May 10, AppleTalk Conference Call

 AppleTalk Conference Call Summary
Tuesday, May 10, 2016, 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments,

May 10th Call download: Click Here

Tree Phenology
Trees are currently in full bloom Chippewa, Eau Claire and parts of southeastern WI.  Many locations in southern Wisconsin, Northern Illinois and the upper Mississippi River Valley are now at petal fall.  In the Galesville, WI area Zestar are reported at 8 mm, McIntosh at 6-7 mm and Haralson at 5 mm.

NEWA Station Location Degree Days Base 50°F Primary Scab Ascospore Maturity
Woodstock, IL 252 99%
Gays Mills, WI 256 94%
Lake City, MN 254 67%
La Crescent, MN 242 94%
Elgin, MN 244 90%
Hastings, MN 263 57%

Table 1. Degree-day accumulation and primary ascospore maturity, January 1 to May 11, 2016

Captan phytotoxicity reminder
Captan phytotoxicity can result from complex tank mixtures, especially when mixed with single-site fungicides, e.g., Fontelis (penthiopyrad), that are compounded with petroleum distillates or other ingredients that promote excessive wetting or uptake.  Although complex mixtures of captan + single-site fungicide + insecticides + nutrients may be appealing during petal fall and first cover sprays, they should be avoided to reduce injury.  Make tank mixtures with captan as simple as possible.

For more information and photos see, Feeling the Burn! Chemical Injury on Apples Following Tank Mixtures of Captan, Single-site Fungicides, and Adjuvants, New York Fruit Quarterly (pg. 11-14)

Organic growers should also be aware these symptoms can express themselves when liquid-lime sulfur and sulfur are applied, as these can cause similar fruit-finish issues.

Thinning weather
The basic weather parameters which influence thinning are temperature and cloud cover.  On days that are cloudy and warm, there is high stress and there will be a greater thinning response.  When it is sunny and cool, tree stress is low and there will be less of a thinning response.

The Apple Carbohydrate Thinning Model can provide utility when determining thinner rates and application timing.  The general carbohydrate balance the model calculates has been found to correlate well with tree sensitivity to natural drop and with sensitivity to chemical thinners.  Cool sunny periods of good carbohydrate supply leads to reduce natural drop and less response to thinners.  Cloudy hot periods give carbohydrate deficits and lead to stronger natural drop and stronger response to thinners.

The carbohydrate models does not apply during bloom or petal fall.  Fruit must be actively growing before we apply the model.  Since carbohydrate demands do not influence thinning at bloom or petal fall, it makes these periods a relatively safe time to begin thinning, compared to when the fruit are between 6 and 18 mm in size.

The carbohydrate model is described in detail at, for more information

Learn even more about the carbohydrate model:

Apple scab
Current NEWA models suggest we are nearing the end of primary ascospore release.  However, some locations still have significant amounts of primary scab ascopores to be released.  Our recent weather patterns have included cycles of five to seven days of dry weather followed by significant wetting events 24 to 48 hours in length, with cool weather and slow drying conditions.  This pattern has allowed for primary scab ascospores to mature and then be released during these rain events and are long enough to cause scab infections.  Mature spores are released at the beginning of a rain event and the infection occurs when drying time is long enough to allow scab to penetrate into the leaf tissue.  John Aue did find a small lesions last week that he suspect may be scab, it typically requires 14 to 21 days for scab to become visible depending on temperature conditions.

The amount of rainfall will influence timing and need for reapplication.  Studies from Michigan State indicate that after one inch of rain, we lose 50% of our fungicide and insecticide coverage.  If we consider both fungicide loss and unprotected tissue from rapid-leaf growth, reapplication of protectant fungicides will almost always be advised after one inch of rain.

Powdery mildew
Petal fall is the critical time to protect against powdery mildew infections on new shoots and fruit.  This week’s cool and wet weather is not conducive to powdery mildew infections.  Growers reapplying a fungicide for scab may not need to apply a fungicide specifically for powdery mildew, e.g., sterol inhibitors (DMIs) or sulfur, at this time.  Powdery mildew infections are more of a concern during periods of warm dry weather.

Cedar apple rust
John collected eastern red cedar (Juniperus virginiana) leaves with cedar apple rust (CAR) or quince rust lesions in a glass jar, sprinkled with a little water and revisited after 15 minutes and noticed that the previously dry galls had swelled in size.  The short time it took the galls to transition from dry to swollen suggests that they only need a little water and humid conditions to quickly produce spores.  Infections occur during long-wetting events with little rain.

CAR 1  CAR 2

Photo 1. Galls on red cedar before and after spore release.

