May 18th AppleTalk Summary

AppleTalk Conference Call Summary
Tuesday, May 11th, 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

 May 18th Call Stream: CLICK HERE

Location Green Tip Date Ascospore Maturity (%) Ascospore Discharge (%) to date Degree Days

(Base 50°F)

Eau Claire, WI 4/3 91% 55% 170
Galesville, WI 3/21 97% 72% 198
Gays Mills, WI 4/3 97% 72% 217
Mauston (Northwoods), WI 3/30 96% 90% 214
Mequon (Barthel), WI 4/4 65% 38% 155
Rochester (Ela), WI 3/30 93% 87% 190
Verona, WI 4/3 85% 59% 211
La Crescent, MN 3/23 93% 60% 237
Hastings, MN 4/5 86% 35% 181
Harvard, IL 3/30 89% 64% 217

Table 1. Degree days and ascospore maturity downloaded on 5/18/21 from Cornell NEWA system. Find your local station today: http://newa.cornell.edu.

Regional summary
Warming temperatures and increasing likelihood of rain across the region will bring with it increased risk of scab infections; the first signs of plum curculio activity and the start of codling moth monitoring. Fire blight risk is minimal for varieties at petal fall, but non-bearing trees or trees still in bloom will be at risk of fire blight infections, if the forecasted rain materializes.

Soil moisture management
Inadequate soil moisture still widespread, with all AppleTalk participants in areas classified by the National Weather Service as a “Moderate Drought”. John has observed soil temperatures around 69F at 7″ and this rapid warming of soil reflects its dryness. June beetles are emerging earlier than normal, reflecting very warm soil temperatures.

The importance of water trees now, before summer heat sets in cannot be understated. We have been getting by because the cool temperatures are keeping transpiration rates low. However, with warm weather comes increased transpiration. The goal should be to apply one inch of water per week (0.67gal. per sq. ft.) on all but semi-dwarf trees. That is approximately 6-gallons per week for a mature Bud9. It has been so dry that John has observed water from drip irrigation sucked out two feet away from the tree via capillary action. We should consider that 7 – 14-year-old Bud 9 trees still have a small root system and small amount of soil they can tap into for their moisture.

Diseases
Spring disease complex (apple scab, powdery mildew, cedar apple rust)
The warnings and forecast to be prepared for big scab infection period have been discussed in detail over the last month. As we near the end of primary scab season, keep in mind that mature inoculum will remain present until released during a rain. Some amount of rain is forecasted across the region and orchards should be receive protectant fungicides prior to this rain.

The need to apply a single site fungicide, e.g., strobilurin, sterol inhibitor or an SDHI, is largely dependent on your historical disease pressure from scab, powdery mildew, and cedar apple rust. The conditions over the next week remain excellent for the spread of powdery mildew and at the current temperatures, a wetting period of four hours is all that is needed for a cedar apple rust infection. Powdery mildew has been observed already in parts of western Wisconsin and southeastern Minnesota, likely a result from the first round of 80F weather we experienced two weeks ago.

It is also around the end of petal fall when black rot begins spreading its inoculum. Good captan coverage is important to stop fruit infections and if you have had black rot infections in the past, considering including a strobilurin, e.g., Flint or Sovran, in your tank mix.

Considering the severity of the forecasted infections, Organic growers should consider application of sulfur for powdery mildew and scab ahead of rain.

Fire blight
As blossoms begin to age and turn brown, their overall susceptibility to fire blight decreases. However, where bloom persists, this week will pose fire blight risk for trees with open blossoms. It has been a long fire blight season and is reflective of an extended bloom period.  We are in a situation where there are Zestar with 10mm on king fruit and other varieties with bloom still opening. Growers to the north (Lake City, Eau Claire, Minneapolis, or further north) will need to protect whole orchards/blocks still in full bloom. Growers in Lacrosse to Green Bay and further south into Illinois, will only need to spot spray. If you planted trees this spring, these may be opening into bloom over the next two weeks and as their blossoms open, fire blight risk will be dependent on rain fall.

