June 15 AppleTalk

AppleTalk Conference Call Summary
Tuesday, June 15th, 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 15th 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 4/3 868 591 529
Galesville, WI 3/21 945 605 545
Gays Mills, WI 4/3 872 594 536
Mauston (Northwoods), WI 3/30 894 606 546
Mequon (Barthel), WI 4/4 776 542 490
Rochester (Ela), WI 3/30 861 557 504
Verona, WI 4/3 882 601 541
La Crescent, MN 3/23 918 592 551
Hastings, MN 4/5 799 550 482
Harvard, IL 3/30 884 587 529

Table 1. Degree days and ascospore maturity downloaded on 6/15/21 from Cornell NEWA system. Find your local station today: http://newa.cornell.edu.

Regional roundup
The next couple of days will continue with temperatures in the 80s and 90s, however, low temperatures at night will dip into the upper 50s and by next week a cool front will move in with cooler temperatures in the 70’s and possibly some rain. The current high-pressure ridge has prevented fronts from moving through that would normally develop into rain and storm fronts. There have been just a few convection related storms, some last week on Friday and Saturday morning and not a single NEWA station received more than 3/100 of an inch of rain. A few orchards received an inch of rain and are the exception.

Codling moth degree days (DD) (base 50°F) from the biofix that occurred between May 13th and May 19th are now between 500 and 600 DD, which is the peak egg hatch for the first generation. Fruit with injury from codling moth and other pests should now be apparent. First generation moths will continue to fly for a few more weeks as there are about 1,000 DD in each generation. Most growers are applying their second larvacide at peak egg hatch and depending on how strong the flight is, a third may be necessary, but only if traps go over threshold in the coming week. This season the flight has been slow and steady, and traps have not always gone over threshold. If traps capture five moths in a week, they should be treated.

Plum curculio (PC) activity has been minimal in most orchards around the region, however, fresh PC injury was found this week in an orchard and is a reminder that PC will continue to be active through the end of the month, if there was not enough management during their emergence.

Management of summer diseases should begin after 175 leaf wetting hours (LWH) have occurred after 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.

UW Fruit News
There are several important articles growers should read regarding irrigation and weed management under drought conditions. As it relates to weed management, pre-emergent herbicides need water to be activated and if it is dry, the seeds will still germinate and push through the herbicide.  Post-emergence herbicides require actively growing weeds and in blocks where there is no irrigation, efficacy of these applications may be reduced.

Horticultural Issues
Drought resilience in cultivars
Use the current drought conditions to compare performance of different rootstocks and cultivars on trees less than ten years old that are not on irrigation. Look for flagging and leaf cupping that occurs under these drought conditions later in the afternoon. John is observing differences in trees less than ten years old, and these differences may translate into their ability to flourish over the next ten years. Trees that are showing less cupping and flagging in non-irrigated orchards, may be more resilient to climate change and weather-related stress

Frost
There is now a significant amount of fruit injury showing up that is not easily associated with any disease or insect, some of this injury has characteristics of a classic frost ring, but most is not. This injury is still likely from frost.

June drop
Some thinners did not thin as completely as desired. Most of this fruit should drop, but some may mummify on the tree and could be a source of fruit rots late this year and early next year. Look for fruit that is still hanging and but has stopped growing. This has mostly been observed on Gala, Honeycrisp and maybe some early fujis and this is suspected to be associated with NAA applications.

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:

Summer pruning and leader singulation
Summer pruning always comes with a ton of caveats and the window is very narrow, typically a few weeks in early July. Our tree phenology is nearing what we generally observe in early July, with terminals beginning to set, fire blight risk decreasing, etc. This year the concern about timing summer pruning in July is it could increase risk of sunburn injury if drought conditions persist. Fruit with direct sunlight early in the season, somewhat acclimate to that exposure, if summer pruning in mid-July exposes otherwise shaded apples, this may be an increased risk of sunburn. This may also be observed as the canopy shifts as fruit grow and weigh branches.

