Production and pest update brought to you by the OMAFRA Apple Team: 

Erika DeBrouwer, Tree Fruit Specialist and Kristy Grigg-McGuffin, IPM Specialist

Growth Stages

It just wouldn’t be an Ontario spring anymore without warm, dry weather one day and cool, wet weather the next! The unseasonably warm temperatures earlier this week put growth in overdrive with many areas now near or at half-inch green. The earliest regions are even seeing tight cluster in some cultivars! This puts many about 1 week ahead of “normal”.  

That-Which-Should-Not-Be-Named

Not to jinx things, but with growth moving along, it is important to review critical temperatures, frost mitigation strategies and frost damage assessments:

The Horrid F Word: Frost

Scab: Are We There Yet?

With the development of green tissue and warm days to encourage ascospore maturity, this rain event much of the province is currently experiencing may be the start of the first apple scab infection period of the year.

Even with the cool temperatures, it is possible for ascospores to continue to mature. Afterall, they started maturing under snow cover earlier this spring.

We’ve had some very warm daytime temperatures recently over 20C to push ascospore maturation, ready for release with the current cool rains. While the time required for maturation and infection to occur is much longer in lower temperatures, it is still possible to reach this critical timing so long as the leaves stay wet. And while mature spores are released more during warm rains than in colder rains, they can still cause infection nonetheless if they land on green tissue during these wet periods.

If you’re looking for more information on how temperature and leaf wetness affect scab infection, check out the table Relationship of Temperature and Moisture to Apple Scab Infection.

Covered in Rainy Stretches

Apply protectant fungicides (e.g., mancozeb, captan, folpet) now if not already covered. Most of the available mature spores are discharged within 2 hours after the start of a wetting event. If using protectant fungicides alone, remember these are contact fungicides and do not provide effective post-infection or anti-sporulant activity.

If heavy rains greater than 2″ occur, residues will have likely been washed off. Reapply at any break in the rain over the next few days if that is the case. Be prepared to cover again once things dry up.

If there are any concerns about residue wash-off, you may want to consider going in after the rains have stopped with a post-infection, or kickback product. Refer to Characteristics of Apple Scab Fungicides for more information.

• Cooler weather products that may offer some kickback protection include Syllit (do not use beyond tight cluster), Scala, Inspire Super, Luna Tranquility and Buran.
• Other products belonging to Groups 3, 7 or 11 can also be used, especially if things are further along in development and more broad-spectrum disease control is needed.
• Where possible, tank-mix systemic fungicides with a protectant such as a Group M (mancozeb, captan, folpet) or a biological product.
• Allegro does not offer post-infection activity.

What About Mildew?

While it might seem a little pointless mentioning powdery mildew in the midst of rain (hint: rain deters powdery mildew development), things will eventually dry up. High powdery mildew pressure in recent years followed by the mild winter could be an unwelcome mix resulting in an early spring arrival of this disease.

Be sure to consider a mildew protectant such as a low rate (3-5 kg/ha) of sulfur in your early season scab program, especially on susceptible cultivars or orchards with a history of powdery mildew. Continue this until tight cluster when more systemic fungicides with mildew activity like the Group 3, 7 and 11s start to be used.

As mentioned, rain washes off powdery mildew spores. Instead, mildew is spread by wind and thrives in dry weather and high relative humidity. So, protectant sprays may still be required during dry periods when there is little risk from apple scab.

Mapping Fire Blight Plans

With bloom quickly approaching, the Ontario fire blight prediction maps are now being updated 3 times per week until petal fall is over in all areas of the province.

Fire Blight Prediction Maps

These interactive maps show the 7-day predicted risk based on the Cougar Blight model. Growth stage is not considered in this prediction – if there are no open blossoms in the orchard, there is no risk of infection!

Considering Prebloom Options

Now is the time to apply prebloom fire blight protection products such as Lifegard or Regalia Rx (replacing Regalia Maxx) if these are being considered. These products work by boosting the immune response of the tree to better fight off disease, also known as System Acquired Resistance (SAR) or Induced Systemic Resistance (ISR). Because of this mode of action, these products should be proactively applied in advance to conditions conducive for disease development to allow time for the immune response to kick in. Note, Lifegard is toxic to bees so cannot be applied during bloom or if hives have already been brought into the orchard.

Save the Date! Apple IPM Workshop

Looking for a chance to refresh your knowledge of apple IPM? New to growing or scouting apples?

JOIN ME FOR AN APPLE IPM WORKSHOP
WEDNESDAY, MAY 1, 2024
9:00AM – 12:00PM
VIRTUAL

We will discuss orchard scouting including monitoring techniques for various insect and disease, tools of the trade, safety protocols and tips for success. Time will also be available to answer any pest-specific questions regarding the pre-recorded presentations available on the ONhortcrops YouTube channel.

You can join this workshop virtually via Zoom.

Pre-registration is required.

Other IPM workshops are also being offered over the coming weeks. More information to come!