June 26, AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, June 26, 2018, 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org

June 26th Call Stream: CLICK HERE

Note: There will be no AppleTalk conference call on Tuesday, July 3, 2018. The next call will be held on Tuesday, July 10, 2018.

Photo-slide show of insect and disease injury: June 26th AppleTalk photos 062618

Beneficial insects
Small wasps that parasitize virtually all apple pests, e.g., aphids, stink bugs and codling moth eggs, are present in higher numbers than previous years. These parasitic wasps typically migrate into orchards at bloom and decrease in numbers or are completely wiped out when broad-spectrum insecticides ae applied at petal fall. For many years we have recommended Avaunt (indoxacarb) as our petal-fall spray for plum curculio.  Even though Avaunt is pretty soft on predatory mites and other beneficial insects, we have observed significant mortality of parasitic wasps.  This year, many IPM growers were recommended to use the neonicotinoid, Belay (clothianidin), for plum curculio and early codling moth management.  Growers applied one or two applications to treat for these pests as well as apple curculio and San Jose scale. Observing these large populations of parasitic wasps and beneficial insects are encouraging due to the damage insecticides can often cause to these populations, especially when applied later in June. Growers should avoid using broad-spectrum insecticides, e.g., Imidan (phosmet) until apple maggot is captured.

Codling moth
Most locations have accumulated 500-600 degree days (DD) since codling moth biofix. At this stage, about 95% of moths should have flown, and 70-75% of eggs should have hatched by now, according to the NEWA model. Flight activity should continue to decrease, and the remainder of second generation flights will likely conclude as degree days accumulate over the next two weeks. Growers should replace soaked liners after large amounts of rainfall and replenish pheromones on time to keep trap counts reliable.

When neonicotinoids were first used to manage codling moth, first-generation control often resulted in “stings” or “bites,” however, these stings have diminished over the years. Reasons for the decline are unknown, but improved application timing and adoption of appropriate usage are suspected contributors. Growers who used Belay (clothianidin) for combined plum curculio and codling moth management should scout for stings and deeper fruit entries since it’s rated less-effective than acetamiprid (Assail) against codling moth. Removing hand-thinned fruit from the orchard can be a way to check for CM injury. If a fourth codling moth spray is needed, growers should rotate to a different mode of action after three sprays, however, this needs to also be different than what you will apply for second generation codling moth!

Pheromone trap maintenance
The lifespan of our pheromone traps is dependent on three primary factors, the amount of pheromone load, the lure material or medium which regulates the pheromone release and the ambient temperature which can degrade pheromones during extended periods of high heat.  Several extended-life lures exist with varying life spans.  These should all be replaced at the beginning of July, and depending on their life span, they may last the rest of the season or may need to be replaced mid-August.  Any 1x lure used for codling moth, obliquebanded and redbanded leafrollers, oriental fruit moth, lesser appleworm and dogwood borer should expect a lifespan of two to three weeks during periods of extended heat in July and August.

Lure Type Lifespan for 1st Generation Lifespan for 2nd Generation
1x red septum1 3 weeks 2 weeks
10x red septum2 3 weeks 2 weeks
Super Lure2 6-8 weeks 6 weeks
MegaLure (Trece)1 6 – 8weeks 6 – 8 weeks
Biolure CM10x (Suterra brand)2 4 – 6 weeks 4 weeks
CMDA combo lure 8 weeks Probably less than 8 weeks3
Biolure CM1x (Suterra brand)1 6 to 8 weeks Probably closer to 6 weeks3
CM L21 8-12 weeks Probably closer to 8 weeks3

Table 1. Codling moth lure lifespan for first and second generation flights.

1 http://msue.anr.msu.edu/news/using_pheromone_traps_to_monitor_moth_activity_in_orchards1

2 http://entomology.tfrec.wsu.edu/stableipm/WorkshopPDFs/cmmonitoring.pdf

3 No data was available on the lifespan during second generation, but we should presume decreased life of these pheromones based on average temperatures in July and August that have potential to decrease duration of pheromone release.

Plum curculio
Plum curculio migration from overwintering locations has concluded; however, the weevils may still be laying eggs in orchards, if insecticides were washed off and not reapplied prior to the end of their migration. If this is the case, under both organic and conventional IPM, growers should be alert for signs of continued egg-laying such as the small crescent-shaped oviposition scars on fruit that is not turning into a June drop.

