June 30 Conference Call

AppleTalk Conference Call Summary

Tuesday, June 30, 2020 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM,
Moderator: Peter Werts, IPM Institute of North America; questions or comments, or send to Josie Dillon, .

June 30th Call Stream: CLICK HERE

Guest Speaker Schedule Reminder

  1. July 7: No AppleTalk call
  2. July 14: Dr. Sara Villani, North Carolina State University presenting on Summer Fruit Rots
  3. July 28: Wisconsin DATCP presentation on Spotted Lanternfly

Regional update

Location Degree Days from January 1st

 (Base 50°F)

Petal fall Date Degree Day Accumulation from Petal Fall (Base 50°F) Leaf Wetting Hours (LWH) from Petal Fall Codling Moth Biofix Date Degree Day Accumulation from Codling Moth Biofix (Base 50°F)
Eau Claire, WI 858 May 28 535 100 June 1 491
Gays Mills, WI 905 May 27 592 79 May 24 660
Hastings, MN 953 May 27 633 76 June 1 600
Rochester (Ela), WI 819 May 31 498 57 May 24 625
Trempealeau (Ecker’s), WI 929 May 26 619 110 May 24 662
Verona, WI 895 May 29 569 88 May 24 679

Table 1. Degree-day accumulations as of June 29, 2020 using data reported by Cornell NEWA Network.

Over the next week, highs will be in in the 80’s and 90’s and lows in the 60’s. Orchards are between 600 and 700-degree days (DD) base 50°F from codling moth (CM) biofix, which is towards the end of peak egg hatch. Several growers had an increase in trap catches between June 7th – 11th. A larvicide should be applied at 250 to 450 DD after this flight to protect blocks where CM were over threshold. If trap catches are currently at zero, look back ten to 14-days and if any trap counts went above threshold then, a larvicide should be applied 250-450 DD later.

Sooty blotch and flyspeck applications may begin at 175 leaf-wetting hours (LWH) from petal fall. Most locations are at 75-110 LWH from petal fall. This does not mean no fungicide applications will be made, as captan applications will still protect against black rot and white rot.

Heat and water stress
The hot temperatures over the next week may lead to a significant amount of heat and water stress. If trees were dry two to three weeks ago, they will be more likely to experience dieback and are at a greater risk of infection from black rot. John has observed yellowing leaves or leaves falling off trees. Growers need to assess whether the leaf loss is localized to certain branches or parts of the tree. Often, the damage to the leaves may have occurred when first emerging in the spring, e.g., freeze events. John is not too concerned about a small percentage of leaves affected by this. However, if shoot dieback is occurring, it is recommended to remove the dead shoot and infected wood from the orchard. It is not critical but will reduce potential spread of fungal diseases going forward.

Growers who did not receive much rain in June need to remember that small amounts of rain will not adequately replenish depleted soil moisture. Irrigation may be needed, especially in younger trees. There is an evapotranspiration model in NEWA where by entering the green tip date, in row/between row spacing, trees per acre and age, it will use this information combined with rain fall and irrigation totals to predict the amount of water surplus or loss in the block.

NEWA Evapotranspiration Model: http://newa.cornell.edu/index.php?page=apple-irrigation.

Water pH
It is important to be aware that highly alkaline water pH can make pesticides very unstable. The half-life of most pesticides in solution is at its greatest when the spray solution pH is between five and seven. For example, Captan has a half-life of ten minutes at a pH of 8.5, a half-life of 8-hours at a pH of 7 and a half-life of 32 hours at a pH of 5. Growers can use pH test strips and should be regularly testing water. A pH buffer should be added to the water if pH is too high, e.g., LI 700. For more information see: https://www.canr.msu.edu/news/effect_of_water_ph_on_the_stability_of_pesticides. 

