June 18th AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, June 18, 2019, 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org

June 18th Call Stream: CLICK HERE

Regional update

Location Degree Days 6/17/2019
(Base 50°F)
Petal-Fall Date (NEWA) Accumulated DD (Base 50°F)
from Petal Fall
DD remaining to 308 DD from Petal Fall CM Biofix (NEWA) Accumulated DD

(Base 50°F) from CM biofix

Eau Claire, WI 422 5/28/2019 282 111 6/8/2019 111
Gays Mills, WI 522 5/30/2019 268 40 6/6/2019 156
Hastings, MN 509 6/1/2019 259 49 6/7/2019 156
Harvard (Royal Oak), IL 488 5/23/2019 328 0 6/6/2019 145
Lake City, MN 508 6/1/2019 246 62 6/3/2019 219
Mauston (Northwoods), WI 474 6/1/2019 222 86 6/7/2019 127
Mequon (Barthel), WI 341 6/6/2019 113 195 6/15/2019 18
Preston, MN 487 5/31/2019 249 59 6/3/2019 205
Rochester (Ela), WI 421 5/23/2019 304 108 5/30/2019 215
Trempealeau (Eckers), WI 486 5/31/2019 249 59 6/6/2019 159
Verona, WI 518 5/30/2019 268 40 6/5/2019 179
White Bear Lake, MN 479 6/3/2019 230 78 6/8/2019 127
Woodstock, IL 570 5/26/2019 332 0 5/28/2019 303


Table 1. Degree day accumulation to 6/17/2019.  Note: Degree days for plum curculio and codling moth are estimated by NEWA.  Actual dates must be entered by users and are not saved.  This year DD are as much as five days off grower-observed codling moth flights. *All degree days are calculated using a lower-temperature threshold or base temperature of 50°F.

Regional update
The forecast for the region includes highs in the 70s and lows in the 50s with spotty rain showers towards the end of the week and into the weekend.  Most locations only have 75-100 DD remaining until they have reached 250 DD from CM biofix.  NEWA is not reporting correct petal fall dates for many locations.  Growers located within the areas on the DD table may send us their petal fall date and we will update the table with this data.

Codling moth
Orchards should now have a biofix set for some time in the first or second week of June.  Degree days are between 150-280 DD from biofix.  If your orchard did not reach a cumulative trap count of five until last week, applying a larvicide at 250 DD is not necessary and it is recommended to wait until 350 DD.  If a large flight occurred in the last week of May, depending on the numbers, waiting until 350 DD may not be the best option.

Codling moth (CM) have two generations per year in our region and will accumulate about 1,000 DD between first and second-generation biofix.  Once a biofix is established, the first cohort of the entire generation’s population will begin at 250 DD from biofix.  This will only account for about 3% of all the eggs that will hatch in the generation.  As more degree days accumulate and more moths fly, a greater percentage of the entire population’s eggs will begin to hatch.  At 350 DD from biofix, roughly 15% of eggs are hatching and as 450 – 700 DD accumulate from biofix, 50% of the eggs will hatch.  After 700 DD from biofix, eggs are still hatching, but are a much lower percentage of the total potential population.

The importance of timing right at 250 DD or delaying the first spray is relative to the size of the CM population in the orchard.  Where growers have low populations, the first spray may be delayed to 350 DD because there will not be many codling moth larvae hatching right at 250 DD.  Fruit from these early hatches often fall to the ground from thinning or June drops and the injury may never be visible.  If 15, 20 or 30 moths were caught during the first flight, then 3% represents a lot more eggs that will hatch, than if only caught 1, 3 or 5 moths were captured in a trap.

Understanding wash-off rates are critical for timing the reapplication of insecticides.  Spinosyns, e.g., Delegate (spinetoram), diamides, e.g., Altacor (chlorantraniliprole), Exirel (cyantraniliprole), and Avaunt (indoxacarb) are very rainfast, whereas neonicotinoids, e.g., Assail (acetamiprid) and Belay (clothianidin) are less rainfast.  If 0.5” of rain falls on a neonicotinoid in the first week, there will be adequate residue, but an inch of rain within 24 hours of application will require reapplication.  No insecticide can be exposed to two inches of rain and effectively control CM or plum curculio.

Terpene-based stickers, e.g., Nu-Film help improve rainfastness and may be tank mixed with Delegate or Altacor.  Nu-Film is applied at 8 oz. per 100 gal. of water.  Do not use a sticker surfactant if applying a neonicotinoid, as these products do not stay on the surface but are absorbed into the leaf.  IMPORTANT: Read product label to determine minimum application interval and maximum permitted applications per season.  Read John Wise’s full article on rain-fast characteristics of insecticides, http://msue.anr.msu.edu/news/rainfast_characteristics_of_insecticides_on_fruit

The recommended trap density in recent years for monitoring codling moth has been to place one trap per five to ten acres in blocks not using mating disruption.  In orchards where mating disruption is being used, trap density should be increased to one trap per 2.5 acres.  Additionally, blocks that are not uniform in size or have undulating or rolling topography, should have additional traps.  A recent study further documents the flight behavior and attractiveness of male codling moths to the pheromone traps.  There is a difference between the effective range of the plume, e.g., the distance that a male can locate the pheromone trap and the effective coverage of the trap.  Males cannot find the pheromone plume unless they are within five meters, or 15-16 feet of the trap.  However, the paper also concludes that the effective radius of a trap is 21 hectares (52 acres), e.g., only one trap is needed per 52-acre block.  Even though the maximum-effective radius of a CM may be larger than we thought, the need for a high density of traps is explained by the flight pattern of males.  Male CM are poor fliers and tend to move around a lot so the traveling distance to the trap is many times greater compared to their sensing ability.  This does not mean growers should only deploy one trap per 45 acres.  The authors state that if deploying traps for every five acres, trap catches may be creating a lot of “noise” being that trap numbers can vary widely.  Varying trap catches will often not reflect the actual CM population next to the trap and larvicide applications for the whole orchard should be based on the trap with the highest count, rather than the lowest.  For more information on this study, CLICK HERE.

Plum curculio
Most locations are at or near 308 DD from petal fall.  Make sure to continue monitoring for fresh oviposition strikes.  Avaunt (indoxacarb) may be used for a final plum curculio (CM) spray, rather than a neonicotinoid as it will have offer efficacy for CM and will have a longer effect on adult PC.  Tank mix another product if planning on applying a neonicotinoid, e.g., Assail or Belay, for late PC.

Insecticide options for codling moth and plum curculio
Trade name (active ingredient) Plum curculio Codling moth Notes
Avaunt(indoxacarb) X X Less long-term control of codling moth compared to Delegate or Altacor.  Rated as ‘fair’, reapply after 7-10 days.
Actara(thiamethoxam)* X Apply with CM insecticide, e.g., Altacor, Delegate.
Altacor(chlorantraniliprole) X Apply with PC insecticide, e.g., Avaunt, Actara.
Delegate(spinetoram) X Apply with PC insecticide, e.g., Avaunt, Actara.
Exirel(cyantraniliprole) X X Same insecticide group (28) as Altacor
Belay(clothianidin)* X X Use only if CM pressure is low, e.g., less than 10 moths/week/trap.  If Belay is used and pressure is high tank-mix with CM specific insecticide.
Assail(acetamiprid)* X X
*Note: If a neonicotinoid is used exclusively for PC and first generation CM control it cannot be used alone for second generation CM and apple maggot (AM) control.  An imidacloprid, e.g., Admire Pro, Montana, Wrangler, tank-mixed with Altacor or Delegate or applying Exirel alone will offer AM control and mitigate resistance concerns for CM; do not treat more than one generation of a target pest with any of these insecticides.

Lepidopteran species
Obliquebanded leafroller (OBLR) usually begin hatching in mid-June but may be delayed until late June or early July due to cooler spring temperatures.  These larvae are small-green worms with caramel to black head capsules.  Scout fruit, if cultivars have set terminals.  Damage will be on the surface of the apple and at harvest will be difficult to distinguish from other lepidoptera.  Large flights now are a result of the overwintering generation not being controlled, which may lead to a higher second-generation population.  These worms will be the offspring from the first flight of OBLR this season, which has been delayed.  Worms at petal fall and first cover are overwintering larvae from last year’s second-generation flight.  In addition to feeding on foliage, larvae will also feed on fruit and are capable of causing economic damage.  Altacor (chlorantraniliprole), Delegate (spinetoram) or Entrust (spinosad), applied for codling moth, except granulosis virus and mating disruption, should provide adequate management of OBLR.  Beneficial insects should also aide in suppression of this pest.  Second-generation larvae can be more problematic and more difficult to control than first generation OBLR.  High populations may lead to fruit injury and significant damage to terminals on young and non-bearing trees.

Scouting for fruit and foliar feeding should begin seven to ten days after moths are caught in pheromone traps.  There are no established action thresholds and trap counts do not correlate well to the potential for feeding injury to fruit or growing terminals.  OBLR is resistant to many of the organophosphates and most of the neonicotinoids are not very effective on OBLR.

Large trap numbers of redbanded leafrollers (RBLR) were observed in mid-May and monitoring non-bearing trees and bearing orchards for larvae feeding on terminals or fruit is important. These RBLR began to hatch in the beginning of June and some hatches have been quite significant with populations well over threshold.  These larvae are also causing some fruit damage, known as cat-facing, where the surface feeding on the fruit resembles cat scratches.  RBLR larvae have been found to be over the 3-5% threshold in non-bearing orchards.  In bearing orchards, if growers are using a neonicotinoid for plum curculio, this will not offer much efficacy on leafrollers.  Currently, the RBLR are mainly second and third-instar larvae which are visible to the naked eye.  Typically, RBLR hatch at petal fall and are part of the spring-lepidopteran complex.  They fly quite early in the spring and are one of the first traps deployed.  Seeing any RBLR larvae in mid-June means they are delayed, likely due to cooler spring temperatures.

