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It looks like wet weather may be in the forecast for the southwest in the coming days. Temperatures jumped this week, moving growth along quite quickly. The earlier regions of the province are starting to see some bloom. This means disease risk could be high during this upcoming rainy stretch.

Apple Scab

It’s very likely there will be a significant scab infection period during this time. The rate of ascospore maturity will have increased in the warm weather this week which means a large amount of spores could be ready to be released in the next wetting event. With temperatures above 15C, only 6 hours of leaf wetness are required for germination to occur.

Be sure leaves are covered with a protectant fungicide before any potential infection event. Ideally, these products are better absorbed in dry conditions and become rainfast over several days after application. If that timing is just not possible, do try to avoid spraying within several hours before a rain as much can be lost to wash-off regardless of formulation.

If there is any concern about coverage, reapply during a break in the rain and consider a product with post-infection activity. Keep in mind though, this kickback is generally only effective if applied within 48-72 hours of an infection depending on the temperature. Anything after this and there will be no efficacy. Remember, post-infection activity is not the same as post-symptom activity. While I haven’t heard reports of symptom development yet, if lesions are present, do not apply a post-infection product.

Fire Blight

Blossom Risk Is Out There

If you’re not already watching the Ontario fire blight prediction maps, now is the time to key an eye out. With the warm weather, predicted rains and the start of bloom for many, fire blight risk is also taking a big jump in the coming days. Most areas in the southwest could potentially see high to extreme infection risk into next week.

Fire Blight Prediction Maps

The risk of fire blight infection is possible if the following conditions are met:

1. Flowers are opened and/or are opening – There is no risk of infection if bloom is not present in the orchard despite the fire blight maps stating caution to extreme; however, keep an eye on any early signs of bloom as it can happen quickly.
2. Enough heat units have accumulate based on forecasting models – The fire blight maps use Cougarblight but this applies to MaryBlyt as well. Similar to degree days, daily temperature is accumulated and must reach a certain point before risk increases.
3. A wetting event is predicted – Any type of wetting event will wash the bacteria into the open bloom including rain, dew or even the artificial rain shower you create with the sprayer during critical infection periods.

Blossom Blight Management

Fire blight bacteria multiply rapidly in a very short period of time when temperatures are above 18⁰C and relative humidity above 90%. Bacteria can be transferred to new blooms by rain, wind or insect. Bees and other pollinators are very active in the orchard right now and can easily spread the bacteria around.

Frequent protective sprays may be needed if risk remains high as new blossoms are opening daily and will not be protected by sprays made while these blooms were closed. As well, 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. For resistance management with antibiotics, rotate between Streptomycin and Kasumin.

Consider alternatives to antibiotics during the early bloom period, especially if risk is low to moderate but fire blight has been an issue in your orchard before. These include:

• Biologicals – eg., Blossom Protect, Buran, Serenade, Regalia or Double Nickel
• Surface sterilant – eg., Oxidate
• Copper labelled for in-season use – eg., Cueva – note that copper and some fungicides are not compatible with certain biologicals. Check the label before use.

The early timing for products like biopesticides is important for a number of reasons.

• Firstly, because most of these products work by competitive exclusion, inhibiting growth or triggering a defense mechanism in the plant, they need time to colonize and become established. A good approach to timing for biologicals is when risk is coming in the next 3-4 days.
• Many of these products provide only limited control under high pressure or during certain environmental conditions.
• Using these suppression products when there are few blooms and risk is lower, allows you to save your uses of antibiotics like Streptomycin and Kasumin for peak bloom (50-80% bloom) and high infection risk events.

Research trials in the Northeast US by Quan Zeng (Connecticut Agricultural Experiment Station [CAES]), Dan Cooley (UMass) and Neil Schultes (CAES) looked at non-antibiotic control methods such as Double Nickel, Blossom Protect, Bloomtime, Cueva and Oxidate over 4 years on Red Delicious. Blossom Protect consistently out-performed the other products as a stand alone program and was not significantly different from Streptomycin control in some years. This efficacy was only improved with the addition of the surface sterilant, Oxidate. The recipe for the most effective non-antibiotic method they found were:

• Early to full bloom – 2 applications of Blossom Protect
• Full bloom – 1 application of Oxidate
• 24 hours after bloom – 1 application of Oxidate, if pressure is high or if there is a history of fire blight in the orchard

Prebloom Management

For those orchards still approaching bloom, you may want to think about the potential benefits a pink application of Apogee could have on fire blight management. Following the label, Apogee can be applied between 2.5-5.5 cm of new shoot growth. That early range can easily occur prebloom depending on the spring.

The use of Apogee has been known to reduce shoot blight when applied at king bloom petal fall largely due to the thickening of the cell walls within the shoot, preventing infection from occurring. Research published by Anna Wallis and Kerik Cox from Cornell University proposed Apogee could do the same to reduce blossom blight by thickening the cell walls of blossom pedicels. With their trials on mature Gala, they saw over 70% control of blossom and shoot blight with a pink application of Apogee and minimal effect on tree growth.

Pink is also an important timing if using the Bacillus product, Lifeguard. This product works by activating the tree’s defense mechanism and is most effective when it is applied before infection occurs or when added to a fungicide rotation. It’s important to note that since this is a biological product, it should not be tank-mixed with antibiotics such as Streptomycin and Kasumin. Initial inducement of plant defense response occurs soon after application but 3-5 days are required to attain maximum level of protection. Once bloom hits, however, avoid application as this product is toxic to bees. Applications can pick up again at petal fall after hives have been removed.

Spring-feeding caterpillar

The first signs of caterpillar damage can be found on growing terminals and fruit buds. In general, an insecticide is usually recommended when the action threshold of 12-15 larvae per 100 terminals and fruit buds is observed. If spring-feeding caterpillar such as leafrollers, spongy moth, budmoth or green fruitworm have been a problem in previous years, keep an eye out for damage and consider management if pressure is high.

That said, supporting beneficial insects in the orchard such as ladybugs and lacewings will help suppress these pests. I am seeing plenty of ladybugs out there already. Consider this when deciding if a prebloom insecticide is worthwhile.

Apple leafcurling midge

As mentioned in last week’s update, adult leafcurling midge flight has begun. With the warm weather this week, trap catch has spiked. The first leafcurling midge eggs were found in new terminals. Signs of leaf curl are likely to begin within the next week or two should these warm temperatures continue.

Apple IPM Workshop

The Apple IPM workshop was held virtually last Friday, May 6th. The recording is now available on the ONhortcrops YouTube channel (see direct link below) along with pest-specific presentations. If you would like the PDF of these presentations and other resource materials provided to attendees, please email me at kristy.grigg-mcguffin@ontario.ca.