Disease management
Post-infection fire blight management
Once a fire blight infection is active, the only time that streptomycin should be applied post-bloom is after a significant weather event, e.g., hail, windstorm. One option to help reduce the spread is using a tank mix of Cueva (copper soap) and Double Nickel (Bacillus amyloliquefaciens strain D747). It can limit the spread of fire blight but will not cure infection already there. A Certis representative, said that Double Nickel works to help reduce some russeting risk from Cueva. The risk of some russeting may be worth saving the tree since there is likely some russeting risk when any copper product is used this time of year. It is recommended to use 1.5 quarts per acre of Cueva and one quart per acre for Double Nickel. These products are also available for organic growers. This tank mix is not 100% proven but is a relatively cheap spray and has been showing promising results for growers in Michigan. Applying a few back-to-back sprays a couple weeks apart is likely worth it.

Trees with strikes in older, established semi dwarfs vs. in younger high density orchards require different approaches. Higher density trees, particularly if they have not set terminals yet, have an increased risk of fire blight spreading. Trees with established terminals have lower risk, though it does not mean strikes shouldn’t be removed. Temperatures in the 90’s will be much too hot to apply Cueva. These applications also should not occur in the evening at night because it will increase the drying time. Early morning before it heats up would be the best timing under the forecasted conditions for the next ten days. If anyone does make an application, please report back on efficacy.

Insect management
Apple maggot
Apple maggot (AM) emergence is often spotty in late June and early July. Several growers have captured the first AM south of Madison and in the La Crosse area. Traps need to be hung this week if not already. We expect trap captures to increase as we move into mid-July and through the month of August. The last decade many growers have been moving away from Imidan (phosmet) and other organophosphates to manage AM. Avaunt (indoxacarb) was one product that growers tried five or more years ago and have found this to not perform very well. This has left us with neonicotinoids as the primary organophosphate alternative for AM management. Assail is often a popular choice because it may be used for both AM and second-generation CM. The downside has been poor management of the summer generations of leafrollers. Subsequently the use of generic imidacloprid products, e.g., Admire Pro, Wrangler, Montana, in a tank mix with a spinosad or diamide insecticide, has been quite popular. This tank mix results in a reduced risk, yet broad spectrum spray which can manage AM, CM, and summer leafrollers, e.g., obliquebanded and redbanded leafrollers.

Even though we have been successfully managing AM this way, imidacloprid and most of the neonicotinoids do not offer extended-contact knockdown of the female AM fly. Assail does have more mortality on the adult fly and wears off quickly. The main control from Assail and imidacloprid is in the egg laying as an ovicide and survivability of the eggs, and as a repellant. Overall, we have found this strategy to perform well and are yet to hear about AM failures from using the neonicotinoids. However, this does make it hard to spot spray for AM. Historically, we used to be able to just apply tanks of insecticide in the sections of the orchards that had captures or employ strategies like alternate-row middle sprays. Due to how these insecticides perform, complete block or orchard sprays are recommended. When it comes time to apply the final AM spray of the season, an insecticide that is going to kill the adults, e.g., Exirel at high rate or Assail to a lesser degree, are needed, rather than something that impacts egg laying or egg survival.

There is not anything new regarding the timing of AM sprays. If we are relying on baited or unbaited spheres, the narrative suggests that if catching maggot flies on red spheres, they are laying eggs and there is no safe interval to wait to spray. The threshold developed by Cornell is an average of one fly per sphere, where three unbaited spheres are used per ten acres. When using a baited trap, this threshold increases to an average of five flies per sphere.

There is no standard rate for how many apple maggot spheres should be used. Where yellow-sticky boards are used, it is important to remember they only last two weeks. When these sticky boards catch apple maggot, no action is needed. The current threshold from Cornell uses three traps per ten acres. If we increase the density, e.g., one trap per two to five acres, it will better improve our ability to identify where they are coming in from outside sources or identify edges that are hot spots. Orchards with lots of woods along their edge would benefit from a higher density. Keeping this high density along wood lines is beneficial because we can’t anticipate changes in wild hosts in the woods. Even if woods are some distances away, they can fly a pretty good distance. Baited spheres are not going to offer maximum utility until trees have received hail or where we have early varieties, e.g., summer apples, that produce an in-house population that are there year to year. Monitoring these trees separately from the rest of the orchard is important. Unbaited traps work well for most of the season and as we get closer to harvest, growers can consider using baited spheres.

