It’s been a busy season on the conference calls. This week we took a breather of sorts and spent the hour discussing the current status of a range of insects and diseases with John. Download the recording, see the detailed list of call topics, and read the full transcript below.
Download the recording of the June 12 callÂ here.
- Conference Call Updates
- Updates on diseases
- Powdery mildew
- Question on Sooty blotch and Fly speck development
- Updates on insects
- Apple maggot
- Codling moth
- On mating disruption for Codling moth
- On CM control for organic growers
- Update on scale crawlers
- Update on Oblique-banded hatch
- Update on Potato leaf hopper
- Question on summer pruning
- Question about mysterious internal fruit damage
Conference Call Updates
Alex: Next week we will most likely have Larry Gut back on the line to talk with us about Codling moth, Oriental fruit moth, and Lesser apple worm. Send your questions into John as soon as you have them!
John: Obviously, weâ€™re a little far along in first-generation Codling moth to have Larry on, but I think that we have enough questions having to do with our weird year and the strange flight of CM that weâ€™ve seen, as well as with Lesser apple worm and OFM, for Larryâ€™s visit to be a benefit.
Updates on diseases
John: As far as I have been able to tell, I havenâ€™t seen any scab out there that is recent. Some of the lesions Iâ€™ve seen look pretty intense, but when I look at where the lesions are located on the shoots, Iâ€™ve seen that almost all of them are located near the base of the shoots, on the old growth. If the recent shoot growth is scab-free and all of your lesions are toward the base of the shoots, then thatâ€™s an indication that those lesions have been around for a while, and that either:
1)Â Â Â Â Â Your scab control program has been working, or
2)Â Â Â Â Â Youâ€™ve had low scab pressure because of the heat (among other things). Even if the lesion looks pretty nasty, temperatures in the high-80s or 90s will lower the chances of those conidia being viable.
So, thatâ€™s just a heads-up. If youâ€™re concerned about cutting off your sprays (particularly with a light crop) and you are worried about scab, go figure out where on the shoot your scab is located. If you donâ€™t have anything on the newest 3, 4, or 5 leaves of the shoots, then there is far less chance that you have any actively growing scab in the orchard, and far less chance that youâ€™ll have problems if you cut off your sprays.
John: Where I have seen it, it jumps out at you. It is on the terminal growth. The shoots that are infected are shriveled and covered with white mycelial growth. When you see it, itâ€™s hard not to know exactly what it is.
The big question is whether you should do anything about it. Whether you do anything about it depends on whether or not your trees are continuing to have shoot growth.
Whether you have a light crop or not, if you see some Powdery mildew, it is likely to be confined to certain varieties. If the terminal leaf on the shoots of those varieties has set, then Powdery mildew wonâ€™t be able to spread any further than where it is today and presents much less risk. If the terminals have set, then the need to put on a spray for PM is greatly diminished.
The state of the terminals varies by geographical location. There are a lot places that have set their terminals.
If you do need to put a spray on, then Sulfur is a good one, whether you are organic or not. Many conventional growers (especially in New York and Michigan) who used the sterile inhibitors like Nova and Rally for many years for scab control saw that Powdery mildew in their orchards developed resistance to the sterile inhibitor class of materials. Sulfur is a good choice if you do have resistant PM or are concerned about it.
If Powdery mildew is a concern, Iâ€™d point you to a great article on PM in the Scaffolds issue from yesterday.
Question on Sooty blotch and Fly speck development
Peter: Where are we at, generally speaking, with accumulation of wetting periods for Sooty blotch and Fly speck? Are we ahead? Itâ€™s been so dry.
John: Itâ€™s a good question, Peter, and I donâ€™t know the answer to it. Itâ€™s been so dry that I havenâ€™t paid much attention. Iâ€™d really like to find somebody that has a relative humidity monitor in their orchard in addition to a leaf wetness monitor, and use that for comparison. But, basically, the leaf wetness model that weâ€™ve been using would indicate that go 175 leaf wetness hours since petal fall (or, if you put on an EBDC or strobulurin after petal fall, since about a week after that application).
But as faras the tree phenology goes, youâ€™re right, Peter. In some years, weâ€™d probably be getting pretty close to Sooty blotch and Fly speck time.
It appears that relative humidity is actually a better indicator than leaf wetness hours for us in the Upper Midwest. So, if I can get a hold of somebodyâ€™s relative humidity hours and let people know where we are, Iâ€™ll do that.
