July 28th AppleTalk Summary

AppleTalk Conference Call Summary
Tuesday, July 28, 2020 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 or send to Josie Dillon, jdillon@ipminstitute.org.

July 28th Call Stream: CLICK HERE


Regional update

Location Degree Days from January 1st

 (Base 50°F)

2019 DD from January 1

(Base 50°F)

Petal fall Date Leaf Wetting Hours (LWH) from Petal Fall 2019 LWH from Petal Fall Codling Moth Biofix Date Degree Day Accumulation from Codling Moth Biofix (Base 50°F)
Eau Claire, WI 1491 1441 May 28 212 250 June 1 1131
Gays Mills, WI 1583 1552 May 27 130 230 May 24 1342
Hastings, MN 1622 1618 May 27 137 June 1 1264
Rochester (Ela), WI 1488 1422 May 31 146 238 May 24 1290
Trempealeau (Ecker’s), WI 1595 1541 May 26 197 185 May 24 1334
Verona, WI 1577 1541 May 29 161 161 May 24 1363

Table 1. Degree-day accumulations as of July 27, 2020 using data reported by Cornell NEWA Network.

This week, highs will be in in the 80’s and lows will be in the 60’s. The differences in leaf-wetting hours between 2019 and 2020 highlight the variability in rainfall across the region.

Summer Apple Nutrition and Pre-Harvest Stop-Drop Sprays: Recap of Brian Smith’s article in WI Fruit News: https://fruit.wisc.edu/2020/07/22/summer-apple-nutrition-and-pre-harvest-stop-drop-sprays/

Dr. Brian Smith references the most important aspect of tree nutrition is having adequate soil moisture and describes this as maintaining soil moisture at 50-70% of field capacity. This is very relevant as all the nutrition points we discuss in AppleTalk are dependent on adequate soil moisture. Not everyone has irrigated trees, but water can be delivered to these trees, even if it is labor intensive, do it.

Field capacity is an old term in soil science and is somewhat vague. The textbook definition refers to field capacity as the amount of moisture soil can hold after excess water, i.e., water the soil cannot hold, has drained away. The field capacity Brian is suggesting we target is a middle range of soil moisture, where there is no free water and not so dry that roots cannot pick up moisture. Even if there is still some water in the soil, if the soil is too dry, roots may begin to die. A foot of soil can hold upwards of two inches of rain that trees can access. The lighter or sandier the soil, the lower the water-holding capacity and as soil-organic matter, silt, or clay content increases, so does the soils water-holding capacity, which could increase above two inches.

The most easily assessed metric for assessing water stress is to use the evapotranspiration (EVT) models available via local NEWA sites. Considering the EVT rates over the last month, a significant amount of water has been removed from the soil. It is worth the investment in soil tensiometers and other tools that will help assess soil moisture. As a reference point, corn growers often discuss needing an inch per week. This is likely a minimum amount for fruit trees and could require more depending on EVT rates. Therefore, if we have not had four inches of rain in July, the trees are likely under significant tree stress.

Questions on soil moisture and fruit drop: Will starting a water wagon regime help to stop premature fruit drop?

  • Yes, frequent watering should help to prevent this early drop. Additionally, fruit low in Mg or high in K or B, are more likely to be at risk of dropping.

Bitter pit
Calcium (Ca) is important and necessary to maintain fruit quality. The majority of Ca is absorbed into the fruit during the cell expansion phase lasting from petal fall to the end of July (~50 days after petal fall). After this period, the xylem in the fruit losses efficiency, especially in the calyx end. Calcium does not easily move into the fruit from the soil and is relatively immobile within the tree. Concentrations can vary between foliage, fruit, and soil.

Note: Foliar Ca levels will be greater than what is in fruit because leaves have a high transpiration rate and accumulate more Ca material. The following factors can influence Ca levels and incidence of bitter pit: Nutrient imbalances with nitrogen (N), potassium (K) and boron (B), soil moisture levels and fruit size.

 Strategies for reducing bitter pit

  1. Submit foliar, fruit and soil samples for nutrient and pH analysis. It is recommended to test samples for all available macro/micronutrients as many complex interactions exist. For example: an excess amount of magnesium (Mg) or potassium (K) will compete with Ca for uptake.
  2. Keep soils adequately hydrated throughout the growing season.
  3. Reduce excessive vegetative growth. Reducing vegetative growth will redirect the transport of Ca from foliage to fruit. Apogee (prohexadione calcium) can be applied to curb vegetative growth. The pre-harvest interval for Apogee is 45 days.
  4. Lite crops or excessive thinning can result in large fruit. Calcium levels can be diluted in large fruit; Ca concentrations typically vary from stem to calyx end (location where bitter pit symptoms are most pronounced), excessively large fruit usually have exacerbated symptoms.
  5. Calcium sprays can begin at petal fall and continue to end of August; up to six applications may be necessary. Coverage is important – Ca must contact fruit to be effective. The recommended rate is one-to-two pounds of Ca per 100 gallons of water. If visible symptoms of bitter pit are present, it is not too late to apply Ca to prevent further injury.

