June 2 Conference Call

AppleTalk Conference Call Summary

Tuesday, June 2, 2020 8:00 – 9:00 AM
Guest Speaker: Dr. Brent Short, Trécé
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 2nd Call Stream: CLICK HERE

Guest Speaker Schedule Reminder

  1. 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)
Eau Claire, WI 324 5/28 93
Gays Mills, WI 345 5/27 114
Hastings, MN 363 5/27 117
Harvard, IL 311 5/28 118
La Crescent, MN 363 5/27 127
Mauston (Northwoods), WI 302 5/29 71
Mequon (Barthel), WI 245 5/30 46
Rochester (Ela), WI 252 5/24 149
Trempealeau (Ecker’s), WI 352 5/26 107
Verona, WI 313 5/29 71

Table 1. Degree-day accumulations as of June 2, 2020 using data reported by Cornell NEWA Network.

This week will be very warm with highs in the 80’s and lows in the 60’s. If winds are low and no precipitation occurs, this will be excellent conditions for codling moth flights. Last week, several growers reported their first codling moth flights and by June 6 to 9, these sites are likely to be at 250 DD from biofix.

Plum curculio emergence is underway, and injury has been observed across southern Wisconsin and in the Lacrosse area. The majority of sites are between 100 and 150 degree days base 50F from petal fall and may continue to emerge past the 308 DD threshold this year.

Most locations are at 100% scab ascospore release and discharge. The first lesions have been observed in orchards in the last week. It may be another couple of weeks before a second-generation explosion of scab lesions on leaves or fruit is observed. Maintaining five to seven-day intervals on fungicide sprays through second or third cover is important until it is clear there is no scab in the orchard.

Fire blight and powdery mildew have been relatively low, though some cedar apple rust has been observed on susceptible cultivars. Scab typically coincides with the end of thinning, which has been a relatively short period of time due to rapidly growing fruit. Blossom blight should be appearing in the next seven days, remember the Maryblyt and CougarBlight models assume that blossoms are open. If you don’t have open blossoms, the model no longer applies, and streptomycin should not be used.

Disease management

Powdery mildew
Powdery mildew (PM) has been observed at orchards around the region in the past week. This week will provide excellent conditions for powdery mildew, especially if no rain occurs over the next 48 hours as this washes away PM spores. 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 frequent rain events. This was once a rather rare disease in the upper Midwest but shoot infections have now become quite common. In the southern United States, powdery mildew is much more severe and can spread to fruit and cause russeting. At this point, there’s 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. Note: Sulfur applications when made during hot weather, e.g., over 80°F, may cause russeting during application. If applied under cooler conditions and warm weather follows several days later, the risk for russeting decreases. Russeting potential decreases significantly when the sulfur is out of solution and dry on the plant surface. 

We are past primary scab season and secondary scab infections are now releasing millions of conidia during rain events. Secondary scab will likely be located only on varieties where scab has been a problem the previous year and control was not achieved during primary ascospore release. Avoid treating secondary scab with single-sight fungicides, e.g., Aprovia, Flint, Rally and Sovran that were used during primary scab season. Captan should be the only fungicide used to reduce the spread of scab once secondary infections are found. Organic growers have the option of wettable sulfur or bio-fungicide to slow down secondary scab spread.

Insect management
Plum curculio
Historically, at 308-degree days from McIntosh petal fall, all PC have moved into the orchard from their overwintering sites and no new immigration will occur. With very limited sightings so far, it may be possible PC have been slow to enter orchards due to cooler spring weather. Keep monitoring for PC around the edges of the orchard and check for oviposition stings on fruitlets. This management approach presumes that PC is effectively managed each year. Organic orchards or orchards with poor PC management, can develop resident populations within the orchard. Under these scenarios, growers need to scout all portions of the orchard, rather than limiting scouting to the perimeter. Many locations in southern Wisconsin and a few sites within the Mississippi river valley will be at 250-degree days from codling moth biofix this weekend or early next week. If applying a product for plum curculio, look at products that also have efficacy against codling moth larvae.

Obliquebanded leafroller
Obliquebanded leafrollers are similar to CM in that they are poor fliers and therefore may need extra traps in the orchard. Most growers only deploy one or two OBLR traps, which may not be enough to accurately capture the population density and pressure. If the goal is to save an insecticide over the next month, it is important to deploy additional OBLR traps. If OBLR traps are not yet hung, they should be hung over the next week. Typically, the second generation can cause injury at harvest and larvicides applied during their first generation can significantly reduce summer populations. If trap counts are high, e.g., in excess of 50 in a week, then larvicides for OBLR may need to be applied. Note: There is no threshold for OBLR traps, this is just a nominal number based on what we typically observe under high-pressure scenarios.

Discussion with Dr. Brent Short on mating disruption and codling moth lures

  1. Can you review how the CIDETRACK MESO mating disruption works and how this is different to other mating disruption products? Traditional mating disruption only disrupts the male moths that are seeking female moths, but I believe this product is intended to disrupt behavior of both male and female moths and possibly even larvae?
  • In general, all mating disruption works by keeping the male moth from finding and mating with the female moth. The dispensers are emitting a synthetic version of the female-mating pheromone. The male first follows the false trail instead of actual female pheromone. After sustained contact with the pheromone, the male moth becomes desensitized to the scent and will shut down and give up trying to find a female.
  • The MESO should be hung in the upper 1/3 of the tree and applied prior to the moth flight, or as early as possible, as the product will last six months. The material formulation, which is a PVC dispenser, creates a smoother release compared to some other products. Employ them at 32 per acre for a moderate population. If you have a history of CM, put up 35 per acre and they should all be evenly distributed among the block. The other mating disruption products for codling moth, i.e., Checkmate, Cidetrak CM, Isomate TT, on the other hand use 100 to 300 dispensers per acre and therefore one of the goals of the 200 per acre, and using CIDETRAK MESO is also intended to help reduce labor expenses.
  • The DA (pear ester) component in the CIDETRAK MESO has been shown to disrupt female oviposition behavior, which was discovered and researched in the Pacific Northwest and does not affect larval behavior.
  1. The most recent information suggests there is not currently a threshold for the CMDA + AA lure when used with the CIDETRAK MESO mating disruption products. If this is true, how do you recommend we determine if the mating disruption is being effective? Is there a provisional threshold that you would recommend? Could several of the L2 lures still be used to monitor for trap shutdown of the male population?
  • There are no thresholds for any CM mating disruption, though researchers are working on developing thresholds now. Larry Gut, Michigan State University, has often mentioned if trap shutdown, i.e., no moth captures, is achieved when using L2 lures along with mating disruption, mating disruption is being effective. Some growers do use one L2 lure along with the mating disruption and if one moth is captured, this would be considered at threshold and warrants an insecticide application.
  • Brent has seen orchards where the L2 lure had moths but didn’t see any damage. He recommends when using a new monitoring system, to maintain a frame of reference, e.g., comparing L2 lures vs CMDA+AA.
  • Brent has observed that many orchards do not use the right number of traps per acre and growers tend to place traps in the same location each year. It is risky to rely on one trap to determine how the CM pressure is across the farm. One trap per 2.5-5 acres increases the quality of the data, rather than placing a single trap per 10 acres.
  • The CML2, 1x lures and most of the lures used to monitor RBLR, OBLR, OFM, etc. are referred to as a septa, there are also CML2-P lures, which is a black PVC that gives a more consistent pheromone release over the life of the lure. Growers that have used these L2-P lures in a mating disruption orchard have gotten better results. It is a 12 week lure and is currently being researched at Penn State.
  • The L2 lures are listed as lasting 8 to 12 weeks and are recommended to be changed every eight weeks. The longevity of the lure is a function of temperature and the warmer it is, the more pheromone that will be released.
  1. We have a lot of small orchards in Wisconsin and for blocks that are between two to seven acres, do you have a recommendation on which mating disruption product is a best fit and how we should approach use of MD in these orchards? How might we need to adjust our expectations for performance of MD in these smaller blocks? It seems that even if we cannot achieve 100% management of CM with MD in a small block, it is still worth implementing multiple strategies to manage this pest to mitigate against resistance and to have some protection after rain events.