Dennis Norton (Royal Oak Farm, northern Illinois): John, Iâ€™ve got relative humidity hours. My disease model for Sooty blotch actually kicked in toward the end of April.
John: Thatâ€™s the problem with a lot of these programs. They donâ€™t differentiate when the start time/biofix is. You have to be able to punch that in after the start period. Itâ€™s that way with scab, too. Itâ€™ll tell you that you had a scab infection yesterday, even though youâ€™re well past having any primary innoculum out there.
Dennis: As of yesterday, we were at about 406 relative humidity hours, starting from March 1.
John: So, can you get it from May 10 or May 15? That would be more accurate.
Dennis: Itâ€™s 71 cumulative leaf wetness hours from May 10.
John: So, if we use 175 as the trigger, then weâ€™re still about 100 hours away from having to worry about that.
Also, youâ€™re down there in northern Illinois. Your relative humidity is probably about as intense there as it is in anybodyâ€™s orchard.
Dennis: Yeah, the humidity here seems to me like itâ€™s worse than any place else.
John: Iâ€™ll check in with you in the coming weeks and let people know when weâ€™re getting close to that 175-hour mark.
Updates on insects
John: Apple maggot traps should be placed earlier than normal. It used to be July 1, but for the least few years weâ€™ve been saying that June 15 is a better time, to make sure that we are covered. We have indeed have catches of Apple maggots in the middle of June for several years now. This year, as dry as it has been in most cases, you might think that the Apple maggot would not be around so early. however, I remember a couple of years ago having no moisture in June but seeing an amazing flight of Apple maggot. The messsage: donâ€™t wait.
People used to think that Apple maggot could be predicted by a â€œtriggerâ€: if you had 1/2’â€ of rain after July 1, then you should expect to see Apple maggots coming out of the ground. But that correlation doesnâ€™t seem to have held over the years.
Because everything else has been early this year, and other things that overwinter in the soil have been early (like June bugs), then we should expect that things like Japanese beetle and Apple maggot (which are also overwintering in the soil) will be early, as well.
So, try to get some traps out this week if you can.
A refresher on trap scenarios: I donâ€™t use baited red balls unless I had Apple maggots in the orchard last year. If you have an in-house population of Apple maggots, then you donâ€™t have to worry about these baited lures pulling Apple maggots from some wild tree into your orchard (which they will do). But, if you had AM in a variety or two last year, then go ahead and bait the red balls, because you want to make sure that youâ€™re doing everything you can to accurately monitor whatâ€™s going on.
With a baited red ball, you can use a threshold of 5. With an unbaited red ball, the threshold is 1.
Itâ€™s generally ideal to place the balls around the perimeter of the orchard. Itâ€™s also useful to put some in the inside of a block, particularly if that block has varieties that are susceptible to Apple maggots. Susceptible varieties would include any summer apple â€“ Lodi, even Redfree. Those easrly varities that tend to be droppy may have a population of maggots right underneat them, near the drip line. Around those kinds of varieties, itâ€™s highly recommended that you put up a red ball trap.
On using the yellow baited cards: Those yellow cards are not baited with the same compound as the red balls. They use an ammonium acetate instead, which is a feeding attractant. The yellow cards are very useful to put up if you have the wherewithal to change the cards or reapply the ammonium acetate on a weekly basis. They need to be changed about every 7 days for them to work. Thatâ€™s the reason that I gave up on them years ago. If you can keep them refreshed, then the yellow cards can give you an advantage: when the Apple maggot female first climbs up out of the soil, she needs to feed and mate before she first lays eggs. Itâ€™s during that first week that she would be attracted to those yellow cards. If you had some of the yellow traps out there and caught some maggots on those, then youâ€™d have a little bit of lead time to figure out what to spray, when to spray, and where to spray it. If you catch the maggots on the red ball alone, then you donâ€™t have as much of a lead time: at that point, the female is already attempting to lay eggs.
In either case, I would never use the yellow cards alone; Iâ€™d always put the red balls up, as well.
If you put up traps, stay on top of them, and let me know if you catch any.
Weâ€™ll talk more about AM in the next few weeks.
Grower: I did put up a yellow card, and with the little bit of rain that we got yesterday morning, I did find a fly on the card.
John: Was it an Apple maggot fly?
