AppleTalk Conference Call Summary
Tuesday, August 15 2017, 8:00 – 9:00 AM
Guest speaker: Patty McManus, Plant Pathology, UW-Madison
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments,
August 15th Call Stream: CLICK HERE
Thank you for a successful season of AppleTalk! Your participation makes this program possible. Please keep an eye on your email for information on our annual survey and Apple a Day IPM Calendar. We would like to collect your favorite photos from your orchard and bring this calendar to print by the end of November. John Aue, Thomas Bernard and Peter Werts will continue to scout orchards through September and are available to answer questions.
Summer disease management with Dr. Patty McManus, Plant Pathology, UW-Madison
Bitter rot
Bitter rot has been discussed extensively this season during other AppleTalk calls, please look at past posts for any information that may not be addressed here. Bitter rot should not to be confused with bitter pit, the calcium disorder.
Bitter rot has historically been more of an issue in the Mid-Atlantic States, yet over the last decade it’s becoming more problematic in our region. This increase may be due to milder winters or the rise of varieties, such as Honeycrisp, that are more susceptible to this disease. However, there isn’t a definitive explanation as to why we are seeing more bitter rot. Similar to sooty blotch and flyspeck (SBFS), bitter rot has a lot more genetic diversity than previously thought, and while not immune to resistance, we are currently not very concerned about resistance developing to our current fungicide programs.
Characteristics of bitter rot, fruit:
– Bitter rot is ubiquitous in the environment and its host range includes other fruit crops, grasses, broadleaf weeds, deciduous trees and shrubs, e.g., peach, grape, lilac, chestnut. Spores likely enter the orchard from hedgerows earlier in the season, e.g., June, but researchers are not entirely sure if these are from overwintering inoculum within the orchard or from other sources.
– It generally takes several weeks following infection before symptoms develop, and bitter rot may become visible before other rots. If a lot of fruit are found with bitter rot it may suggest that the source of inoculum is nearby rather than spread via wind or rain. This pathogen can overwinter on dead wood, e.g., fire blight canker, or rotten or mummied fruit; hand thinned fruit on the ground or fire blight infected shoots can become can become colonized and begin to sporulate by late July. Note: fallen fruit do not decay very well on bare ground, e.g., herbicide strips.
– Symptoms first appear as small, light-brown, circular spots. Many spots per fruit may be found. Fruit infected with bitter rot is often observed in groupings and clusters all on several branches or a section of a tree. While bitter rot does not cause big cankers, it can infect clean fruit pretty quickly. In strawberry and blueberries, infections can happen in four to six hours during wetness, which is shows a pretty aggressive fungus.
– Infections can continue to appear post harvest, although the fungus is not going to thrive in the absence of vegetation.
– Heat-stressed fruit also seem to be more susceptible. When humidity is high, evapotranspiration is reduced and fruit have difficulty cooling. Therefore, making sure trees are well irrigated or applying a sun protectant material, e.g., Surround (kaolin), before hot weather arrives can help.
– Under high temperatures initial lesions may rapidly enlarge and change to dark brown in color.
– 1/8 to 1/4 inch in diameter lesions are distinctly sunken or saucer shaped.
– When lesions reach 1/2 inch in diameter, small, black fruiting bodies appear in the sunken lesion; fruit bodies may be arranged in concentric rings. Fruiting bodies will begin to ooze a gelatinous, salmon-pink mass of spores, which is washed by rains or insects onto other fruit. Black rot and white rot also produce black fruiting bodies, but do not produce salmon-pink mass of spores, and usually only one spot occurs per fruit, a characteristic that distinguishes black rot from bitter rot.
– Beneath the surface of the spot, the flesh is light brown and watery in a cone or V-shaped area, with the small end of the cone toward the fruit center. The flesh of black rot infected fruit usually remains firm and leathery.
– Cankers can form on vegetative tissue, but are rare.
Management options:
– Strobilurins, SDHIs (with strobilurin component) and/or captan are the best options for bitter rot. If captan is used alone high rates are required. For best performance tank mix a strobilurin or SDHI with a medium rate of captan.
