June 6, AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, June 6 2017, 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 6th Call Stream: CLICK HERE

Thinning is when growers spend a lot of time looking at fruit, and can often be surprised by some of the fruit injury they observe at this time.  What are some guidelines for determining causes of fruit damage at thinning time?

  • When scouting, assess whether injury is clumped or randomly distributed, and consider if it is specific to a certain cultivar or found across the entire block or orchard. Clumped distribution can rule out hail injury, which can look like a lot like feeding injury from our spring-lepidopteran complex, e.g., green fruitworm, obliquebanded leafroller and redbanded leafroller.  If the injury is caused by green fruitworm or leafrollers it is often clumped and not widespread.  Early plum curculio injury is not usually found throughout the orchard and will trend towards early sizing varieties, whereas now, when all fruit is attractive, it may be more uniform.  Tarnished plant bug feeding injury is unique and easily diagnosed by a smooth, conical-shaped depression with no scar tissue, often located near the calyx end of the fruit.  No other insect causes this type of damage.
  • When inspecting injury, use a hand lens (10x) to look for smooth or irregular-shaped edges. Often the small scab lesions we see on fruit are only several millimeters across and may only be seen as a dark spot.  Smooth edges are more likely to be from a pathogen, compared to a spot with rough edges that might be phytotoxicity.

We will be discussing the use of ovicides for codling moth that will offer overlap management with other pests.  What is the application timing to get the most from insecticide rotation if we are using both ovicides and larvacides?

  • When selecting insecticides to manage codling moth (CM) we need to consider the intervals of when they are applied. If an ovicide such as Esteem (pyriproxyfen) is used first, it needs to be applied earlier in the lifecycle, i.e., 50-150 DD, base 50°F from biofix, than if a larvacide such as Altacor (chlorantraniliprole) is used first and applied at 250 DD.  If a larvicide is applied after an ovicide the application interval can be extended beyond 250 DD.  Depending on rainfall you may not need to reapply in 10 – 14 days, rather you can go back in 17 – 21 days.  The interval needs to be shorter if a larvacide is applied before the ovicide.

Review of degree-day accumulation from McIntosh petal fall and developmental thresholds

  • The number of days between sprays or a biofix and egg hatch means nothing to insects.  This is simply a convenient way for us to divide up and track insect development over time.  Insect development is linked to degree-day accumulations (DD).  For example, a week ago we were only accumulating about 10 DD per day, but now with the warmer temps, we are accumulating 15 – 20 DD every day and it will only take 10 – 14 days between a biofix and the need for a larvacide application.  By early next week we may be accumulating >20 DD per day and can reach our target application interval much faster.  Codling moth will develop faster in hot weather and will allow us to use less insecticide application to manage first generation.  If we are calculating our degree-day accumulations by hand, remember the developmental threshold which includes the upper limit (86°F) and lower limit (50°F); temperatures in the 90s will not speed up CM development.

Use the following formula to calculate degree days for codling moth development

The upper and lower developmental parameters for CM are 86° and 50°F.  If the daily high/low temperature is warmer or cooler than the upper or lower limits use the upper or lower developmental parameters (86° or 50°F) instead of the daily high/low temperature.

DD calculation

(Click over calculations to enlarge)

Some growers had a very strong CM flight around May 14, while others have had a slower or delayed flight.  What guidelines may be helpful to determine if codling moth larvacides need to be applied directly at 250 DD, the start of egg hatch, or if the application may be delayed to 350 DD from biofix?

  • The treatment threshold is five moths per trap per week. If you had a flight of more than five, then technically a larvacide needs to be applied at 250 DD.  If you caught 15, 20, 30 moths on the first flight, then subsequently caught nothing in 10 days, you need to focus on this flight since most females lay eggs in the first few nights after emergence.  If you started slow and now CM flights are picking up, either wait to 350 DD or set a second biofix to act on.  It is essential to manage the first generation more closely than being lax in the first generation.  For first generation it is recommended to treat the entire orchard if one trap goes over threshold; second generation can make spot sprays to blocks.

I’m still confused, can you explain the development model and treatment caveats for codling moth again?

  • Codling moth have two generations per year in our region and will accumulate about 1,000 DD between first and second-generation biofix. Once we have a biofix 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 we accumulate more degree days from biofix and as more moths have flown, 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 we reach 450 – 700 DD from biofix 50% of the eggs will hatch.  As we move past 700 DD, eggs are still hatching, but it is a much lower percentage of the total potential population.  We should consider this is all relative to how large a CM population you have.  Where growers have low populations, we often delay the first spray to 350 DD because we recognize there will not be many codling moth larva hatching right at 250 DD.  Fruit from these early hatches often fall to the ground and we may never see the injury.  As mentioned earlier, if 15, 20 or 30 moths were caught during the first flight, then 3% represents a lot more eggs that will hatch, than if a grower only caught 1, 3 or 5 moths per trap.
  • Weather conditions will also greatly influence the flight behavior and fecundity of female codling moths will only fly and mate when the weather is warmer than 62F, it is not raining and the wind speed within the orchard and tree canopy is less than 2 – 3 MPH. They also only fly between 6 – 11 pm.  Therefore, these flight parameters must be met during this time each day.  If these conditions are not present, the moths will not fly.
  • A more nuanced consideration is that the fecundity of female moths reduces about 20% per day, for each day they cannot fly and mate, after they have emerged. This suggests that when early codling moths fly, if it has been cold, windy and rainy, it is very likely the moths have been waiting in angst to fly and mate.  If they have been emerged for several days to a week, the viability of the eggs is often significantly reduced.  Our cold, wet rainy spring is a good example of conditions where female moths may have been emerged, but could not fly and mate.  Again, if you had low populations, this provides additional evidence to support delaying your first spray until 350 DD.