Plant growth regulators
Blush (prohydrojasmon) can enhance color development, especially on the backside of the fruit that does not color well. Blush does not accelerate ripening. Some growers prefer to not apply blush to Honeycrisp, so pickers can use visual cues based on harvest parameters.

ReTain (AVG-HCl) reduces amount of ethylene produced to prevent the abscission layer from forming between the fruit stem and spur. The general recommendations for use of ReTain on Honeycrisp are to apply a half rate 30 days before harvest. Other recommendations would allow a ¼ rate to be applied within 14 days of harvest or to include NAA, e.g., Fruitone, at 10 PPM with the ¼ or ½ rates. Honeycrisp does not produce a lot of ethylene and therefore is more sensitive to Retain. This means that a “half rate” is essentially a full rate. The use of Retain with NAA can extend harvest another seven to ten days. The combinations can continue to promote ripening and inhibits separation at the abscission zone.

It is not recommended to apply these materials in complicated tank mixes and to also read product label for compatibility statements. When first using these materials experiment with application timing and rates for specific varieties to help determine what works best for your orchard.

Insect management
European red mite problems have been very minimal in the last half of June and first half of July. In the last seven days populations are becoming more visible. The August threshold increases to an average of 7.5 mites per leaf and we don’t want mites to blow up in mid-August, so now is an important time to determine if populations are increasing or reaching thresholds by comparing baseline measurements taken at the end of June or early July.

If bronzing is occurring while mite populations are below threshold, action is required to prevent further economic injury to the plant. This happens when a population of predators have remained active long enough to keep populations below threshold, yet enough mite feeding has occurred to cause leaf bronzing. Once leaf bronzing occurs, economic injury is happening to the tree and a miticide should be applied. This scenario is referring to what we call mite days, where the duration of mite activity is just as important as the actual population. This year may be an interesting one regarding mite days, since we have not had mite populations early on. If we reach threshold and still cannot see significant damage on any leaves, we may be questioning whether we need to make a miticide application.

Second generation codling moth
Most locations have now accumulated the 1000 degree days between first generation codling moth biofix and second-generation biofix. Not all locations are reporting a biofix and sometimes can come as late as 1200 DD from the first generation biofix. Most of the time trap counts drop off and we can see a distinct gap in the flights. However, for some growers with high pressure, the flights never drop off to zero. This is when we need to use our degree days to decide on when a flight is now part of the second generation and to switch insecticide modes of action.

Unlike in the spring, insecticides targeting second generation codling moth should not be delayed past 250-degree days (DD), base 50°F, from biofix, which takes 10-12 days of degree day accumulation. We can delay in the spring, because adverse weather conditions and rain during the first flight often reduce the fecundity of female codling moths. In late summer, we have excellent weather for codling moth mating and can expect a strong flight to require treatment at 250 DD, base 50°F. Peak egg hatch for the generation will likely not occur until two to three weeks into August and right up until Labor Day. On average, 650 DD accumulate during the month of August.

The treatment threshold is five moths per trap and after a biofix has been established, blocks that do not go over threshold may not require treatment. This could be helpful as we near harvest and allow for spot treatments only of blocks which caught five moths or more in a weeks’ time. While recording trap numbers are important, codling moth injury to fruit is also a great indicator of potential second-generation population presence in the orchard.

One larvicide application, no matter what product, will not carry you through August and into the first week of September especially if significant rain occurs. If rain is forecasted, do not apply the highest rate of the material even if it has been three weeks since the last application. Apply a low application and follow up if need be. Keep in mind that Altacor (chlorantraniliprole) has a minimum interval of 10 days. Excluding neonicotinoids, at this stage it is a good idea to incorporate a sticker with an insecticide application. If growers are catching 5-15 moths, this is not a massive threat. John considers catching 20+ moths to be more of a threat in terms of urgency to apply an insecticide.

Dogwood borer
How do we distinguish DWB and lesser peach tree borer from other clear wing moths?

Wisconsin has 30 different species of clear wing moths that share some of the same pheromone components as dogwood borer. When monitoring DWB with a pheromone trap, the mix of pheromones does make a difference. Over the last two years the Trecé lures seem to be catching a lot more dogwood borer and a lot fewer of other species. Dogwood borer can be defined by the following characteristics:

  • They are smaller than most other clearwing moths caught in a pheromone trap and will have a blue/black translucence.
  • Yellow banding is very common and may be a faint yellow, almost white in appearance.
  • The DWB moths have clear wings with two black stripes on their wingtips.
  • Lesser peach tree borer is very similar in appearance to DWB and has many other species in similar size and are harder to identify. According to a Penn State Extension bulletin, are smaller than LPTB with a wingspan of ¾”. Therefore, clearwing moths with a similar appearance of DWB, but that are larger, could possibly be LPTB.

