June 20, AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, June 20 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 20th Call Stream: CLICK HERE

-The Organic Fruit Growers Association is hosting a summer field day on Thursday June 22 on implementing management systems for diversified fruit at Blue Fruit Farm in Winona MN, https://www.organicfruitgrowers.org/events-1

-Spotted Wing Drosophila (SWD) alert for cherry and other small or soft-skinned fruit that are ripening, https://fruit.wisc.edu/wp-content/uploads/sites/343/sites/36/2017/06/Wisconsin-Fruit-News-vol2i5.5-Invasive-Supplemental-.pdf

-Why are the strawberries so small this year? June 13 2017 article by Michigan State University Extension and MSU Department of Horticulture, http://msue.anr.msu.edu/news/why_are_the_strawberries_so_small_this_year

-Scaffolds Fruit Journal, June 12 2017, FIELD DAYS – What’s New in Insect Pest Management for Organic Apples – hosted by NOFA-NY (page 4), http://www.scaffolds.entomology.cornell.edu/2017/SCAFFOLDS-6-12-17.pdf

-Brown marmorated stink bug (BMSB) – if in county reporting presence in 2016 be vigilant and set traps, https://fruit.wisc.edu/wp-content/uploads/sites/343/sites/36/2017/06/Wisconsin-Fruit-News-vol2i5.5-Invasive-Supplemental-.pdf.

Black rot and white rot
After primary scab season ends, it is common for growers to extend the intervals between their summer fungicide sprays. The length of the interval between summer fungicides in either organic or IPM scenarios should reflect pressure from a variety of summer diseases, e.g., black/white rot, sooty blotch & fly speck and bitter rot.  Where pressure from apple scab is high, extending fungicide intervals may not be possible.  The pressure from these pathogens may dictate protective sprays independent of the threat of secondary scab.  Continuing to apply a low rate, e.g., 2-3 lb./acre, of captan will offer protection against black/white rot and summer diseases.  If scab is present continue using captan and do not use single-site fungicides for management of summer diseases or secondary scab management.

If limbs or trees infected with black or white rot are removed they need to be removed completely from the orchard and destroyed. Black and white rot are decomposers and removing pruned limbs to edge of orchard is not enough to remove inoculum from orchard.

Sooty blotch and fly speck (SBFS) management
The first model for SBFS was developed in 1995 by Brown and Sutton model, and tracked leaf wetness hours greater than 4 hours starting 10 days after petal. The threshold to start treatment began approximately at 220 hours of leaf wetness. Newer models now account for better technology to monitor leaf wetting and new advances in the science (McManus & Gleason) which suggest using the accumulation of relative humidity hours are a better prediction of SBFS infections in our region.

We begin monitoring these wetting events at petal fall, because it is at this time, the first influx of spores are released from wood lots, e.g., raspberries. This typically occurs during first cover when scab fungicides are still be applied. After about 175 hours of leaf wetness, sporulation will occur and result in the second spore release. This can happen between three and 11 weeks post-bloom, with an average of seven weeks post-bloom. It is important to apply a fungicide for summer disease at this time. Follow the first application with a protectant program. The reapplication interval following the first application is dependent on rainfall and weathering of the material. A 2-3 lb. rate of captan is greatly reduced after two inches of rain or 14 days, higher rates may offer added protection.

McManus’ research on summer disease focused on the development of a forecasting model for the upper Midwest. Relative humidity (RH) was used rather than leaf wetness hours (LWH) to predict infection periods. It was found that 192 hours of RH above 97% was a better predictor than 175 hours of leaf wetness for our region. During the summer, dew usually contributes to more wetting hours than rainfall. Within the tree canopy, RH is more stable. Regardless of research Dr. McManus recommends using LWH because the instruments are more precise. It is important to place the leaf wetness plates within the canopy to accurately record LWH.

In addition to captan and Topsin (thiophanate-methyl), the SDHI, strobilurin and DMI fungicides may be used for SBFS. When apple scab is not a problem, these can be attractive because of their ability to also manage black rot and bitter rot.  The potential for SBFS to develop resistance to these single-site fungicides is minimal because new spores are coming in from outside the orchard and disease is really a complex of more than 50 different pathogens. If apple scab is present, it is essential to avoid exposing these single-site fungicides to secondary scab populations.  If you find yourself in this second scenario this season, it is recommended to apply high rate of captan or captan + Topsin.

Petal fall dates and accumulated leaf-wetting hours (LWH) for select locations

  • May 4: Woodstock IL, 198 LWH
  • May 6: Poplar Grove IL, 226 LWH
  • May 12: West Madison WI, 172 LWH
  • May 14: Gays Mills WI, 176 LWH
  • May 12: La Crescent MN, 161 LWH
  • May 15: Elgin MN, 124 LWH
  • May 14: Lake City MN, 149 LWH
  • May 14: Hastings MN, 140 LWH

Nutrient deficiencies in young trees
Younger trees growing rapidly will begin to show nutrient deficiencies, e.g., manganese and potassium.  It would be beneficial to look up visual symptoms of nutrient deficiencies before attributing it to another source.  When collecting leaf samples for nutrient analysis, a block of trees expressing visual nutrient deficiencies should be collected as a separate sample.

