June 16 Call

AppleTalk Conference Call Summary
Tuesday, June 16, 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 16th Call Stream: CLICK HERE

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) Codling Moth Biofix Date Degree Day Accumulation from Codling Moth Biofix (Base 50°F)
Eau Claire, WI 555 May 28 304 June 1 261
Gays Mills, WI 595 May 27 346 May 24 346
Hastings, MN 631 May 27 359 June 1 296
Rochester (Ela), WI 476 May 31 247 May 24 374
Trempealeau (Ecker’s), WI 599 May 26 371 May 24 413
Verona, WI 570 May 29 310 May 24 420

Table 1. Degree-day accumulations as of June 16, 2020 using data reported by Cornell NEWA Network.

The weather forecast is calling for highs in the 80’s and lows in the 60’s this week, with chance for rain over the weekend.

Most locations are past 308 DD base 50°F from petal fall which notes plum curculio movement into orchards. A reminder that movement may still occur due to a cooler spring and delayed overwintering emergence. The DD model is the end of when plum curculio (PC) are migrating from overwintering sites to the orchards. If a PC spray was missed or was late and active PC are present in the orchard, they can continue to cause injury.

There are two general codling moth (CM) biofix dates this year, May 24, and June 1. All locations are past 250 DD base 50°F from biofix and locations with a May 24 biofix date are at 350 DD base 50°F.

Disease management
Black and white rot
Black and white rot are fungi in the genus botryosphaeria that primarily affect woody plant tissue, and less commonly infect fruit. These two pathogens are ubiquitous and any place where you have deciduous trees around you, black and white rot can be found. These are weak pathogens and avoiding tree stress is the best way to mitigate against the risk of infections. These diseases do have a period of time when they are sporulating. There are no spores October through April, but June is the peak time for black rot spread. Generally, we need a trauma event to allow the pathogen in, e.g., pruning cut or limb breakage or fire blight canker. Trauma stress is the key to focus on, rather than water or heat stress, to mitigate against an infection. Summer applications of captan is the primary way to protect against infection.

Organic growers applying compost teas or plant-host resistance inducers, which could offer some protection against black and white rot, should avoid applications of sulfur, since the sulfur may reduce the efficacy of these bio-rational fungicides. Trees with black rot infections can be managed for the long term, especially once trees are several years old. Young trees are more susceptible to black rot and less able to fight off infection. Larger trees most likely have reduced susceptibility.

Currently, there has been ideal weather for making small pruning cuts and training trees due to low relative humidity and lower temperatures. Captan will provide protection to leaf material but the cuts are susceptible to infection. If making several cuts, it is important to paint them with copper, especially if fire blight is present. Over the next month to six weeks, rain with warm temperatures will increase the risk for canker diseases.

Sooty blotch and flyspeck
We begin monitoring leaf-wetting hours for sooty blotch and flyspeck (SBFS) beginning at petal fall, which is when the first influx of spores from SBFS are released from adjacent woodlots. Local NEWA stations have a model for summer diseases and the weather summaries can be used to track leaf wetting hours. At petal fall, many growers are still applying single-site fungicides, which eradicates these early infections that occur between petal fall and first cover. The potential for SBFS to develop resistance to single-site fungicides are minimal because new spores are coming in from outside the orchard and disease is a complex of more than 70 different pathogens.

After 175 to 220 leaf-wetting hours (LWH), a second spore release occurs and fungicides targeting SBFS should be applied. This can happen between three and 11 weeks post-bloom, with an average of seven weeks post-bloom. 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. When single-site fungicides are applied following the accumulation of 175 LWH, symptoms are eradicated before they show up. Single-site fungicides are attractive because of their ability to also manage black rot and bitter rot. The reapplication interval following the first application is dependent on rainfall and weathering of the fungicide. Most importantly, the model is reset, and we begin counting LWH again until another 175 LWH benchmark is reached, before timing another fungicide.

Other disease management reminders

  • Powdery mildew: This disease needs heat, dry weather, and higher relative humidity to spread. If young trees are growing, right now is a great time to apply sulfur on young trees with shoot elongation and remember that captan does not affect powdery mildew.
  • Phytophthora: Several growers have been applying phosphoric acid fungicides like Aliette, Rampart, and Phostrol within the last week. This is a great time, with warm temperatures and low relative humidity, to put out these materials, which will be readily absorbed. If making the first application, growers should increase the rate in case a second application cannot be applied.
  • Scab: John, Peter, and Josie have not observed high scab pressure in many orchards this year, though have been seeing a few secondary lesions. Keeping up with the Captan applications will be important and spray intervals can be extended out to 10 or 14 days, depending on rainfall.

Insect management
John has been seeing some parasitic wasps, which is usually an indication that prey is available.
Aphid populations have been very low this spring. Woolly apple aphid (WAA) colonies are beginning to appear in historic hotspots. 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. If Movento (spirotetramat) is used it must be tank mixed with a spray adjuvant that has spreading and penetrating properties, e.g., LI 700, to maximize leaf uptake and systemic activity of the active ingredient. If WAA have not been a chronic issue, there is no need to treat preemptively.

