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If you listened close enough, you may have heard the collective exhale across the province as we move out of frost watch from last week. While the nights are staying cooler, it doesn’t look like areas will be dropping below freezing again any time soon – hopefully for the remainder of the season. It sounds though like many growers are feeling optimistic about the frost events, with growth stages still being quite early. Only time will tell if damage was done to developing buds.

With the cooler temperatures, growth has been moving quite slowly this week. Regionally, growth stages are fairly spread out depending on cultivar and proximity to water:

• In Essex, Chatham-Kent, Lambton, Middlesex, Elgin, Norfolk, Brant and Niagara, early cultivars are at tight cluster. However, many remain at half inch green.
• In Grey, most cultivars are green tip to half inch green.
• In Durham, Northumberland and Quinte, most cultivars are at green tip to half inch green with some in very early tight cluster.
• Further along the St. Lawrence and into the Ottawa Valley, apples are at green tip.

Dealing with cold temperatures

With the freeze on everyone’s mind lately, a reminder to be careful not to add insult to injury when it comes to applying pesticides shortly after a cold event. The damaged tissue can be susceptible to the uptake of spray materials for 24-48 hours after a freeze before leaves have a chance to heal. This damage can serve as entry points allowing some products such as oil, copper or captan to be easily absorbed into the plant causing phytotoxicity.

Also, while it hasn’t been reported yet this year, cold-damaged spur leaves can appear small, narrow or crinkled if growth was far enough along for susceptible tissue to be damaged. If you notice this, be mindful to ensure early season mite and disease pressure such as powdery mildew are kept at bay since the spur leaves provide much of the energy required for fruit set.  

Diseases

Rainfastness of Fungicides

With the on-going rainy weather, I thought it would be important to touch on rainfastness of fungicides. Timing fungicides can be a challenge. Infection for most diseases requires rainfall. Fungicides are used mostly protectively so work best if applied before rain. But how well do fungicides stand up to rains that occur after application?  

A general rule of thumb often used is that 1 inch (2.5 cm) of rain removes approximately 50% of protectant fungicide residue and over 2 inches (5 cm) of rain will remove most of the residue. However, many newer formulations or with the addition of spreader-stickers, some products may be more resistant to wash-off. However, avoid putting on fungicides within several hours before a rainstorm as much can be lost to wash-off regardless of formulation. As well, there are exceptions to the general rule in regard to truly systemic fungicides such as Aliette and Phostrol.

The following are some points to consider to improve fungicide efficacy during wet weather:

• During rainy periods, systemic fungicides tend to perform better than protectant (or contact) fungicides since they are less prone to wash-off.
• Applying a higher labelled rate can extend the residual period.
• Apply protectant fungicides such as captan (Supra Captan, Maestro), mancozeb (Manzate, Dithane, Penncozeb) and folpet (Folpan) during sunny, dry conditions to allow for quick drying on the leaves. These types of fungicides are better absorbed and become rainfast over several days after application.
• Apply systemic fungicides such as sterol inhibitors (Cevya, Nova, Fullback, Inspire Super), SDHI (Excalia, Fontelis, Sercadis, Kenja, Aprovia Top, Luna Tranquility) and strobilurins (Flint, Pristine, Merivon) under humid, cloudy conditions. The leaf cuticle will be swollen, allowing quicker absorption. In dry, hot conditions, the cuticle can become flattened and less permeable, so product can breakdown in sunlight, heat or microbial activity or be washed off by rain.

Scab

Regions that have seen some decent precipitation have had multiple potential scab events since the start of the season. Early areas have reached the period of rapid ascospore maturation (or 125 DDC), at about 30-50% of ascospores (or more) matured.

As I mentioned last week, even with the freezing temperatures, it is possible for ascospores to continue to develop.

Based on the Mills Table I included in last week’s update, primary infection requires a minimum of 11 hours of leaf wetness at 10 degree Celsius. The minimum number of hours decreases with increasing temperature. This requirement will be met in many regions of the province if rain continues as predicted this week.

Apply protectant fungicides now if not already covered. 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.

Consider including a post-infection, or kickback product if you are concerned about coverage. For more information on apple scab fungicide characteristics, I’ve included the table Characteristics of Apple Scab Fungicides below.

Characteristics of Apple Scab Fungicides

Product	Protectant Activity (pre-infection)	Post-Infection Activity (hours)1	Post-Symptom Activity	Retention (50 mm rain)	Redistribution (12 mm rain)
Buran	N	350 degree hours (base 0°C)	VG	N	—
Copper 53 W	G	—	—	G	G
Copper Spray	G	—	—	G	G
Cosavet DF Edge	F	N	N	F–G	F–G
Cueva	G	—	—	G	G
Dithane Rainshield	VG	18–24	N	E2	G–VG
Flint	VG	48–723	G	E	G
Follow WDG	VG	18–24	N	VG	G
Folpan 80 WDG	VG	18–24	N	VG	G
Fontelis	E	48	—	E	F–G
Inspire Super	VG	483	E	VG	G
Kumulus DF	F	N	N	F–G	F–G
Luna Tranquility	E	48	—	E	F–G
Maestro 80 WSP	VG	18–24	N	VG	G
Manzate Max	VG	18–24	N	E2	G–VG
Manzate Pro-Stick	VG	18–24	N	E2	G–VG
Microscopic Sulphur WP	F	N	N	F–G	F–G
Microthiol Disperss	F	N	N	F–G	F-G
Nova	F	72–963	G–VG	F2	F2
Parasol Flowable	G	—	—	G	G
Penncozeb 75 DF Raincoat	VG	18–24	N	E2	G–VG
Scala SC	G	48–72	N	G	—
Senator 50 SC	F	18–24	VG	G	F
Sercadis	VG	48	F	E	G
Sharda Captan 48 SC	VG	18–24	N	VG	G
Supra Captan 80 WSP	VG	18–24	N	VG	G
Syllit 400 FL	VG	18–24	VG	VG	G

