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Dry, hot weather continues across the province. Some areas have received a few days of rainfall while others have seen very little since June.

For information on irrigation, check out some of these resources from Rebecca Shortt, Water Quantity Engineer:

• Ontario’s Irrigation webpage – includes great video series on drip irrigation and monitoring soil moisture
• Recent ONfruit posts Hot weather impact on plant water demand – how can we measure? and 3 Secrets of Irrigation Water Taking Permits Revealed
• More Crop Per Drop (Episode 5) of the What’s Growing ON? podcast

Terminal buds have set in most regions by now. Without new shoot growth, there is no longer a risk of powdery mildew. It is possible to see a flush of new growth later in the season, especially if these dry conditions change and we get some moisture back into the trees.

Fire Blight

With terminal bud set, the cell walls thicken, stomata on the shoot stem are no longer active and the base of the shoot starts to harden off and form bark. All of which results in a significant reduction in fire blight movement. This is a good time to start to prune out fire blight strikes if you haven’t been already. Choose days of dry weather and leave the pruning cuts in the row middles to dry up before mulching them down.

Looking for a quick refresher for pruning fire blight? Check out this video from Dr George Sundin, Michigan State University:

The unsettled weather we are experiencing may continue to bring hail, strong winds or heavy rains that could still trigger trauma blight from terminal set until harvest. These could be very isolated events, occurring in one area but not another nearby. Assess for signs of damage in all blocks following any storm.

Be sure to apply Streptomycin (PHI 50 days) or 0.5-0.8% Cueva as soon as possible after the trauma event, especially if foliage damage is extensive or fire blight is known to be active in the orchard (ie., cankers, etc). New research is now suggesting ideal timing is 4 to 12 hours after a storm. Anything applied later runs the risk that the bacteria will have already established and begun to grow, reducing the efficacy of the product.

Efficacy of copper may be increased with the addition of Double Nickel.

Summer Disease

Now is the time to start considering summer disease management. While symptom development doesn’t really start to appear for fruit rots, fly speck and sooty blotch until later in the summer or into the fall, infection actually happens now.

We have had ideal bitter rot infection conditions over recent weeks with the hot, humid weather followed by a rain storm. With hand thinning continuing, be sure to toss thinned fruitlets to the row middle and mulch. These fruit have been known to cause infection of remaining fruit on the tree by splashing spores during rain events.

Infection timing for fly speck and sooty blotch should also be considered. In wet years, infection typically begins 2-3 weeks after petal fall. With many regions so dry following bloom, it’s possible activity could have been delayed. There is a fly speck forecasting model that predicts the start of infection beginning 175 leaf wetting hours after petal fall. For some areas, this threshold has been reached.

For management of summer diseases, follow a 14-21-day application interval until harvest to ensure fruit remains protected. Table 1 summarizes activity of fungicides that could be used for summer disease control. Residual protection will vary depending on the product used. For example, Pristine can provide reasonable residual control of summer disease up to 3 weeks at the labelled rate in ideal conditions; however, captan should not be pushed further than 14-days between sprays particularly since it is not as strong on fly speck and sooty blotch as other control products. In all cases, reduce interval to 7 days during times of hot, wet weather.

Table 1. Activity of registered fungicides on fly speck/sooty blotch, black rot and bitter rot

Product	Group	PHI	Scab	Fly speck / sooty blotch	Black rot	Bitter rot
captan	M	19 days*	+++(+)	++(+)	+++(+)	+++
Folpan (NR)	M	1 day	++(+)	++(+)	++(+)	+++
Senator (NR)	1	1 day	+++	++++	+++	+
Cevya (NR)	3	0 days	+++(+)	++	++	++
Aprovia Top	3+7	30 days	++++	+++	—	—
Inspire Super	3+9	14 days	++++	+++(+)	—	—
Pristine	7+11	5 days	+++(+)	+++(+)	+++(+)	+++(+)
Merivon	7+11	0 days	+++(+)	+++(+)	+++(+)	+++(+)
Flint	11	14 days	++++	++++	+++	++(+)
Allegro	29	28 days	++	+++	+	+++
Phostrol	33	1 day	—	++	—	—
Regalia Maxx	P5	0 days	+(+)	+(+)	++	+(+)

Be sure to keep in mind preharvest intervals for all early and late-harvest varieties. Some products that may be most effective for summer disease cannot be used for fruit that will be harvested in coming weeks. At the same time, residues will need to be maintained on late-harvested varieties into the fall, especially if the hot weather trend continues in September and October.

Important cultural management recommendations include:

• Prune and thin clustered fruit to facilitate drying and improve fungicide coverage.
• Remove potential sources of inoculum such as dead branches, fruit mummies (where possible), infected fruit on the orchard floor and alternate hosts including brambles (blackberry, raspberry) from surrounding hedgerows or woodlots.
• Toss pruning cuts and thinned fruit in the row middle and mulch.
• Reduce tree stress by irrigating and/or applying a sun protectant, especially ahead of a heat wave.

Mites

The hot, humid weather has resulted in an increased activity of European red mite (ERM), two-spotted spider mite (TSSM) and apple rust mite (ARM) in some orchards. Those growers that are seeing populations reach threshold quickly are opting for miticides with relatively quick knock-down.

Keep in mind, thresholds for mites increases through the season as the tree canopy becomes more dense. From June to mid/late July, the threshold for most products is 7-10 active mites/leaf. Consider 5 mites/leaf for products like Nealta or Kopa. However, late July to August, the threshold for most products can be delayed to 10-15 active mites/leaf.

