The first call of the 2012 season! We had Dr. Dave Rosenberger from Cornell on the call to discuss a range of issues related to tree disease. Find the recording, topic list, and full transcript below.
Recording
Download the recording of the April 3 call here.
Related References
Dave Rosenberger’s recent article on apple mildew: http://www.scaffolds.entomology.cornell.edu/2012/SCAFFOLDS%204-2-12.pdf
An article on canker problems in apples:Â http://www.nyshs.org/pdf/fq/20
Dave’s presentation on the use of copper sprays in tree fruit:Â http://shaponline.org/wp-content/uploads/sites/343/2012/03/Rsnbrgr-Wed-945am-copper.pdf
Dave’s presentation on glyphosate’s effect on apple tree canker problems:Â http://shaponline.org/wp-content/uploads/sites/343/2012/03/Rsnbrgr-Thus-glyphosate.pdf
Call Topics
- Orchard update
- New FRAC 7 fungicides
- Powdery mildew control
- On the effectiveness of squash mounts for monitoring apple scab
- On Black rot cankers in renewal pruning cuts
- On other new fungicides (Oxidate, etc)
- Insect updates: codling moth, aphids, thrips
Call Transcript, April 3, 2012
Conference Call Intro & Logistics
Welcome to the 2102 EcoApple conference calls! These calls will run weekly from now until the first week of August.
This season, we will begin to experiment with a “webinar†format. A webinar is essentially a conference call with visuals. You will be able to call into the webinar sessions on a regular phone, but to take full advantage of the visual element of these sessions, you will need to have access to a computer and an internet connection during the call (or at any time afterward, if you choose to download and watch the recording instead). We plan to host about one webinar per month. The webinars will have a login process separate from your normal conference call login process, so please keep your eyes out for an update about
Orchard Update
John:    This is the run-down that I really don’t need to do because pretty much everyone knows where we’re at as far as this screwy spring goes. Growers throughout the region – whether you’re in SE Wisconsin, Northern Illinois, or SE Minnesota – most of you guys are at about the same point in terms of tree phenology, and that is at Full Pink on a lot of things, with possibly some Zestar starting to open up. There is an orchard here and there that is in bloom, presumably as a result of a microclimate. Some of the orchards up around the Twin Cities and up around Chippewa Falls are a little bit behind; they still have some varieties at Tight Cluster, I believe.
Obviously, throughout the region, March ran somewhere between 14-18 degrees above average. As everyone knows, though, things have cooled off, and we have seasonable temperatures forecast for the next 7-8 days, and the trees have slowed down correspondingly.
On FRAC 7 Fungicides
John:               With that in mind, I’d like to start with the questions for Dave. First, I’d like to ask you to address the new fungicides – the FRAC-7 fungicides – and tell us how you feel about those and what their purpose is.
Dave:   As far as I know, you have two of those fungicides registered at this point, or two different chemistries in that group: the Luna group and Fontellis from DuPont. These are interesting products. I think they’re going to help us out to some degree, especially in orchards where the DMI group – Rally, Vintage, Inspire Super – are no longer performing well. But they’re not going to be anywhere near as strong, in my opinion, as the DMIs were when they were introduced. It appears that Fontellis and Luna Sensation, which are the only two I’ve tested, are quite good on Scab. Luna Sensation is very good on mildew, as well. And probably of less concern to you out there is that none of the products in this group control rust diseases very well.
Luna Sensation, as you probably know, is a combination of this new SPHI chemistry with pretty much a full rate of Flint fungicide in the package mix. So you can expect what you get from Flint with a little more kick to it because of the SDHI Luna chemistry that is included in that mix.
Fontellis is a stand-alone product of similar chemistry. The company is giving you the option of what to combine it with. It has performed well in my tests combined with Flint, but I’m reluctant to use just a Flint-Fontellis mixture, because both of those products are subject to resistance development, and therefore if you were to put Fontellis with Flint, my felling would be you should still add Captan or Mancozeb. With the Luna Sensation, I have the same recommendation: that it be combined with a contact fungicide. I think that’s going to make these products fairly expensive. The manufacturers are in agreement, I think, that they’d like to see 2-3 applications per year, maximum. At least for the NE part of the US, our feeling is that those applications are best made at tight cluster and pink, or at pink and bloom. They could be made at petal fall on first cover, but that’s probably less desirable, especially where we have rust diseases, because of their weaknesses on rust. So that’s sort of a quick run-down.
Luna Tranquility, they were not going to register at all in apples until Michigan said, “Well, Flint no longer works, and we won’t use any of them if you don’t register it.†So that’s sort of a late-comer to the party, and it really hasn’t been tested in university trials very much. Luna Tranquility is a combination of Luna with Scala fungicide. Scala, in my opinion, is considerably weaker than Flint. The company has compensated by putting a higher rate of Luna product into that mixture, or the rate they’re recommending, but we don’t have enough experience to know for sure how that will fit. I guess if I were going to use Luna Tranquility, I’d probably be planning to use it at half-inch green and tight cluster, a bit earlier than Luna sensation, because I think Scala is a product that fits better in those very early sprays, whereas I think Flint, as you folks have been using it, is commonly used during the tight cluster, pink, and bloom time period, and maybe also at petal fall first cover.
Do you have any more specific questions on those?
John:               The question about using Luna Sensation mixed with Scala is problematic if you’re applying it at that point while trying to get powdery mildew control, because you’re effectively using just the FRAC-7 material, since Scala has no activity against mildew. Is that correct?
Dave:              That’s correct. Again, I think we know a lot more about development to resistance in scab than we do in apple powdery mildew. So how quickly we might select for mildew resistance by using the Luna Tranquility, where we only have one active mode against mildew, I don’t think anybody could really comment on that on this point. But you’re absolutely right. And that’s another reason to keep the use of that one to the earlier part of the season – green tip, half-inch green, maybe tight cluster at the latest.
John:               One question: I mentioned that we have not gotten any confirmed Strobilurin strains of apple scab here as they do in Michigan. However, assuming that a number of orchards across our region are probably on the way – and I understand, as I recall, that it’s not a quantitative type of resistance, like with the DMIs – if you apply one of these products tank mixed with Flint (whether it comes that way or whether you add the Strobilurin yourself), does the fact that you have this new material in there going to clean out the scab resistance that’s been building against Strobilurins?
Dave:               I don’t think we know the answer to that. My guess is that it’s probably not going to clean it up, but it will stop the progression, at least for a while. Obviously, if there’s resistance to the Stroblurins, then there’ll be more pressure on the SDHI chemistry of these new products. But there’s just not been enough research to really know what’ll happen in orchards where we’ve already moved in some degree toward resistance to Strobilurins. That’s one of the reasons, though, that I think I and many others feel pretty strongly that we do need to include a contact fungicide. So we’re going to end up with 3 fungicides in the tank whenever we use a Luna product. That’s been the case, at least in New York; we’ve always combined a contact fungicide — by that I mean either a Captan, Mancozeb, or Polyram, with Inspire Super, as well. We’re moving toward a three-way mixture of fungicides in early-season apple scab control in a big way. As you know, Pristine is a package mix. So if we use that with a contact fungicide, we’re also putting three products in the tank, by using a package mix plus a contact. The contact fungicides will prevent spore germination, so if that contact fungicide is in place, it’s going to be doing, I’d say, 90-99% of the work by knocking out spores before they germinate and really minimizing the selection pressure on these other products. The ones that escape the contact will be picked up by the products that have a little better activity. Although we don’t want to advertise that this SDHI chemistry does give us at least 2 days of post-infection activity, if there are a few things that slipped by, or if you’re a little late after a rain with your contact fungicide, you do have some extra protection from this chemistry groups. And also from the Strobilurins, if they’re still working well.
John:               When you mentioned the contact fungicides affecting spore germination, you’re just referring to the ascospores, not to any possible conidia that might arise here in the next couple weeks. Is that right?
Dave:              Well, they’ll basically stop germination of any spore they contact, so if there’s conidia that’s in a lesion and you get good spore contact with the Captan or Mancozeb that’s applied, the conidia that are exposed to that will not germinate. But the lesion can continue to produce new conidia; it doesn’t eradicate the lesion. So it still is a contact fungicide against all the spores that are present at the time of application, or that are exposed to the residue by rainfall after the application.
