July 17 AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, July 17, 2018, 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org

July 17th Call Stream: Click Here 

Questions and announcements
The Organic Fruit Growers’ Association also has a Summer Field Day coming up on August 5th in Hutcheson, MN, https://www.organicfruitgrowers.org/.

Now and into early August is a good time to take soil and plant-tissue samples for nutrient analysis. Managing an orchards tree health requires a maintenance program based on the previous years’ analysis. Nutritional insights gathered from samples now are needed to inform corrections made in future seasons because nutrition deficiencies are nearly impossible to correct mid-season. Trees that showed signs of deficiencies should be sampled separately from other varieties showing no signs of deficiencies.

Some growers submit leaf samples several times throughout a season to routinely inform micronutrient applications and trees managed under this practice that showed signs of stress have been able to rebound completely. In addition to adjusting micronutrients, routine tissue-sample analysis can inform applications of boron, zinc or magnesium to tweak tree physiology for calcium uptake and to increase the storage of the fruit at harvest.

Managing bitter pit with calcium
Apples rely on calcium for the formation of calcium pectate, which cements fruit-cell walls to one other in a pectin layer called the middle lamella. Fruit ripening creates ethylene gas that dissolves the calcium pectate and reduces the middle lamella. There is a fixed number of cells in an apple that reaches a maximum early in the season while apples are relatively small. When apples develop further, the diameter of these cells grows, ultimately determining apple sizing rather than the number of cells in each fruit. As the cells expand, more calcium pectate is necessary to bind cells together tightly. A deficiency of calcium pectate can cause cells to become unbonded as they grow.

Second generation codling moth
There are approximately 1000 degree days between the biofix for first and second generation codling moth (CM).  Traditionally we have discussed biofix as a significant biological event where traps catch large amounts of codling moths overnight.  This is easily defined when we have a week with no trap captures between generations. However, the codling moth flight does not necessarily need to reach zero before we begin to count catches as second-generation moths. When counts are low and degree-day (DD) accumulations since first generation biofix exceed 1000, we can comfortably assume second generation codling moth have begun to fly.

Most growers experienced a large flush of moths at the beginning of the season with much lower counts through the remainder of the flight, but this may not occur the same way for our second generation. Second-generation population is dependent on the success or failure of management during the first generation.  When fruit are infested early in the season, they generally stop sizing and remain considerably smaller than healthy fruit. Larvae found in fruit now reflect a management failure from pesticide wash off or a missed spray within the last three weeks, rather than at the beginning of the season.

Good first-generation control should result in low second-generation numbers. However, wash off during the frequent rain events this season may have allowed fruit to be infested. With as small as 0.2 percent infestation, orchards will appear clean yet can still generate high trap counts and significant CM pressure. The second generation is often more difficult to control than the first generation and can easily grow tenfold in population by harvest.

Location Biofix date DD from biofix (Base 50°F) DD from January 1st (Base 50°F)
Woodstock, IL 5/26/2018 1131 1511
Harvard, IL 5/28/2018 1024 1428
Burlington, WI 5/27/2018 1093 1475
Eau Claire, WI 5/28/2018 1058 1459
Gays Mills, WI 5/26/2018 1092 1551
Mauston, WI 5/27/2018 1119 1503
Mequon, WI 5/31/2018 949 1245
Merrill, WI 5/30/2018 928 1248
Richland Center, WI 5/27/2018 1101 1498
Rochester, WI 5/27/2018 982 1498
Trempealeau, WI 5/27/2018 1165 1568
Verona, WI 5/27/2018 1113 1503
Hastings, MN 5/26/2018 1188 1589
La Crescent, MN 5/27/2018 1190 1588
Lake City, MN 5/27/2018 1155 1553

Combined management strategies for codling moth and other pests
Other pests that overlap with second generation codling moth management include apple maggot (AM), potato leaf hoppers (PLH), redbanded and obliquebanded leafrollers and Japanese beetles (JPB). Neonicotinoids make up growers’ first line of defense against AM, PLH and JPB. A second-generation codling moth application such of a larvacide, e.g., Delegate (spinetoram) or Altacor (chlorantraniliprole), can be made in tandem with neonicotinoid applications which target AM, PLH and JPB. An insect-growth regulator can be included, e.g., Intrepid 2F (methoxyfenozide). Note: Intrepid is labeled as suppression only for codling moth, however where infestations are very light this may be an adequate option, if a different mode of action is required.

If CM counts are below threshold and an application for one of these other pests is needed, growers should still tank mix the lowest labeled rate of a codling moth insecticide, especially as larval hatch approaches 250DD from their date of capture. If no second-generation moths have flown, then there is less resistance risk, but most growers will still set a second-generation biofix and target at 250 DD for a cover spray of Delegate or Altacor and combine with ease neonicotinoid spot sprays. Another strategy would be to time cover sprays of materials like Assail (acetamiprid) or imidacloprid that are effective against both AM and CM.