Codling moth (CM)
First generation codling moth activity is nearing its peak egg hatch and we can expect to begin seeing signs of injury, if any codling moth escaped due to wash off or poor spray coverage.  Where mating disruption is used, consider presence of alternate hosts, e.g., shagbark hickory, that could have allowed mated females to enter the orchard edge and lay eggs.  In blocks without mating disruption, consider where you had high captures and look on the outside rows of these blocks for early injury.  Any fruit within the tree with any damage, e.g., russetting, hail, scab, green fruitworm injury, anything that alters the surface of the skin of the fruit could be more susceptible to codling moth injury since the insecticide does not adhere as well to this surface as clean-green skin of the fruit.

The family of moths known as Tortricidae include all leafrollers, oriental fruit moth (OFM), lesser appleworm and codling moth (CM). Where mating disruption for CM or other pests is being used, need to keep monitoring these other pests that can cause internal damage.  If you are not applying a larvacide, we need to keep our eye out for injury from these species.

Apple maggot
Sentinel traps should be set or go up.  Apple maggot have been caught as early as June 15. If you have had issues with AM or have early ripening cultivars, e.g., Lodi, yellow boards or red spheres for AM monitoring can begin to be deployed. Yellow boards can provide an early warning system by attracting AM 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. It is advised to set up a minimum of three traps per ten acres at the beginning of July; trap density should gradually increase to one trap every 200-300 feet along the orchard perimeter, 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.

Secondary insect pests
A unique characteristics of many of our secondary pests is they are not intimately associated with apples and may often have a much broader host range.  This creates the potential for short-term yet explosive interactions with our crops.

Rose chafer, John has seen many more of these than in his entire lifetime. They are related to other scarab beetles, e.g., Japanese beetle and has been seeing them in many new places.  The injury from them looks the same as Japanese beetle, https://datcpservices.wisconsin.gov/pb/pests.jsp?categoryid=37&issueid=281

Japanese beetle (JPB) activity is right around the corner and JPB were recently found feeding on terminal shoot of Honeycrisp in northern Illinois this past Monday.

Two-spotted spider mites (TSSM) populations are appearing well over threshold. This is not normal for mid-June.  They don’t winter on trees and are active on broadleaf weeds in alleyways and under the tree’s dripline.  When these weeds mature and dry, TSSM will climb up the trees.  It is not clear what is driving them up into the trees.  The action threshold is very low in June.  Stay vigilant with mite counts on susceptible cultivars; TSSM are more difficult to count and see compared to European red mites. It does not take much loss of chlorophyll right now to create problems.

Potato leafhopper are growing in a lot of second-growth alfalfa. Depending on where your orchard is located, there may be big influxes.  Continue to scout growing terminals of non-bearing trees.  Adults will likely be laying eggs and it is the nymphs which cause leaf curling and injury to the growing terminals.

Rosy apple aphid have now moved onto other hosts, though we may still find signs of their activity on fruit spurs and terminals.  First colonies of apple grain aphid or green apple aphid/spirea aphid are establish.  We are seeing gall midge larvae, minute pirate bug, and lady beetle larvae aphid predators on plantings that have not been treated with neonicotinoids.  Pictures of these beneficial insects were circulated in a separate email several weeks ago.

Wooly apple aphid (WAA) colonies are quiet small and blocks treated with Movento have not shown much WAA activity.  Growers who treated WAA with the insect growth regulator Esteem (pyriproxyfen) should note this is slow acting and might not see effects yet on WAA. The Ontario IPM program has developed some additional guidelines for monitoring green aphids, http://www.omafra.gov.on.ca/english/crops/facts/greenaph.htm

Obliquebanded leafroller (OBLR) trap data should be used to schedule scouting terminals 10-14 days after peak flight where you look for injury to terminals or small larvae. Since non-bearing trees are often managed differently, this is a good place to look for OBLR activity.  Larvacides applied for codling moth will manage OBLR and if not applied to non-bearing trees, larvae will likely be there feeding.  If you see anything wrong with a tiny leaf that has just emerged, it is likely OBLR that could be hatching this week.  The first instar is very difficult to see, even with a 10x hand lens.  This year we are observing that flights were short and intense.  Even though there is no threshold based on trap captures.  Trap catches are reflective of pressure e.g., five OBLR v. 50 OBLR, suggest significant pressure in the later.

Dogwood borer (DWB) are active and John has identified significant flights in other orchards, but have also seen plenty of other clearwing moths in DWB and lesser peachtree borer (LPTB) traps. To properly identify borer pests, we can use the wing length to get a general idea if it is the right species, since the pheromones are not species specific and it can be easy to miss identify them.  Use a caliper, ruler or tape, to measure the forewing.

Clear-wing borer Forewing length (mm), approximate
Dogwood borer 9
Lesser peachtree borer 12
Greater peachtree borer 13.5 – 15