On Powdery Mildew
John:    I’m going to shift to powdery mildew, then I’ll open it up for questions. I wanted to mentioned that Dave had an article on powdery mildew in the Scaffolds issue that was published yesterday. So if you’ve got further questions about powdery mildew in apples, take a look at that article, because it’s a good synopsis.
Dave, on the subject of powdery mildew: I’ve been considering that we’re maybe going to have more inoculum this year than we’ve had in a long time because of the mild winter, and I think you mentioned that in the article. We have not had a major problem with powdery mildew here in my experience. So when you talk about DMI resistance in powdery mildew, initially I had the impression that we didn’t have that resistance. On the other hand, in the last 4 or 5 years, we’ve started to see more powdery mildew show up. It’s not been terrible, but it’s definitely more prevalent. I guess the one explanation for why that is could possibly be the emergence of some DMI resistance. Would that be a fairly safe assumption?
Dave:   Well, I guess it could be a number of factors. I don’t know what your last series of winters have been like, but I think at least in our part of the country, we’ve had a series of rather mild winters. Even when we’ve had a lot of snowfall, the temperatures haven’t dropped very low. And as I indicated in that article, you need to get down to at least -5 degrees F to get any significant kill of the powdery mildew buds so that you reduce the inoculum in the spring. It’s even more effective if you get down to -11F, based on the literature.
So we may be seeing more mildew pressure, and I think that, yes, if you’ve been using DMIs for the last 20 years, there probably is some shift in the sensitivity of mildew. As an example, as I’ve mentioned in some previous articles I’ve written, when Bayleton (which is no longer available) was introduced, a lot of the growers in the NE were getting excellent control using only 1.5oz/acre of Bayelton. (Bayelton, of course, had no scab control.) By the time that product was removed from the market, about 5 years ago, people were telling me that it only worked if they were up at about 4oz/acre. That was roughly the same rate per acre that we were using with Nova, so there was no longer a price advantage to using Bayleton for mildew control. People had been using Bayleton if they were on a Captan program and needed some mildew control.
I cite that just as evidence that we know that this population has been shifting. And also, I put into that article that we had some pretty bad mildew experience in NY state in 2010 when a lot of growers had come off of a bad scab year and switched to Inspire Super instead of Rally. Inspire Super, as it turns out, is considerably weaker on mildew, especially after it’s shifted a bit toward DMI resistance. So while the Inspire Super helped them get control of scab where they’d had some serious outbreaks the previous year, they ended up with a big mildew problem because it was just that much weaker that it allowed the DMI-shifted populations of mildew to survive the treatments at petal fall and first cover.
So, I think you’re right. If mildew is becoming more prevalent, it’s probably just part of this gradual shift toward resistance. You mentioned in your email that you’re commonly using Flint in some pre-bloom sprays. That’ll definitely help to keep mildew down, and therefore if you’re using a pre-bloom fungicide or a pink and bloom application of a Strobilurin, that can help to reduce the pressure on DMIs that might be applied at petal fall and first cover. A lot of our NY growers were ignoring mildew control until petal fall, depending totally on the post-infection of the DMIs to take care of mildew at that point. They did that quite well for many years, but it’s no longer working very well.
John:               Powdery mildew has not been on our radar screen in any large degree. Quite frankly, the growers that I’ve spoken with this Spring have primarily focused on non-bearing trees and trees that are not fully-grown yet, as opposed to worrying too much about it on mature trees. In your article in Scaffolds, you talk about beginning your spray program for powdery mildew at pink or thereabouts and continuing it through a fairly long period. I was rather hoping that if we applied a Strobilurin or a DMI or this FRAC-7, the SDHIs, two times before petal fall, that we would nip it in the bud. But you’re suggesting that where powdery mildew may be a concern, you need to continue to apply one of those materials that are active against it. Is that right?
