June 22 AppleTalk

AppleTalk Conference Call Summary
Tuesday, June 22nd, 2021, 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM, jgaue@mwt.net
Moderator: Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org

 June 22nd Call Stream: CLICK HERE

 

Location Green Tip Date Degree Days

(Base 50°F)

Jan 1 – Present

CM May 13 Biofix

(86/50)

CM May 19 Biofix

(86/50)

Eau Claire, WI 4/3 915 707 644
Galesville, WI 3/21 978 725 664
Gays Mills, WI 4/3 949 722 665
Mauston (Northwoods), WI 3/30 970 725 665
Mequon (Barthel), WI 4/4 810 644 593
Rochester (Ela), WI 3/30 897 678 625
Verona, WI 4/3 951 728 667
La Crescent, MN 3/23 989 737 673
Hastings, MN 4/5 877 682 N/A
Harvard, IL 3/30 942 708 650

Table 1. Degree days and ascospore maturity downloaded on 6/22/21 from Cornell NEWA system. Find your local station today: http://newa.cornell.edu.

Regional roundup
This next week returns to cooler temperatures with highs in the 70s and low 80s, and cool evening temperatures in the low 60s.  If we are lucky, temperatures in the 90s will not return until the beginning of July. There are several more chances of afternoon thunderstorms later this week, however it should not be too humid.

Horticultural Issues
NAA and return bloom
Ethephon and NAA can be used to promote return bloom in all varieties but are particularly helpful in biannual varieties, like Honeycrisp. There has been more emphasis on using NAA than Ethephon as it seems to perform better for promoting return bloom in Honeycrisp. The flower bud formation for the next year can begin as early as petal fall in Honeycrisp. Any NAA that is applied at petal fall or on 10mm for thinning are also helping with bud formation for next season.

Michigan State recommends three applications of NAA that are applied at five, seven and nine weeks after bloom. Most growers are just now at the five-week mark from bloom and may begin making those sprays. The label recommends rates between 3-5PPM and to begin at five or six weeks after bloom with two additional applications made on seven to ten-day intervals.  NAA may be applied as a tank mix or alone. Some extension articles do recommend leaving out a surfactant or adjuvant if applied as a tank mix. If using a surfactant, reduce to 2.5ppm, though typically it is recommended to use 5ppm and leave out adjuvants and surfactants.

Resources:

Water management
Please review the rainfall totals at the end of these notes. The duration of the rains compared against totals can also reflect intensity of the storm and likelihood of absorption vs. risk of rain running off.

The accuracy of rainfall totals is dependent on proper rain gauge function.  If you have a NEWA station, it would be beneficial to have a secondary rain gauge where you can compare totals. Orchards to the north of Red Wing MN did not receive any rainfall and orchards near Chippewa falls, WI only received rain during the second storm. Orchards in NE Illinois and SE Wisconsin received very little rain. Only a handful of orchards received a significant amount of rain. It is essential to continue with watering programs, even if you received rain this past weekend. For example, orchards in Richland County, WI lost 4.65” of water through evapotranspiration in June but have only received two inches of rain. Therefore, these orchards are still running a water deficit.  Evapotranspiration rates in Wisconsin can be monitored here: https://agweather.cals.wisc.edu/sun_water/et_wimn.

Disease management
Last week John was calling for reduced rates of captan due to phytotoxicity risk associated with open stomates on apples. Now that it is cooler, reapplication of captan at higher rates would be fine. This may be a benefit to orchards that received hail or wind damage, where tree wounds could open up to canker fungi, and will provide protection against apple scab as we move through an active weather cycle over the next week.

