Fresh plum curculio damage on apple fruitlet
Apples Diseases Insects Pest Management

Apple Pest Update: June 14, 2019

Petal fall to first cover pest activity continues for apple orchards across the province

The never-ending apple bloom saga of 2019 seems to finally be over for most areas of the province and fruitlets have begun to size – though slowly in some regions. The few sunny and dry days this week have been a welcome sight amidst the cloudy, rainy days that have been typical of this spring.

Based on the ONvegetables Vegetable Crop Report for June 13, 2019, most counties are marginally to significantly behind their respective growing degree day (base 5°C, accumulated since March 1st) averages of the previous 10 years with exception to Essex and Huron counties which are at average and above average, respectively. While some regions are now receiving near average temperatures, the lack of sun and cooler night temperatures has slowed the growth and development of both crop and pest development.


Fire Blight

The risk of blossom blight has passed in most orchards. However, growers should still be on the lookout for rat-tail bloom or late bloom in spring planted blocks. Rat-tail bloom has been very common this year and can be easily missed in a block. Be on the look-out if you know fire blight is an issue in your orchard. If ideal conditions continue and secondary bloom is not removed or protected, the bacteria can easily wash into the blossom initiating infection.

Friday, June 14th was the final update for the fire blight prediction maps. While the maps show predictions until June 20th, keep in mind this model is using forecast data which may change over the week. Presently, the maps are being updated with the actual infection risk that occurred during bloom across the province. This will be posted shortly.

There have been a few reports of fire blight, particularly on (but not limited to) Mutsu. As well, strikes are developing in the fire blight experimental block at Jordan Station. This indicates conditions were conducive to infection during bloom this year despite many cool days. Continue to watch any problem blocks closely over the upcoming weeks for signs of blossom or shoot blight.

Apple Scab

Low levels of apple scab infection can be found in some orchards across the province. Though overall, many orchards still appear to be clean at this time. There is a very good chance that with the amount of precipitation the province has seen, the majority of orchards have had 100% mature ascospore release, signalling the end of the primary infection period. However, it is recommended to continue a protectant spray program for at least 3 weeks while monitoring for signs of scab lesions. Be sure to take a good look in the top part of the canopy as coverage can often be inadequate there. As mentioned in the Apple Pest Update for May 20, 2019, lesions may take longer to develop in the cooler weather. Before reducing fungicide rates, be sure your orchard is completely free from primary scab.

Powdery Mildew

Surprisingly, despite all the rain, powdery mildew has gotten a hold in some orchards. Warm, humid weather favours this disease. Free-standing water actually inhibits germination of powdery mildew and rain or dew can wash spores off leaf surfaces. Continue to protect susceptible varieties such as Gala, Honeycrisp, Cortland, Idared, Crimson Crisp, Goldrush, Russet, Fuji and Spy. This disease does not invade mature leaf tissue, so spread stops by terminal bud set.


Summer Disease

While often considered mid- to late summer diseases, now is the time to start thinking about management of fly speck, sooty blotch, bitter rot and black rot. Frog-eye leaf spot (black rot) can already be found in orchards, indicating spores are being actively released during rain events. The developing fruitlets are now at risk of infection by these fungi despite symptoms not actually appearing until mid-summer. Consider fly speck, sooty blotch and fruit rot efficacy when selecting petal fall and first cover sprays and continue to keep fruit protected throughout the summer with 14-21 day intervals after primary scab is over. Refer to Table 2-3. Activity of Fungicides on Apple Diseases in 2018-2019 Publication 360, Fruit Crop Protection Guide for product efficacy ratings.

Frog eye leaf spot on apple


Insecticide Rainfastness

In the Apple Pest Update for June 5, 2019, I summarized work done by John Wise (Michigan State University) on rainfast characteristics of various insecticide classes.  To read Wise’s full article, see Rainfast Characteristics of Insecticides on Fruit. The following should also be considered when determining the impact of rain on an insecticide’s performance:

1. Penetration into plant tissue is generally expected to enhance rainfastness.

  • Organophosphates have limited penetrative potential, and thus considered primarily surface materials.
  • Carbamates and pyrethroids penetrate the cuticle, providing some resistance to washoff.
  • Spinosyns, diamides, avermectins and some insect growth regulators (IGR) readily penetrate the cuticle and move translaminar (top to bottom) in the leaf tissue.
  • Neonicotinoids are considered systemic or locally systemic, moving translaminar as well as through the vascular system to the growing tips of leaves (acropetal movement).
  • For products that are systemic or translaminar, portions of the active ingredient move into and within the plant tissue, but there is always a portion remaining on the surface or bound to the waxy cuticle that is susceptible to wash-off.

2. Environmental persistence and inherent toxicity to the target pest can compensate for wash-off and delay the need for immediate re-application.

  • Organophosphates are highly susceptible to wash-off, but are highly toxic to most target pests, which means re-application can be delayed.
  • Carbamates and IGRs are moderately susceptible to wash-off, and vary widely in toxicity to target pests.
  • Neonicotinoids are moderately susceptible to wash-off, with residues that have moved systemically into tissue being highly rainfast, and surface residues less so.
  • Spinosyns, diamides, avermectins and pyrethroids are moderate to highly rainfast.

3. Drying time can significantly influence rainfastness, especially when plant penetration is important. For instance, while 2 to 6 hours is sufficient drying time for many insecticides, neonicotinoids require up to 24 hours for optimal penetration prior to a rain event.

4. Spray adjuvants that aid in the retention, penetration or spread will enhance the performance of an insecticide.

Internal Feeders

Areas that control for oriental fruit moth have passed the spray window. Ideal timing would have been at petal fall/calyx when most growers would have used a product effective against fruit moth.

The next internal lepidopteran pest on growers’ radars is codling moth. Catch has been rather sporadic this year with a biofix range set in some areas due to variation in catch from site to site. Timing is very important with codling moth as the larvae often tunnel into the fruitlets within 24 hours of hatch. For early regions, it is too late for insect growth regulators, such as Rimon (petal fall timing) or Intrepid (83-111 DDC) as they need to be on early to interrupt regular development. Contact or ingestion larvicides are applied typically around 138 DDC. This timing may also help with early obliquebanded leafroller hatch, too. However, no sustained obliquebanded leafroller catch has been reported yet.

European apple sawfly catch has been relatively low in many orchards as of late. The extended bloom in some areas may have resulted in a period of limited protection against this pest. Damaged fruit can be found. Growers are applying an early petal fall insecticide.

Mating disruption for dogwood borer continues to go up in orchards with a history of this pest. This can be a very effective form of management for this pest if used properly, especially given the long period of activity for adult emergence. 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.

Plum Curculio

Plum curculio damage has been found on developing fruitlets. Activity is a little later than previous years in some regions. Often movement into the orchard follows a period of sustained warm weather and rain. Some research suggests weather patterns (sun/cloud) affect whether curculio migrate into the orchard by crawling or flying. If weather is cool at bloom and petal fall as we experienced in many regions this year, adults may not migrate into the orchard until after petal fall.


Mullein Bug

Mullein bug populations remain high in some orchards despite a targeted petal fall insecticide being applied. This may be a result of an asynchronized or split hatch due to the cooler weather. The critical time for damage from mullein bug is generally dime to quarter-sized fruit. Up to this point, very little damage has been reported.

Nymphs with red bellies can be found indicating they have become predaceous and are feeding on mites, aphids and other soft bodied insects. Interestingly, a significantly high number of mullein bug can be found in apple leafcurling midge terminal damage. It is possible mullein bug are feeding on these larvae.

Apple Leafcurling Midge

Leafcurl damage from apple leafcurling midge can be easily found in many orchards. Larvae within the rolled leaves are beginning to turn orange in early regions, which is a sign of late instar stages just prior to pupating. Second generation adult emergence has typically occurred in mid-June to early July in previous years.

Apple leafcurling midge

San Jose Scale

San Jose scale adults have been trapped since mid-May in monitoring orchards in Norfolk County. Based on degree days, 1st generation crawler emergence is predicted:

  • Essex County (Harrow) – June 17
  • Middlesex County (London) – June 26
  • Norfolk (Simcoe) – June 24-26
  • Grey (Thornbury) – July 9
  • Durham (Oshawa) – July 3

Crawler activity (ie., movement to new shoots and developing fruit) will continue for 4-6 weeks. Registered products including Closer, TwinGuard and Sivanto Prime should be applied at the beginning of crawler activity and reapplied 10-14 days later due to the extended generation. Movento is a slow-acting product and should be applied at least 1 week prior to predicted crawler emergence, again followed up 10-14 days later. Depending on the product, this timing may also have efficacy on leafcurling midge and/or woolly apple aphid.

Other Insects

Rosy and woolly apple aphid colonies can still be found. Management of woolly apple aphid should start early while colonies are still building close to the tree (eg., under bark, around pruning cuts or cankers). Once they are visible in the outer canopy mid to late season, control is not as effective. Movento or high rate of Closer applied at scale timing and again 2 weeks later are good options.

Potato leafhopper can be found but no signs of hopperburn yet.

Mite populations remain low due to the wet spring.

Brown marmorated stink bug traps have gone up. Activity is expected to begin shortly, if not already. 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.

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