Dave:   Well, I think it really depends on the amount of inoculum in the area, and on whether you have abandoned apple trees in hedge rows, or woodlots, or homeowner settings that might contribute mildew to your block. My concern is that from petal fall through second cover, you’re getting a tremendous number of new terminal leaves formed, and all of those newly-formed terminal leaves are going to be very susceptible to mildew if there’s any inoculum there. Now, in a low-inoculum orchard, I would agree that if you cover at pink, bloom, petal fall, or two out of those three, you may have good mildew control if there’s not inoculum.
If you see “flag shoots†in your orchard – and by flag shoots I mean the primary infections on terminal buds where every leaf comes out mildewed – you’re going to have inoculum from that that will persist and move to new leaves until you get to terminal bud set. As the growth slows down, there’s less of a problem, because there are less infections or potential infection sites, but I know several growers in NY have stopped spraying at petal fall when there was a lot of inoculum, and by June the orchards looked really sick, because there was enough inoculum to spread. Now, we’re talking about Macintosh in this case, which usually doesn’t get a lot of mildew. But if there’s Cortland or Paula Red planted with the Macintosh, which supply inoculum, then all bets are off.
So it really depends on inoculum pressure. And probably your own grower experience is a good a teacher there as anything else when it comes to how many spays you’re going to need.
John:Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Questions about powdery mildew or new fungicides?
Peter Werts I have a question about powdery mildew. When would we expect to see visual signs of mildew on leaves after those infection periods?
Dave:   If the flower cluster buds are infected, you can see these (at least if the growing conditions are right) at least at about tight cluster. In the Scaffolds article, I show a picture of buds at tight cluster with a healthy bud compared to a mildewed bud. In some years, it may be too cold or the conditions may not be right, but certainly by pink it would be evident in flower buds. But those buds are smaller and you’re not going to see them from the tractor seat as easily as you would the terminal shoot buds.
The terminal shoot buds are visible probably by petal fall to 5 days after petal fall, depending on how carefully you observe.
John:Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â People who are scouting their orchards for Rosy apple aphid or other arthropods would be able to pick out that powdery mildew in the flower clusters fairly readily.
Peter               So right now is our opportune time to be catching it – right now.
Dave:              Yes, in the flower buds. And then, again, just as a routine protectant spray, you really want to have those protectant fungicides – like Flint or the Luna Sensation – in place by pink so that you’re avoiding any of the spores from the primary infections moving on and creating many more infections that will show up around petal fall to first cover.
John:               And by the way, just to finish up, in Dave’s article yesterday, he also talks about using sulfur, whether you’re certified organic or not. I wanted to throw that out there, because there probably are a few organic growers on the line. If they have some concerns about powdery mildew, sulfur does work well on that critter. So read his article.
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On squash mounts for monitoring apple scab
John:    I’d like to switch and ask you to respond to the question regarding degree-day model vs. squash mounts for apple scab. Just so the growers know what we’re talking about. This year, we had a very early bud break. But if you had your weather station up, you’d have seen that we were also accumulating scab maturity degree days at a rapid rate. A grower who does squash mounts and looks for ascospore maturity is finding that there is a tremendous, dramatic lag this year between what the degree-day model says about what scab maturity should be and what he’s finding in his squash mounts.
The full question:
Minnesota growers continue to pay for perithecial squash mounts and associated ascospore maturity readings. One of the growers who is knowledgeable and has been doing his own squash mounts for twenty years has these questions:
Scab model question 1)Â Specware shows 74% spore maturity on April 1st. Psuedothecia are just swelling to the point that we can find them on the leaves, squash mounts are showing only very immature spores. It appears the model does not adapt well to our northern climate or to our races of scab. Does Dave have a better explanation?
Scab model question 2) Please explain how a predictive model can be more accurate than the actual observation and statistical analysis of the developing spores.
Dave:   I have a technician who has done squash mounts for about 37 years. A group of us at Cornell and the New England states got together back in the early 1990s and had a whole bunch of people doing squash mounts agree to read the same slide sets. So a person prepared squash mounts, and we then passed those slides around. I think 18 different people read those same slides to see what numbers they’d come up with in terms of maturity. This was all published in a refereed journal back in the early 1990s.