Fire blight
There was a limited amount of hail during the recent storms, with reports coming from western Wisconsin and southeastern Minnesota. If tree or fruit damage occurred from hail or high winds, there is an increased risk of fire blight and black rot creating infections from this trauma. Orchards with a light crop are still susceptible to trauma due to the increased amount of vegetative growth this year. Trees with recent storm trauma and that had fire blight in the past could receive a streptomycin application or a copper application (Cueva). Streptomycin must be applied within 24 hours and some research suggests even sooner. If fire blight appears in young trees, the best option going forward would be to 1. Remove infect limbs by cutting 12 – 24” below the lowest part of the limb showing fire blight symptoms; 2. Apply a growth regulator like Apogee at a high rate (Only beneficial if terminals are still growing); and 3. Apply a copper product, especially if fruit finish is not a concern. Many terminals are already set as a result of the drought and heat we have been experiencing.  If the shoots are no longer growing, fire blight bacteria will not spread as easily, however, open wounds can still receive bacteria and become infected.

Summer diseases
The recent rains brought much needed moisture for our trees but did not drive accumulation of leaf-wetting hours over the threshold of 175 leaf wetting hours (LWH). Accumulation of LWHs has been variable and ranges between 65 and 135 LWHs, from petal fall. The accumulation across the region is slow and in the absence of significant rainfall, monitoring heavy dew and how long the trees remain wet is important.  LWH shorter than four hours will not trigger an infection. The accumulation of LWHs should be tracked from petal fall or whenever the last single-site fungicide was applied. Where single-site fungicides were applied at first or second cover, even few LWHs have accumulated.

Secondary scab
Do not use single-site fungicides, e.g., Flint, Rally, Indar, Merivon, if you have found scab in your orchard. The only exception would be if you already know you have strobilurin resistance to apple scab, then these fungicides, e.g., Flint (trifloxystrobin) or Sovran (kresoxim-methyl) could be used for summer disease management. 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.

Captan will remain effective for 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.

Codling moth
Codling moth degree days (DD) (base 50°F) from the biofix that occurred between May 13th and May 19th are now between 650 and 725 DD, which means peak egg hatch for the first generation is winding down. Fruit with injury from codling moth should be visible. Another 275 to 350-degree days must accumulate until we reach 1000-degree days which mark the end of the first generation.  However, cool evening temperatures this week will not likely result in many moths flying, as we move into the end of the generation. Additional larvicides should only be needed if A. you received two inches or more of rain in the recent storms and codling moth traps were over threshold in the last seven to ten days, or if traps continue to go over a treatment threshold of five per week. If in the last two weeks your orchard had a late flight, there is a good chance these moths are likely hatching.

The insecticides we use to manage codling moth, while somewhat rainfast, will not be able to withstand more than two inches of rain. If wash-off occurs, review trap captures at 150-250 degree-days prior to the rain event to determine if a reapplication is warranted. Recently hatched codling moth larvae, while very small, do not drown during the severe rain events we have been experiencing, and any flight that exceeded threshold between 200-250 degree-days prior to the rain will require reapplication.

If weekly codling moth trap counts are 5-15/week, there is some flexibility on when to reapply an insecticide for hatching larvae. Captures exceeding 40-60/week are dangerous levels and does not offer much flexibility in timing an insecticide.

Not all adjuvants can improve insecticide rainfastness. Adjuvants that are surfactants allow sprays to seep deeper into a plant’s nooks and crannies but do not improve the pesticides’ rainfastness. Other adjuvants that do not promote rainfastness are buffers or water conditioners that ensure the proper degree of acidity, and penetrants or activators like LI 700 or Regulaid that help systemic pesticides, e.g., neonicotinoids or Movento (spirotetramat), or plant-growth regulators to enter the leaf cuticle.

Adjuvants advertised as “stickers” like Nu Film P or Nu Film 17 may help improve rainfastness by creating a physical barrier over the surface of the pesticide. This prevents weathering of the pesticide by wash-off and ultra-violet oxidation since pesticides degrade from exposure by both rain and oxidation from ultra-violet rays. A sticker can be applied when rain is forecasted soon after a larvicide application. Stickers have a wide application range for different intended effects, but John recommends a median rate when using sticker-type materials. Find more information on spray adjuvants from the Penn State Extension here, https://extension.psu.edu/spray-adjuvants.

Maintaining a cover of a codling moth larvacide when rains are frequent support the benefits of using mating disruption. Even if a full rate of mating disruption is not used, a low rate of mating disruption would offer some suppression of codling moth under these current conditions. Table 1. Adapted from ‘Rainfast characteristics of insecticides on fruit’ posted on June 7th, 2018, by John Wise, http://msue.anr.msu.edu/news/rainfast_characteristics_of_insecticides_on_fruit.