– Phosphorous acid fungicides, e.g., Aliette, Phostrol, are not effective on bitter rot.
– Organic options are pretty limited. In some trials Patty found, results suggested that liquid-lime sulfur had 9% injury, Serenade Optimum (Bacillus subtilis) 10%, and the control had 7% bitter rot injury. This suggests that none of these fungicides performed better than the control.
– Cultural controls: Removing and mowing over fallen fruit is likely just fine, the key is getting fruit to decompose, which will destroy the inoculum. A flail mower is likely to destroy the fruit better than a rotary mower.
– Bitter With The Sweet – Preventing Bitter Rot in Apples, Scaffolds Fruit Journal, August 29 2016, http://www.scaffolds.entomology.cornell.edu/2016/SCAFFOLDS-8-29-16.pdf
Sooty blotch and flyspeck
This year the first timing for SBFS applications came in June. Normally growers have not had to make applications until mid-July, but due to the unseasonably wet spring, disease pressure from SBFS came early. Growers using leaf-wetness sensors from NEWA stations or Spectrum Technologies stations made their first applications at 175 leaf-wettness hours (LWH) from petal fall. We can also use this same accumulation of LWH to determine when we can lay off sprays this fall. From your last SBFS spray, track wetting hours up to harvest, and if only 150 LWH have accumulated at the start of harvest, you are likely fine. However, if accumulations of hours are low, an additional spray prior to harvest may be beneficial.
While SBFS is not disfiguring, infections can cause fruit to dry out since the fungi grow within the waxy cuticle of the fruit. We do not have resistance concerns with these pathogens since the spores are coming from outside the orchard. If a strobilurin is going to be applied, be aware that most of these fungicides have a 14 or 30 day pre-harvest interval (PHI). See the PHI chart attached and for additional discussion on SBFS, see recent articles in Wisconsin Fruit News (https://fruit.wisc.edu/wp-content/uploads/sites/343/sites/36/2017/07/Wisconsin-Fruit-News-vol2-issue8-1.pdf) and previous AppleTalk call summaries.
Phytophthora
We have seen many first through fourth-leaf trees in significant decline this season. Results from the UW Plant Disease Diagnostic Clinic indicate varying severity of Phytophthora infections in many of these trees. However, it is possible with some of these samples that this decline is not caused by this pathogen alone. Phytophthora requires free and available water for the oospores to germinate and infect the roots. This requirement of intense soil saturation can also cause the soil biota to become anaerobic. When this happens, tree roots can also die from a lack of oxygen. This root death can happen in as little as three weeks of continuous soil saturation. The fall of 2016 was very wet in many locations of southern Wisconsin and 2017 has been an extremely wet season. Therefore, it is equally possible that Phytophthora infections came in after root death, or roots began to die simultaneously with Phytophthora infections.
Crown rot (when the crown or basal stem is attacked and girdled by the pathogen) looks a lot like fire blight cankers with orange and spongy rotten wood, yet has a sharp demarcation between infected and healthy tissue. Infected roots are often blackened, but as mentioned above, it is possible they were not killed by the phytophthora. If the crown of the tree is completely girdled there is nothing that can be done to save the tree. However, if it is only root infections/decay that are present, it is possible that some fungicides may help fight off additional infection while the trees go through another flush of root growth in the fall. These would include the phosphorous acid fungicides, e.g., Aliette (aluminum tris), Rampart (phosphorous acid), or Ridomil Gold (mefenoxam). Ridomil Gold GR has a 12 month PHI and this interval is really only available for non-bearing trees. Ridomil Gold SL does not have a PHI and may be applied on both bearing and non-bearing trees. For organic producers, there are several of the phosphorous acid fungicides that are OMRI approved. Since these fungicides are most effective before trees begin to show symptoms, an application of the phosphorous acid fungicide would be the best options for trees that have been water logged for a significant amount of time.
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
Silver leaf
Trees with the silver leaf symptoms have appeared in large numbers this season. Occasionally an entire tree is found covered with silver leaf, but more often we are seeing lots of scaffold branches in a block with silver leaf. The literature suggests it should only be on decrepit trees, but this year we have been seeing it on plenty of vibrant high-density plantings. The fungus infects the xylem and produces an enzyme that causes the epidermis of the leaf to separate, causing the silvery sheen. The fungus is xylem limited, until it makes fruiting body, which means trees could be without symptoms the following year. Consider marking infected trees to see if symptoms reappear or if vigor is impacted next season.
Patulin
Patty will be writing an article in an upcoming Wisconsin Fruit News on patulin, stay tuned for this issue. Visit August 4 2015 AppleTalk for food safety discussion with guest speaker Dr. Keith Warriner, University of Guelph, Canada. During this call Dr. Keith Warriner discusses basic biology and lifecycles of Listeria and patulin; essential procedures that should be implemented during harvest, packing and processing to mitigate risk of contamination; recommended cleaners and sanitizers to use on packing lines. http://www.ecofruit.wisc.edu/appletalk/august-4-appletalk-conference-call/.
Insect updates
Apple maggot
It is essential to continue monitoring for apple maggot through the end of August. At this juncture in the season we often ask, “How late do we need to monitor? If we catch AM on Labor Day weekend, do we need to spray?†Some literature suggests these late catches don’t need to be treated. An occasional catch is okay to ignore, but if you are getting multiple flies on multiple unbaited traps, you may need to apply an insecticide. Most of the insecticides we use have a seven day PHI; Exirel (cyantraniliprole) and Sevin (carbaryl) have a three day PHI.
San Jose scale
The second generation of San Jose scale (SJS) crawlers are beginning. If you have found SJS on fruit or young shoots continue to monitor for this pest. As harvest begins, or while hand thinning, look for first generation adults (black cap stage) on fruit and continue to check scale tape on infested limbs for crawlers.
2nd Gen. San Jose Scale Nymph Emergence & Peak Flight of Codling Moth & Continuing Larval Emergence, The Jentsch Lab, August 11 2017, https://blogs.cornell.edu/jentsch/2017/08/11/2nd-gen-san-jose-scale-nymph-emergence-peak-flight-of-codling-moth-continuing-larval-emergence-10th-august-2017/
Woolly apple aphid
Continue to monitor for woolly apple aphid (WAA). If WAA is not changing in population size, this suggests there are good predators and parasites keeping the colonies in check. If a cover spray of carbaryl is applied for apple maggot this could destroy the parasitic wasp that is working on WAA, and could lead to a population explosion at harvest. If you blow off the fluff, you may find one of three things: A. a mass of purple aphids that are healthy and vibrant; B. black, mummified aphids that have been parasitized or; 3. minimal fluff and no aphids, which suggests predation by syrphid fly larva or another beneficial.
Codling moth and obliquebanded leafroller
Codling moth is still flying in many places and based on current degree-day accumulations, we may have hatch continuing through the beginning of September. Depending on how long the obliquebanded leafroller (OBLR) flight is, larvae may hatch over an extended period of time and feeding can continue into September. If your final application of the season is Assail (acetamiprid), please note this does not manage OBLR very well. If treatment for OBLR is warranted consider applying another material, e.g., Altacor (chlorantraniliprole), Exirel, Delegate (spinetoram), Entrust (spinosad), or a Bt (Bacillus thuringiensis) product, e.g., Agree, Deliver, Dipel.
Other useful links
• An international perspective on agricultural labor, https://www.fruitandveggie.com/federal/an-international-perspective-on-agricultural-labour-challenges-20246?custnum=1933409&title=President&utm_source=E927&utm_medium=email&utm_campaign=170809E
• Family Farm Succession Planning, https://www.familyfarmsuccession.ca/next-gen-owners/tips-for-young-farmers-getting-started-on-farm-transition-planning-15?custnum=1933409&title=President&utm_source=E927&utm_medium=email&utm_campaign=170809E