The bottom line was that there was tremendous variation based on individuals. Then, about 6 individuals agreed to re-rate those slides at about two-month intervals, so they wouldn’t remember what they looked like, and they’d come back and do them all over again. And even more appalling to me was that many individuals came out with totally different results when they read those slides a second time and a third time.
All of that goes to say that reading squash mounts is more of an art than a science, because you’re trying to look at basically a whole bunch of overlapping spaghetti, keep track of which ones you’ve already counted, and accurately assess spores. My technician, as it turned out, ended up being one of the more reliable people in terms of his repeatability. Therefore, I put a great deal of faith in the counts that he provides. But I’m throwing this out just as a caution that a squash mount reading isn’t necessarily accurate, because it’s so much in the eye of the beholder. It can be very accurate if the observer is consistent. And even though any one observer may differ from anyone else, if you want to know how to the calibrate the results of your own observations, then being aware of those differences becomes valuable.
That’s some background to illustrate why the developers of the ascospore maturity model feel that their model is probably more accurate than individual observers. The model is based on a lot of years of data of actual spore trapping. It’s not based on someone observing spores; it’s based on how may spores were trapped in Burkhart spore traps related to the time of bud break and the temperature degree days.
Nevertheless, we continue to use the squash mount data provided by my technician, because I fully agree that in some years there is a big delay. A question I have is this: this year you gather than scab is way behind the trees. Did you have a lot of time when the leaf litter was dry – either freeze-dried during winter because there was no snow, or because of lack of rain this spring?
Grower:         This was a low-snow winter, and the ground dried a lot. The spring hasn’t necessarily been very dry, but they have been freeze-dried and gotten wet and freeze-dried several times over the winter.
Dave:   Most of the maturation, as I understand the cycle, goes from late January and mid-February when the asci – the two mating types in the leaves – begin to coalesce and form the perfect stage, the ascospores. My guess is that if you have a lot of leaf drying between, say, early February and the time the trees leaf out, then ascospores are going to be delayed. That seems to be the only reason that I can think of (and there’s some reason to support that) where we may end up with significantly-delayed ascospore production compared to tree phenology.
I think in general the model is fairly accurate. I would argue that after the first 10 days from green tip, I’ve never found any particular reason to continue spore counts. My feeling is that our spore counts in the Hudson Valley where I am can sometimes save a grower one spray, or maybe in an occasional year two. But by the time we get more than 10 days out from green tip on the trees, we almost always have some mature spores and some risk of infection.
Grower:         In Minnesota, with doing the squash mounts for over 20 years, what I’ve seen is that we have that same phenomenon, but it’s much closer to pink and early bloom as opposed to green tip.
Dave:   Yeah, you know, I used to have a lot more faith in using squash mounts to time the first sprays as long as we had DMI chemistry that would erase any errors if there were just a few infections early in the season. As we’ve gotten DMI resistance, what we’ve found is that if a grower misses even a few early infections because they’ve delayed their applications, there’s no way to catch up because there’s no other chemistry that will totally shot down sporulating lesions and get you home free through the summer. So, while it’s a great IPM strategy as long as you have some redundancy like a good fungicide to cover your tracks should there be any error or miscalculation, I’m much less keen on using that tool in the era of DMI resistance. We just have seen too many orchards that either take a chance intentionally or they can’t get in due to having brush in the orchard or too much rain – and we can’t stop the scab, we end up spraying high rates of Captan through the entire summer to keep it off the fruit in orchards where there’s DMI resistance.
If it’s working for you, fine. But I’m really a little gun-shy of using that as a reliable strategy. I have a little more faith in using the PAD evaluations in the fall and saying that orchards that have virtually no scab in the trees in the fall, we know we can delay by several weeks, because there’s just such a low number of ascospores that nothing will be out early. That early, low amount of discharge amounts to zero in orchards that have low inoculum. But in orchards that have high inoculum, forget about spore counts and just make sure you’re covered.
So I think that the amount of inoculum in your orchard is probably more critical, in many ways, than the spore maturity itself.
