Disease

Fire Blight

Very little fire blight has been reported. However, with the wet weather predicted this week, those orchards with active cankers could be found oozing. According to Dr George Sundin, Michigan State University, each fire blight ooze droplet can contain approximately 1 billion cells while it only takes 100-1,000 cells to initiate shoot infection. That means a single ooze droplet could have the potential to infect every shoot in an orchard if spread by insect, rain, wind or even workers and contaminated equipment. It is best to do any hand labour activities such as thinning, pruning or removing suckers in dry conditions in these blocks to avoid the potential spread of bacteria.

While many orchards may have got through bloom period without signs of fire blight, infection can still occur through open wounds caused by strong winds, heavy rain and hail, insect feeding, pruning or mechanical damage. Blossom blight does not need to be present for other parts of the tree to be affected such as shoots or rootstock. In fact, inoculum can be spread large distances throughout a region during storms.

Cueva and Double Nickel are registered for the control of shoot blight following a trauma event. Like all coppers, there is the risk of russeting with Cueva. However, if fire blight is active in your orchard at the time of trauma, better to lose some fruit this season than trees later. The preharvest intervals for Streptomycin and Kasumin are 50 and 90 days, respectively.

Fire blight ooze (red arrows) can appear clear to orange-red in colour and can often be found in early morning, during days of high humidity or following wet conditions

Shoot blight developing on apple branch

Fire blight infected blossom

Scab

Apple scab continues to develop in some orchards. Most lesions can be found on older leaves suggesting infection likely occurred during the extended wet periods late April and early May. Fruit scab can also be found. In these orchards, a protective fungicide program should continue during periods of potential scab infection. Spores will be released from existing lesions during rain or other wetting events and infect surrounding leaf and fruit tissue. This secondary infection period will continue through to harvest.

Powdery mildew

In the earlier regions, terminal bud set has begun. Powdery mildew requires actively growing tissue to complete its cycle so fungicides with efficacy against this disease should continue until terminal growth stops. Infected shoots will not cause damage to fruit at this point in the season. Fruit damage is a result of early infection that occurred in the flower buds. However, infected shoots will be the inoculum source for next year. Prune out any strikes that are present.

Apple scab on leaves and developing fruitlet

Powdery mildew on new terminal growth

Summer Disease

With many growers now beginning to relax back on scab management for the summer, it is important to still consider fungicide sprays for summer diseases, especially since fly speck and sooty blotch appear more frequently during years with cool, wet springs. Summer applications should be made every 14-21 days depending on the product used if there is a history of summer disease in the orchard. Shorten application intervals to 7 days if frequent rain is experienced. If possible, time an effective fungicide application just prior to a rain to prevent fruit from rain-splashed spores. Always rotate products to reduce the potential for resistance development.

Insects

Internal Feeders

The spray timing for 1^st generation codling moth egg hatch is on-going. There have been no reports of fruitlet damage yet. Activity has been rather delayed and/or sporadic this year, likely due to the coolers, wet weather. This has resulted in some difficulties setting a biofix in some areas.

Heavy rains have many growers concerned about residue wash-off. In general, 2 inches of rain will removed residues for all products and require immediate re-application. With less rain, there are some insecticide classes such as the spinosyns (Delegate, TwinGuard) and diamides (Altacor, Exirel, Harvanta) that have a high rainfast rating.

It’s important to note for resistance management, if re-application is required for control of a pest with discrete generations, use the same product within a generation. For instance, codling moth is still in the first generation window. Second generation activity will not begin for another few weeks – typically early August. Rotate to another insecticide class at that time to ensure each generation is only exposed to one active ingredient.

Trap catch still remains quite low for obliquebanded leafroller. Biofix has been set for some but not all regions. Control timing will begin over the next couple for weeks across the province.

European apple sawfly fruit damage can be found. This is no surprise given the length of bloom in some orchards causing a gap in residue that would normally help prevent egg laying.

Apple maggot traps are currently going up ahead of adult emergence. Emergence is closely linked to soil moisture levels, which has not been an issue this year. Males generally begin emerging before the females but by peak emergence (about August) the sex ratio is about 1 to 1.

San Jose scale

San Jose scale adult flight has declined this week. First generation crawler emergence is predicted to begin over the next few weeks. Based on degree-day models, earlier regions should start to see activity this week while later regions should see activity picking up in early July. As of Monday, June 24, no crawlers have been found in orchards that I am actively monitoring.

Since Movento is slow-acting, ideal application timing is 1-2 weeks prior to crawler emergence. If planning to use this product and it has not gone on yet, applying as soon as possible may still provide some efficacy for later emergence due to the extended pest activity.

