August 10 AppleTalk

AppleTalk Conference Call Summary
Tuesday, August 10, 2021 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM,
Moderator: Peter Werts, IPM Institute of North America; questions or comments,

August 10 Call Stream: CLICK HERE


City State Rainfall Total City State Rainfall Total
White Bear Lake MN 4 Mt. Horeb WI 7.1
Shafer MN 5.7 Verona WI 9.1
Afton MN 3.8 Brodhead WI 6.2
Hastings MN 3.9 Brighton WI 3
Chippewa Falls WI 10.7 Rochester WI 4.6
Eau Claire WI 11.3 Genoa City WI 6.5
Lake City MN 6 Woodstock IL 11
Dakota MN 14.3 Harvard IL 9.7
La Crescent MN 15.5 Poplar Grove IL 2.6
Trempealeau WI 12.8 Mequon WI 10.1
Gays Mills WI 17      

Table 1.  Rainfall totals between June 1, 2021, and August 9, 2021 from Cornell NEWA system. Find your local station today: Historical average rainfall between June and August is 12”.

Regional update
After heavy rains over the last five days, weather across the region will remain hot and humid for the next few days before cooling off with highs in the upper 70s over the weekend.  Cooler nights should help fruit put on good color and the recent rainfall for some will be good for fruit sizing.

Codling moth
The timing of our second-generation codling moth flight continues to be less predictable than first generation with biofixes occurring as early as July 9 and as late as July 25. There are a few instances of second generation biofixes in early August. The range in these dates reflects how well codling moth was controlled during first generation and when or if there were any wash-off events or missed sprays during the first generation.  For example, an early July biofix correlates to survival of moths earlier during the first generation, whereas a later biofix indicates good control early in the generation, but moth survival later during the first generation. Generally, the degree days from first-generation biofix are less important and especially when there is successful reproduction within the orchard from the 1st generation. Orchards that experienced an early second-generation biofix are between 600 and 700 DD, just passing peak egg hatch.  Where the biofix occurred later, these orchards are anywhere between 350 and 500 DD, or just entering peak egg hatch.  All growers should be monitoring codling moth traps into the first week of September and should remember that any moths that fly after August 20th, will be hatching out in early September.

Timing August cover sprays
Many growers are considering the need to reapply after the recent rainstorms and with the possibility of these storms dropping intense rainfall in a short amount of time.  The need to maintain long-lasting residues for 10 – 14 days is largely dependent on your target pest. Codling moth, lesser appleworm and obliquebanded leafroller require sustained pesticide residue to manage these pests and should be reapplied after rains to maintain the effective residue.  Conversely, insecticides may only need to be active for 12 hours to a few days to effectively suppress populations of Japanese beetle, apple maggot, mites or woolly apple aphid. Fungicide applications for summer diseases and bitter rot may not need to be reapplied immediately after a heavy rainstorm. Once an application of Topsin, Flint or Merivon is applied, the fungicide moves into the plant tissue and eradicates the infection of sooty blotch and flyspeck, or bitter rot. If you are protecting against these diseases with Captan or OMRI products such as potassium bicarbonate or Regalia, these would need to be reapplied after heavy rains wash off residues.  A terpene-based stickers, e.g., Attach or Nu Film P, could improve rainfastness for certain pests including OBLR and Japanese beetle, but would not likely maintain enough residue for codling moth or apple maggot, especially after four inches of rain.

Apple maggot activity has been minimal over the last few weeks, but with the recent rain, there is a good likely hood of growers catching late apple maggot at the end of August that would require treatment. Even if it is unlikely, you would make a late spray, it is really important to maintain trapping into September to prevent any surprises and develop an understanding of what kind of overwintering population may emerge. Where codling moth has been managed using mating disruption or if trap captures have been low, continue to monitor lesser appleworm with either an LAW or OFM lure. OFM is typically not a problem here, but LAW is present. If these numbers are high enough, e.g., ten or more a week, you may want to consider OFM MD next year and should consider a larvacide this year. Note: OFM/LAW are much easier to disrupt than CM.

A note on neonicotinoids: Assail (acetamiprid) is one of our best active ingredients to achieve combined management of apple maggot and codling moth.  However, it is very easily washed off, which is counter intuitive, since we consider that neonicotinoids are absorbed into the fruit.  If Assail is applied for JPB or apple maggot, a half of rain will leave enough residue to manage these pests, however, after half to one inch of rain, a half inch of rain after 7 days, will not leave enough residue for codling moth.

Organic codling moth management
Research trials have found that adding brown sugar and yeast to tank mixes of Virosoft, Madex HP, (Cydia pomonella granulosis virus), similar to adding sugar to improve efficacy of imidacloprid for AM, greatly improves the efficacy of this product.  The research was completed by Alan Knight, USDA Research Entomologist based out of Yakima, WA.  In his trials, Knight mixed bread yeast, sugar with Virus and tested against codling moth and found in both lab assays and field trials it resulted in significantly less damage from codling moth and reduced overwintering moths. The trials used 3 lb. of each material (brown sugar, yeast) per 100 gallons of water.  Organic and conventional growers could consider this if there are late CM, since these products have a zero day PHI.   

Secondary pests
Besides the direct fruit pests, we are seeing some resurgence of various secondary pests, including European red mites (ERM), woolly apple aphids (WAA), San Jose scale (SJS) and Japanese beetle (JPB). These pest populations are often found with various bio-control species predating or parasitizing them, but since temperatures in August are hotter than normal, the pests are completing their life cycles faster and the biocontrol’s are not keeping up, in some instances. Under this scenario growers will need to consider spot-sprays for these potentially very damaging pests where the PHI of the pesticide is compatible with the harvest dates of the affected cultivars.  Please consider the following:

Orchards that used Assail and/or Belay for first generation codling moth management have experienced minimal impact on WAA predator populations and have had nearly 100% of their WAA colonies were parasitized. However, in some orchards, there is not much bio control and if this is the case, it is likely there could be WAA round the stembowl of the apple at harvest and need to manage this August population as early as possible, since it can explode in September.