If you are going to apply streptomycin, remember that Regulaid only needs to be applied once. If streptomycin plus Regulaid was already applied, the petals have already been penetrated with Regulaid, the second application a few days later does not need Regulaid.  However, late bloom that was not exposed to Regulaid, will still need this if you want to use the lower rate of streptomycin.

Once you are at or past petal fall and fruit is sizing to 5mm, streptomycin applications should cease. If you have established trees with a history of fire blight, Cueva and Double Nickel can be applied as a tank mix.  This tank mix has been found to stop the spread of existing fire blight infections and may be used preventatively at and after petal fall to help prevent shoot blight infections. Cueva is a copper and with any copper, there is always a risk of russeting. Supposedly, the combination of Cueva PLUS the Double Nickel is to have a reduced risk of russeting.

Insect management at petal fall
Codling moth
Many orchards in southern Wisconsin caught their first codling moth between May 11th-14th.  However, a flight one night does not necessarily constitute a biofix. The first codling moth (CM) capture has traditionally been around petal fall or 180 DD, base 50°F and most sites are between the 180 to 250 DD base 50°F from January 1st; within the required-degree day accumulations needed prior to the first codling moth (CM) flight.

There is a reasonable probability that orchards to the north (Lacrosse, Chippewa Falls, Eau Claire, and possibly the southern end of the Twin Cities) could have a flight this week with the warmer weather. Codling moth traps should be checked nearly daily to establish the first CM flight. Codling moth biofix is marked by a significant biological event, or first sustained flight, where moths are captured multiple days in a row or exceed a threshold of five moths per trap per week. Once a biofix date is established, begin tracking degree-days (base 50°F) and monitor traps weekly. If you are calculating degree-days by hand, be aware that codling moth has a top developmental threshold of 86°F, which means all temperatures above 86°F should be counted as 86°F, e.g., a high of 95°F would be changed to 86°F degrees, if calculating by hand. Degree days are also available from your nearest NEWA station here, http://newa.cornell.edu/index.php?page=degree-days.

If mating disruption is used, hang at least one CM combo lure (CMDA) per block and at least two oriental fruit moth (OFM) traps per orchard. The CMDA lure will attract female and male CM moths. The Trecé Combo Meso boxes only cover half as many acres as the CM Meso box because there are two species being disrupted.

Codling moth fly between 6pm and 11pm when wind speeds are between three and five miles per hour and when temperatures are above 62°F, without rain. Assign the biofix date for the warmest, calmest night. When checking traps, fluttering CM had likely flown within the last 48 hours. Most female CM can live for seven to 14 days yet will mate and deposit the majority of eggs on the evening they emerge. Every day that a sexually viable female emerges and is not able to fly, egg fecundity is decreased by 20%.

Beware of the CM look alike! Proteoteras is genus of moths belonging to the family Tortricidae. Codling moths are also in this family, but belong to the genus Cydia, and have some similarities in appearance and can be confused with these moths. Proteoteras has a similar wingspan, but is slightly narrower and lacks the bronze coloring on the wing tips of CM. For photos of CM and two look-alikes visit: http://www.mda.state.mn.us/Global/MDADocs/pestsplants/applefieldguide/cm.aspx

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 (Trecé)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.

Plum curculio
The temperatures expected over the next week will likely trigger plum curculio migration from overwintering sites. One orchard in southern Wisconsin that has historically high pressure has reported some PC feeding injury but no oviposition injury.  Prioritize scouting varieties such as Zestar, Ida red, Paula red, Liberty, etc. that size first. This year’s cool weather has likely prevented any significant movement of PC into the orchards, but the current weather now offers perfect conditions for PC to begin moving into the orchards and it is essential to scout the perimeter of the orchard and focus on historical hot spots and locations that have the largest fruits.

Plum curculio (PC) emergence begins between bloom and petal fall, and movement into the perimeter of orchards begins when temperatures are above 60°F. This is a gradual process and requires several days of warm weather. PC are primarily nocturnal, and the greatest amount of activity will occur when temperatures at night remain warm. The entire population does not migrate into the orchard at the same time and fruitlets become susceptible to PC egg-laying when they reach 5 mm. When PC first move into the orchard, they must feed and mate for a period of about seven days, before egg laying begins and the typical crescent-shaped scars appear.

Please make note of the 95% petal fall date and report back to us. Tracking degree days from petal fall may be used to predict when their emergence from overwintering sites ends, which occurs after 308 DD base 50°F have accumulated. These degree days from petal fall will be included in the next summary table if you submit them to us. Without your actual petal fall date, NEWA estimates petal fall based on degree days accumulated from January first, which is likely to be inaccurate.

Spraying perimeters more frequently is one option to reduce cover sprays. If PC injury is found past the perimeter, e.g., first four or five rows of trees, a full cover spray is recommended. In the past, many assume that thinning sprays with carbaryl will offer protection against PC. Thinning with carbaryl at one pint per acre delivers a half pound of actual carbaryl, whereas if carbaryl was used as an insecticide, this rate would be delivering two to four pounds of actual carbaryl per acre. Therefore, the rates used for thinning are not going to deliver insecticidal activity. Reducing rates of carbaryl may help lessen the impact on beneficial insects in the orchard.

Avaunt (indoxacarb) has been the most applied organophosphate alternative to manage PC. Many of the newer insecticides use a combination of contact mortality, systemic activity as an anti-feedant or ingestion, to manage PC. The neonicotinoids Actara (thiamethoxam), Assail (acetamiprid) and Belay (clothianidin) offer a few days of contact mortality and after several days the insecticide penetrates the fruit and acts as an anti-feedant and oviposition repellant. Exirel (cyantraniliprole), a diamide insecticide related to Altacor (chlorantraniliprole), may be used to manage PC and CM. It has similar activity to Avaunt, which requires ingestion.

Note: Belay is very toxic to beneficial insects and pollinators and will remain toxic to pollinators for more than five days after an application. It is critical to wait until bees are out of the orchard and there are zero blossoms left on the trees and minimal bloom in the groundcover before applying Belay.

To date, PyGanic (pyrethrum) continues to be the most effective insecticide for organic production. PyGanic is very short lived and very unstable when exposed to ultraviolet light.  This means that PyGanic should always be applied at night and typically only will last 12 to 24 hours, or less. Considering this, be vigilant with scouting and wait for the first signs of PC feeding or oviposition injury before making a spot spray or perimeter insecticide application (this advice could be headed by anyone that wants to move the needle on minimizing excess pesticide use).

Regarding perimeter sprays, it is common to see growers apply perimeter sprays anywhere from one to four rows deep.  Realistically, the perimeter is whatever width you can get away with while still having an effective treatment.  Growers with light PC pressure should consider spraying only one row.  If you have abandoned trees or heavy pressure, more rows should be sprayed. There is no “textbook” definition of what defines the perimeter.

Thinning
Preliminary observations suggest that fruit set generally looks better than expected, especially where freeze damage to blossoms was the primary issue rather than lack of return bloom. Early sizing cultivars in the most advanced orchards are nearing 10mm Kings now, although within the same orchards late blooming varieties still have fresh blossoms, so assess and thin accordingly. Once fruit size to 5mm, fruit are probably not falling off in next five to ten days. Fruitlets may stick and stems remain green for a week after petal-fall, before abscission proceeds, which means do not rush thinner applications until you’re certain what will size to the 5mm-7mm range. The weather in the three days after a thinner is applied is the most critical factor in its effectiveness, so except for the possible rains, the next seven days look excellent for thinning materials to be absorbed and metabolized.

Please see last week’s AppleTalk notes for more links and in depth discussion on thinning using the carbohydrate model.

 

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