May 23, AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, May 23 2017, 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments,

May 23rd Call Stream: CLICK HERE

Degree Days from January 1, 2017

City State DD base 50F from Jan 1, 2017
Woodstock IL 269
Poplar Grove IL 267
Gays Mills WI 222
Madison WI 243
La Crescent MN 242
Elgin MN 219
Afton MN 222

Developing fruit are at many stages and the weather conditions has delayed the application of thinning agents.  Fruit are beginning to swell, but it remains unclear which are going to set and which fruit will drop, as they move into the 7 – 10 mm stage.  Many varieties are between 8 – 10 mm and some locations in southern Wisconsin and northern Illinois are already sizing to 12-15 mm.  In the southern region king blooms have been observed to fall off of Honeycrisp and other varieties.  Typically, the carbohydrate model can aid in determining rates of thinners, but the weather has not been conducive to using this model.  The recent cloudy weather has not been warm enough to create the stress required to get more thinning out of an application.  The carbohydrate model works when warm and cloudy days create tree stress and give a better thinning response.  When it is sunny and cool, there are carbohydrate surpluses and little tree stress, which require increased rates of thinners.  This model is particularly helpful when using MaxCel (6-BA) or Fruitone (NAA), which are both dose dependent.  Conversely, Sevin (carbaryl) is not does dependent and will generally provide the same level of thinning regardless of rate.

Scab management and fungicide wash-off
Rain fall has been variable across the region and some orchards have received more than double the average monthly rain fall.  When determining the need to reapply protectant fungicides, e.g., Captan or an EBDC, remember that that one inch of rain removes half of the fungicide and two inches of rain is enough to remove all fungicide protection.  Leaf expansion and development of new plant tissue should also be considered when determining if a fungicide should be reapplied.

Scab has been found in several orchards in southern Wisconsin and lesions found on the top of the leaf surface suggest they are secondary infections.  Lesions from secondary scab infections are typically found on the top of the leaf surface, whereas primary scab is found on the bottom of the leaf.  The presence of scab on the top of the leaf suggest these orchards missed an early primary scab infection.  Most orchards should be past primary scab release, however, many primary scab lesions have not shown up yet and the possibility of scab showing up in the next week is very realistic.

Due to the wet and windy weather, fungicide-cover sprays have been stretched by as much as two weeks.  Where scab pressure is high, these cover sprays may be reapplied on 5- 7 day cycles during primary scab season and then extend sprays once we are certain no scab is present in the orchard.  It is important to carefully watch for scab, as it is often during first cover and when thinners are applied, that scab is found.

Tree decline
This spring there have been increasing reports of tree mortality of 2nd – 4th leaf trees.  This tree decline may be associated with winter injury from the polar vortex of 2013 for younger trees, or for new trees, cold temperatures in March 2017, which came after the 70 degree weather in February.

Western flower thrips
Flower thrips are pest originally that was limited to western states, but have become increasingly present in the Midwest.  Thrips have asymmetrical mouth parts sometimes referred to as rasping/sucking mouthparts.  These mouthparts allow thrips to cause the distinct injury on the midrib of developing terminals on trees.  Their oviposition injury causes a blemish called pansy spot.  This was observed several years ago in 2010 or 2011, when a large population of thrips blew into the region during apple bloom and has not been observed since.  There no established thresholds for terminal infestations on trees and generally there is no reduction in crop quantity or quality from thrips injury.  If thrips infestations are found on newly planted or non-bearing trees, treatments may be made before growth is stunted.  While the injury may be unsightly, thrips should not require an insecticide application on a mature M7 tree or fully mature dwarf trees on Geneva, EMLA or Budagovski rootstocks.  Both Delegate and Entrust are labeled for thrips.

Wooly apple aphid (WAA)
Wooly apple aphids often become a problem in late summer, but the first aerial colonies should become visible in the next few weeks.  Now is a good time to be looking at previous areas where WAA infestations were present last year.  Treatments of WAA with neonicotinoids in recent years have been met with limited success.  Movento is an alternative and offers excellent efficacy, but must be applied shortly after petal fall and before second or third cover.

Potato leafhopper (PLH)
Potato leafhoppers (PLH) have a wide host range and are a common pest on alfalfa.  Heat thermals and southerly breezes bring them up to the upper Midwest in the spring.  Adult PLH do not cause injury to apple trees, but nymphs can be found feeding on growing shoots of trees.  White apple leafhopper (WALH) and PLH adult and nymphs look very similar and the adults of both species fly, while nymphs cannot.  Currently, PHL are in the adult life stage, whereas WALH are nymphs.  Typically leafhoppers are not a problem on bearing trees, but can cause stunted growth on non-bearing trees in their 3rd – 5th leafs.

Rosy apple aphids (RAA)
Rosy aphid colonies are beginning to appear on fruiting spurs.  Their feeding injury curls the leaves and can cause stunted fruit growth on clusters.  They have not been a problem the last two years and this may be a year with higher pressure for RAA.  Interestingly, European studies show that RAA tend to return to the same apple blocks year after year.  The typical recommendations in spray guides are to control at pink, yet most years, they are very hard to detect at this stage.  At petal fall, RAA may be managed with a low rate of a neonicotinoid, Beleaf 50 SG (flonicamid) or Sivanto 200 SL (flupyradifurone).  All of these applications require a high volume of water to ensure adequate coverage.  Lingering bloom and populations of bees that may still be foraging in the orchard make it hard to treat right at petal fall with a neonicotinoid.  Treatment of RAA is further complicated by the secondary lifecycle it has on other plants, e.g., dock and plantain.  Since RAA are going to going to leave the trees, treatments for RAA need to be done very soon, if colonies are present.