Lepidopteran species
Obliquebanded leafroller (OBLR) usually begin hatching in mid-June and the first OBLR have been seen in orchards throughout the region. These larvae are small-green worms with caramel to black head capsules. OBLR are moderate fliers, they fly better than codling moth, but not much better. Two traps per orchard should be used to monitor OBLR. Large flights now are a result of the overwintering generation not being controlled, which may lead to a higher second-generation population. These worms will be the offspring from the first flight of OBLR this season, which has been delayed. Worms at petal fall and first cover are overwintering larvae from last year’s second-generation flight. In addition to feeding on foliage, larvae will also feed on fruit and can cause economic damage.  Altacor (chlorantraniliprole), Delegate (spinetoram) or Entrust (spinosad), applied for codling moth, except granulosis virus and mating disruption, should provide adequate management of OBLR. OBLR is resistant to many of the organophosphates and most of the neonicotinoids are not very effective on OBLR. Beneficial insects should also aide in suppression of this pest.  Second-generation larvae can be more problematic and more difficult to control than first generation OBLR.

Scouting for fruit and foliar feeding should begin seven to ten days after moths are caught in pheromone traps.  There are no established action thresholds and trap counts do not correlate well to the potential for feeding injury to fruit or growing terminals.  Terminal injury totaling 3-5% is a commonly used action threshold.  Look for discoloration and a few holes in the terminal or frass, which is evidence of OBLR activity. If terminals are set, then OBLR will be attracted to the fruit.

Potato leafhopper
Potato leaf hopper (PLH) adults have been observed in several orchards throughout the region, with a few nymphs appearing over the past couple days.  Adults are blown in on weather fronts each year, as they overwinter in Gulf Coast states.  Potato leafhopper adults and nymphs will inject a toxic saliva that causes damage to the leaf tissue.  The first sign of leafhopper feeding includes the cupping of leaves.  Further damage appears as a yellowing “hopperburn” of young terminal leaves.  Hopperburn can be described as a triangular yellowing or browning of the leaf tip.  This injury develops more rapidly during hot, dry weather and most damage come from nymphs.  Leafhoppers often move in a lateral fashion and will quickly go the underside of the leaf if disturbed.  Growers should be most concerned with PLH nymphs, and if needed, an application should wait until nymphs are more commonly observed, instead of targeting the adults.  The main priority is to monitor PLH on leaf terminals in younger trees.  The threshold for PLH is one or more nymph per leaf when hopperburn symptoms are appearing.  For more detailed information, please visit: http://labs.russell.wisc.edu/vegento/pests/potato-leafhopper/

Japanese beetle
The first Japanese beetle (JPB) are beginning to appear in southern Wisconsin. 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.

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 are not 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.

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.

Mites
Mite populations have been relatively low this season, despite poor weather for oil applications earlier this spring. Mite populations have also not exploded considering how strong of a mite hatch John observed during bloom, which suggests an abundance of predators in the orchard right now. Early mite injury can affect fruit bud formation for the mite next year and high populations later in the season can affect fruit finish, size, drop, and this year’s fruit quality. Orchards with a light to moderate crop can sustain mite populations and pressure over a longer period and blocks with a normal to heavy cropload will need to pay close attention to mites.

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 do not 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.

Threshold counts should include all motile mites, which may be difficult to see especially for smaller nymphs. European red mite populations tend to distribute themselves in high heat, allowing for easier counting. Magnification may be necessary to spot all young motile mites for an accurate count. Remember, predator mites can consume European red mite eggs and young. Beneficial mite predators at sufficient numbers on the tail end of a European red mite explosion will often lead to a higher ratio of red females to young or eggs, particularly motile young. Sequential sampling thresholds require inspecting leaves for all motile forms. The models were created to achieve no damage, so orchards with damage from mites may be past time for action. Download the sequential sampling forms in pdf form here, https://nysipm.cornell.edu/sites/nysipm.cornell.edu/files/shared/erm-sampling-chart.pdf

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.