Plum curculio (PC) is primarily nocturnal and becomes active on warm nights in the 60s and 70s.  How have you seen the cool temperatures impact PC emergence and immigration into orchards?  Where should growers be scouting for PC, is the edge still an appropriate place to be looking?

  • Plum curculio emerge from overwintering sites around bloom and begin their migration into orchards, where by petal fall they can be well into the perimeter of an orchard. A model was developed at Cornell to track PC migration from these overwintering sites and predict when the movement would end.  After 308 DD, base 50°F, from McIntosh petal fall PC migration ends from their overwintering sites.  This does not mean egg laying is complete and it’s possible for PC continue laying eggs into early July if they have not been controlled.  If insecticides have been applied for PC, but no damage has been found, continue to scout for injury.  John has been surprised by how little PC activity he has seen in orchards this year.  Perhaps we had severe mortality if they got stuck between overwintering and movement into orchard if they did not have a food source available.  A few females can do a significant amount of injury in just a few warm nights.  If your management strategy is to treat after finding injury, scout every few days and look at the edge and interior of orchard.

What are some of the insecticide options that will overlap with codling moth and plum curculio?  How rainfast are they?

  • Understanding wash-off rates are critical for timing the reapplication of insecticides. Spinosyns, e.g., Delegate (spinetoram), diamides, e.g., Altacor, Exirel (cyantraniliprole), and Avaunt (indoxacarb) are very rainfast, whereas neonicotinoids, e.g., Assail (acetamiprid), Belay (clothianidin) are less rainfast.  If we get 0.5” of rain on a neonicotinoid in the first week, we are fine, but an inch of rain within 24 hours of application you need to reapply.  No insecticide can be exposed to two inches of rain and effectively control CM or PC.  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

 

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.

 

San Jose crawlers are expected to emerge in the next week.  How should these be monitored?  What is the best timing for insecticides and what are some insecticides for scale that will overlap with codling moth sprays?

  • Monitoring for San Jose scale (SJS) crawlers should begin across the region. Older trees with rougher bark are more likely to have this pest.  Monitor known hotspots with black electrical tape applied to infested scaffold branches.  With 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.  Last year’s scale will be concentrated near newer growth.  Increasing the number of monitoring sites may help eliminate false negatives.  Low trap captures do not reflect overall pressure, i.e., false negatives, rather may indicate the beginning of the hatch.  First generation SJS hatches over a narrow period, while second generation hatches over a wide period.  Use 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 with zero on all other tapes, may warrant application.

We are just beginning to see the earliest signs of woolly apple aphid.  Where can we find these colonies?  Again, we have a good opportunity to use insecticides that overlap with management needs of San Jose scale and/or codling moth.  Can you review these insecticides and their timing?

  • Woolly apple aphid (WAA) colonies are beginning to appear in earnest 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.  Although there are many effective beneficial insects which can help control WAA, applying an insecticide early, e.g., before third cover, if WAA is a chronic issue will help manage damage.  If Movento (spirotetramat) is used it must be tank mixed with a spray adjuvant having 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.

Dogwood borer (DWB) is becoming an increasing problem as more tall-spindle orchards are established.  DWB are particularly attracted to trees that produce burr knots.  Can you review where we should be scouting for DWB activity?  Pheromones may be used to monitor, but no threshold exists, how do we best use these pheromone traps in DWB monitoring?  Where should the traps be hung?

  • Growers who have planted a lot of new trees in the last five years should be scouting and monitoring for DWB. Deploy traps now, and place four feet off the ground.  The DWB pheromone is not specific and 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 you are catching DWB adults you need to be looking for evidence of DWB larvae, e.g., frass around the graft union.  Initial stages of DWB infestation may be random, damage may not effect tree immediately but four to five years down the road trees will begin to decline.  Trapping gives us an early warning system to begin scouting, rather than waiting for visible symptoms.
  • If DWB are caught scout at least ten trees scattered throughout the block for infestation. Focus on trees that are three to five years old grown on rootstocks susceptible to formation of burr knots, i.e., M.9, M.26 and Mark series.  Examine the trunk from the soil line to the first scaffold branch for frass protruding from borer holes, burr knots or damaged bark.  Fully remove trees guards while scouting.

 

I once heard that you can burnout scab by applying a maximum rate of Captan on an 85+ degree day, does this work or is this just an old-timer’s myth.

  • Using 5 lb./acre of Captan 80 can burn out and reduce conidia production on surface of the leaf. The conidia production will also drop during the heat of the summer and older leaves have less problems with conidial production and Captan can suppress it for a while.  If we have significant leaf scab or fruit scab avoid single sites and apply Captan.  Variable rates of Captan should be applied prior to wetting events.  The maximum amount of Captan 80 that may be applied during the season is 40 lb. per acre; Captan 50 is 64 lb./acre/year.  If secondary infections are present deciding how much captan to apply should be determined by the amount of forecasted precipitation.  Varieties that don’t have scab, don’t need the same level of protection that blocks with scab do (don’t need to use a high rate of captan orchard wide).

Powdery mildew

  • Where powdery mildew is a concern on non-bearing trees foliar flagging should now be present. Single-site fungicides and sulfur provide protection against powdery mildew, whereas captan does not.  Where we don’t have scab, any of the single-site fungicides may be used without concern of losing efficacy for primary scab management.  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.