin, Norfolk, Niagara and Brant. For assessing bud damage, here is a past article from the Orchard Network Newsletter.

Steady rain during the past week from Thursday until Saturday has put a pause on orchard work and is creating difficulty for getting sprayers into the orchard. Much of the apple growing areas received 50-80 mm.

Diseases

Fire blight

It’s too cold for fire blight, right? Based on the fire blight prediction maps, the cool weather throughout most of Ontario is keeping the risk of fire blight infection low. HOWEVER, it is important to remember fire blight bacteria are capable of growing over a range of temperatures above 4⁰C. If bacteria are present in the orchard or neighbourhood – which in southwestern Ontario is very likely – populations can continue to slowly build on open blossoms if rain-splashed, wind-blown or carried by insect. Once temperatures reach 18⁰C, bacteria can multiply exponentially in a very short period and with any bit of moisture can wash into the bloom, causing infection. Watch the forecast and be prepared should the weather get warmer.

If using biological products for early bloom protection, trials in the northeast have found an increased incidence of russeting with Blossom Protect during extended wet weather particularly on sensitive varieties like Golden Delicious.

If the cool spring continues, it is possible bloom may be extended this year. An extended bloom, especially with a long secondary or rat-tail bloom can lead to a high fire blight infection risk potential. Maintain blossom blight management throughout the entire bloom period or remove any secondary bloom to prevent late blossom blight infection. Extend the use of antibiotics by rotating between Streptomycin and Kasumin during high infection risk periods. Streptomycin has a maximum of 3 applications per season, while Kasumin has a maximum of 5 applications per season.

Apogee has started to be applied in the earliest regions at king bloom petal fall for management of fire blight shoot infection. This product works by: 1) reducing vegetative growth of susceptible shoots and limiting spread of infection, 2) thickening the cell wall to provide a physical barrier from bacterial infection, and 3) stimulating plant defense system to reduce infections.

Apple scab

The spring continues to be challenging for apple scab management. The continuous rainfall most areas of the province experienced last week resulted in an extended primary apple scab infection period. This is in addition to the numerous other infections that have already occurred this year. While the cooler temperatures slowed new growth down, many growers have been concerned about maintaining protectant fungicide coverage with the heavy rains. Systemic fungicides from Group 9 (Scala, Luna Tranquility, Inspire Super) have been a go-to for some looking for good kickback activity particularly in cooler weather. However, post-infection activity is calculated from the start of the infection period so may not provide full coverage in cases of extended infection periods.

Most areas are still within the peak period of rapid scab ascospore maturation based on degree days. Very little moisture – dew or rain – is required to trigger spore release during this time. Protectant fungicide coverage is critical as most of the available mature spores are discharged within 2 hours after the start of the wetting event.

Powdery mildew

A silver lining during the wet weather last week was that powdery mildew infection risk should have been kept relatively low. This is not typically considered a wet season disease. Mildew spores can be washed off by rains. However, the forecast ahead is calling for warmer, dryer weather with relatively high humidity. Most systemic fungicides from Group 3, 7 and 11 applied at this time for scab have good efficacy on powdery mildew. If these products are not being used, consider adding 3-5 kg/ha of a sulphur product (Microthiol Disperss, Microscopic Sulphur, Kumulus, Cosavet) to any protectant fungicide spray. Keep in mind, however, particularly post-bloom, sulphur can impact beneficial insect populations and cause mite flare-ups.

Insects

Insect activity continues slowly in most orchards with the cool, wet temperatures:

• Some aphids and spring-feeding caterpillars can be found though very little damage has been observed on flowers or foliage.
• European red mite egg hatch has begun.
• Oriental fruit moth catch has started in earlier regions with traps up. No biofix has been set.
• Codling moth, European apple sawfly, leafcurling midge and San Jose scale traps have gone up in orchards. No activity has been observed.

Due to the cooler weather, some growers that previously planned to apply a prebloom insecticide (and don’t have European apple sawfly to deal with) have decided not to. Many are anticipating a slow start to insect activity and instead are preparing to target management at petal fall.