This year will be the first for apple growers to tackle disease management with reductions to Group M fungicides in full effect. Unfortunately, as of writing this article, we have not seen any changes to mancozeb labels which means for 2023, the maximum number of applications of this active ingredient that can be applied to apples will be limited to 4, regardless of rate used. Now is the time to start planning your disease management program to strategize how and when to use the tools left to manage apple scab and summer diseases.

Below are some important management points to consider at different times during the season:

Dormant

Orchard sanitation

• Applying urea fertilizer at 45 kg/ha (mixed with 1,000 L of water/ha) and/or shredding fallen leaves with a flail mower are two practical and inexpensive methods to minimize scab pressure (and apple blotch, if this is a problem).
• Ideally, these practices should be done in the fall and/or before green tip if possible, but there may still be some benefit if this is delayed shortly after bud break.

Copper

• Copper sprays applied to green tissue may provide some protection against apple scab overwintering in buds equivalent to mancozeb applied at this stage.
• The use of a softer copper registered for season-long control such as Cueva could be extended in those early spray timings to ½” green or tight cluster in blocks with low scab inoculum (ie., free of scab last year).

Green Tip to Tight Cluster

• Best disease management is EARLY disease management!
• While mature spores are released more during warm rains than in colder ones, they can still cause infection, nonetheless, if they land on green tissue.

Protectant fungicides

• Maintain a protectant program every 5-7 days during periods conducive to disease development or following heavy (greater than 1”) rain.
• Protectant fungicides such as captan, folpet or mancozeb do not provide effective post-infection or anti-sporulant activity.
  • If sprays are applied in less than ideal conditions (ie., windy, alternate rows or washed off in rain), the risk of scab infection is increased.
• Folpet (active ingredient of Folpan/Follow) belongs to the same multi-site group (Group M4) as captan but was not affected by the recent PMRA re-evaluations.
  • General re-entry is 12 hours, with the exception of hand thinning (6 days) and hand harvest (1 day)
  • Similar cautions to captan apply to folpet products, including incompatibility with oil-based products and surfactants. May cause russetting on some varieties when used during bloom to 30 days after petal fall.
• Protectant fungicides do not control powdery mildew.
  • Include 3-5 kg/ha sulphur (Microthiol Disperss, Microscopic Sulphur, Kumulus, Cosavet DF Edge) with the protectant sprays until tight cluster when more effective mildew products will be used.

Alternative fungicides

• Allegro (Group 29) is considered a low resistance risk product so could be considered as a protectant option or tank-mix partner. However, use is limited to 5 applications per year.
  • Since this product is effective against bitter rot, black rot (suppression), fly speck/sooty blotch and mite suppression, save some uses for summer management.   
• During cool, wet springs, protectant fungicides may not be enough. Consider one of the products listed in Table 1 that perform well in cooler temperatures and provide post-infection activity. These could take the place of early season mancozeb to help save uses for more critical timings.
  • Syllit and Scala should be used early season only, up to tight cluster and pink, respectively.
  • Consider any issues with powdery mildew and/or rust in previous years. If these have been a problem, use a Group 9-containing product that also has activity on these diseases as well, such as Inspire Super or Luna Tranquility.
  • Buran (garlic extract) which is registered for scab and powdery mildew can also be used as an eradicant, or for early post-infection activity following a rain event when protectant efficacy may be reduced. This product does not have pre-infection activity for scab.
• In warmer, dryer springs, consider products such as Fontelis or Aprovia Top at the tight cluster stage, both of which have efficacy on scab, powdery mildew and rust.

Table 1. Registered fungicides for apple scab for use during cool, wet springs.

Product	Properties	Timing	Max app	Scab efficacy	Other disease
Syllit (U12)	retention, redistribution, anti-sporulant	Green tip – tight cluster	2	+++(+)1	No
Scala (AP)	post-infection, retention	Prebloom	2	++(+)	No
Inspire Super (DMI+AP)	post-infection, retention, redistribution, anti-sporulant	Prebloom	42	++++	mildew, rust
Luna Tranquility (SDHI+AP)	post-infection, retention	Prebloom	42	+++(+)	mildew
Buran (NC)	post-infection, anti-sporulant	Season long (<22˚C ideal)	—3	++(+)	mildew

Pink to Petal Fall

• By tight cluster or pink, apples are entering 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.

Protectant fungicides

• Mancozeb offers good efficacy on rust, apple blotch (Marssonina) and various rots which are active during this timing. With limited allowable applications of mancozeb (4 applications per year, regardless of rate used), you may want to keep some uses available for this timing.
• It’s best to avoid the use of captan and folpet in general during this growth period to avoid phytotoxicity by complicated tank-mixes, use of adjuvants or other incompatibility issues. Instead, save captan or folpet for summer disease control.
• Biological multi-site products to consider as tank-mix alternatives include Buran, Serenade.

Systemic fungicides

• Incorporate systemic fungicides (Groups 1, 3, 7 and 11). See Table 2 for disease efficacy ratings.
  • Unlike protectant fungicides, which have multi-site activity and low resistance potential, systemic fungicides are typically single-site and are at high risk of resistance development.
• Some groups, in particular Group 7 and 11s have efficacy on fruit rots, fly speck and sooty blotch. It may be worthwhile to save 1-2 applications for summer use.