Table 2 lists registered miticides for summer managment. When choosing a product, consider the abundant life stages that are present in your orchard. For instance, if you are seeing mainly eggs, Envidor may be an option as it is slower acting. However, if the population is mainly nymphs or adults, you may opt for a product that offers a faster knock-down. As mentioned earlier, products like Nealta or Kopa should be applied as populations are building.

Table 2. Activity of Summer Miticides Registered on Apple in Ontario

Product	Target Species	Life Stage Affected	Knock-Down Activity
Acramite 50 WS	ERM, TSSM	nymphs, adults	rapid
Envidor 240 SC	ERM, TSSM, ARM	eggs, nymphs, adults (female)	slow
Kanemite 15 SC	ERM, TSSM	all life stages	rapid
Kopa (soap)	ERM, TSSM, ARM	nymphs, adults	intermediate
Nealta	ERM, TSSM	all life stages	intermediate
Nexter	ERM, TSSM, ARM	nymphs, adults (ERM, ARM) nymphs (TSSM)	rapid
Purespray Green Spray Oil 13 E	ERM (suppression)	eggs, some nymphs	smothers
Suffoil-X	TSSM	eggs, some nymphs	smothers
Vegol Crop Oil	ERM	eggs, some nymphs	smothers

Despite the lush, dense foliage this time of year, do not let mite populations cause extensive damage. Late-season mite pressure and leaf bronzing can result in poor fruit finish and reduce winter hardiness.

Apple Maggot

Apple maggot have been caught in most regions of the province though catch is very sporadic for many. Emergence is closely linked to soil moisture with flushes in flight often following periods of significant rainfall loosening soil. In dry years such as this, pupae can remain within the soil until conditions improve, even remaining until the following year. Those areas receiving good amounts of rain with the events rolling through may see a flush of apple maggot emergence in the coming days to weeks.

With catch on yellow sticky boards, it is important to differentiate between male and female adult flies. Males generally begin emerging before the females, but by peak emergence (August), the sex ratio is about 1 to 1.

Timing for management depends on the type of trap:

• Sexually immature males and females are attracted to the yellow sticky boards, which mimic nectar sources. Insecticides are not needed until 7-10 days after first fly, particularly a female, is captured.
• Sexually mature females ready to lay their eggs are attracted to red spheres, which mimic ripe apples and indicate an insecticide should be applied immediately as damage is imminent.

Many growers make use of an Imidan border spray at this point in the year when the longer re-entry restrictions won’t interfere as much with work that needs to be done. Border sprays are not recommended for other registered apple maggot products.

Table 3, adapted from John Wise, Michigan State University (2019), summarizes the characteristics of apple maggot products. Organophosphates (Imidan) and neonicotinoids (Assail, Calypso) are the only insecticide groups that have activity on the adults as well as a curative effect on the eggs and larvae due to their ability to penetrate into the flesh of the fruit.

Table 3. Summary of Insecticides Used to Control Apple Maggot

Product Name	Chemical Group	Life-Stage Activity	Efficacy	Residual Activity	Mite Flaring Potential
Imidan	Organophosphate	Eggs, larvae, adults	Excellent	14+ days	Low
Ambush, Danitol, Perm-Up, Pounce, Ship, Up-Cyde	Pyrethroid	Adults	Fair-Good	7-10 days	High
Delegate, TwinGuard, GF-120 Fruit Fly Bait	Spinosyn	Adults	Fair	7-10 days	Moderate
Aceta, Assail, Calypso, Cormoran, Theme	Neonicotinoid	Eggs, larvae, adults	Good-Excellent	10-14 days	Low-Moderate
Altacor, Exirel, Harvanta, Vayego	Diamide	Adults	Fair-Good	10-14 days	Low
Surround	Not classified	Adults (deterrent)	Fair	7-10 days	Low

San Jose Scale

In previous years, crawler emergence has generally begun late July to early August. Based on degree days, we seem to be on track this year to see crawlers early August in most areas. For the far southwest (Harrow), emergence is predicted in the last week of July while regions more central could see activity kick off following the long August weekend or later.

Fruit damage from San Jose scale has been relatively low to date this year, especially compared to the high pressure in many blocks in previous years. Those that have a history of damage from this pest may want to consider managing this generation to prevent fruit damage close to harvest. Registered products include Movento, Sivanto Prime, Closer and TwinGuard. For good resistance management, rotate to a different chemical group than what was used for the first generation. If using two consecutive sprays applied 14-days apart, be aware of the preharvest interval particularly on any early varieties.

Potato Leafhopper

Potato leafhopper are quite active. Hopperburn and leaf cupping can be easily found. This is caused by a toxin in the leafhopper’s saliva that blocks vascular system flow, preventing normal movement of water and nutrients to the affected area.

In most high vigour blocks, leafhopper damage is manageable, particularly once terminals harden off. However, nursery trees and non-bearing blocks require control at first sign of injury since vigour and shoot growth can be significantly impacted.

Japanese Beetle

Japanese beetle damage can also be easily found now in many regions. The characteristic leaf skeletonization is quite distinct. Look for damage and congregations of this pest at the top of the canopy as damage often moves down the tree. Honeycrisp is often the most preferred variety.

Most insecticides applied for codling moth should have good efficacy on Japanese beetle; however, the tendency of these beetles to move in from surrounding areas may make multiple applications necessary.  If applying a control product, target timing for early morning while beetles are still relatively inactive on the tree. Once feeding begins, the sex pheromones emitted by females combined with what numerous studies believe to be feeding-induced plant volatiles attract more beetles to congregate in the feeding area. Achieving knockdown before this occurs could help reduce the number of individuals coming into the orchard from surrounding areas.

Good weed control in and around the orchard will also help reduce Japanese beetle pressure. Populations tend to be more abundant in orchards where there is poor control of wild raspberry, blackberry, Virginia creeper and wild grape.