The OBLR will fly in the second half of August and if a neonic is your primary spray for apple maggot and second gen CM, a well-timed Delegate or Altacor in mid to late August will be very important. In 2017 there were late AM and CM that showed up in the fruit, which indicate that CM which flew towards the end of first generation were missed. In some instances, this can result in late season infestations of fruit. If you are concerned about late season codling moth pressure, it is important to save a few insecticides with a short pre-harvest interval.

Exirel (cyantraniliprole), while more expensive, is in the same class as Altacor (chlorantraniliprole) and can be used to manage second-generation CM and AM if neonicotinoids were used against first-generation CM. Exirel will also manage the summer leafrollers too.

Apple maggot: Effective life of maggot sprays
The neonicotinoid class of insecticides has become our primary organophosphate alternative for managing apple maggot.  Unlike pesticides such as Imidan (phosmet) that offer excellent contact mortality against adults,  neonicotinoids are absorbed into the skin of the fruit and act as a repellant or a systemic antifeedant and larvacide. These systemic properties of the neonicotinoids gives the insecticide a long lifespan and boosts rainfastness up to two inches (or one inch if the rain event was within 24 hours of application). Assail and Altacor, for example, can last up to 21 days with very low rainfall. Pesticide rainfastness is much more of a concern for codling moth, , but for apple maggot and Japanese beetle, we may achieve adequate control of these pests even as we reach the maximum of two inches of rain.

Apple insecticide precipitation wash-off re-application decision chart. Expected codling moth control in apples, based on each compound’s inherent toxicity to codling moth larvae, maximum residual and wash-off potential from rainfall.
Insecticides Rainfall = 0.5 inch Rainfall = 1 inch Rainfall = 2 inches
*1 day *7 days *1 day *7 days *1 day *7 days
Imidan Sufficient Insufficient Sufficient Insufficient Insufficient Insufficient
Asana Sufficient Insufficient Insufficient Insufficient Insufficient Insufficient
Assail Sufficient Sufficient Insufficient Insufficient Insufficient Insufficient
Proclaim Sufficient Insufficient Sufficient Insufficient Insufficient Insufficient
Rimon Sufficient Sufficient Insufficient Insufficient Insufficient Insufficient
Delegate Sufficient Sufficient Sufficient Sufficient Insufficient Insufficient
Altacor Sufficient Sufficient Sufficient Sufficient Insufficient Insufficient


Apple maggot: Opportunities for spot sprays
Both baited and unbaited, red spheres are effective for attracting AM because the very mobile pests are attracted to fruit both visually and through olfactory senses. When unbaited spheres are used at three traps per ten acres, the threshold is one fly per trap, while baited spheres have a threshold of up to five flies per trap. Maggot flies are sometimes only caught in isolated sections of orchards. If we are using a good density of traps, we can rely on this trap data to determine what part of the orchard needs to be sprayed.  This can help us effectively use spot treatments to manage AM and is particularly useful if codling moth does not need to be treated. Spot sprays can be an excellent option for AM control, especially in orchards with variable pressure looking to limit insecticide costs or toxicity effects.  Ultimately, it may not be necessary to make an orchard wide application.

Mites and miticides
Mite thresholds have increased from 2.5 to 5 mites per leaf and will increase to seven mites in August.  Some growers have already seen mite captures exceed threshold and growers should be aware that in addition to the wide range in performance of miticides, each orchard’s mite populations respond uniquely to a treatment. Mites don’t travel between orchards and you own your own mites, which means your mites have been exposed to whatever you have applied year after year in your orchard.

Some miticides work only as an ovicide and larvacide, whereas other miticides offer good contact activity on all motile stages. Where mite populations have exploded, miticides such as Zeal (etoxazole) and Envidor (spirodiclofen) will not offer the level of immediate knockdown of adults that is desired. Miticides with good contact efficacy include Acramite (bifenazate), Kanemite (acequinocyl), Nealta (cyflumetofen) and Portal (fenpyroximate).

Many orchards have seen very high populations of predatory mites this year, which poses an interesting challenge. If bronzing is still 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.

An alternative to applying a miticide is an application of a summer oil.  With a short break in the heat and humidity, growers can apply a stylet oil or summer spray oil when evenings are forecasted to drop into the low 70s with low relative humidity. Applying at night rather than during the day may also minimize the risk of treated leaves burning in intense sunlight. Growers should also beware of recent Captan applications when applying oil. If captan has not been reapplied since the last rain events, then the risk of phytotoxicity is reduced.

Weed management
The most critical time for weed management is in the spring and through early July, during the period of shoot elongation.  High density orchards and non-bearing trees are going to be very sensitive to water stress and any weeds in the tree row will also be competing for these water resources, even after shoot elongation ends. For this reason and to reduce risk of rodent injury in the winter, it is beneficial to keep up on weed management through the summer.

If the weeds have got away from you and are now possible 16 – 18” tall or greater, you are going to have a hard time getting good control of these with herbicide sprays.  When weeds get this tall we often the herbicide boom push over the weeds, resulting in poor spray coverage and less than desirable results.  Therefore, mowing or weed whacking overgrown weeds and then applying an herbicide after some regrowth, will likely offer better results.  For organic growers and those not using herbicides, maintaining close mowing under the trees will continue to help trees outcompete the weeds for water and nutrition resources.