Obliquebanded leafroller
Growers who are not spraying for codling moth where mating disruption is being used or trap captures are low, should determine their need to spray for obliquebanded leafrollers (OBLR) using trap counts and the percentage of infested terminals.  The threshold for terminal infestation is 3%. Some growers with orchards exceeding this threshold will still abstain from applying an insecticide to save money since not fruit will be damaged, however, the success of the mid-summer generation is closely tied to the numbers of OBLR hatch in late August and September. More eggs will be laid in August if the pest is not controlled in late-June and July. Small orchards surrounded by woods will be more susceptible to external sources of OBLR than large orchards or orchards bordering agronomic crops.

Dogwood borer
Traps for dogwood borer (DWB) should be set unless trees are older than ten years. Traps should be placed 3-4 feet above the ground as opposed to codling moth traps which are set in the upper canopies of trees. Dogwood borer is a member of over 30 species of clearwing moths in the upper Midwest. The differences in pheromones produced by these species are so slight that pheromones on the market tend to attract several different species of moths within the Sesiidae family. Since the pheromones are not species specific and it can be easy to miss identify them. To properly identify borer pests, we can use the wing length to get a general idea if it is the right species. Moths with a forewing length larger than one centimeter are probably a different species because DWB adults have a relatively small forewing length of 9mm. Use a caliper, ruler or tape, to measure the forewing. Observing damage to graft unions is a great method for monitoring DWB, but by the time injuries become visible it is often too late for treatment to take effect.


Clearwing moths Forewing length (approximate)
Dogwood borer 9mm
Lesser peachtree borer 12mm
Greater peachtree borer 13.5-15mm

Table 2. Comparison of clearwing moth wingspans.

Thrips and potato leafhopper
Thrips were active in the orchards at petal fall and damage to leaves is at least two inches below the current terminals. Superficially this can be confused as potato leafhopper damage. Potato leafhoppers generally only infest the current terminal and will not have as much curling.  There will also be lime-green nymphs or pale green adults on the undersides of the terminal. Non-bearing trees with potato leafhopper infestations should receive an insecticide treatment to prevent growth stunting.

Japanese beetle
Japanese beetles (JPB) have a wide host range including many ornamental plants and horticultural crops including raspberries and grapes.  Within apples, JPB tend to have a preference towards Honeycrisp and can cause significant economic damage when left uncontrolled. Trapping JPB is optional and can help determine when to apply a repellent like Assail (acetamiprid), Surround (kaolin-clay) or Neem (azadirachtin). Insecticides used as a repellent should be applied at the earliest sign of JPB in or around orchards. Once JPB has been detected, traps should be taken down and disposed of immediately. After application, growers should scout adjacent varieties to make sure populations aren’t merely migrating to unsprayed varieties. Assail (acetamiprid) is an effective antifeedant and is toxic enough to eventually kill JPB adults.  The first migrants to move into the orchard will be most susceptible. Surround and neem will not be effective under severe pressure. If growers want to manage JPB without Imidan (phosmet) then early intervention is critical to successful JPB management.

One grower in Illinois reported a return of secondary pests after using carbaryl in 2017 to manage JPB. Carbaryl is only used for thinning and rarely used as an insecticide in orchards, because of the risk of damaging populations of beneficial insects. For most growers who have moved away from broad-spectrum insecticides, beneficial insects will be very susceptible to impacts from use of carbaryl, pyrethroids and organophosphates.

Secondary scab
Do not use single-site fungicides, e.g., Flint, Rally, Indar, Merivon, if you have found scab in your orchard. Captan is the primary fungicide for managing secondary infections, summer disease and fruit rots, once secondary infections are found.  It is recommended to compare the total amount of Captan applied this season to the maximum allotted amount per acre. Do not apply more than 40lbs of Captan 80 WDG per acre per crop cycle. A higher label rate is ideal if scab is present in the orchard, yet it is better to use a lower rate and more applications if you are approaching the seasonal maximum to avoid leaving fruit unprotected. Captan can eradicate many of the spore-producing lesions and reduce the risk of new infections. For eradication purposes, high rates applied in a dilute solution are most effective for optimal coverage in temperatures over 80°F.

