May 22, AppleTalk Conference Call

Regional update

Degree days really ramped up with sunny and warm weather last Tuesday through Saturday. Some areas were held back by brief periods of cold weather, but most locations have accumulated more than 200-degree days. This season’s first codling moth flight was reported in Northern Illinois right on time last Friday around 250 degree days from January 1, and the first injury from plum curculio was also observed in southern Wisconsin this week. Yesterday’s substantial rain event was one of the most significant apple scab infections of the season, where many areas were at or above 80% ascospore maturity at the time of the infection period. Considering last week’s median ascospore maturity was near 40-50%, our region has likely experienced its largest ascospore maturation and release of the season.

Growers are encouraged to routinely check weather data supplied by their local Network for Environment and Weather Applications (NEWA) station for ideal spray application times. Most NEWA stations in Wisconsin are subsidized by the WI Apple Growers Association. To access your local NEWA station, please see the following link: http://newa.cornell.edu/.

Table 1. Degree days and ascospore maturity as of May 22, 2018

Apple scab

Some locations are experiencing the largest ascospore release of the season; however, the severity of this infection period is dependent on the overall inoculum present in the orchard. Past weather data from IA, MN, WI and IL suggest three to four inches of rainfall is typical by this point in the season, and these first three weeks of May some locations have received between two to more than seven inches of rain. Areas that remain an inch or so below the average precipitation, e.g., Mequon, Chippewa Falls, Eau Claire WI and Hastings and Rochester MN, may not have experienced the same threat level due to relatively low wash-off rates. 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. However, single-site fungicides may not be completely washed off during these heavy rains, rather their weathering is influenced more by leaf expansion. Full rates of fungicide should be used during periods of rapid leaf growth and when precipitation forecasted.

Note on EBDCs: Do not combine or integrate the pre-bloom application schedule with the post-bloom “extended application” schedule. If an EBDC, e.g., Roper DF Rainshield (mancozeb), Polyram (metiram), was applied pre-bloom at a rate greater than three pounds per acre, it cannot be applied at petal fall. Captan must be used.

When scouting for apple scab, early season infections may be visible on underside of the first spur leaves, whereas lesions found on the top of the leaf surface may indicate secondary infection. Primary lesions will continue to appear throughout the next two to three weeks, and scouting efforts, while less important this early in the season, should be focused on leaf undersides. At this point in the season, it can be difficult to distinguish between apple scab lesions and other injury, e.g., copper phytotoxicity.

Fire blight

Later blooming varieties in northern and eastern orchards may have high fire blight epiphytic infection periods (EIPs) this weekend. Orchards with newly planted trees should take steps to prevent infections during their later bloom period. Late-blooming varieties and new trees will be susceptible to fire blight during EIPs over 100. Newly planted trees can be protected with Apogee (prohexadione calcium) applications, streptomycin sprays or by removing blossoms. Growers should also continue to monitor the Maryblyt or CougarBlight models if varieties are still in bloom. The CougarBlight model is available on the NEWA sites.

Research discussed during the May 8 AppleTalk call suggests Apogee can be applied to new trees at king bloom petal fall and then three to four times at two-week intervals. It takes between ten days and two weeks for the trees to produce a physical barrier (thickened cell walls) to fire blight infection. Apogee applied at this timing and rate won’t significantly impact growth. The “Apogee effect” will eventually wear off and allow growth to resume in July. Phil Schwallier, Michigan State University – Extension, has noted similar growth in Apogee treated and untreated trees. Newly planted and nonbearing trees treated with should still receive scheduled fertilization. This method to reduce fire blight risk will be discussed with more depth on next week’s call with Phil Schwallier.

Cedar apple rust

Rust is typically not a major problem; however, numerous galls have recently been discovered on red cedar and juniper trees. Cedar apple rust (CAR) cannot spread from apple to apple or from red cedar to red cedar because the fungus experiences a two-year life cycle, alternating between hosts. The infection period for CAR is between tight cluster and first cover. Spores can be carried long distances (three to five miles), yet most infections occur when infected eastern red cedars are within a few hundred yards of apple trees. Spores that land on young apple tissue may germinate and infect if a film of water is present for an adequate amount of time, and symptoms will usually appear one to two weeks after infection. If you have access to red cedars, look for galls that resemble dead leaves. If possible, galls within a mile should be removed and destroyed.