Green apple, apple grain aphid or spirea aphid are all different species but are virtually indistinguishable to the untrained eye. 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.

The Lake Ontario IPM program recommends to start 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.

Apple maggot reminder
Traps can be hung at any time now and may be beneficial to hang early as a warning system. In the past, first apple maggots have been captured as early as June 15. This pest will be discussed further in late June or early July.

Many growers have invested a lot of money into new varieties and plantings in the past ten years and it’s important to better understand borer species to ensure they don’t cause massive tree decline. The primary method that IPM growers have used to control dogwood borer (DWB) is the use of Lorsban (chlorpyrifos), applied after the first flight and as late as in the fall after harvest. This application is usually long lasting and very effective. However, the EPA has been on the verge of pulling the chlorpyrifos registration. Assail (acetamiprid) is another product that has been used as a trunk application, though it is not as long lasting as Lorsban. Growers will need to reapply more often to achieve control.

A grower is planning to use a nematode product to target DWB this this year. Nematodes are microscopic worms that are present in soil, and most species are a part of the cycle of breaking down organic matter. There are many species that attack root systems or are parasitic that can lead to issues in several food crops or are predators of insects. There are nematodes that can be used to control PC larvae in the soil as they pupate, including several borer species. There aren’t many chemical companies that are formulating a nematode material that can be used as a trunk application. They are not as easy to use and are relatively expensive. The nematode products cannot be applied during the day because the nematodes won’t survive the sunlight and low humidity. They must be applied at night and need time to move into the bark tissue to effectively target larvae.

Peter and Josie have been working with WI Department of Agriculture, Trade and Consumer Protection (DATCP) to monitor several invasive species, including black stem borer (BSB). The first round of trap captures has caught BSB in all five orchards, meaning BSB is likely well established. The majority of catches were in semi dwarf and this pest will likely become more important as we monitor and learn more about it.

Chlorpyrifos registration: https://www.reuters.com/article/us-corteva-agriculture-pesticide/corteva-to-stop-making-pesticide-linked-to-kids-health-problems-idUSKBN20023I

Codling moth
When weather is slightly cooler as it has been, CM larval hatch out will take longer. Insecticides work better when larvae aren’t developing as quickly because first and second instar are more susceptible to insecticides that require ingestion. If no rain has occurred and temperatures are in the 70’s after an insecticide application, the material will last longer. Please review previous AppleTalk calls this season for more details on CM management.

John has found more predator mites or eggs than spider mites. Similar to parasitic wasps, these predator mites wouldn’t be present if there wasn’t prey to feed on.

Look for visual cues where there may be mites, which appear as dusty and less glossy leaves. Investigate these leaves closer by looking at the fruiting spurs. There are no thresholds for rust mites, but European red mite has a threshold which is time dependent. The threshold from June 1-30 is 2.5 mites per leaf, from July 1-31 is 5 mites per leaf and from August 1-15 is 7.5 mites per leaf. John is concerned that many secondary pests could appear in August due to being delayed from colder spring temperatures.

San Jose Scale
Monitoring SJS crawlers should begin in hotspots and places where it was visible last year at harvest. This year, our emergence is delayed. If looking at reports from Michigan or Cornell, they report catches of SJS males. Usually, our region is in line with Highland at Cornell which just had first appearance of crawlers. Older trees with rougher bark are more likely to have this pest.

Monitor known hotspots with black electrical tape applied to infested scaffold branches. Place the adhesive side towards the tree and wipe a thin layer of petroleum jelly on the outside of the tape. Double-sided tape can also be used. If populations are high, concentrate a few tapes on younger limbs (2-3” diameter) in areas with greatest pressure and on the sickest looking trees. Last year’s scale will be concentrated near newer growth and increasing the number of monitoring sites may help eliminate false negatives. Low-trap captures do not reflect overall pressure, i.e., false negatives, rather they may indicate the beginning of the hatch. First generation SJS hatches over a narrow period, while second generation hatches over a longer period. Use a hand lens with at least 10x magnification to scan tape for oval, bright-yellow crawlers. Catches of 10-15 crawlers in a couple of days or 10 crawlers on one tape, may warrant an application for management of SJS.

If a special application for SJS is warranted, e.g., evidence of crawlers, Esteem (pyriproxyfen), Sivanto (flupyradifurone) or Centaur (buprofezin), may be applied. Esteem is an insect-growth regulator and will manage OBLR, CM and RBLR. Do not treat at first-crawler detection, rather at 150-200 DD after crawler emergence.

Western flower thrips have been minimal this year. Thrips blow in from the south, similar to aphids. Leaf curling, yellowing and brown marks will appear on the growing point. The damage is most prevalent on the midrib of the leaf and brown feeding scars will be present on the underside of leaves. Thrips will continue to feed until terminals have set and are more of a concern on young or non-bearing trees.

For organic growers, Entrust (spinosad) may be used to manage thrips, while Delegate (spinetoram) is the best option for IPM growers. It is recommended to use a hand sprayer with a high rate of either material to have a significant effect. This is only the case for areas with high density populations as lower populations do not need to be managed.