The rule of thumb for how long captan will remain effective is two weeks or 1.5” of accumulated rain for the full rate. The two-week interval can be extended during dry weather. If you are approaching the seasonal limit on captan, an application of the most effective SI (sterol inhibitor), Inspire Super (cyprodinil, difenoconazole), plus a full rate of captan in an orchard with active scab. The application of an SI or QoI (strobilurin), e.g., Flint (trifloxystrobin) or Pristine (boscalid, pyraclostrobin), fungicide on active, secondary scab lesions greatly increases the chance of resistance developing to those compounds, even when tank-mix with a full rate of captan. The best organic eradicant/protectant is lime sulfur, however, large amounts of lime sulfur at this time can cause tree stress and fruit russeting.

Silver leaf
In June of last year, growers reported a significant amount of silver leaf, a rather obscure disease. It was recommended to flag blocks and monitor for returning symptoms. Occasionally an entire tree is found covered with silver leaf, but more often we observe individual scaffold branches in a block with silver leaf. The literature suggests it should only be on decrepit trees, but in 2017 it was found on plenty of vibrant, high-density plantings. The fungus infects the xylem and produces an enzyme that causes the epidermis of the leaf to separate, causing the silvery sheen. The fungus is xylem limited, until it makes fruiting body, which means trees could be without symptoms the following year.

There has been little research done on this disease and there are no known fungicides that act on the pathogen. The current recommendations are to prune out infections. However, silver leaf infections occur in the plant tissue below the part of the tree which show the visual symptoms, therefore, pruning out branches with silver leaf may not eradicate the actual pathogen. Pictures and additional descriptions of the symptoms are available here, http://msue.anr.msu.edu/news/silver_leaf_of_tree_fruits.

Sooty blotch and flyspeck (SBFS)
We begin monitoring leaf-wetting hours for SBFS beginning at petal fall, which is when the first influx of spores from SBFS are released from adjacent woodlots. At this time, many growers are still applying single-site fungicides, which eradicates these early infections that occur between petal fall and first cover. After 175 to 220 leaf-wetting hours, a second spore release occurs and fungicides targeting SBFS should be applied. This can happen between three and 11 weeks post-bloom, with an average of seven weeks post-bloom. Captan and Topsin (thiophanate-methyl) are the primary fungicides used to manage SBFS, especially where scab is also present. Where secondary scab is not a concern, the SDHI, strobilurin and DMI fungicides may be used for SBFS. These are attractive because of their ability to also manage black rot and bitter rot. Follow this first application with captan, as successive applications of single-site fungicides are not necessary. The reapplication interval following the first application is dependent on rainfall and weathering of the material. A 2-3 lb. rate of captan is greatly reduced after two inches of rain or 21 days, higher rates may offer added protection. The potential for SBFS to develop resistance to these single-site fungicides is minimal because new spores are coming in from outside the orchard and disease is a complex of more than 70 different pathogens. If apple scab is present, it is essential to avoid exposing these single-site fungicides to secondary scab populations.

Research completed on SBFS in the upper Midwest found that relative humidity (RH) rather than leaf wetness hours (LWH), is a better predictor of SBFS infections. It was found that 192 hours of RH above 97% was a better predictor than 175 hours of leaf wetness for our region. During the summer, dew usually contributes to more wetting hours than rainfall. Within the tree canopy, RH is more stable. Since we do not have instruments to gather RH at 97%, it is still recommended to use LWH. It is important to place the leaf wetness plates within the canopy to accurately record LWH.

Table 3. Leaf wetness and risk level data gathered from the NEWA SBFS prediction model.

Fruit rots
Bitter rot and black rot are the other common diseases we encounter in mid to late-summer. Growers should be scouting for small dark brown spots or infected lenticels, especially on Honeycrisp and Cortland. Fruit rots may be quite small right now. They start out as very small blemishes rather than the large quarter-size lesions we typically see in later in July. In the last few days, fruit rots have already been seen on Cortland where fruit is approaching two inches in diameter.

Winter injury and nutrient imbalances
As we move into mid-summer, younger trees can begin to show nutrient deficiencies including manganese and potassium, due to rapid growth. Trees in low areas are at a higher risk of developing nutrient imbalances. Comparatively, trees on well drained soils have shown fewer symptoms of nutrient imbalances, winter injury and tree stress. Growers should look up visual symptoms of nutrient deficiencies to avoid misdiagnosis of irregular growth, especially as roundup injury. When collecting leaf samples for nutrient analysis, a block of trees expressing visual nutrient deficiencies should be collected as a separate sample.