Dogwood borer
The standard recommendation is to scout for larvae in blocks with trees on dwarfing rootstocks that are prone to producing burr knots, e.g., M.9, M.26, NIC29, since DWB females find these burrknots to be an attractive medium on which to lay their eggs.  Another critical area to scout is beneath tree guards on all dwarf trees even if they don’t look in decline or have reduced vigor.  Tree guards, regardless of style, e.g., wraps, corrugated, grow tubes, can cause the “protected” bark to remain humid and damp long after the surrounding environment dries.  The dampness can be exacerbated by tall weeds or grass in the tree rows.  These conditions can cause the bark to crack or degrade, which create an area for the female moths to lay eggs and hatching larvae to burrow into the bark.  When scouting for larvae also look for empty pupae casing near to or protruding from borer holes.  Even if borers are not found other surprises may exist below the tree guards, e.g., woolly apple aphids, ants, etc.Growers who have planted new trees in the last five years should scout and monitor for dogwood borer (DWB).  The DWB pheromone attracts multiple species of native clear-wing moths.  If moths are caught in traps, they need to be appropriately identified to confirm species.  There is not a trap-based threshold for DWB, rather if adults are caught, look for evidence of DWB larvae, e.g., frass around the graft union of trees.  Initial stages of DWB infestation may not affect the tree immediately and symptoms of tree decline may take four or five years to appear.  Trapping acts as an early warning system to begin scouting, rather than waiting for visible symptoms.  Make sure traps are at the correct height of three to four feet above the ground.

Usually DWB injury is found right above or around the graft union.  DWB have also been observed in the scaly bark that is not covered by tree guards, e.g., winter injury or herbicide injury, or even on pruning cuts just above the tree guards.  Small diameter dwarf trees are more prone to girdling, caused by continuous infestation; feeding often needs to happen for several years before trees shows decline in vigor and possible death.  Even if feeding does not impact the vigor of the tree, it can produce an entry point for disease, e.g., black or white rot. Over time, long term DWB infestation can kill a tree.  Leaves will wilt and curl up in comparison to healthy trees.  Phytophthora has a similar effect, except leaves will often have a reddish hue.

An alternative to Lorsban (chlorpyrifos) for a trunk spray is Assail (acetamiprid).  Assail should be applied with at least 50 gal./acre with a hand wand, not with the bottom nozzles on the sprayer.  Unlike Lorsban, Assail must be applied around peak flight, followed by a second application 14-21 days later.  The goal is to have the product penetrate the bark, so a penetrating surfactant like Regulaid is also recommended at a higher rate.  Make sure to drench the area with plenty of water.  An additional application may be required the following season.

Western flower thrips have been minimal this year, but John has observed high numbers in a few areas, mainly entering orchards towards the end of bloom.  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) or Delegate (spinetoram) are the best options for thrips management.  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.

San Jose scale (SJS)
Monitoring SJS crawlers should begin hotspots and places where it was visible last year at harvest.  John observed the first crawlers within the past week.  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 tree, 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, 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.

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.

Adult potato leafhoppers have been observed in orchards and nymphs will be visible in the next few weeks.  Scout terminals of non-bearing trees or vigorous trees such as Cortland.

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.  This dusty substance could also be confused with ash that has accumulated from forest fires in Canada and out west.  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.

Managing secondary scab
The region is well past primary scab season and secondary scab infections are releasing millions of conidia during periods of high heat and rain.  Young tissue on trees remains highly susceptible to scab and even if heat is present, apple scab can remain a persistent problem.  If no scab has been observed in your orchard, intervals between sprays may be stretched out and rates can be adjusted, but it is important to consider that protecting tissue from black rot and white rot would still warrant applications of captan.

Secondary scab is primarily found on the top side of the leaf, though can also be observed emanating from primary lesions on the underside of leaves.  If significant scab is present, try to contain the infection within the block with captan and do not apply a single site fungicide unless necessary for summer disease control.  Apply captan renewal sprays on infected varieties more often than the entire orchard and pay attention to the weathering of captan residues.

Organic growers may apply Serenade (Bacillus subtilis) or Regalia (Reynoutria sachalinensis) on scab-susceptible varieties.  Sulfur should be used sparingly now since applying too much sulfur is not healthy for the trees and it would be better to wait for a good opportunity to apply lime sulfur.  The weather this week in the upper 70s could be a good time for an application of lime sulfur.

Preparing for summer disease management
Black rot may be managed with a high rate of captan, since locations have had frequent enough rain and warm enough temperatures for development of this disease.

When scouting fire blight, look for where the infection stops along the length of the branch.  This year, winter-injury symptoms have a similar appearance to fire blight.  Fire blight will affect the entire length of the branch, including new growth with water soaked and browning leaves and will have shepherds crook at the end of the terminals.  Winter injury has fire blight like symptoms but ends at the node of the one-year growth and does not progress further down the length of the branch nor does it have bacterial ooze.

If you have experience using Apogee (prohexadione calcium) for fire blight, please let us know as we are interested in the effectiveness.  If you have not made any Apogee applications, it is okay to attempt one application now at a higher rate, even though the first application should have been made at king-bloom petal fall.