Dogwood Borer

Dogwood borer trap catch is beginning in orchards with a history of problems with this pest. However, adult emergence will continue through to early September with peak flight typically occurring mid-July. During this time, females lay eggs on the surface of burr knot formations, pruning cuts, cankers, and wounded bark, after which the larvae use as entry points to bore into the tissue to begin feeding.

If pheromone traps have not been placed in the problem orchard yet, these need to be installed as soon as possible since adult flight has begun. Four traps per site, placed in low scaffold limbs, are recommended. Use a minimum distance of 50 m between traps, and monitor twice a week. Record the number of adults captured – graphing the results – to identify peak flight time. This information can be used to time trunk applications of a registered insecticide.

Currently, pyrethroids, Altacor, Delegate and Rimon are registered for control of borers. Rimon 10 EC is an insect growth regulator (IGR) that must be absorbed by eggs or ingested by larvae to be fully effective. The optimal timing for this product is around 25-75% egg laying, or approximately peak flight. Delegate and Altacor must be ingested by the larva in order to work; therefore it must be applied at the beginning of egg hatch, or a few weeks following peak flight. With all products, a repeat application 14 days later is recommended.

An alternative management option for dogwood borer next year is the mating disruption product, Isomate DWB. Dispensers (250-375 dispensers/ha) should be applied before adult borer emergence, or approximately the end of May. Researchers from Rutgers and Cornell University feel that Isomate DWB can adequately control light to medium dogwood borer infestations and give equal control to trunk drenches after multiple years of use.

However, the best way of avoiding dogwood borer infestations is to prevent burr knot development. If possible:

• Select rootstocks with a lower tendency for burr knot formation to reduce attractiveness to borers. Rootstocks particularly susceptible to burr knot formation – and attack by borers – are M9, M26 and Mark.
• Use wire mesh mouse guards rather than solid guards. Borers prefer shaded, protected habitat. Solid guard restrict air circulation and prevent bark hardening, pre-disposing the tree to winter injury and providing good borer egg laying sites.
• Apply white latex paint to trunk to deter egg laying and, if applied thick enough, suffocate borers already in the wood.
• Keep the area around the tree weed-free to avoid shade and high humidity.

Woolly Apple Aphid

Woolly apple aphid colonies have been building. Still more commonly found inside the canopy around pruning cuts, cankers or split bark, there are some cottony masses that are beginning to move throughout the canopy.  Most products timed for San Jose scale should have some efficacy on woolly apple aphid as well. Many beneficial insects such as lady beetle can be found feeding on colonies.

Mullein Bug

Mullein bug stings on developing fruitlets have been reported in orchards. However, overall damage from this pest has been fairly low. This is especially surprising in some orchards especially given the high numbers of mullein bug nymphs have been tapped out during weekly monitoring. At this point in the season, damage is not a concern as most mullein bugs are late stage nymphs (with wing pads) or adults and fruit is larger than dime- to quarter-sized. In fact, mullein bugs are very effective predators of many orchard pests so supporting these populations from this point on in the season is encouraged.

Woolly apple aphid colonies on old cankers on apple trunk

Mullein bug sting appears as a small, raised bump on developing fruitlet

Brown Marmorated Stink Bug

Brown marmorated stink bug has begun to be caught in monitoring traps in established areas. These are the overwintering adults becoming active. However, they are not attracted to apples at this time of the year as a food source. Damage is likely to not occur in apples until later in the season but it is never too late to add stink bug to your monitoring program. For more information and regular updates, go to ontario.ca/stinkbug.

Other Insect Pests

Damage from leafcurling midge, tarnished plant bug, potato leafhopper and plum curculio continue to be found. Both European red mite and two-spotted spider mite are active; however, populations remain low.

Tarnished plant bug damage on developing apple fruitlet appears as sunken or dimpled spot

Hopperburn caused by potato leafhopper on terminal. Notice the yellowing and downward curl of leaf edges

Potato leafhopper

Events

The 3^rd Apple Virtual Study Group Lunch ‘N Learn webinar will be Wednesday, July 3^rd from 12:15pm to approx. 1:00pm. Dr David Rosenberger, Professor Emeritus in Plant Pathology from Cornell University will join us to discuss summer disease management. Webinar details coming soon.

Contact Information

The Ontario Public Service is streamlining telephone services to eliminate duplication. Effective  immediately, my telephone number is 519-420-9422. This mobile service replaces my telephone landline. Feel free to call or text me. These changes do not affect my email service which remains kristy.grigg-mcguffin@ontario.ca.

For an updated contact list of other OMAFRA Agriculture Development Branch specialists, please see the Info-Go directory at http://www.infogo.gov.on.ca/infogo/#orgProfile/210/en.

I’d also like to remind you that our Agricultural Information Contact Centre is at your service at 1-877-424-1300 and ag.info.omafra@ontario.ca.