  • A historical recommendation is that five acres tends to be the minimum acreage for use of codling moth mating disruption. This is based on and relates to probability of the search area for the moths. Mating disruption basically blindfolds the moths and the larger the area, the more likely they will not find each other. However, the more moths there are, the greater the possibility they will find each other especially in smaller blocks. If there is very high pressure, smaller blocks will be more susceptible to the border effect of mated females flying in from outside the orchard and laying eggs.
  1. We know the MESO LR product is registered to disrupt codling moth, hickory shuck worm, pandemis leafroller and obliquebanded leafroller. Has it been evaluated against other lepidopterans, i.e., redbanded leafroller or fruitree leafroller? Are there other mating disruption products for apple pests that you see on the horizon, e.g., dogwood borer?
  • Currently, there is a CM + LR (OBLR, pandemic leafroller), CMDA + OFM (oriental fruit moth) and OFM product. Last week Trece got a registration for a sprayable product, which is not a MESO product and will expect to be registering in states next year. Each state is very different with the registration process and it is slower than normal right now due to COVID-19. Even under normal circumstances it can take a month or two to be approved. The product is far more rainfast, and trials show 2-4 weeks of efficacy. The label says three weeks of efficacy and it is recommended to add a sticker with the product. It is called CM-MEC as of right now.
  • An OBLR standalone product has been submitted and currently waiting on feedback. There are no reports of flights of other leafrollers, e.g., RLBR, fruitree leafroller, tufted leafroller, being disrupted by the OBLR lure. Though, sometimes the OBLR lure will capture RBLR.
  • Trece’ is researching a mating disruption product for dogwood borer and Peachtree borer. This product would be similar to CIDETRAK and be placed at 32 per acre. Currently, researchers are running trials and it has not been submitted to the EPA.
  1. The product CIDETRAK DA MEC is the same pheromone that is put into CM lures, but in a liquid form. It can be applied along with an insecticide. After 50+ moths were captured in several traps, is it recommended to add the DA MEC product to achieve a higher efficacy?
  • DA MEC is a micro encapsulated product that is tank-mixed with an insecticide application. It enhances the activity of the insecticide, by augmenting the larvae’s searching and feeding behavior. When exposed to the DA MEC, the larvae become confused and disoriented and disengages with its searching behavior to find a fruit. The DA MEC will not kill the larvae and is designed to be mixed with a pesticide. Studies have shown a 40-60% increased control by using DA MEC.
  • A study looked at a control, DA MEC alone and DA MEC plus an insecticide. DA MEC alone showed some effectiveness with control but was not proven effective as a stand-alone treatment and still was outperformed by the tank-mix of DA MEC plus a pesticide.
  • DA MEC is effective for the similar duration of other codling moth larvicides, e.g., 10 – 14 days depending on rainfall, fruit growth, etc. and contains very small micro capsules that are five nanometers in diameter. They adhere well to the plant, and if applied with a sticker, efficacy would likely be longer than 14 days.
  1. Have you heard any reports or have any research on OFM mating disruption shutting down lesser apple worm (LAW) flights?
  • Both OFM and LAW are in the same genus. For example, hickory shuck worm is on the CM label because both are within the Cydia genus. Brent has heard this reported before though can’t speak a lot on the extent that LAW is disrupted by the OFM dispenser.
  • Brent noted he has received more informational requests on OFM and does suspect that LAW would be affected by the OFM but not sure to what extent.

Grower questions

There has been some concern with the heat this week with thinning and growers are unsure if it is safe to thin. 10-15mm fruitlets are still thinning size. Is it safe to apply thinning products in warm temperatures in the 80’s and 90’s?

  • If NAA is applied in hot temperatures, e.g., 90+ degrees, it will cause leaves to curl and the tree to droop. It is a stressor that can increase fruit drop when considering the carbohydrate model. As soon as the temperatures drop into the 80’s over the rest of the week, it will be okay to apply NAA. Phil Schwalier has recommended reducing the amount of NAA by half if applied with a penetrant like Regulaid.
  • If side fruit are 10mm or less, growers may have two opportunities to thin. Growers may want to go out tomorrow with a half rate of NAA and Regulaid and re-evaluate this weekend to decide if a second application is necessary.