June 29 AppleTalk

AppleTalk Conference Call Summary

Tuesday, June 29th, 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 29th Call Stream: CLICK HERE

 

Location Green Tip Date

(Estimated)

Mac Petal fall

(Estimated)

Degree Days

(Base 50°F)

Jan 1 – Present

CM May 13 Biofix

(86/50)

CM May 19 Biofix

(86/50)

LWH from Petal Fall
Eau Claire, WI 4/3 5/16 960 853 790 150
Galesville, WI 3/21 5/7 1008 877 816 210
Gays Mills, WI 4/3 5/12 1031 871 814 107
Mauston (Northwoods), WI 3/30 5/10 1032 874 814 154
Mequon (Barthel), WI 4/4 5/18 862 770 719 122
Rochester (Ela), WI 3/30 5/12 940 826 772 129
Verona, WI 4/3 5/12 1037 888 828 139
La Crescent, MN 3/23 5/9 989 902 838 126
Hastings, MN 4/5 5/17 965 841 773 76
Harvard, IL 3/30 5/11 1013 856 798 156

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. Note: Leaf wetting hours for sooty blotch and flyspeck use an estimated petal fall date, unless entered by the station operator. NEWA model allows you to add your last systemic fungicide or petal fall date.

Regional roundup

As we move into the 4th of July weekend, we sit in a holding pattern as first-generation codling moth wind down, and accumulation of leaf wetting hours for summer disease management ramp up. Growers should be setting apple maggot traps and refreshing codling moth pheromones. The active weather pattern has offered short-term relief for many, though sub soils are unlikely to have been adequately replenished.

Disease management

Sooty blotch and flyspeck

Captan and Topsin (thiophanate-methyl) are the primary fungicides used to manage SBFS, especially where scab if scab is 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 of Topsin or a single-site fungicide 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.

John has observed a number of brambles around orchard perimeters and a few instances of brambles 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.

Several years ago, our now retired fruit crop plant pathologist, Dr. Patty McManus authored an article highlighting the modern approach to SBFS management using the NEWA stations: https://fruit.wisc.edu/2019/07/05/apple-sooty-blotch-and-flyspeck/

Obliquebanded leafrollers

The first of two summer generations of OBLR are hatching and have been observed across the region at varying growth stages or instars.  Unlike codling moth where it is important to use the maximum rate of an insecticide, lower rates of our normal codling moth insecticides may be used. The neonicotinoids are generally poor at managing OBLR.  If Avaunt, Bacillus thuringensis or an insect growth regulator such as Intrepid or Esteem was used to manage these before petal fall, an insecticide with a different mode of action should be used now. This generation will mostly feed on the terminals of trees, and non-bearing trees are particularly susceptible.  Some fruit injury may occur now, but a majority would occur during the second summer generation in late August.  Managing OBLR now will minimize pressure later in the summer.  If you had a bump in codling moth a week ago, then using lower rates of codling moth insecticides to target OBLR is not advised.

Apple maggot

This week several growers located in southern WI and SE Minnesota sent me photos of their first apple maggot trap captures.  I have come to see a very widespread in the emergence of apple maggot in our region.  Meaning, one of the growers who sent me the photo, always seems to capture AM early, whereas other growers still may not capture their first fly until the end of July.  Either way, the insects can always surprise us, and it is a good idea to get those traps hung, if not already. 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 cannot 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.

Japanese beetle

The first Japanese beetle (JPB) have been observed throughout the region. Reduced risk insecticide options for JPB are limited, with the neonicotinoids being the most effective option. 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.

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.

Mites

Mite populations have begun to increase over the last few weeks.  This should be expected partly due to the hot dry weather we have been experiencing over the last six weeks, but also because of the difficultly many growers had in applying dormant oil sprays this spring. 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.

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.

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 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, 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.

 

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