Codling moth + 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 2. 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.

Japanese beetle
The first Japanese beetle (JPB) have been observed Northern Illinois, in the La Crosse area and near Lake City, MN. JPB females do not like to lay eggs in grass over three inches long and grass that is kept a bit longer may help prevent some egg laying within the orchard. Therefore, close mowing of the alleyways should be avoided when Japanese beetles are active in the orchard. Japanese beetle has a strong preference towards Honeycrisp. If populations are widely dispersed, it is advised to treat the entire orchard rather than making a targeted spray to the heavily infested blocks.

Management of JPB should be tied in to targeting second generation codling moth. Growers who are moving away from organophosphates are limited to the neonicotinoids. They are mostly effective as a repellant and anti-feedant, e.g., generic imidacloprid, Assail (acetamiprid). It is important to put out an application before large populations form. Most of these products will also provide protection against apple maggot, potato leafhoppers and aphids. If a product like Assail is used towards the end of July, this would manage second generation codling moth, too. Though it can be effective, growers should avoid using carbaryl products.

Organic and IPM growers also have the option of using neem products (azadirachtin). There are several different formulated products, in addition to using raw neem oil. Neemix and Aza-direct are two formulated products. Most labels do not talk about the ability to act as a repellant, but even though it will not kill adults, neem oil does repel Japanese beetle from immigrating into the orchard. Organic growers wanting to use a raw-neem oil with an emulsifier should check with their certifier to ensure the emulsifier is OMRI-approved. When using a formulated-neem product, the OMRI certificate can be downloaded and generally should be kept with the spray records. Do not apply neem oil during the heat of the day and apply in the evening or nighttime. There is also a Bacillus thuringensis product called BeetleGone, which is quite expensive but should be applied as a spot spray rather than a full orchard application.

Mite populations have been relatively low this season, but there is still ample time population explosions to occur. Managing mites in August is never the goal and now is an important time to determine where populations exist. Sampling now will set a baseline for future population assessments. The hotter it gets, the faster mites eat, reproduce and eggs hatch. Many insects overwintered well and often we see first spider mite populations going over threshold after petal fall. This has not been observed yet and is not a guarantee they will not hit threshold. There may be more predators out there controlling population numbers. At this stage, rather than using a general leaf count to assess numbers, look at older leaves in problem areas like we do earlier in the spring. Using a 10x hand lens, look at the underside of leaves for mite eggs and assess about half a dozen leaves per tree.

Mite thresholds will increase from 2.5 to 5 mites per leaf in July and will increase to seven mites in August. Some growers are just beginning to see mites emerge and in addition to the wide range in performance of miticides, each orchard’s mite populations respond uniquely to a treatment. Mites don’t travel between orchards and you own your own mites, which means your mites have been exposed to whatever you have applied year after year in your orchard.

Some miticides work only as an ovicide and larvicide, whereas other miticides offer good contact activity on all motile stages. Where mite populations have exploded, miticides such as Zeal (etoxazole) and Envidor (spirodiclofen) will not offer the level of immediate knockdown of adults that is desired. Miticides with good contact efficacy include Acramite (bifenazate), Kanemite (acequinocyl), Nealta (cyflumetofen) and Portal (fenpyroximate).

If bronzing is still occurring while mite populations are below threshold, action is required to prevent further economic injury to the plant. This happens when a population of predators have remained active long enough to keep populations below threshold, yet enough mite feeding has occurred to cause leaf bronzing. Once leaf bronzing occurs, economic injury is happening to the tree and a miticide should be applied. This scenario is referring to what we call mite days, where the duration of mite activity is just as important as the actual population. This year may be an interesting one regarding mite days, since we have not had mite populations early on. If we reach threshold and still cannot see significant damage on any leaves, we may be questioning whether we need to make a miticide application.