By tight cluster, apples are typically entering into a time of critical infection period for scab and powdery mildew with higher daily temperatures, large amounts of lush growth and rapid maturation of spores. Management programs at this point should begin incorporating systemic fungicides (Groups 3, 7 and 11). However, unlike protectant fungicides like Group M, which have multi-site activity and low resistance potential, systemic fungicides are typically single-site and are at high risk of resistance development. For resistance management, half to full rate protectant fungicides should still be included with all applications and rotate between chemical groups.

Rust

With tight cluster, we are also entering into the activity timing for rust. While captan does not provide effective rust control, mancozeb does. If you know this disease can be a problem in your orchard or neighbourhood, be sure to keep mancozeb as the protectant tank mix particularly at petal fall. It’s best to avoid the use of captan in general during this growth period anyways to avoid phytotoxicity by complicated tank-mixes, use of adjuvants or other incompatibility issues. Instead, save captan for summer disease control if the use restrictions and preharvest intervals fit with the activity going on in your orchard.

Insects

Spring feeding caterpillar

The cool weather has been keeping insect activity at bay so far. However, half inch green to tight cluster is the time to start seeing small caterpillars feeding on new terminal growth and developing fruit buds. While not a stand alone control tactic, supporting beneficial insects in the orchard such as ladybugs and lacewings will help suppress some pests such as spring feeding caterpillars. Consider this when deciding if a prebloom insecticide is worthwhile.

Over the last few years, we have been seeing the peak activity in the 7-10 year cycle of spongy moth (formerly referred to as gypsy or LDD moth). In an effort to use inclusive language, the entomology community is transitioning away from the use of “gypsy moth” and so you will be hearing me using the term “spongy moth” moving forward.

It was estimated a record-breaking 1.8 million hectares of Ontario saw varying levels of defoliation. Some of these areas include apple growing regions and a number of apple orchards experienced extensive pressure from this pest, causing both defoliation and fruit damage.

Good news is that the natural predators and pathogens in our region have been doing a great job to collapse the outbreak. While defoliation is still anticipated this year, pressure is expected to be less than 2021. The following map shows Ministry of Northern Development, Mines, Natural Resources and Forestry’s projected 2022 spongy moth defoliation and hot spot regions.

Spongy moth egg hatch is expected to begin shortly from tight cluster to bloom. Larvae will feed on leaves, fruit buds and developing fruitlets until about July. Management is most effective when targetting young larvae (black head capsule, less than 2.5 cm long) with Bt products such as Dipel, Bioprotec).

A great resource for spongy moth identification is the 2021 webinar hosted by Jen Llewellyn, OMAFRA:   

Apple leafcurling midge

Adult catch in pheromone traps has begun in regions that are monitoring for apple leafcurling midge. While the freezing temperatures may have slowed activity, it has been only temporary. There are still no signs of egg laying but I imagine this will begin in the coming weeks. I will continue to provide updates on egg laying as well as regional degree day predictions.

Scale

Trying to find a window for dormant oil targeting scale timing was difficult in some areas this year. Another prebloom timing to consider is a tight cluster to pink application of Sivanto Prime or Closer to target the maturing scale. The high rate of Closer at this timing will also have efficacy on leafcurling midge, woolly apple aphid, tarnished plant bug and mullein bug.

Aphids

If this spring continues to be on the cool, wet side, be prepared for rosy apple aphid populations to build, especially with the higher pressure many regions saw last year. Egg hatch is likely on-going currently but infestations really start to be observed into tight cluster. Pay particular attention to fruit clusters of susceptible cultivars like Cortland, Idared, Golden Delicious and Ambrosia.

Oriental Fruit Moth

Pheromone traps for oriental fruit moth are going up around the province. This will kick off degree day modelling for targeting first generation timing. Terminal flagging, especially on young plantings can be an issue early season by this pest. A new granulovirus product called Madex is now available for growers this year that has efficacy on both OFM and CM. Timing for this product is on the early side compared to some of the more standard products since it needs to be ingested to be effective.  

Events

A reminder for anyone interested, the Apple IPM workshop will be held this Friday, May 6th from 10:00am to 1:00pm. This will be a virtual event but registration is required to receive the Zoom link.

If you would prefer self-guided learning, you can follow the Apple IPM Workshop series on the ONhortcrops YouTube channel: