April 6, 2020 VOLUME 29, No. 3 Geneva, NY

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IN THIS ISSUE...INSECTS v Early season scale management v Black stem borer survey

DISEASES v Tree decline and novel viruses v Errata

PEST FOCUSUPCOMING PEST EVENTSPHENOLOGIESTRAP CATCHES

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scaffoldsF R U I T J O U R N A L

Update on Pest Managementand Crop Development

protected by a gray circular scale covering approximately 1/16 inch in diameter.

No eggs are laid externally; the female gives birth to live nymphs, which are known as crawlers. The adult male, which has legs and wings but no functional mouthparts, develops

under an oval-shaped gray scale cov-ering slightly smaller than that of the

female. It is active just before dusk at tem-peratures above ~65°F and when the wind does not exceed 4 mph. The female produces a mating pheromone to attract the males, which have a short lifespan (2–3 days) and can fly less than 100 yards. However, in spring, if conditions are not favorable for flight, the males can disperse by crawling over the branches to find females and mate. A more thorough description along with photos of the dif-ferent life stages can be found on the NYS IPM Fact Sheet for San Jose Scale: (https://hdl.handle.net/1813/43128)

GETTING OUT FROM UNDER(Art Agnello, Entomology, Geneva;

ama4@cornell.edu)

vv San Jose scale is one of the historically important fruit pests that has taken advantage of our changing in-secticide programs during the last 10–15 years. The disappearance of broad-spectrum organo-phosphates like Penncap-M and Lorsban from our list of summer spray materials has been partly responsible for the fact that SJS persists or has returned to active pest status in a number of orchards. San Jose scale, Quadraspidiotus perniciosus (Comstock), is native to China, and was introduced into California on infested plant stock in the late 1800s. It primarily attacks stone fruits, pome fruits, and also walnut. In zones with a moderate climate (such as NY) it can be a key pest that, after 4–5 years of infestations, can cause severe damage to production; in cold-er areas, its importance is secondary and can be considered a sporadic nuisance. The most fre-quent source of an outbreak is usually via infest-ed nursery plants or infestation from wind-dis-persed crawlers arriving from other hosts in the vicinity. Three major factors promoting SJS in-festations are: its high number of potential host plants (over 700 species); high female fecundity (potential for 100–400 nymphs/female); and an absence of effective natural controls in com-mercial orchards subjected to standard pesticide programs.

Life History and Description The adult female is immobile, shaped some-what like a pyramid, bright yellow in color, and

SCALEBACK

I N S E C T S

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scaffoldsis published weekly from March to September by Cornell University—Cornell AgriTech at the NYS Agricultural Ex-periment Station (Geneva) and Ithaca—with the assistance of Cornell Cooperative Extension. New York field reports welcomed. Send submissions by 2 pm Monday to:

scaffolds FRUIT JOURNAL Dept. of Entomology Cornell AgriTech at NYSAES 15 Castle Creek Dr. Geneva, NY 14456-1371 Phone: 315-787-2341 FAX: 315-787-2326 E-mail: ama4@cornell.edu

Editor: Art Agnello

This newsletter available online at: http://www.scaffolds.entomology.cornell.edu/

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San Jose scale is found mostly on the woody tissue of branches and twigs, but when infesta-tions are high, they can occur on the fruit surface. In these cases, the scales tend to be found in the ar-eas of the stem and calyx. On rare occasions they occur on the foliage, in which case the individuals present are generally males. This insect tends to be distributed non-uniformly within both the tree and the orchard. In infestations originating from the nursery, scales are located up and down the tree, from the base to the growing point tips. San Jose scale overwinters principally as immatures under scale covers called "black caps", although a small percentage can also be present as "white caps" or else as gravid females that mated the pre-vious summer and did not complete development of the scale cover. There are generally 2 genera-tions per season in New York, but a 3rd generation can occur in years having a long, warm season, particularly in the Hudson Valley. Emergence pe-riods of adult males as well as crawlers are well defined and distinct for each generation. Crawlers emerge about mid-June and again in early August in western NY, and can be timed by using degree day accumulations: 310 DD (base 50°F) after the 1st adult catch of the 1st generation (or about 500 DD from March 1), and 400 DD after the 1st catch of the 2nd generation. Refer to the NEWA Apple Insect Models page (http://newa.cornell.edu/in-dex.php?page=apple-insects) to get an estimated date of SJS crawler emergence in your area.

Damage The most important damage is caused by feeding, but the indirect damage stemming from presence on the fruit surface can result in down-grading and rejection by the fresh market. San Jose scale crawlers insert their mouthparts into the woody tissue and suck the sap, weakening the plant and reducing fruit and shoot growth, and ul-timately desiccating the foliage and causing death of the affected areas. Infested portions of the tree generally have less foliage, smaller fruits, and even sunscald arising from direct exposure to the sun. In fruits, a reddish halo surrounds the point of the scale's attachment on the fruit surface, which

is caused by a reaction of the plant to a toxin in-jected with the insect's saliva. In general, smooth-skinned fruits are more vulnerable than those with a roughened or "velvety" texture, like peaches. Problem populations are more common in larger, poorly pruned standard size trees with inadequate spray coverage.

Control Ensuring clean plant stock is obtained from the nursery, plus having knowledge of any poten-tial hosts in the area, especially those located up-wind of a planting, are some preventive measures that can help to reduce the incidence of SJS infes-tation in commercial orchards. Although San Jose scale has a number of natural enemies (mainly par-asitic wasps), their impact in managed orchards is limited and at times negligible, due to the normal pesticide-based management programs. In areas of high infestation, early season pruning can re-move infested branches and open up the canopy for better coverage. This can substantially reduce population levels, which would otherwise serve as a perpetual source of infestation for the rest of the orchard.

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Dormant sprays of 1.5–2.0% horticultural oil, alone or in combination with an insecticide, are the most effective means of controlling this pest. These should be applied at a high volume to completely wet the wood surfaces. Normal recommendations are to complement this tactic with 1–2 summer sprays directed at the crawlers. Severe infestations require two early summer ap-plications against the first generation of crawlers, on a 12–14-day interval. Moreover, it should be emphasized that an optimal management program should incorporate the use of insecticides with different modes of action, to avoid the develop-ment of resistance. Options include neonics such as AdmirePro or Assail (summer use); IGRs such as Centaur or Esteem, organophospates such as Lorsban (pre-bloom only) or Imidan (summer), or novel a.i.s like Movento (summer), Sivanto Prime or Venerate. In this regard, it is important to under-score that San Jose scale has developed resistance especially to some contact materials through their habitual use in insect control programs. Most no-tably, in 1914, the country's entire apple industry was threatened with extinction because of SJS re-sistance to lime sulfur – the first documented case in the US! Tragedy was averted because of the in-troduction of a new product – lead arsenate (which also did not work out well).

White Prunicola Scale Another scale we've been seeing in upstate NY orchards that might otherwise have been identified as white peach scale (Pseudaulacaspis pentagona) is almost certainly a closely related species (P. prunicola), which has the common name of white prunicola scale. According to scale authorities, this species is so closely related to P. pentagona that for years no one was aware that the white peach scale was not one but two species. Evidently, white prunicola scale is more common in temperate climatic zones (e.g., from Pennsyl-vania south), and scales found in upstate NY and New England will most likely be P. prunicola. Infestations on apple and cherry as well as peach, are characterized by numerous white scales

that cluster on the trunk and scaffolds during the summer, giving them a whitewashed appearance. Feeding reduces tree vigor, and foliage of affected trees may become sparse and yellow; heavy in-festations can cause death of twigs, branches and entire trees if left unattended. This species over-winters as an adult female and deposits eggs in the spring. The management recommendations for San Jose scale are also appropriate for this species: Horticultural oil is recommended as a dormant spray in April, and insecticides can be used against crawlers in mid-June through early July (about 700–1150 DD base 50°F from March 1, a bit later than the SJS timing). Materials such as Movento or Centaur would be two good candidates at such a time. [Refs: Johnson & Lyon 1988, Insects that Feed on Trees and Shrubs; Davidson et al. 1983. Proc. Entomol. Soc. Wash. 85: 753-761]. vv

BLACK STEM BORER SURVEY Black stem borer is a destructive pest of apple trees that is becoming more problematic around New York and other eastern states, particularly in high-density dwarf plantings. We are work-ing with a regional IPM Working Group (based in Georgia) focused on these ambrosia beetles to gain a better understanding of their biology, behavior, and ultimately effective management around the country, not only in apples, but also in other commodities such as nursery ornamentals, pecans, avocados, and forest/shade trees. We are making available an online survey on Black Stem Borer ambrosia beetles to document their impact, and to use in grant proposals to support further re-search on these pests. If you are having problems with this pest, we ask that you please fill it out to assist us in this effort; responses will be anony-mous, and it should take no more than 5 minutes of your time. You can access the survey at: https://ugeorgia.ca1.qualtrics.com/jfe/form/SV_0ojFgygi2BFmQ1n

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point no one knows if these novel viruses really do anything harmful to our modern apple cultivars and rootstocks.

Based on what I have been able to learn, it seems quite possible that all of the new viruses are latent in most apple cultivars, just like the four previously-recognized latent viruses: apple stem pitting virus (ASPV), apple stem grooving virus (ASGV), apple chlorotic leafspot virus (ACLSV), and apple mosaic virus (AMV). The common la-tent viruses are not totally benign because they can cause significant yield reductions, and AMV can cause leaf symptoms in some years. However, they generally do not cause tree death or decline except for trees of uniquely susceptible cultivars or rootstocks.

The new viruses that are currently being de-scribed may eventually be shown to fit into one or more of the following categories: (i) They may have little or no effect on trees; (ii) They may cause yield losses like other latent viruses in ap-ples; (iii) They may weaken trees, thereby making them more susceptible to winter injury, herbicide damage, black stem borers, etc; (iv) They may cause graft union disorders that directly result in tree decline and death; (v) They may contribute to obscure fruit markings and/or apparent variabili-ty in germplasm of some cultivars (e.g., Honey-crisp). Determining which viruses are associated with which of the above possibilities will require a lot of money and many years of research.

The rest of this article describes several of the new apple viruses that have recently been re-ported from various locations around the world. But first, some background on modern virus de-tection methods may be helpful. As I understand the process (and this is an over-simplification), virologists today collect plant tissue, grind it up, and determine the sequences of all of the nucle-ic acid chains or snippets present in the sample.

TREE DECLINE ANDNOVEL VIRUSES(Dave Rosenberger, Plant Pathology, Highland; dar22@cornell.edu)

vv In last week's issue of Scaffolds, I summa-rized some information from a conference on apple decline that was organized by Dr. Kari Peter and held in Winchester, VA, last December. The arti-cle last week focused on the potential relationships between herbicides and young tree decline. This week I will summarize some of the information on novel apple viruses that was presented at that meet-ing, along with other recently published informa-tion on new apple viruses. Relevant literature cita-tions are included in a slightly expanded version of this article that will be posted later this week on my blog: http://blogs.cornell.edu/plantpathhvl/blog.

At the meeting in Winchester, Dr. Kari Peter provided some background on tree decline prob-lems in Pennsylvania and described how associates in the Pennsylvania Department of Agriculture and USDA were able to find a previously undescribed luteovirus in some of the declining trees. Dan Do-nahue from the Eastern NY Commercial Horticul-ture Program described tree decline in the Hudson Valley and showed the multi-year progression of tree decline in a Zestar orchard near Hudson, NY. Dr. Ruhui Li from USDA reported on the genomes of apple luteovirus and another new virus, CCGaV, which was also found in apples.

None of the presentations provided any clear linkages between new viruses and apple tree de-cline. None of the newly discovered viruses men-tioned at the workshop or described in recent liter-ature have so far been shown to cause new diseases in apples, although several are associated with pre-viously known diseases that were assumed to have viral etiologies but for which no virus had ever been described. The initial reports on new viruses of apple provide no information on the worldwide distribution of these viruses or on differences in cultivar and rootstock susceptibilities. Thus, at this

DISEASES

VIRUSESAMONG

US

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was long assumed to be a virus and was called ARWV. It was shown to cause some apple cul-tivars (especially the indicator cultivar "Lord Lambourne") to lose wood stiffness. Trunks and scaffolds of affected susceptible cultivars bend down and trees are stunted. In Washington State, two forms of ARWaV were discovered in several Honeycrisp trees. One west coast researcher at the conference last December told me that he suspects that it is widespread in Honeycrisp. However, it does not cause the rubbery wood symptoms or any other symptoms in Honeycrisp so far as any-one knows at this point. Older studies showed that trees of some cultivars with ARV had reduced yields, and in one case it increased the susceptibil-ity of the apple rootstock MM.104 to Phytophtho-ra root rot. Finding ARWaV in apples is disheart-ening because, as with most of the latent viruses, clean stock programs in the 1960s and 1970s had pretty much eliminated this virus from commer-cially produced nursery stock.

Apple geminivirus (AGV) was found in seven apple cultivars, including Gala and Fuji, in vari-ous provinces in China. Gemini viruses are DNA viruses long known to cause diseases in vegetable crops and that more recently were found in citrus and grapes. Its importance in apples remains un-known.

There are additional reports of other newly dis-covered viruses in apples, in some cases, with still obscure linkages to previously known graft-trans-missible diseases of apples. The list will undoubt-edly continue to grow. A report in 2006 stated that there were approximately 4,000 known viruses, of which 1,000 occurred in plants. However, after molecular methodology was adopted for studying viruses, a publication in 2013 estimated that there was likely to be at least 320,000 undiscovered vi-ruses in mammals, with many thousands more in plants and other non-mammalian life forms. De-termining which of these new viruses are import-ant and which can be ignored is a daunting task,

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Computer programs can quickly sort through all of the nucleic acid sequences and discard any that match parts of the apple genome. The remaining sequences are then sent through a different com-puter program that looks for matches or similari-ties with all known viruses. Further work is then required to prove that the actual virus suggested by this process is present in the trees.

Following is a description of several new vi-ruses reported in apples over the past few years:

Apple luteovirus (ALV) was discovered in PA and is a member of a virus group that is usual-ly transmitted by aphids. A different luteovirus has long been known to infect barley, and several others have recently been detected on stone fruits. ALV has been detected in several commercially propagated apple cultivars in PA, WV, and NY, and in a number of different rootstocks in Korea.

Citrus concave gum-associated virus (CCGaV) was detected in apples on the west coast in 2018. Previously, it was discovered in citrus trees affect-ed by a graft-transmissible disease called concave gum-blind pocket that was described more than 80 years ago. Diseased citrus trees have trunk abnor-malities (distortion, uneven growth). It is called an "associated" virus because, although found in diseased citrus trees, it has not yet been proven to actually cause the disease. CCGaV is similar to other viruses in the bunyavirus group that, prior to the discovery of CCGaV, consisted mostly of ar-thropod-borne or rodent-borne viruses that caused various diseases in humans. The bunya-like virus-es in woody plants are distinct from bunyaviruses previously described in human medicine. They are called "bunya-like" because they have not yet been officially classified as bunyaviruses.

Apple rubbery wood-associated viruses (AR-WaV-1 and ARWaV-2) are also new bunya-like viruses associated with a long-known graft-trans-missible disease called apple rubbery wood. Be-cause it was graft-transmissible, the causal agent

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not only for apples and other major crops, but also for human survival, as illustrated by our current struggles with Covid-19.

Errata: Kerik Cox, Plant Pathology & PMB, Geneva; kdc33@cornell.edu

In the Mar. 23 article on Early Season Disease Management, there were two references to sin-gle-site fungicides that were not worded clearly. In the 3rd last paragraph, the 1st sentence should have said '...consider some of the modern prod-ucts that contain single-site fungicides (e.g., Luna Tranquility, Luna Sensation...'. Also, the 2nd to last sentence in the article should have said 'As we proceed toward bloom, additional applications of products that contain single-site fungicides (e.g., Luna Sensation, Merivon)...'. vv

Highland: Oriental Fruit Moth 1st catch today, 4/6

PEST FOCUS

PHENOLOGIES

Geneva: Highland:Apple Apple (Gala): 92% half-inch green(McIntosh, Empire, Idared): green tip (as of 4/2) (McIntosh): 50% half-inch green (Red Delicious): 80% green tip (Ginger Gold): 94% half-inch greenPear: 50-100% swollen bud (Red Chief): 88% half-inch greenSweet Cherry, Tart Cherry: swollen bud (Smoothie): 41% half-inch greenPeach: early bud burst (Empire): 82% half-inch greenPlum: swollen bud– (Honeycrisp): 53% half-inch green early bud burst (Zestar): 100% half-inch greenApricot: 50% bud burst (Jersey Mac): 82% half-inch green Pear (Bartlett): 89% bud burst (Bosc): 74% bud burst Sweet Cherry 100% swollen bud Peach 87% half-inch green

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UPCOMING PEST EVENTS (corrected)

43°F 45ºF 50°FCurrent DD* accumulations (Geneva 1/1–4/6): 103.1 77.0 35.1 (Geneva 1/1–4/6/2019): 52.3 38.1 15.1 (Geneva "Normal"): 94.7 73.4 37.3 (Geneva 1/1-4/13, predicted): 117.0 – 37.9 (Highland 1/1–4/6): 198.9 – 78.6 Upcoming Pest Events (Geneva): Ranges (Normal ±StDev):Green apple aphids present 111-265 38-134Green fruitworm peak fllight 91-226 34-106Pear psylla 1st oviposition 40-126 11-53Pear thrips in pear buds 118-214 50-98Redbanded leafroller 1st catch 111-176 40-81Spotted tentiform leafminer 1st catch 120-217 45-102Red Delicious green tip 110-161 39-75

*all DDs Baskerville-Emin, B.E.

NOTE: Every effort has been made to provide correct, complete and up-to-date pesticide recommendations. Nevertheless, changes in pesticide regulations occur constantly, and human errors are possible. These recommendations are not a substitute for pesticide labelling. Please read the label before applying any pesticide.This material is based upon work supported by Smith Lever funds from the Cooperative State Research, Education, and Extension Service, U.S. Department of Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

INSECT TRAP CATCHES(Number/Trap/Day)

Geneva, NY Highland, NY 3/30 4/2 4/6 3/23 3/30 4/6Green fruitworm 2.5 0.5 3.5 Green fruitworm 1.0* 0.0 0.0Redbanded leafroller 0.0 0.0 0.0 Redbanded leafroller 7.0 19.5 110.0 Spotted tentiform leafminer 0.0 12.5* 237.0 Oriental fruit moth 0.0 0.0 0.5* * first catch