Brown marmorated stink bug and native stink bugs
This year BMSB has been rather light across the region, though populations generally do not increase until September.  Mid-August is when we begin seeing more BMSB and mostly nymphs are what has been observed. Dane and Rock County in southern Wisconsin have the most established population of BMSB. Injury has already been observed this season in these orchards, with most being on the edge of the block. Native stink bugs are also very common and more widespread through the state.  The injury from native vs. BMSB is indistinguishable and can be confused with cork spot, bitter pit or even hail.

In collaboration with the Wisconsin Department of Agriculture Trade and Consumer Protection, the IPM Institute monitored brown marmorated stink bug (BMSB) in Wisconsin orchards between 2015 and 2020. The spread and emergence of BMSB have been tracked, starting with pyramid traps in 2015 or 2016 and later improving to a two-lure trap. In 2020 traps were set at 30 locations with additional traps at the University of Wisconsin Madison and at CSA community farms and gardens.

The pest has a strong preference for apples, but the host range for BMSB extends to tomatoes, sweet corn, peppers, green beans, woody perennials and has over 300 suitable hosts in North America.

All growers statewide should monitor BMSB with a trap or visually along the perimeter and interior of the orchard during harvest. Unlike many of the other apple pests, BMSB does not settle down at harvest. Growers should order and set up traps along orchard perimeters or in the front yard. Putting traps in the middle of blocks is not advised. Based on emergence patterns, we can expect to find this pest in higher numbers in our homes and buildings for about a season before they pose a more serious agricultural risk. Be aware of BMSB in your packing sheds and homes in addition to monitoring in the orchard.

Insecticide efficacy and performance varies greatly across and within different chemical classes. Imidan (phosmet) has performed poorly in bioassays and field trials against BMSB. The best performance against BMSB has been from the older synthetic pyrethroids, e.g., Brigade (bifenthrin). The neonicotinoids have limited efficacy but can be used. Actara (thiamethoxam) has performed the best, however, its use is limited by its 35-day pre-harvest interval (PHI). There are two newer neonicotinoids called Venom and Scorpion (dinotefuran) with a shorter PHI, but these have only been registered for apples under emergency registration exemptions out East. If BMSB became a problem, these materials will likely become registered for growers in the Midwest.

In addition to monitoring BMSB with traps, growers should scout within 100 feet of the orchard perimeter. When stink bugs find an orchard, they tend to spend several days to a week in the perimeter before moving into the interior of the orchard block. This results in a strong edge effect. When scouting, growers realistically won’t be able to see incision injury from proboscis injury. This will, however, result in a deep cork spot where juice has been sucked out, whereas other insect damage, bitter pit or bruising will be much shallower. When stink bug feeds on an apple, there are often multiple feeding sites. Find more information on distinguishing bitter pit, apple maggot and BMSB damage in MSU’s 2017 article,

Another good resource is This is a national clearinghouse for all the current research on BMSB.

Black stem borer
Remember to monitor the edges of blocks of young trees for two weeks this month.

Fruit size
Most cultivars across region have light to moderate fruit set because of poor return bloom or multiple frost events this spring. Some cultivars may have problems with fruit size, where fruit size is determined by multiple factors, many of which are weather related, from poor pollination to frost damage to heat or water stress during the growing season. In particular, Honeycrisp greatly varies in size and often within the same tree. Some of these small Honeycrisp are now coloring and ripening much earlier than the normal sized fruit on the same trees. Most of the small fruit seem unlikely to achieve market size and while it is tempting to simply attribute these small apples to a lack of water or an excess of heat, evidence from irrigated blocks suggest the fruit were damaged during the spring freezes. It’s also possible the extended bloom that produced this fruit were caused by insufficient chilling hours during late dormancy or from weather stress during last year’s growing season, was causative. It would be helpful if growers could make notes at harvest regarding the fate of these small fruit on the various cultivars affected as that information may help tease out the actual causative factors.

Pre-harvest interval reminder

Product Pre-harvest Interval
Actara (thiamethoxam) 0 – 2.75 oz./acre: 14 Days
2.75 – 5.5 oz./acre: 35 Days
Acramite 7 Days
Altacor (chlorantraniliprole) 5 Days
Assail (acetamiprid) 7 Days
Avaunt (indoxacarb) 14 Days
Captan 80WG (captan) 0 Days
Centaur 14 Days
Sivanto Prime 14 Days
Delegate (spinetoram) 7 Days
Envidor (spirodiclofen) 7 Days
Esteem (pyriproxyfen) 45 Days
Exirel (cyantraniliprole) 3 Days
Flint (trifloxystrobin) 14 Days
Indar 2F (fenbuconazole) 14 Days
Luna Sensation (fluopyram, trifloxystrobin) 14 Days
Merivon (pyraclostrobin, fluxapyroxad 0 Days
Nealta (cyflumetofen) 14 Days
Portal (fenpyroximate) 14 Days
Pristine (boscalid, pyraclostrobin) 0 Days
ReTain (-trans-2-Amino-4-(2-aminoethoxy)-3-butenoic acid hydrochloride 7 Days
Topsin (thiophanate-methyl) 1 Day
Wrangler (imidacloprid) 7 Days

Pesticides and pre-harvest intervals