There is always a risk of reinvigorating the tree anytime summer pruning is done and if completed too late, it can affect crop quality and fruit finish and stimulate growth too late in the season, where new growth will not harden off and will risk winter injury.  Only summer prune if the trees really need it and if your orchard is irrigated, has no fire blight, has a light crop, and has some varieties that are overgrown and need to have some larger branches removed. The benefit being, it is dry, and trees would heal and minimize exposure to canker fungi.

Regarding non-bearing trees, stimulating new growth through leader singulation is the goal. The heat and lack of rain is causing terminal buds to set earlier than normal and in non-bearing trees and newly planted trees, removing competing leaders right now can help stimulate additional growth, while still allowing time for trees to harden off later this summer.

If normal weather patterns return and we get rain, then summer pruning should be avoided next week. Avoid making big cuts over an inch or two inches that will require more than a week of dry weather to heal. If you have active fire blight, consider avoiding summer pruning all together. If your young trees have set terminals, it is not too late to water and fertilize the tree and get more growth out of the tree.

Chemical injury to foliage and fruit
Captan, sulfur and copper are toxic to plants and if these fungicides/bactericides penetrate the leaf cuticle or apple, there is risk of injury to the plant cells.  John’s concerns last week related to the millions of stomates that would be wide open during the heat to support transpiration.  When these stomates open, John is unsure how likely captan could penetrate the stomates but suspects that some of the injury we see to lenticels could be from captan injury. To mitigate risk of injury we can cut the captan rate. This same concern applies to other penetrating crop inputs such as NAA, Apogee and foliar fertilizers. Now that it is getting cooler at night, growers can resume applications of NAA, Apogee and foliar nutrients at night and early in the evening. The note in last week’s blog post was specific to last weeks hot evening weather.

Disease management
Disease summary
There are some secondary scab lesions in the orchards and in the absence of heavy dew or rain, they will not create secondary infections.

IPM growers who applied a single-site fungicides at petal fall with captan, would have eradicated the first sooty blotch and flyspeck (SBFS) infections that may have occurred. These SBFS infections would have required rain after petal fall and require more than four hours of leaf wetting to be successful. Orchards that did not receive rain in the two weeks after petal fall would not likely have had an infection.

Canker diseases such as black and white rot that are normally spreading in the weeks after petal fall will not be spreading canker fungi, so long as weather remains hot and dry. We will see trees with existing canker infections take advantage of stressed trees where branches or the whole tree may collapse. You have some time to prune out black rot infected limbs, but until we get rain, there will be no spread of this disease.

Sooty blotch and flyspeck
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. If the first application is Topsin or another single-site fungicide, this application will eradicate the infection when made after the accumulation of 175 leaf-wetting hours from petal fall.  A second application may be made using only captan to protect against future infections, this will allow growers to minimize the use of successive applications of single-site fungicides. 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 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. Remember to track RH and the NEWA station to assess whether the readings may be off.

Brambles are very common around orchard perimeters and in a few instances can be observed growing within the orchard around the base of older trees. The brambles include blackberries, raspberries or other Ribes species. This is where the pathogen overwinters and is where sexual development occurs. The chance of resistance to summer diseases to Topsin (thiophanate-methyl) or Incognito (thiophanate-methyl) is relatively small which is why we have been able to use these products for decades. It may be worthwhile to remove any of these species where SBFS may overwinter.

Summer fungicide applications for apple scab and black rot
If growers are wondering about reapplying a fungicide and no scab is present, the focus should shift to managing canker diseases, e.g., black rot, white rot, and fruit rots. John has observed small, round lesions that are a couple of millimeters in diameter, though are hard to know if they will continue to develop. Right now, a captan application with no scab in the orchard is hard to justify. Cover the orchard as needed for insect management rather than scab. This is all on the caveat that no scab is present, and growers may spot spray blocks with scab. Fungicides may be reapplied every ten days if there have been frequent rains to slow or reduce spread of summer diseases.

Powdery mildew
This season has been a strong year for Powdery mildew (PM) and has been observed in many orchards this spring on Honeycrisp, Cortland, and MN-55 (First Kiss). This disease flourishes in hot and dry conditions. Spores are easily washed from infection sites, but the fungus can grow on terminals, in the absence of rain. Once the terminals have set, PM stops growing, but the damage remains. If you fertilize and continue to water young trees, you will see some growth on these young trees and PM could continue to grow.