Mullein plant bug
Mullein plant bugs are both pest and predator.  Their eggs overwinter on apple and pear trees and begin to emerge during bloom and will have two to four generations during the season.  The nymphs during this first generation can cause raised-wart like bumps on developing fruit.  Nymphs of subsequent generations are considered a generalist predator that will feed on aphids, mites and sometimes lepidoptera larvae.  Mullein plant bug nymphs are small and translucent green and about the size of an aphid.  Unlike aphids, they are faster moving, will not have large colonies and will not be producing honey dew on the leaves.

Plum curculio
During the week of May 11-16 warm weather across the region was conducive to plum curculio activity and PC injury has now been observed in orchards between far southern Wisconsin to La Crescent Minnesota.  Orchards where PC was found last week, all have had a history of early PC injury and are not surprised to see this activity at these sites.  The current pattern of rain and cooler weather will make it hard to determine when to treat.  While not the ideal conditions for PC activity, temperatures in the 60s-70s and even with nights into the 50s can still result in some PC activity.  Typically this pest becomes very active when the temperatures are in the 70s – 80s.  Make a note of the McIntosh petal fall date and begin counting 308 degree days from this date.  At this time PC activity should be ended and PC will no longer be emerging from their overwinter sites.  This does mean internal populations could still be working on PC and would remain a concern in organic systems.

Spraying perimeters more frequently is an excellent option to reduce cover sprays.  Thorough scouting should be done beforehand, as it is possible PC have moved in well past the perimeter at this time.  If PC injury is found past the perimeter, e.g., first four or five rows of trees, a full cover spray is recommended.  In the past, many assume that thinning sprays with carbaryl will offer protection.  Thinning with carbaryl at 1 pint/acre delivers a half pound of actual carbaryl, whereas if carbaryl was used as an insecticide, this rate would be delivering two to four pounds of actual carbaryl per acre.  Therefore, the rates used for thinning, e.g., one pint to one quart, are not going to deliver much insecticidal activity.  Reducing rates of carbaryl may also help lessen the impact on beneficial insects in the orchard.

In John Wise’s recent article, “Effectively controlling plum curculio in stone and pome fruit”, he outlines how the variety of organophosphate alternatives work on managing PC.  Many growers have been moving away from the organophosphate insecticides over the last decade and until recently, Avaunt (indoxacarb) has been the most commonly applied OP alternative.  Many of the newer insecticides use a combination of contact mortality, systemic activity as an anti-feedant or ingestion, to manage PC.  The neonicotinoids Actara (thiamethoxam), Assail (acetamiprid) and Belay (clothianidin) have contact mortality for only a few days, after several days the insecticide penetrates the fruit and is more of an anti-feedant and keep the female from laying an egg.  Likewise, they can kill the egg if successful oviposition does occur.  Note: Actara does not work on codling moth, however Belay may be used on first generation codling moth and Assail is labeled for both first and second generation codling moth.  All of these neonicotinoids have different wash off potential, costs and manage other pests including aphids.  John Wise has developed most of the wash off research based on management of codling moth larvae survival.  A PC weevil is going to eat much more tissue and consume more insecticide residue that may otherwise not control codling moth, so even with some rain, these insecticides may still be working on PC.

Venerate (Heat-killed Burkholderia spp. Strain A396 and spent fermentation media) is a new product approved for organic production is available for PC management.  As described in the active ingredients name, Venerate is a bacterial by-product.  According to the label, “VENERATE™ controls insect targets by enzymatic degradation of exoskeletal structures and interference with the molting process leading to mortality through contact and/or ingestion”.  In a recent report from John Wise, Michigan State University entomologist, he suggests Venerate is showing good control of plum curculio in organic orchards.  However, efficacy data from trials in apples is still not available. Venerate would need to be applied as a complete cover, not a perimeter, perhaps with kaolin clay.  Since Venerate needs to be ingested, it should be applied as a complete cover and it may be best to apply after initial PC activity has been detected.

Other insecticide options for PC include Avaunt and Exirel.  Avaunt is a gut poison, which requires ingestion and has a slower knockdown and we often see a number of individual spots where a female PC laid eggs on a tree before it was killed.  It is broad spectrum to leafrollers and is fairly resistant to wash off and could be a good option before a lot of PC injury has been found.  Exirel, a diamide insecticide related to Altacor and may be used to manage PC and codling moth.  It has similar activity which requires ingestion.

Codling moth
There was a strong codling moth flight between May 15th and May 17th.  In many cases, moths flew in numbers that had not been seen last year.  Most of the places where CM was caught last week, there was not a biofix established.  However, locations where five or 10 or 15 moths were caught in traps would be considered a biofix.  This suggests there will be enough larval hatch at 250 DD, a larvacide for CM would be needed right away at 250 DD.  These high numbers may be explained by CM that emerged during the nice weather, but did not fly if it was too cold, windy or rainy in the evenings.  Once the flight conditions were met, CM flew in larger than normal numbers.  Typically, a large percentage of overwintering codling moth do not survive the winter and it is possible our mild winter allowed more to survive this year.  If this is true, expect to see increased CM numbers this season.

A note on PyGanic
PyGanic is an organically approved broad-spectrum insecticide.  All pyrethroids, even the synthetic ones, are very unstable when exposed to ultraviolet radiation.  Synthetic pyrethroids are stabilized by adding piperonyl butoxide to help reduce degradation in the sun.  Since PyGanic does not have this added synergist, it will rapidly degrade in several hours, once exposed to ultraviolet radiation.  Therefore, it is recommended to apply in the early evening, to prolong its activity and reduce exposure to bees.  This would also be the best timing to apply for PC.  Additionally, pyrethrum degrades rapidly in acid and alkaline spray solutions and therefore it is not recommended to tank mix PyGanic with liquid-lime sulfur, sulfur, or soap solutions.

Additional resources