Apple rust mites (ARM) have often been viewed as food for predatory mites, however, in high-density plantings and non-bearing trees, we are beginning to see more issues with ARM. The ARM will inhibit shoot growth on young trees and populations that appear while the trees are still pushing growth may need to be managed. Terminals are set on most trees and most non-bearing trees; however, some locations are still actively growing. This year we are beginning to see some damage from growing rust mite populations on terminals. Injured terminals will not recover and may not make it through the winter. This does not set the young trees up for a healthy fall and winter, if heavily damaged with rust mites or leaf hoppers. ARM is much less of a concern in mature trees or semi-dwarf orchards.

Envidor works well on rust mites but does not work on two spotted spider mites or European red mites. If these other mite species are a concern, other options are available that will manage all three. Make sure to read the labels, some newer products such as Nealta, do not control apple rust mites.

Pear psylla
If you have pear trees, look for pear psylla injury. Currently they are flying as adults and nymphs that are hatching out. Look for black spots on the leaves, if you find honey dew on the leaves, then tap some branches and see if little leaf hopper size insects appear. To read more about pear psylla: https://extension.psu.edu/tree-fruit-insect-pest-pear-psylla.

San Jose scale
Crawler emergence has been late this year and crawlers are now currently moving. If you have had scale in the past and have not applied Esteem (pyriproxyfen), Movento (spirotetramat) or Sivanto (flupyradifurone). it is important to tape a few scaffolds and see if you are catching them. If you have been clean for a few years, then it is worth applying a half dozen tapes on scaffold branches in historic hot spots.

Woolly apple aphid
WAA populations have been very low this summer though observations of occasional colonies have been more widespread. If you see a white tuft at a shoot and there is only one aphid, it is most likely a single-adult female, even though they look bigger with their “fur coat”. Do not get too concerned at the first sign of the little-white tufts. The colonies are forming relatively late and may have a good opportunity for biological control. Each grower should respond differently to an increasing WAA population based on historic pressure and scouting for biocontrol species, such as, parasitic wasp (Aphelinus mali), syrphid fly larvae and generalist predators that can affect WAA colony growth.

The insecticides Movento (spirotetramat) and/or Beleaf 50 SG (flonicamid), remain the best options to manage WAA, yet need to be applied at petal fall or first cover to offer optimum performance. If these applications were not made, assessing WAA pressure now is critical. If areal colonies are observed and still remain small and isolated and you still have growing terminals on trees, an application of Beleaf 50 SG may offer some efficacy or slow down population growth enough to allow beneficial insects to keep populations low later in the summer. Both Beleaf 50 SG and Movento are sequestered into the tree through young and succulent growth. Once terminal buds are set and shoots stop growing, it is less likely for these two insecticides to offer their desired level of management.

Closer (sulfoxaflor) may perform better than neonicotinoids since it belongs to a newer subclass of insecticides that have not been widely used. Do not apply a sticker-type adjuvant, e.g., NuFilm, with insecticides for WAA since the insecticide needs to penetrate the white-waxy coating of the colonies to be effective. Azadirachtin, e.g. Neem oil are probably the best option for organic producers.

Weed management
The most critical time for weed management is in the spring and through early July, during the period of shoot elongation. High density orchards and non-bearing trees are going to be very sensitive to water stress and any weeds in the tree row will also be competing for these water resources, even after shoot elongation ends. For this reason and to reduce risk of rodent injury in the winter, it is beneficial to keep up on weed management through the summer.

If the weeds have got away from you and are now possible 16 – 18” tall or greater, you are going to have a hard time getting good control of these with herbicide sprays. When weeds get this tall, we often the herbicide boom push over the weeds, resulting in poor spray coverage and less than desirable results. Therefore, mowing or weed-whacking overgrown weeds and then applying an herbicide after some regrowth, will likely offer better results. For organic growers and those not using herbicides, maintaining close mowing under the trees will continue to help trees outcompete the weeds for water and nutrition resources.