Spotted lanternfly discussion with Shahla, Werner, Plant Protection Section Manager
Wisconsin Department of Agriculture, Trade and Consumer Protection
The spotted lantern fly (SLF), (Lycorma delicatula), is a planthopper native to Asia (China, India, Japan, Vietnam) introduced into South Korea and first found in the United States in Pennsylvania in 2014. The SLF has now been found in six states including: Delaware, Maryland, New Jersey, Pennsylvania, Virginia, and West Virginia. The SLF has been detected in New York, but not considered established

The SLF are weak fliers and can only travel only short distances on its own, by walking, jumping, or flying. The spread of SLF to other regions is achieved most likely by egg masses that have been laid on nursery stock, firewood, shipping containers, bricks, stone, cars, trucks, trailers, rail cars, and other materials moved by humans around the country.

Host Plants
There have been zero observations of damage to hops, fruit trees or hardwoods in Pennsylvania. The adult SLF prefers to feed on grapevines (Vitis vinifera) and tree-of-heaven (Ailanthus altissima). The most significant losses to agricultural crops have been in grapes and have required Pennsylvania growers to increase frequency of insecticides from three to ten applications per year. Tree-of-heaven is another preferred host and is a restricted invasive species in Wisconsin, most prevalent in SE WI.

Nymphs have a wider range of hosts and feed on:

  • Apples
  • Stone fruits: cherries, plums, peaches, nectarines, and apricots
  • Ornamental nursery plants: especially roses
  • Grapes
  • Hops
  • Hardwoods: maple, walnut, oak, and poplar

Spotted lanternfly is a sap feeder and neither nymphs or adults feed on foliage or fruit. Rather nymphs and adults feed on vascular tissue of branches, stems, and vines, where they will remove a large amount of sap from the plants vascular system that ultimately results in the plants decline and mortality. It is not known if SLF transmits or vectors any plant diseases. This feeding reduces the plant’s ability to photosynthesize food, weakening the plant and eventually contributing to the plant’s death. These feeding sites leak sap after SLF wounding, causing a fermented odor. The SLF excretes honeydew during its feeding, which promotes black, sooty mold growth and attracts pests. The honeydew may be observed on leaves and fruit, even though feeding takes place on the woody tissue of the plant.

In Pennsylvania, where SLF is most established, there has not been significant feeding on fruit trees and while adults may swarm orchards in the fall, no leaf curling or sooty mold from feeding has been observed in PA orchards to date, although this may change if there are limited suitable hosts.

Spotted lantern fly life cycle and biology
Spotted lantern fly is suspected to only have one generation per year in northern regions and it is unknown if there is a second generation in the southern United States. For example, brown marmorated stink bug only has one generation in WI, but two generations in the mid-Atlantic and further south.

The spotted lanternfly lays eggs in fall on host plants and may also lay them on any smooth surface. There is no preferred host for egg laying and SLC will indiscriminately lay eggs on just about anything, which is why egg masses are found on rail cars and shipping containers. The eggs hatch in late spring and early summer, and the nymphs start feeding. Egg masses are between one and two inches long and look waxy and gray at first, then become hardened and cracked as the season goes on. After hatching, individual eggs are noticeable, looking like four to seven rows of dark brown “seeds”. The wingless nymphs that emerge from eggs are black with white spots. Later stage nymphs are red and black with white spots. The nymphs develop into adults after late July and continue feeding and may move onto other hosts, e.g., SLF adults do not necessarily remain on the same host plant as the nymphs. The SLF needs 2,100 GDD (Base 50°F) to complete their lifecycle, where adults are observed July 23-Nov 12. The SLF adults have wings that are pinkish purple with black spots when folded. When outspread, the upper wings are white to tan, and the lower wings have distinctive red, black, and white markings. The tips of both sets of wings are dark brown to black. Adults are 1 inch long and 1½ inch wide when wings are outspread. Adult females have yellow coloring on sides of their abdomen when they are mated.

  • Note: BMSB 2nd and 3rd instar nymphs resemble the early instars of SLF and may be confused as look-alikes. These life stages may occur at roughly the same time during the WI growing season as well.

States with exterior SLF quarantines:


  • No pesticides currently registered in Wisconsin specifically for SLF.
  • A pesticide must be labeled for a use site, such as apples, but the pest itself does not need to be listed on the label for a grower to use a pesticide against it.
  • https://www.kellysolutions.com/WI/ for WI registered pesticides.
  • In states where spotted lanternfly is present, research has found that dinotefuran is effective (oil/bark/trunk treatments for adults and eggs).
  • As many as 10 sprays per season have been needed to control SLF in vineyards.

What is DATCP doing?

  • Monitoring for SLF with traps and visual Tree-of-Heaven, orchard surveys. There is no known pheromone or attractant.
  • Conducting outreach via social media, trade shows, mailings, meetings with producers and other targeted industries (railroads, transportation industries)
  • Considering potential regulations, based on risk and industry feedback.

 How you can help: