June 23 Conference Call

AppleTalk Conference Call Summary
Tuesday, June 23, 2020 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 or send to Josie Dillon, jdillon@ipminstitute.org.

June 23rd 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

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 740 May 28 429 90 June 1 386
Gays Mills, WI 779 May 27 480 79 May 24 547
Hastings, MN 817 May 27 507 56 June 1 444
Rochester (Ela), WI 704 May 31 387 47 May 24 514
Trempealeau (Ecker’s), WI 804 May 26 506 90 May 24 549
Verona, WI 768 May 29 455 72 May 24 566

Table 1. Degree-day accumulations as of June 23, 2020 using data reported by Cornell NEWA Network. 

The next couple of days will be cooler, in the 70’s. The rest of the week will be warmer with highs in the 80’s and lows in the 60’s. There is chance for rain over the weekend and into next week across the region.

Codling moth degree days (DD) (base 50°F) from the May 24th biofix are now between 450 and 550 DD, which is the peak egg hatch for the first generation. 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 or sometimes a fourth larvicide may be necessary. This season there was a strong flight in late May and early June that lead to a strong population that needed to be treated. Trap counts have now dropped off over the last two weeks and many orchards have reported below-threshold populations. If any traps go over threshold within the next couple of weeks, those can be treated as a “B” hump or a “mini-biofix” where a larvacide is applied after another 250 DD have accumulated.

A summer disease application is needed after 175 leaf wetting hours (LWH) have occurred after petal fall. The accumulation across the region is rather variable and most locations have only accumulated half the number of leaf-wetting hours that are necessary before the first application for the first sooty blotch and flyspeck is needed.

Fruit with injury from codling moth and other pests should now be apparent. Now is also a good time to observe and flag trees that are struggling with nutrient deficiency or dieback. If young trees continue to decline, it may be worthwhile to pull the tree and submit for testing. Overall, the trees are very lush and green and leaves are still young, making it easy to distinguish trees that are not looking very healthy. Nutrients are transient and with less rainfall occurring, there is a lack of moisture in the soil to pull up into the tree. Limb dieback will also stand out more in about a month to six weeks. Flagging these trees will allow growers to investigate further if the decline continues. Cutting off limbs of larger trees that are in decline, e.g., an M7 or M26, is wise as they can be a source for black rot and white rot fungi. Take pictures of tree decline or injury you are unsure about and send to Peter, John, or Josie.

June rainfall
The average rainfall in June has varied from as much as seven inches in the Lacrosse area, three to four inches for south central Wisconsin and as little as an inch and a half for southeastern Wisconsin.  Northern Illinois has had a similar deficit as southeastern Wisconsin with receiving less than two inches of rain in June. Evapotranspiration rates have been relatively high due to the high heat at the end of May and the extra sunlight from longer days that has boosted growth. Evapotranspiration has removed about four inches of moisture from the soil in the first three weeks of June. This suggests the half inch of rain that many orchards received over the weekend will not last very long and irrigation may now be necessary.

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.


Disease management
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.

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.

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.

Insect management
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. 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.

Brown marmorated stink bug
Orchards in Dane county and throughout southern Wisconsin are beginning to catch brown marmorated stink bug (BMSB). These early BMSB captures are not very concerning. Everyone should have a BMSB trap in their orchard and should not be afraid about the risk of pulling in BMSB from outside the orchard, because if one is caught in the trap, they are already there. Getting the early warning is critical to manage this pest. Traps for BMSB may be ordered from Ag Bio Inc., http://www.agbio-inc.com/stink-bug-traps.html. The national-clearing house for all information relating to BMSB is on the website: www.stopbmsb.org. Here you can read about all the existing research and different management strategies for different crops.

John has observed more stink bugs and egg masses this year than we have in the last few years. That does not mean other stinkbug species will be a problem but may be a sign that stink bugs overwintered well. Native stink bugs are beneficial insects mid-season and can cause fruit injury later in the season, e.g., the native brown stink bugs are generalist predators in the adult life stage, though can also cause injury to the fruit. BMSB became a major pest in the Mid-Atlantic ten years ago. Before the concern over BMSB, researchers were researching impacts of native stink bugs in specialty crops. This research effort was refocused on BMSB and has taken over the primary stink bug pest of concern. Last year was the first year where several growers in isolated locations around the Madison area reported economic injury and other locations were observing threshold levels of stink bugs in traps. The threshold for the panel traps are ten adults in a week.

Stink bugs can lay several hundred eggs and the second instar nymphs can cause injury in softer apple varieties. Injury that occurs right now typically will not show up at harvest as they are so small, the fruit will grow out of it. However, injury in a few weeks may show up at harvest. Stink bugs can continue to cause injury once insecticide applications end in the fall right before harvest. The visual scouting threshold is one stink bug observed on every 100 feet of the perimeter. They will spend four to five days on the perimeter before moving into the orchard. This research was performed on smaller blocks, about five to ten acres in size. This could give us the opportunity to apply a perimeter spray. It is too early to apply insecticide applications but monitoring for stink bugs will be important. At this point, stink bug injury should not catch anyone by surprise at harvest.

Apple grain aphid
Green apple aphid, apple grain aphid or spirea aphid are all different species but are virtually indistinguishable to the untrained eye. John has observed some terminals where aphids were observed were winged, which means they are just coming in from alternate crops. Unlike RAA, these will continue to infest terminals throughout the canopy and can be a season long secondary pest. They rarely require their own treatment and neonicotinoids applied for plum curculio or apple maggot should suppress these populations. Management is more critical on young, non-bearing trees as it will reduce vigor and growth of shoots. Honeydew produced by the aphids may drip onto fruit allowing sooty fungi to grow. Scout younger trees and terminals for building populations.

Japanese beetle
John has not observed Japanese beetle, but a few were observed in Dane and Rock county on June 10th. The region may see higher populations due to a milder winter. Japanese beetle tends to have 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. Early signs of visible feeding damage warrants application of a repellent like neem oil or a full rate application of a Neonicotinoid, Assail (acetamiprid), Belay (clothianidin), Wrangler/Alias/Montana (imidacloprid).

Note: Actara (thiamethoxam) is not as effective of a neonicotinoid as these other products. Where large aggregations are present and require immediate knockdown, options are limited and include BeetleGone (Bt), or Imidan (phosmet). If large aggregations of JPB are present in orchards, Assail will be the best alternative to organophosphates or synthetic pyrethroids.

Dogwood borer
Dogwood borer mating disruption has been available in Wisconsin since 2019 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).

Grower questions and comments

  1. If not spraying a fungicide on brambles, should we worry about removing them?
  • If somebody is able to spot spray the brambles with roundup or cut them out, it is recommended to do so. If a spray of Topsin hits the perimeter, then yes, it is a resistance issue but if it is not hitting the brambles, it is not likely an issue.
  1. A grower has observed rust mites in a certain area every year. Leaves are becoming discolored and seeing some russeting on a few apples. Have you observed many rust mites this year?
  • It is easier to see the damage from rust mites, though numbers have been down in high population areas. There are a few products that can be used, like Envidor (spirodiclofen), but rust mites are more of an economic problem on younger trees rather than on mature trees. John has seen predator mit