June 23, AppleTalk Call Summary

AppleTalk Conference Call Summary
Tuesday, June 23, 2015, 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 23rd Call download: Click Here

Apple scab
We are well past the threat of primary scab season and orchards which are free of scab, may choose to increase the application interval and reduce application rates of captan for summer diseases.  Captan may be applied as a half rate every three to four weeks if the following parameters are consider:

  1. History and pressure of black rot, fruit rots, sooty blotch and flyspeck.
  2. Fruit is greater than or equal to one inch in diameter is less prone to infection.
  3. As terminal buds begin to set the leaves become moderately resistant to scab infections.
  4. Varieties with scab infections will require a protectant fungicide program through the summer.

Summer diseases
The Brown-Sutton-Hartman model has traditionally been used as a warning system to time fungicides for control of sooty blotch and flyspeck (SBFS).  The model is designed to help improve timing of fungicides for SBFS based on the accumulation of 175 leaf wetting hours (LWH) from petal fall or the last systemic-fungicide spray applied either at petal fall or first cover.  New research suggests this model, developed in the Mid-Atlantic States, may not accurately predict the development of SBFS in other growing regions.  Research conducted by Patty McManus, University of Wisconsin, and Mark Gleason, Iowa State University, adapts the original Brown-Sutton-Hartman model for the Upper Midwest.  Their research suggests tracking the hourly accumulation of relative humidity (RH) ≥ 97% is a more accurate predictor than LWH, when predicting the first appearance of SBFS.

Table 1 summarizes accumulated LWH and relative-humidity hours (RHH) for locations in the Upper Mississippi River Valley and the Door Peninsula.  This data include accumulations from May 25, where many orchards in the region had a petal fall date between May 15 and May 29.  If no systemic fungicides were applied at petal fall, then counting accumulated LWH or RHH from petal fall may be used.  If systemic fungicides have been applied, begin counting the accumulation of LWH and RHH from ten days after the last systemic fungicide was applied.

Location Leaf Wetting Hours Relative Humidity Hours > 90%
Gays Mills, WI 115 172
La Crescent, MN 131 177
Lake City, MN 125 173
Sturgeon Bay, WI 145 N/A

Table 1. Accumulated leaf-wetting and relative humidity hours from May 25, 2015

Growers in the southern half of Wisconsin tend to have greater SBFS pressure and may use 175 RHH for timing fungicides for summer disease.  Orchards in the northern part of the state, e.g., Eau Claire, WI to Hastings, MN or those who feel they have not had a history of SBFS, may choose to wait until 220 RHH have accumulated.  If systemic fungicides were applied at petal fall, this may offer additional protection against summer diseases.

SBFS fungicides
If any of the following materials were used during primary scab season and scab lesions are present, DO NOT USE for summer diseases, especially strobilurins and DMIs.

  • Topsin M (thiophanate-methyl). Topsin M is the best choice for SBFS in orchards where scab is present.
  • Strobilurins, e.g., Flint (trifloxystrobin), Pristine (boscalid, pyraclostrobin), Sovran (Kresoxim-methyl).
  • DMIs, e.g., Indar (fenbuconazole), Inspire Super (difenoconazole, cyprodinil). Older DMIs, e.g., Rally (myclobutanil), do not function against summer diseases.
  • During the winter Wisconsin Apple Grower Association meeting and trade show Patty McManus presented on a range of soft chemistries for summer diseases, powdery mildew, apple scab and fire blight. An overview of the results from her research trials is available online, http://eventmobi.com/api/events/6411/documents/download/57cb3d36-52a9-49b9-bc61-5f3605dde1a9.pptx/as/F&V-2015-softchem-apples.pptx
  • OMRI approved fungicides
    • Oxidate (hydrogen dioxide)
  • Kaligreen (potassium bicarbonate)
  • Regalia (Reynoutria sachalinensis)
    • Serenade (Bacillus subtilis)
    • Sodium bicarbonate
    • Regalia (Reynoutria sachalinensis)

Flower thrips
Scout terminals and shoots for curled leaves.  Brown-feeding injury will be present on the underside of the midrib of the leaf.  Thrips will continue to feed until terminals have set and may be a concern on young or non-bearing trees and is usually not a concern on mature trees.

Potato leafhopper
Potato leafhoppers are appearing on terminals and shoots, particularly orchards in close proximity to hay and alfalfa fields.  These are also often only a problem on young and non-bearing trees.  Symptoms include upwards, cupping of leafs on terminal shoots.  Potato leaf hoppers do not overwinter in the upper Midwest and are brought to our region on heat thermals and in warm-summer storms with winds from the south. 

Apple rust mite
Apple rust mites (ARM) function as food for beneficial mites and mite predators, and traditionally have not caused damage in established orchards.  High infestations of ARM in young, non-bearing trees may result in economic damage.  While scouting use a hand lens with 10x or greater magnification to scan the upper and lower surface of leaves.  Visual symptoms include yellowed and distorted foliage, prolonged feeding by high populations will cause a leathery silver or bronzing and curling of the leaf.  Feeding on developing fruit may damage the skin and cause russeting.