Grower: I didnâ€™t check the wing pattern too closely to make sure it wasnâ€™t a Cherry maggot or something, but Iâ€™ve only seen Apple maggot here in the past. So that means sheâ€™s out of the soil and looking to mate. How long would it be until they start attacking the fruit?
John: It would be anything from a few days to a week. Do you have any red balls up?
Grower: Not yet, but with what iâ€™ve just heard, I will.
John: The reason I ask is that, in my experience, I might catch one AM on a yellow card but catch 15 on a red ball in the same time period. So, the red balls are much more highly attractive than the yellow cards. If you caught one on the yellow card, thatâ€™s a good heads up. But that doesnâ€™t give you an idea of how intense the pressure is. You should get a couple of red balls up there close to the yellow card and see what happens with it. If you get only one AM female on a red ball, that is technically meets the threshold, but it doesnâ€™t send off alarm bells like if you find 20 females on a ball. Finding 20 females n an unbaited red ball means that you have a nightmarish infestation, and you really need to be on top of things.
Dennis Norton: Iâ€™ve gotten some Cherry fruit fly, but no Apple maggot yet.
John: Yeah, Cherry fruit fly would be expected. But considering how early some of the other things are, it wouldnâ€™t surprise me to see Apple maggots this week. To make sure what youâ€™re seeing is AM, though, you do need to look at the chart and compare the wing patterns.
John: Codling moth has been a little deceptive this year in terms of its flight. Based on the little bit of information Iâ€™ve gotten from my weather stations and from the growers I spoke with this morning, it looks as though in most areas of our region, weâ€™re somewhere between 450 and 570 degree-days from the first biofix. There is a big caveat here: the growers who have seen very little CM this year will probably have a very different biofix than growers who have a larger population.
Dennis: John, I did a little investigating, and back in March we had enough degree-days here for them to fly and lay eggs. We were just short of degree days back in March for those eggs to have hatched.
John: Are you using the Washington model?
Dennis: Iâ€™m using multiple models.
John: The reason I ask is because most models donâ€™t have a set trigger based on degree-days alone starting with January 1. About three years ago, Washington started using a model like that, which doesnâ€™t depend on trapping to set a biofix. As far as I know, Larry Gut hasnâ€™t been using it and hasnâ€™t verified it. To use the Washington model, we would have to adjust it for our latitude.
I see no reason to question the biofixes that we ended up getting this season. So, while itâ€™s possible, I think thereâ€™s a pretty low chance that we had an early flight in March. But if we put out stations in April some time, or even by May 1, and got biofixes some time in the next couple of weeks, then I would think that thereâ€™
So, my question is: how many degree-days had you had in March?
Dennis: We accumulated something in the neighborhood of 300 degree-days just between March 1 and April 1.
John: Yes, that sounds right. March was a scorcher. But weâ€™re using the age-old model where we just put out traps and try to set a biofix and base everything else from that biofix. Thatâ€™s the way weâ€™ve done it for years. I think it would be wonderful if we could all use something like Washingtonâ€™s model: start counting degree days from January 1 and not even have to put out traps to set the biofix. To date, though, that information hasnâ€™t been verified for our area. For now, I think weâ€™re better off using the biofix that occurred somewhere between May 4 and May 20, depending on the orchard.
Dennis: Our counts have been right at or below threshold. I had to end up bypassing any ovicide because I was trying to get a biofix on a consistent flight. We had a very inconsistent flight. I ended up with a May 15 biofix, but I only trapped moths in 2 out of my 10 traps on successive days. During that time period, I never trapped any more than 3 moths in any one trap. So, I bypassed the ovicide I usually use and went straight to the larvacide.
John: That is one of the question for Larry. On earlier calls, we talked about whether the CM would be early based on the heat in March, or whether they would be light and late because of the freezes we had in April. He wonâ€™t know the reason why the early CM numbers were down. But it looks to me like the CM might be responding to a little of both effects: in some places, CM numbers have been lighter than previous years, and in other places theyâ€™ve been heavier. Remember, the CM overwinter on the trees as fully-grown worms. When they start activity in the spring, in temperatures above 50 degrees, they have to transform themselves from a fully-grown worm into a pupa, and then into a moth. During tha process, they are considerably less hardy. If we get down to, say, 22 degrees during that time, then itâ€™s possible that they experienced some mortality. The light numbers that we saw in some areas suggest that this might have indeed occurred.