Grower:         With the conventional growers that are going to continue to use the squash mount data, given the increasing resistance to the fungicides, do you think that they should go with a presence-absence 1% threshold instead of the old established 5% mature spores threshold? I think it’s a lot easier to tell an absence-presence of pseudothecia and maturing asci than actually counting and getting a percent. So what if they waited until, say, 1% and then started their spray (as opposed to the 5%)? Because if there’s a lot of discrepancy [between observed and actual presence], 5% may actually be 15%.
Dave:   That’s true. The other option to consider is to run spores in a discharge tower and actually looking for ascospores at discharge. In our squash mounts, my technician will bring in fallen leaves from under a tree. He’ll cut every leaf in half right across the mid-vein. Half of those he drops in boiling water so the spores won’t actually be discharging under his microscope slide when he looks at the pseudothecia. But the other half he puts into a tower after soaking for about 20 minutes. We then turn on a vacuum. The tower has little holes in the bottom so that any spores that are released are drawn down through the air column through these little holes and they impinge on greased slides. He then looks for spores on those greased slides. Over the years, given the method that we use – the number of leaves and the way you arrange them are all part of this – we’ve found that, in these highly-scabbed leaves from abandoned trees, until we see about 60 spores that are actually released and countable on his slides, we’re below an economic threshold. So, I combine the spore discharge data with the squash mount data to come up with the recommendation for growers.
So I would say that, in addition to a squash mount, if you can look at whether there are actually any spores being released, that would be one form of redundancy you could bring to your counts.
John:               The other thing that there’s no reason we can’t do is differentially spray the orchard, since nearly every grower has a fraction of their orchard devoted to Honeycrisp and other varieties that are far less scab-susceptible than Macintosh and its ilk. So, instead of putting in these early sprays on the entire orchard, you can save some money without risking an awful lot, at least as far as scab goes.
Dave:              Yeah, I’d agree with that. Also, as we all know, some of those cultivars have green tissue much earlier than others.
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On Black rot cankers in renewal pruning cuts
John:Â Â Â Â What about the question about cankers forming from renewal pruning:
We’re beginning to hear about cankers associated with stubs left from renewal pruning. The presumption is they’re caused by one of the Botryosphaeria. Is this likely considering when the sporulation periods of Black and White rots, and that these renewal cuts are made during dormant period – up to ~ bloom?
Dave:              Yeah, that’s an interesting one I hadn’t heard of before. How old are the trees where the cankers are showing up?
Grower:         They’re 10-15 year old Honeycrisp. And there’s considerable damage from the Black rot in the renewal cuts.
Dave:   Here’s my perspective on the Black rot – White rot canker. I’m not sure everyone would agree, but I’m going to throw this out based on observation, because it’s almost impossible to prove the hypothesis that I’m going to give you. I think that Black rot is never a primary pathogen. Black rot tends to move into trees that have already been colonized in the older xylem by basidiomycetes. Those are the fungi that cause bracts [or “bracketsâ€] on dead apple wood – you know, the little white shelf fungi that’ll pop out when an apple limb is killed. Those shelf fungi get into pruning cuts and particularly are a problem if the tree has been winter-injured at some point in its life. Winter-injured trees can no longer heal shut the pruning cuts the way a healthy tree would. Those bract fungi gradually take over more and more of the xylem on the inside of the tree and weaken the tree basically by eliminating parts of the wood that could still be used for nutrient storage during winter, I believe. The bottom line is that once those limbs are compromised, then Black rot can move into the outer part of the bark and cause a canker. We call it Black rot canker, but it’s really the end of a long chain of events, and there’s really nothing we can do about that.
Now, if you want to prove me wrong, then I would love to see a photograph of a fresh cut through a limb where there’s been this canker form that shows no internal browning of the wood. A healthy apple tree, believe it or not, does not have dark wood in the center. The dark wood is always an indication of secondary invaders in the old xylem. I think in every case I’ve looked at Black rot canker, there’s being a large ring of dark wood in the center of the tree and then Black rot moving into the outside.