Cedar apple rust cannot spread from apple to apple or from red cedar to red cedar.  The fungus must go through the two-year life cycle, alternating between hosts.  The infection period for CAR is between tight cluster and first cover.  Spores can be carried long distances, i.e., 3-5 miles, yet the majority of infections occur when infected eastern red cedars are within a few hundred yards.  Spores that land on young apple tissue may germinate and infect if a film of water is present for an adequate amount of time.  Symptoms appear one to two weeks after infection.  EBDCs applied from tight cluster to first cover provide good control when applied as a protectant, but offer no post-infection activity.  However, we have still observed CAR infections in orchards using the extended spray schedule of EBDCs through petal fall.  Susceptibility of cultivar and proximity to infected host will influence disease pressure.  Unlike scab, rusts require and alternate host and inoculum is not reflective of how much rust was in your orchard last year.

For more information visit and table on temperature and moisture requirements for CAR periods:

Codling moth
The first codling moth (CM) capture has traditionally been around petal fall or 180 DD, base 50°F, and pheromone traps should be hung as soon as possible.  The long-life lures (CM L2) are active for eight weeks, the standard-lure (1x) need to be replaced after three to four weeks.  Hang CM pheromone traps in the upper third of canopy.

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.  Damage caused by OFM is very similar to CM damage.  OFM lures will also attract lesser appleworm (LAW); OFM has three flights per season, first flight can begin as early as pink.  LAW flights correspond with CM.

Codling moth fly between 6-11 PM and will not fly when wind is in excess of 3 mph, temperatures are below 62°F or if it is raining.  As orchards enter petal fall, and CM flight parameters are met begin checking traps every several days to determine an accurate biofix.  Biofix is our first sustained flight, where we capture moths multiple days in a row.  Begin keeping track of degree days accumulated from biofix.

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:

Spring lepidoptera
Bacillus thuringiensis (Bt) products, e.g., Agree, Deliver, Dipel, applied during bloom will reduce incidence of spring lepidoptera, e.g., green fruitworm, obliquebanded leafroller, redbanded leafroller, spring cankerworm feeding on blossoms and fruitlets through petal fall.  Cool temperatures this week are not conducive to an application of Bt.  If spring lepidoptera need to be controlled, and plum curculio is not a concern there is no need to apply a broad-spectrum insecticide, e.g., Avaunt (indoxacarb).  A lower risk insecticide such as a spinosyn, e.g., Delegate (spinetoram), Entrust (spinosad), or diamides, e.g., Altacor (chlorantraniliprole), Belt (flubendiamide), can be applied at petal fall.  If a spinosyn or diamide is applied at petal fall, the same insecticide must be used for first generation codling moth.

Plant bugs
Tarnished plant bug (TPB) and mullein plant bug (MPB) are native plant bugs that can cause feeding damage to blossoms and fruitlets.  TPB feeding damage aborts developing flowers, and can cause some damage to fruit.  If Avaunt is applied at early petal fall for plum curculio it will also control TPB.  Frequent mowing of the orchard floor can increase injury to fruit because TBP and MPB are pushed into the canopy.  If high populations are observed, mowing prior to the petal fall spray will push them into the canopy where insecticide applications will contact them.

Note: Mullein plant bug has recently hatched, and can be seen with the naked eye as tiny white specks on leaf surface.  If MPB hatches before bloom it can cause similar damage to TPB.  If MPB hatches during bloom or petal fall it will feed on mites other insect pests.

White apple leafhopper
Begin scouting for first or second instar white apple leafhopper (WALH) on the bottom side of leafs.  These small nymphs can be seen with the naked eye.

Plum curculio
Plum curculio (PC) emerge around 250 DD, base 50°F, 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.  The temperatures we experienced from May 4-8 in the upper 60s to 80s F, were likely enough to get PC moving out of their overwintering sites.  PC are primarily nocturnal and the entire population does not migrate into the orchard at the same time and fruitlets become susceptible to egg-laying when they reach 5 mm.

The current forecast does not show temperatures that will speed up migration into orchards.  Growers should begin scouting the orchard borders and interiors when early-sizing cultivars reach 5 mm.  Due to cool temperatures, a perimeter application may be all that is needed at this time if injury is found on the edge, but not the interior of blocks, or to prevent migration of PC into the orchard.  Plum curculio need to be in the tree and consume the insecticide, e.g., Avaunt (Indoxacarb), Actara (thiamethoxam), for control.  If the weather is too cool following an application this may not occur.  Note: If Sevin (carbaryl) is applied for thinning, this will also suppress plum curculio activity.

We can use a degree day model from 95% McIntosh petal fall to predict the end of PC migration from overwintering sites.  It is expected that after 308 degree days, base 50°F, PC will no longer be moving into orchards from overwintering sites.  If no additional injury is found at this time, insecticide applications for this pest can stop.

Organic orchards have the option of applying Surround (kaolin clay) to the orchard at petal fall.  Another strategy is to leave trap rows of early varieties, without Surround, that would be targeted with an insecticide, e.g., PyGanic (pyrethrins).  An insecticide can be applied during warm nights when PC are active.