At one time, this a rather rare disease in the upper Midwest, but shoot infections are now commonplace. In the southern United States, powdery mildew is much more severe and can spread to fruit and cause russeting. At this point, there is no need to worry if powdery mildew appears on trees other than to note its location for next year. Single-site fungicides and sulfur provide protection against powdery mildew, whereas captan does not. Where there are no active-scab infections, single-site fungicides with efficacy on powdery mildew may be used with minimal concern of losing efficacy for primary scab management. Growers may have new trees that brought in PM or have some resistance. Sulfur may be used as a tank mix to mitigate resistance and organic producers may also use sulfur as a protectant against powdery mildew. Nurseries have different management programs, and it is important to keep an eye out for PM on first-year trees and to remember there is potential for this disease to develop resistance.

Insect management
Codling moth + trap maintenance
This season trap captures in non-mating disruption orchards are experiencing the classic B hump or secondary flight of the first generation of codling moth.  If you had a large flight ten days to three weeks ago, there may still be eggs hatching. In mating disruption (MD) orchards that use the high rate, e.g., 200+ disruptors per acre, a capture of more than one moth in a week could pose a thread. If you catch five moths in an MD orchard (meso or traditional), a larvacide should be applied.

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.

 

Insecticide options for codling moth and plum curculio
Trade name (active ingredient) Plum curculio Codling moth Notes
Avaunt(indoxacarb) X X Less long-term control of codling moth compared to Delegate or Altacor.  Rated as ‘fair’, reapply after 7-10 days.
Actara(thiamethoxam)* X Apply with CM insecticide, e.g., Altacor, Delegate.
Altacor(chlorantraniliprole) X Apply with PC insecticide, e.g., Avaunt, Actara.
Delegate(spinetoram) X Apply with PC insecticide, e.g., Avaunt, Actara.
Exirel(cyantraniliprole) X X Same insecticide group (28) as Altacor
Belay(clothianidin)* X X Use only if CM pressure is low, e.g., less than 10 moths/week/trap.  If Belay is used and pressure is high tank-mix with CM specific insecticide.
Assail(acetamiprid)* X X
*Note: If a neonicotinoid is used exclusively for PC and first-generation CM control it cannot be used alone for second generation CM and apple maggot (AM) control.  An imidacloprid, e.g., Admire Pro, Montana, Wrangler, tank mixed with Altacor or Delegate or applying Exirel alone will offer AM control and mitigate resistance concerns for CM; do not treat more than one generation of a target pest with any of these insecticides.

Obliquebanded leafroller and lesser appleworm
Obliquebanded leafroller (OBLR) and lesser appleworm (LAW) are two lepidopteran species that will require additional monitoring in orchards using mating disruption or in non-mating disruption orchards that have been applying neonicotinoids this spring.  Even though trap counts for CM have been down over the last two weeks, OBLR and LAW can cause economically significant fruit injury. If CM numbers remain low over the next few weeks and an insecticide is not required, make sure to not overlook these two insects. There are no thresholds and therefore no recommendations for spraying if “x” number are captured, rather trap counts are relative reflections of the population. If the OBLR trap catches quite a few, there is more pressure and the same applies for LAW. Provisionally, if less than ten LAW are captured, John would not recommend applying an insecticide. However, if catching 25, note when that flight occurred and assume that in around 250 DD or in two weeks, LAW larvae will hatch out and an insecticide application may be necessary. Obliquebanded leafroller larvae begin emerging at 700-degree days base 43 from biofix. Scout for larvae by looking at terminals, or younger trees. John would recommend an application for any OBLR catches over ten. Remember, these applications need to fit in with CM resistance management. Assail (acetamiprid) is effective on LAW but is not on OBLR.

OFM or LAW lures may be used and virtually all moths we catch are LAW.  John is using almost all LAW lures and am catching more LAW than ever, with high counts upwards of 300 LAW moths in the last two weeks. Since these cause the same damage as CM, even though these do not go to the core, they are a problem and there is no threshold.

The OBLR flight has traditionally flown significantly in a short time and then not fly for a while. This year the flight seems to be a bit slower, e.g., 50 in a trap over ten days. Most large counts occurred in the first week of June. Depending on when the trap went out, this flight may not have been captured. You will need to assess larval hatch in terminals if there was a significant flight. It is too hot for OBLR and growers may not need to spray for OBLR, just keep scouting for OBLR hatch and wait until we see evidence rather than applying a larvacide ahead of time.

Tarnished plant bugs and stink bugs
Tarnished plant bugs (TPB) and a few stink bugs have begun to appear in orchards as the understory begins to dry up. These observations have mostly included stink bug egg hatch and adult TPB moving into trees as ground cover begins to dry up.  Along with these pests, could be a wide array of other insects that come into trees, generally not worried about some of these other pests. However, TPB is a pest to add to the list to scout and spray for.

The Lake Ontario IPM program recommends starting monitoring aphids at petal fall and continue until terminals harden off (late July or August). Check 100 terminals in a 10- 15-acre block weekly throughout the summer. Pick 10 terminals per tree on 10 trees randomly, without visual bias towards infested terminals. The action threshold for green apple aphid is 400-600 aphids per terminal on 10% or more of terminals checked. Be sure to look for predators when assessing aphid populations in orchards.  If more than 20% of the aphid colonies have natural enemies, delay, or eliminate an insecticide application. Resample orchards with weekly, to determine if predators are providing control.

Wooly apple aphid
The first wooly apple aphid (WAA) colonies have been showing up in the last week and along with them signs of parasitic wasp activity active on these colonies. Older trees with scaly bark are more likely to have this pest. Scout for developing colonies on pruning cuts and vegetative shoots. There are many effective beneficial insects which manage WAA, but an insecticide may still be necessary before third cover, where WAA is a chronic problem. Since terminals are beginning to set sooner this year, products such as Movento (spirotetramat) will be less effective.  Beleaf 50 SG would be an alternative product to use if WAA colonies begin to grow over the next few weeks and are not managed by predators.

Parasitoids and predatory insects
There are lots of parasitic wasps active on WAA and hoping they will lay eggs on aphids and leafroller larvae. These parasitic wasps lay their eggs inside the aphid and once we see the hole in the aphid, the parasitic wasp has already hatched. Many growers have been using neonicotinoids this spring and it seems these parasitoids are not being impacted by this class of insecticides, but this is not known for sure. If the next cover can be delayed a few days this week to give these parasitoids a few more days, that would be ideal. The risk of stretching codling moth sprays to 17 days may be okay, as John thinks there has been some mortality of CM eggs due to the heat.

Dogwood borer
The Dogwood borer (DWB) flight has begun and growers with two to ten-year old trees should be monitoring this pest. Mating disruption is available in Minnesota and Wisconsin and requires a ten-acre minimum to treat. The labeled rate for IsoMate DWB is 100-200 per acre with a maximum of 2,721 per acre. In comparison, CM mating disruption twin tube has 100-200 per acre with a maximum of 392 per acre. Growers do not need to go up to this number but might consider putting out more than the 100-200 per acre. Larry Gut, Michigan State, discussed that OBLR and DWB are more like CM in terms of difficulty in being controlled with mating disruption. All three are localized fliers, where insects like OFM or LAW are much easier to disrupt. This reflects their flight range. There are alternatives to mating disruption for DWB but is quite costly and impactful, e.g., trunk spray of Lorsban (chlorpyrifos).

Potato leafhoppers
The first Potato leafhoppers (PLH) were observed in northeastern IL in the upper Mississippi River Valley and are problematic on non-bearing and high-density orchards. Potato leafhoppers come to the region during spring storms where warm air masses from the Gulf of Mexico pick them up, as the system moves north. To date, numbers reported in other host crops, as per the Wisconsin Department of Agriculture Trade and Consumer Protection Pest Bulletin, were still relatively low. The first large leafhopper immigration into orchards tends to occur after the second cutting of hay, which is happening now.

Mites
Apple rust mites are exploding in the last nine days on trees and should be scouted and consider a miticide if populations are rapidly increasing. European red mite (ERM) populations have been quite low and stayed low and are seeing lots of mite predators.

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