Apple maggot
Apple maggot (AM) have been caught as early as June 14th in some years. If you have had injury from AM or have early ripening cultivars, e.g., Lodi, yellow boards or red spheres for apple maggot monitoring can begin to be deployed. Yellow boards can provide an early warning system by attracting apple maggot during their feeding period. If bait is used in addition to visual traps replace volatile lures according to the manufacturer’s directions, e.g., seven to ten days. It is advised to set up a minimum of three traps per ten acres at the beginning of July; trap density should gradually increase to one trap every 200-300 feet along the orchard perimeter, as the season progresses. Locate traps along perimeter where wild hosts are present and near early ripening cultivars. Hang traps at eye level, and make sure they are visible. Traps are usually hung in early-season varieties that exist on the interior of block around July 4th. Putting a trap or two out now can give a good heads-up as well.

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.

 

 

Location

Rain total (in) Rainfall duration

(Hours)

Rain total (in) Rainfall duration

(Hours)

Total “
June 17/18   ~June 20   thru 6/21
Afton MN 0 0.34 4 0.34
Burlington WI 0.91 3 0.12 8 1.06
Brodhead WI 0.33 ? 0.5 ? 1.43
Chippewa Falls WI 0.22 1 1.6 8 1.84
Dakota MN 1.54 2+ 0.31 7 1.93
Eau Claire WI 0.69 1 1.15 9 2.1
Elgin MN 0.39 4 1.54 5 1.92
Gays Mills WI 1.63 3 0.38 6 2.01
Genoa City WI 1.04 3 0.14 >10 1.2
Harvard IL 0.95 3 0.64 >10 1.59
Hastings MN 0 0.56 6 0.56
La Crescent MN 1.08 2 0.5 4 1.6
Lake City MN 0.34 2 0.8 >3 1.14
Mequon WI 0.95 4 1.05 12 2.05
Merrill WI 0 0.88 >7 3.04
Mt. Horeb WI 1.47 3 0.62 9 2.09
Poplar Grove IL 0.43 2 0.32 2+ 0.85
Preston MN 0.27 2 0.52 6 0.79
Richland Ctr WI 2.16 >3 0.37 8+ 2.54
Rochester WI 0.73 2+ 0.09 6+ 0.84
Shafer MN 0 0.25 6+ 0.3
Galesville WI 2.43 4 0.13 4+ 2.57
Verona WI 0 0 0.42
White Bear Lake MN 0 0.39 8+ 0.42
Woodstock IL 0.37 1 1.83 6+ 2.47
Note: Rainfall hours followed by (+) received ~0.01” in a contiguous hour
         Rainfall hours followed by (>) had one or more hour-long gap without precipitation

 

 

Rainfastness rating chart: General characteristics for insecticide chemical classes
Insecticide class Tradename Rainfastness ≤ 0.5 inch Rainfastness ≤ 1.0 inch Rainfastness ≤ 2.0 inches
Fruit Leaves Fruit Leaves Fruit Leaves
Organophosphates Imidan Low Moderate Low Moderate Low Low
Pyrethroids Asana, Danitol, Warrior Moderate/High Moderate/

High

Moderate Moderate Low Low
Carbamates Sevin Moderate Moderate/

High

Moderate Moderate Low Low
IGRs Esteem, Intrepid Moderate Moderate/

High

Moderate Moderate Low Low
Oxadiazines Avaunt Moderate Moderate/

High

Moderate Moderate Low Low
Neonicotinoids Assail, Actara, Belay, Alias/Wrangler Moderate, Systemic High, Systemic Low, Systemic Low, Systemic Low, Systemic Low, Systemic
Spinosyns Delegate, Entrust High Moderate High Moderate Moderate Low
Diamides Altacor, Exirel High High High Moderate Moderate Low
Avermectins Agri-Mek Moderate, Systemic High, Systemic Low, Systemic Moderate, Systemic Low Low

https://www.canr.msu.edu/news/rainfast_characteristics_of_insecticides_on_fruit

 

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