Now I want to comment just a bit further, though. White rot, Botryosphaeria dothidea, is an active pathogen that will move into trees under drought stress. So if you don’t have trickle irrigation and you go through severe drought stress, a year later you can see a lot of cankering due to White rot canker. It’s present all the time in the surface of the tree, but the tree really isn’t susceptible to it until the tree is under drought stress. Then, it can take off and cause some various types of canker on the tree surface.
Usually what’s showing up at the pruning cuts is Black rot, but it’s there because the trees were previously compromised by cold injury and other things affecting the tree. Again, there are other canker fungi like Nectria, but they would produce orange spores and a number of other odd things.
John:Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Can you generalize about the basidiomycete that would be the primary pathogen that opens the way for the Botryosphearia?
Dave:   Well, the most common one in our area – and I think it does vary by area – is Schizophyllum commune. It produces a tiny little white bract, usually about the size of a pencil eraser.
If you’re curious about what’s in these, one way to tell is to take a limb that you’ve removed – say 1.5†to 3†in diameter – take all the leaves and branches off of it, get a foot-long section, and stick it in a bucket of soil that has drain holes in the bottom, but so the bottom of the bucket stays wet, so the wood can absorb moisture. In probably 30-90 days, you’ll see bract fungi pop out all over the exterior. That can be a way to diagnose which one is in there.
Turkeytail fungus is another common one that I see up in the northern parts of NY near Vermont and Montreal area.
John:               We sort of think we know when the Botryosphearia are sporulating – at least when they begin. What about these things? Is there anything we can do in terms of our fungicide program that might slow these guys down?
Dave:   I don’t think so. I think the inoculum from these is so endemic, and so all over the place, that you’re really trying to protect a compromised host. When you have trees that have been compromised by one factor or another, it’s really tough to keep them protected. I’m not aware of any studies that suggest that you could prevent either the basidiomycetes or the Black rot from getting in once those are compromised.
My predecessor here back in the 1960s did a study on big old trees. He showed that Black rot is more of a problem if you’re pruning from green tip to bloom than if you’re pruning earlier in the year, because the fungus really can’t grow at sub-freezing temperatures, and the pruning cuts dry out so quickly that Black rot can’t invade that damaged bark you create when you’re making a pruning cut. In orchards that have this problem, you’d probably be well-advised to do your pruning before bud-break so that the pruning cuts dry out before Black rot becomes active. But that’s probably the only thing that I could suggest. Those spores are everywhere, even in a well-sprayed orchard. Mancozeb doesn’t control them very well. The DMI chemistry doesn’t control them very well. But the biggest problem is that the host is so compromised that it’s pretty hard to protect.
John:               That’s pretty good information. Pruning in the dormant period and being hesitant to prune if you suspect either drought stress or winter injury in that particular block of trees.
Dave:              Yeah, although you do have to prune even if they’ve been winter-injured. Winter injury is just one of those things that we can’t deal with very well; it just happens.
John:Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â The thing about renewal pruning is that it leaves dead stuff sitting out there, as opposed to regular pruning. It just seems to hang there forever, asking to be invaded.
Dave:Â Â Â Â Â Â Â Â Â Â Â Â Â Â One other point is that there is some evidence that all kinds of stresses can contribute to this. There was one orchard where fairly young trees were developing Black rot. He actually went through and bermed up the soil around the trees to drain water away from the crowns. The Black rot problem disappeared. In his case, it was wet feet or water stress that was making the trees more susceptible. I think when thinking about new orchards, if you have any question about soil drainage, putting in a slight berm to plant your trees on could go a long way to eliminating this kind of problem 12 years down the road.
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On other new fungicide products (Oxidate, etc)
John:Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Dave, could you throw out a couple of opinions about these other fungicide products on the market? The plant inducers and other bacterian stuff. There are a lot of different formulations and a lot of different brands, now, and they make some pretty spectacular claims. Do you see any role for those products either in organic or conventional fruit?
Dave:   I think the resistance-inducers have a fairly mild effect and are generally not going to be very effective on an aggressive pathogen like apple scab. They may have more of an effect on something like the Black rot canker we just talked about, but even there, I think it’s questionable.