San Jose scale
Monitoring for San Jose scale (SJS) crawlers should begin across the region.  Monitor known hotspots with black electrical tape applied to suspect scaffold branches.  With adhesive side towards tree, wipe a thin layer of petroleum jelly on the outside of the tape.  If populations are high, concentrate a few traps in areas with greatest pressure.  Increasing the number of monitoring sites may help eliminate false negatives.  Low trap captures do not reflect overall pressure, i.e., false negatives.  Low trap captures may indicate the beginning of the hatch.  First generation SJS hatches over a narrow period, while second generation hatches over a wide period.  Catches of 10-15 crawlers over several days or 10 crawlers on one tape with zero on all other tapes, may warrant application.  If no crawlers are captured after three weeks of monitoring no further trapping is necessary.

Japanese beetle
Japanese beetle have not been seen where they have become a nuisance in past years (Illinois and Wisconsin state line, Eau Claire County).  Under favorable conditions beetles can quickly move into new locations.  After the first few years of introduction, populations grow exponentially and quickly become the predominant pest.  Once established, the population decrease as a result of biological control.

Scout for Japanese beetle in raspberries or locations where beetles have been spotted early in the season.  Chemical control is only effective when populations are low and immigrating into the orchard.  Control is very difficult to achieve when large populations are established.  Beetles release an aggregation pheromone to attract more beetles, therefore dying beetles are still attracting others.  When timing an application note the daily location of beetles; beetles feed in trees during the day and move to orchard floor at night.

Dogwood borer
Dogwood borer traps can still be set in orchards.  Trap counts will provide information on hatching larvae in a few weeks.

European red mite
Summer populations of European red mites should be visible in orchards.  Identify hot spots now.

Apple maggot
It is advised to hang yellow boards or red spheres by July 1.  Yellow boards can provide an early warning system by attracting apple maggot during their feeding period.  If bait is used in addition to visual traps replace volatile lures according to the manufacturer’s directions, e.g., seven to ten days.  A minimum of three traps per ten acres should be deployed at the beginning of July; trap density should gradually increase to one trap every 200-300 feet as the season progresses.  Locate traps along perimeter where wild hosts are present and near early ripening cultivars.  Hang traps at eye level, and make sure they are visible.  Traps can be placed in early season varieties that exist on the interior of block, since the trees can harbor resident populations that may not affect neighboring varieties.  Always apply more Tangle-Trap then you think is necessary, insect should be easily caught in the adhesive film; spray-on formulation should begin to drip.  If you do not apply enough Tangle-Trap it can lose its tackiness and wear off in the rain.

June drop
A dramatic ‘June drop’ is being observed this season.  The variability in the size of fruit being shed may reflect the weather during pollination.  Growers are recommended to take notes on the size and quantity of fruit being shed and compare to weather during pollination and thinning.

Obliquebanded leafroller
Obliquebanded leafroller (OBLR) are beginning to hatch in the southern half of the state.  Larvae are small and green 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, is a result of the overwintering generation not being controlled; may result in high population for second generation.  These larvae are offspring from the first flight of OBLR this season.  Larvae at petal fall and first cover overwintered 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, in some instances.  Products, i.e., Altacor (chlorantraniliprole) or Delegate (spinetoram), applied for codling moth, except granulosis virus and mating disruption, should provide adequate control of OBLR.  Beneficial insects should also aide in suppression of this pest.  Second generation larvae can be more problematic and more difficult to control then first generation OBLR.  High populations may cause damage to fruit and significant damage to terminals on young and non-bearing trees.  It is recommended to scout and treat the larvae during this generation rather than waiting to treat second generation larvae in mid-August and early September.

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.

Note: Neonicotinoids, i.e., Assail (acetamiprid), have low rainfastness and does not have activity on OBLR.  Altacor, Belt (flubendiamide), Delegate, Entrust (spinosad), Exirel (cyantraniliprole) are options that will offer management of OBLR.  Delegate and Altacor the most resistant to rain.  Bt (Bacillus thuringiensis) products work well on OBLR but not well on codling moth.

When to recover for codling moth?
Base the decision to reapply codling moth (CM) insecticides using degree day accumulations from biofix and trap captures following the date of the first insecticide application.  Continue to closely monitor degree days and trap captures until 650-700 DD from biofix to determine the flight timing of a large cohort of moths.  Most flights should occur by 700 DD.

Reapplication threshold
Look at the trap captures since you applied the first application and disregard counts from the first seven days after the application.  Eggs laid in first seven days will hatch in the second seven days after application.  Then count 250 DD after treatment to determine if another application is required at 14-17 days.  Checking traps more than once per week will allow more accuracy when determining to treat a cohort.  Note how many CM are alive when you check traps.

High rate of Altacor has been found to be effectiveness for up to three weeks with no rain.  A high rate of Delegate will not provide protection past 14 days.  Lower rates will be effective, but for a shorter period of time.  Rate is also a function of pressure.  If you are treating eight moths per trap, could get good control with a middle rate, on the other hand if the cohort is 30-40 in a trap, then the high rate is required.

Note: it is advised to test the pH of spray water multiple times a year.  Pesticides can rapidly degrade if pH is not within acceptable range.