Table 2. Efficacy of registered systemic fungicide groups on apple scab, powdery mildew (PM), rust, black rot (BR), bitter rot (BtR) and fly speck/sooty blotch (FSSB) on apples.

Fungicide Group	Scab	PM	Rust	BR	BtR	FSSB
1   (Senator)	+++	+++	—	+++1	+1	++++1
3   (Cevya, Fullback, Nova)	+++(+)2	++++	++++	++ (Cevya only)	—	+++ (Cevya only)
3+7  (Aprovia Top)	++++	+++	+++	—	—	+++
3+9  (Inspire Super)	++++	+++	++++	—	—	+++(+)
7   (Aprovia, Excalia, Fontelis, Kenja, Sercadis)	++++	++(+)	+++ (Fontelis only)	—	—	—
7+9  (Luna Tranquility)	++++	+++(+)	—	—	—	—
7+11  (Merivon, Pristine)	+++(+)	+++(+)	—	+++(+)	++++	++++
11   (Flint)	++++2	++++	—	+++1	++(+)1	++++

Summer Sprays to Harvest

• If primary scab was controlled, the rates of fungicides may be reduced and the interval between sprays may be lengthened for the remainder of the growing season.
  • Maintain a regular 14-21 day fungicide program until harvest to protect against summer disease, especially during conditions conducive to infection (ie., warm, wet weather).
• Consider the preharvest interval (PHI) restrictions that may apply (ie., based on tree size, export restrictions, etc), particularly with early-maturing cultivars.
• See Table 3 for preharvest intervals and disease efficacy ratings.

Table 3. Efficacy of summer fungicide options on scab, black rot (BR), bitter rot (BtR) and fly speck/sooty blotch (FSSB) on apples.

Product	PHI	Scab	BR	BtR	FSSB
captan	15 days (HD)	+++(+)	+++(+)	+++	++
folpet	1 day	+++	+++	—	++
Pristine	5 days	+++(+)	+++(+)	+++(+)	+++(+)
Merivon	0 days	+++(+)	+++(+)	+++(+)	+++(+)
Allegro	28 days	++	+	+++	+++
Buran	when dry	++(+)	—	—	++(+)1
Regalia	when dry	+(+)	++	++	+(+)
Serenade	when dry	+(+)	++1	++1	++1

Resistance management

• Fungicides are grouped based on their mode of action, or how the product actually affects the disease. For example, all products in Group 3 have the same mode of action, so using one product is virtually the same as using all other products within that group.
• In pre-mix fungicides, both groups need to be considered in all rotation decisions.
• One key strategy to good resistance management is rotating between products of different chemical groups. Figure 1 shows which fungicides belong to Groups 3, 7, 9 and 11.
  • For instance, since Aprovia Top belongs to Group 3 and 7, it should not be followed by other Group 3 (Cevya, Fullback, Nova), Group 3+9 (Inspire Super), Group 7 (Excalia, Fontelis, Kenja, Sercadis), Group 7+9 (Luna Tranquility) or Group 7+11 (Merivon, Pristine).
• For resistance management:
  • Where possible, include at least half rate protectant fungicide
  • Do not use products containing the same chemical group in consecutive applications.
  • Do not use Group 3 fungicides including Nova, Fullback and Inspire Super after bloom as they are weak on fruit scab. Trials with Cevya have indicated good efficacy on fruit scab.
  • Do not use systemic fungicides for post-infection activity.

Summary

The following description and Figure 2 summarizes many points from this article but is only an example conventional scab management program and does not include all control options available. Select products that fit best for your operation, cultivars, resistance management program and disease pressure as well as current weather conditions. Product choices in this example were based on a hypothetical cool, wet spring followed by a warm, humid summer and used a somewhat “worst-case scenario”, or combination of 4x mancozeb (77-day PHI) and 2x captan (19-day PHI).

1. Dormant – Begin with a delayed dormant copper application between silver tip and ½” green. This will have efficacy on any early season activity of overwintering fire blight cankers or scab infection periods.
2. Green tip to pink – Consider a protectant fungicide program such as mancozeb (especially at pink for rust control), folpet and/or Allegro. For high-density orchards where more applications of captan are allowed (maximum 10 per year), this active ingredient could also be considered here. Be cautious of potential tank-mix incompatibilities when using folpet or captan (for this reason, use is not shown at this timing in Figure 2). Early season alternatives, particularly in cooler springs could include Sylitt, Scala, Inspire Super or Luna Tranquility or post-infection timing using Buran.
3. Bloom into first covers – Incorporate systemic fungicides belonging to Groups 1, 3, 7 and/or 11 tank-mixed where possible with mancozeb.
4. Summer – A rotation of Merivon/Pristine tank-mixed with half-rate captan or folpet, Allegro, Serenade, Regalia and Buran as summer cover sprays will provide good control of scab, fruit rots and fly speck/sooty blotch. Allegro can be used up to 3 consecutive sprays before rotating to another fungicide group.
5. Preharvest – A late season application of folpet or Merivon/Pristine just before harvest (if not exporting) will protect against pinpoint scab and any other fungal infections that may occur.
6. Postharvest – Reduce inoculum by applying urea and/or flail mowing in the fall following harvest or as soon as the orchard can be entered in the spring.