I’m quite concerned about the amount of money people are spending on products that have no data to substantiate their effectiveness. In my opinion, any reputable company should be able to provide you with at least one or two tests with replicated treatments by good scientific method to show that their product actually has worked better than alternative products. So I’m pretty skeptical of most of these, but that’s not to say that they won’t work.
I think with things like Oxidate, the timing is absolutely critical. Oxidate will kill the things it hits at the time that it’s applied, but it’s probably inactivated within 30-40 minutes after application. That means, for example, that if you’re going to try to control Fire blight with Oxidate, you would want to be applying it to the open blossoms within the 20-30 minutes before the wetting event that’s going to trigger an infection. I suspect it might work if your timing can be that accurate. If you apply it in the morning and you have a hot day, then it rains in the evening, I suspect that the bacteria, at least in some flowers, would build up again in that interval, because the Oxidate will provide no residual activity.
Things like Serenade, that to some extent have a mycotoxin or a toxin that affects the organism, or that have live organisms to colonize, that may of some effect.
John:               So you’re saying that those products may have a little more of an effect over the long term than things like Oxidate?
Dave:   Well, I think that’s where you really need to understand the product. If your objective is to colonize – say, with fire blight – the surface, then you want the product you’re applying to be there. For example, one that’s available now is Blossom Protect. It’s actually an Aureobasidium species. That is a nutrient scavenger. I think the concept is that you get it there before the Erwinia (fire blight) and it eats up all the nutrients so that the Fire blight bacteria can’t survive because there are no available nutrients. I’m still skeptical of that working, but in that case you would want to apply it early so that it has time to build up, whereas with Oxidate you want to apply it as late as possible to kill the maximum amount of pathogen just before an infection event.
So, I just use those as illustrations of just how complex it can be to time these. Really, there hasn’t been much research dedicated to it because most of these companies aren’t willing to support research, and it’s quite expensive to run these kinds of trials. There have been some published reports on Fire blight, and really, compared to Streptomycin – if you would give Streptomycin a 10 in terms of Fire blight control, I’d say none of the rest of these would come in above a 3, at the best.
One other caution: I did try using Oxidate against apple scab. Where we applied it with a hand gun to drip, we gut fruit russeting from it when we applied it on an every-5-day schedule like we would sulfur. So, you can also get phytotoxicity from some of these.
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John:Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â That covers a lot, and we appreciate the hour you spent with us, Dave.
Dave:Â Â Â Â Â Â Â Â Â Â Â Â Â Â Happy to do it, and hope you have a good season.
John:               As with you, if we get through the next 3 or 4 weeks without any 20-degree nights, we’ll certainly be feeling lucky.
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Insects
John:               If there are any growers left on, I’m going to run down the insect issues that I want you to be aware of.
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Codling Moth
John:               First of all, codling moth traps. We normally put them up the beginning of bloom, so you should have some out soon, if not already. The same goes for mating disruption. Conversely, if you look at the near-term forecast and recognize the temperature parameters that are required for codling moth flight, I don’t know that there are any evenings in this week, for example, where we will be above 61 or 62 degrees, which is the minimum for codling moth to be flying. So there may be a little wiggle room there, but not a lot.
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Aphids
John:               The other issues: I know most people have bees in the orchard now, or are bringing bees in shortly. But there are a large numbers of aphid species in every place that I go. This is the first year I’ve ever seen Rosy apple aphid before bloom. You can readily see the curled leaves. The stem mothers have already matured and are laying young, so colonies are developing. It’s a good time to be checking for those things, because there are a couple of things that we can do for them even at petal fall if we’re on top of it.
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Thrips
John:               One insect I found in several places: thrips. They blew in two weeks ago and they have been around ever since, but it’s been so cold that I have seen almost no damage to the flowers. So, I don’t know that it’s a concern, but if it warms up before all the blossoms open up, it may end up being a concern, and there may be very little we can do about it at that point if we have bees or other pollinators in the orchard.
Grower:         With bees, you don’t want to go after that stuff because you’ll damage your bees?
John:               Yeah, there’s nothing you’ll be able to do at this point. But the good news is that it’s cold enough the thrips are not extremely active. It looks like we’re going to have a fairly slow bloom period, which argues against those thrips being really damaging to those open blossoms.