Now, hereâ€™s one caveat. A couple of growers that had CM in their orchards last year are still catching CM in substantial numbers (now, between about 450-600 degree-days from biofix). There are other orchards that have had much smaller numbers, but over the last week had a spike. This late spike used to be called the â€œB-peak.â€ In first-generation CM, weâ€™d have a single peak, then the numbers would decline a little bit, and then a second, mini-peak (B-peak) would pop up.
The grower I talked to this morning was wondering if the spike of CM that he caught over the weekend was indeed the B-peak.
In any population of individuals, not every individual is going to mature at the same time. From an evolutionary standpoint, the reason that individuals donâ€™t mature at once is because itâ€™s safer to spread out development in case there is any adverse weather event. Once the worms emerge from their period of dormancy/quiescence, they become more sensitive to freeze damage.
So, take, for example, a population of Codling moth worms overwintering on your trees. The ones that donâ€™t start developing early â€“ that is, the ones that delay development until later in the season and become the â€œB-peakâ€ â€“ will be less likely to be killed by freezing in April. So you can theoretically see how we might have a late peak (a â€œB-peakâ€) that is higher than some of the earlier numbers. Keep that in mind.
If youâ€™re not using mating disruption, stay on top of the trapping in the next week or two, because we might be surprised by the peak.
On mating disruption for Codling moth
John: I do need to mention something about mating disruption. Weâ€™ve talked many times about the need to monitor for Oriental fruit moth and Lesser apple worm. This is a complicated issue. If you have mating disruption up for Codling mothÂ and it seems to be working, and youâ€™re not applying insecticide, you really need to look at your Oriental fruit moth and Lesser apple worm numbers.
A couple of orchards that have had mating disruption up for a couple of years have picked up substantial numbers of LAW in the past couple of weeks. The problem with this is that we donâ€™t have thresholds for LAW and OFM, even though when theyâ€™re in the fruit, they look just like Codling moth worms â€“ theyâ€™re almost impossible to differentiate.
So, if you have had any flight of LAW or OFM in your mating disruption orchard in which youâ€™ve applied no insecticide for Codling moth, you need to stay on top of monitoring that fruit for LAW and OFM.
Iâ€™m seeing counts of LAW in the 40 to 60+ range over the course of two weeks. Those are much higher numbers than I normally see on a routine basis. So, even though we donâ€™t know what the threshold is for these two insects, I can tell you that we normally donâ€™t pick up very many of LAW or OFM at any one time.
Even if you have a light crop, I think you need to be concerned about OFM and LAW. You need to have a trap out. Weâ€™re in a critical period, right now. Weâ€™re right at the crossroads between first-generation control of these three internal fruit feeders and the following generation(s). If this first generation gets away from us, it wonâ€™t matter whether you have CM or OFM in your orchard; youâ€™re going to have a bunch of wormy fruit at harvest. And I donâ€™t think that you want to have a bunch of wormy apples to deal with, even if you have a light crop.
So, stay on top of those three internal fruit feeders.
Even if your CM numbers have dropped off in the last couple weeks, make sure your lures are still good and your traps are still sticky. Keep an eye on them to make sure that they donâ€™t jump up on you. Itâ€™s not critical to have a LAW/OFM trap if youâ€™ve already sprayed an insecticide for CM. But if you havenâ€™t sprayed an insecticide, it is critical that you have a LAW/OFM trap up.
Dennis Norton: How critical is it to have those traps for CM placed in the top 1/3 of the tree?
John: Well, they say that itâ€™s critical. When I started doing this 25 years ago, we were putting all our traps at chest height. I think that an awful lot of trap thresholds were developed with traps at 5-6 feet off the ground. However, research has shown that CM feed and mate in the top 1/3 of the tree. So, if you put a trap in the top 1/3, youâ€™re going to catch way more than if you put it in the bottom 1/3 of the tree. So I think itâ€™s important to put the traps up high if you want to be accurate and conservative about not letting things slip past you.
Dennis: For us, I would say that the majority of our frost damage took place in the bottom half of the tree. The majority of our apples are in the top 1/3 of the tree, with nothing below that point. I figured that if all the apples are in the tops of the trees, then the CM would be in the top 1/3 of the tree.
John: Larry Gut has been telling this to us for years: if youâ€™re using mating disruption, you need it in the top 1/3 of the tree, and if youâ€™re using a trap with the same lure, you need it in the top 1/3.