EBDCs applied from tight cluster to first cover should offer adequate control. Susceptibility of cultivar and proximity to infected host will influence disease pressure. Unlike scab, rusts require an alternate host and inoculum is not reflective of how much rust was in your orchard last year. “Heavy” rust infections are produced by long-wetting events with little rain. For more information on temperature and moisture requirements for CAR periods visit: https://ecommons.cornell.edu/bitstream/handle/1813/43082/cedar-apple-rust-FS-NYSIPM.pdf?sequence=1&isAllowed=y.

For fungicide options for managing CAR see: Efficacy of Selected Fungicides Against Apple Diseases, 2018 Midwest Fruit Management Guide, page 33.

Phytophthora

When flooded orchards and soils are saturated for more than a week, the soil biota can become anaerobic. In addition to supplying a conducive habitat for root-injury-causing soil pathogens like phytophthora, water-logged fields pose a severe risk of tree stress and drowned roots. Significant death of tree roots can occur after three weeks of over saturation even without standing water on the soil’s surface. Soils that stay in a clump when squeezed in a fist should be treated with a phosphorous acid fungicide, e.g., Aliette, Fosetyl-Al, Phostrol, Rampart, after the soil has dried out a little bit. The phosphorous acid fungicides are highly systemic and short acting and all function the same way. They are applied as a foliar spray where they are absorbed into the leaves and are translocated to the roots where the fungicides fight off Phytophthora and soil-based pathogens. Overuse of these fungicides may result in pathogen resistance. Make sure to look at the pre-harvest intervals on these fungicides. Generally, two applications about a month apart are recommended.

If you are establishing an orchard on soils that have a high water-holding capacity or are poorly drained, you should consider using rootstocks with Phytophthora tolerance, e.g., Geneva rootstocks. Other rootstocks like M26, M9 should not be planted where Phytophthora has been documented.

Read more about Phytophthora: https://ohioline.osu.edu/factsheet/plpath-fru-06

Codling moth

In addition to last weekend’s first flight observed in northern Illinois, trap captures have been reported in the Upper Mississippi River Valley. Codling moth biofix is marked by a significant biological event, or first sustained flight, where moths are captured multiple days in a row or exceed a threshold of five moths per trap per week. Multiple biofixes can be set for each generation and can vary by block, especially if trapped captures do not consistently exceed the threshold. Once a biofix date is established, begin tracking degree-days (base 50°F) to time the first insecticide application. Continue to monitor traps weekly and be aware of a larger flight that may be more sustained and widespread than earlier flights.

The total population for each generation emerges in a shape of a bell curve over a 600 to 900 degree-day period, where we typically have 1000 DD between each generation of a biofix. This suggests that after 250 DD from biofix, only a small portion of the total population will have emerged – about a three percent hatch. Orchards with high pressure or a large first flight, e.g., more than ten moths per week, often apply the first larvicide at this time. If the initial flight is light or inconsistent due to cooler temperatures or rain a stronger flight can occur after the first biofix, e.g., two-weeks later. If this occurs the first larvicide can be applied at 350 DD. At 350 DD from biofix, 15% of larvae have hatched and at 450-550 DD up to 50% larvae hatch. If five moths are captured over the extent of the orchard, there is no need to apply a larvicide. If one or two traps exceed threshold, it is recommended to apply a larvicide to the entire area. Ideally, one trap should be set for every 2.5 acres. Large, flat, uniform orchards might be able to get by with one trap placed every five acres, but smaller, unevenly shaped blocks should try to stay within one trap for every 2.5 acres because codling moths do not tend to fly very far.

Note: Codling moth (CM) fly between 6pm and 11pm when wind speeds are between three and five miles per hour and when temperatures are above 62°F without rain. Assign the biofix date for the warmest, calmest night. When checking traps, fluttering CM had likely flown within the last 48 hours. Most female CM can live for seven to 14 days yet will mate and deposit the majority of eggs on the evening they emerge. Every day that a sexually viable female emerges and isn’t able to fly, egg fecundity is decreased by 20%.

Plum curculio

Despite excellent conditions for plum curculio (PC) migration, feeding and mating last week, migration into orchards is still in progress. While this pest typically becomes very active when the temperatures are in the 70s and 80s, activity can be expected in orchards with average temperatures near 65°F. Growers are advised to take a note of the McIntosh petal fall date and begin counting 308 degree-days from this date. At this time, PC will no longer be emerging from their overwinter sites and moving into the orchard. This does, however, mean internal populations could still be causing injury if they were not managed.

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 one pint per 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. These neonicotinoids all 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 CM, 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 PC in organic orchards. Since Venerate needs to be ingested, it should be applied as a complete cover, perhaps with kaolin clay, 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 (cyantraniliprole), a diamide insecticide related to Altacor (chlorantraniliprole), may be used to manage PC and CM. It has similar activity which requires ingestion.

Spring lepidopteran complex

As temperatures continue to warm, expect to find obliquebanded leafroller (OBLR), redbanded leafroller (RBLR), spring cankerworm, variegated leafroller and green fruitworm (GFW) larvae feeding on growing terminals and blossom or fruitlet clusters. Larvae from species that overwinter as pupae in the groundcover or soil, e.g., RBLR, GFW, are likely delayed relative to the tree phenology and should progress in this week’s heat – mean temperatures reaching over 80°F in some areas could cause rapid alteration in early lepidopteran populations.

Petal fall sprays for PC or applications of Bacillus thuringiensis (Bt) pesticides, e.g., Agree, Deliver or Dipel, may be applied to manage these pests when the weather is warm, sunny and dry. Bt must be eaten by the insect to be effective, and warm temperatures (>60°F) are needed in the 72-hour period following an application for good mortality. As with most insecticides, young larvae are generally more susceptible than older larvae.

It is essential to scout for larvae following the first application of Bt, as an additional application may be needed. Early detection of a pest is critical for good management. The spray deposit may only last one to three days before it is washed off by rain or broken down by sunlight. Sticker substances that promote adherence to leaf surfaces and UV light inhibitors that protect Bt from photo-degradation may enhance efficacy. For more information on application timing and use of Bt pesticides visit http://nysipm.cornell.edu/organic_guide/apples.pdf.

In addition to Bt, other insecticides that are safe for pollinators are very limited. One option includes, Intrepid (methoxyfenozide) an insect-growth regulator that only works on lepidoptera and does not have effect on honeybee larvae. If blossoms are present, do not apply Esteem (pyriproxyfen). Neonicotinoids used to treat PC will not control the spring lepidopteran complex.

Western flower thrips

Flower thrips are a pest that was originally 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 trees. Both Delegate (spinetoram) and Entrust (spinosad) are labeled for thrips.

If thrips are observed while scouting, a beating tray can be used to determine the extent of the infestation. A beating tray is piece of white cloth on a frame of any size that can be held under a shaken branch to sample insect populations that may not be detected by visual scouting. This scouting technique is highly recommended as a yearly practice, especially for spotting western flower thrips.

Petal fall thinning and use of the carbohydrate model

Developing fruit are at many different growth stages due to the variable weather conditions during bloom and this may make timing thinning sprays at petal fall more challenging.

The carbohydrate model is tool that can be used to help determine rates and to thin more reliably. The model takes some of the guess work out of thinning by using the current weather forecast to determine if thinner rates should be increased, decreased or applied at the standard rate. The general carbohydrate balance the model calculates has been found to correlate well with tree sensitivity to natural drop and with sensitivity to chemical thinners. Cool sunny periods of good carbohydrate supply leads to reduce natural drop and less response to thinners (increase thinner rate). Cloudy hot periods give carbohydrate deficits and lead to stronger natural drop and stronger response to thinners (decrease thinner rate). The carbohydrate model needs to be consulted at the time of thinning to help determine rates. The grower needs to use their experience with thinning and adjust rates based on what they have applied in the past to the target variety and crop stage. This model does not tell you what product to use or what rate to apply. 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.

Find more information in part three of Amaya Atucha’s paper published on pg.11 here, https://go.wisc.edu/3s74m8.

The carbohydrate model is available on NEWA under the crop management section, http://newa.cornell.edu/index.php?page=apple-thin.