When we talk about CM activity, we need to distinguish between the mating period and monitoring during that time VERSUS the oviposition period. While the CM have been shown to feed and mate in the top 1/3 of the tree, the female will clearly fly to an apple on the bottom of the tree to lay eggs. The female can also differentiate between trees that have many apples and trees that only have some. Sheâ€™s not going to lay her eggs willy-nilly; sheâ€™s going to lay her eggs near apples. If those apples are in the top 1/3, thatâ€™s where sheâ€™s going to lay them.
But as far as you monitoring for CM, as I said, the mating and feeding occur in the top 1/3 of the traps. The closer to the top 1/3 of the tree you have your traps, the more accurate those numbers will be.
However, Dennisâ€™ observation does raise a good point about insecticide application. If youâ€™re going to put on an insecticide â€“ whether itâ€™s Surround or Delegate or Altacor or a neonicatinoid â€“ if your crop is in the top 1/3 of the tree, then it should be self-evident that you want the bulk of your insecticide to be up there, too.
On CM control for organic growers
John: For years, a lot of organic growers used Bt in an attempt to control Codling moth. I have not seen anything that contradicts Larry Gutâ€™s assertion that Bt is not a very useful or economical way to control CM. The primary reason is not that the Bt doesnâ€™t kill a CM worm when ingested; the main reason is that the Bt isnâ€™t active for very long once itâ€™s applied. It breaks down quickly. If its effective life is 3-5 days and it costs you $15-20/acre to apply it, and if your egg hatch period is 40 days, then it becomes cost prohibitive as a control measure relative to mating disruption and relative to Surround. Kaolin clay/Surround, I think, is a far more economical method for controlling CM worms than is Bt. And, obviously, mating disruption is even more economical if it suits your orchard.
Update on scale crawlers
John: Anybody that has had an experience with scale in their orchard should keep checking on them. That means to change the double-sided tape every 7-10 days. Whatever you have done or havenâ€™t done, you need to monitor the tape for the next month or so to see how many crawlers youâ€™re actually catching. Thatâ€™s all Iâ€™ll say about that; if you have questions, call me.
Update on Oblique-banded hatch
John: By the degree-day model, we should be seeing Oblique-bandeds. If you caught Oblique-bandeds in your traps 3-4 weeks ago but havenâ€™t yet seen any hatch, then one of two things is happening: either youâ€™re not seeing them because you donâ€™t know why they look like, or something else has caused mortality in their population. They are susceptible to weather events as well as to predators.
Their hatch period extends for several weeks, so keep an eye on it. In a light crop year, Iâ€™m really not going to worry much about the Oblique-bandeds, the Red-bandeds that will be flying soon, and their subsequent egg hatch â€“ compared, at least, to CM, Apple maggot, and Plum curculio, which can all search out isolated fruit. OBLR and RBLR are not obligatory fruit-feeders. With a light crop, your chance of having an uncontrolled attack on the few fruit that you have is far less probable. If you have a light crop, you can probably withstand the OBLR and RBLR hatches over the next few weeks with minimal risk.
With a heavy crop of apples, if you donâ€™t control OBLR and RBLR, youâ€™re likely to see a few percent of your apples damaged.
Update on Potato leaf hopper
John: Iâ€™ve said it before: the Potato leaf hoppers are much more damaging to young trees than they are to mature trees. If you have a light crop, then Iâ€™d guess that the fruit will see much speckling damage from the PLH honeydew. So, with mature trees with a light crop in the top 1/3, I think you can forget about controlling PLH.
However, PLH can really shut down 1- or 2-year-old trees. So, focus your attention on the young trees.
Question on summer pruning
John: A grower asked me what the purpose of summer pruning is. The main purpose that I can see is to open the trees up for air movement as well as for coloring of fruit. As far as I can see, we have less reason to do that this year. But as a general rule, you cannot prune when the tree is still growing. If you prune before the terminals have set, youâ€™ll just induce the tree to grow more. You have to wait until all of the shoots of set their terminal buds before pruning. Once the vegetative growth has finished for the year, the summer pruning will be far less likely to induce regrowth.
Even though some varieties like Honeycrisp might already have set their terminals, I would still be very hesitant to start pruning on June 12, at this stage. I think it would be safer to do that pruning a month from now, if you want to do it.
Question about mysterious internal fruit damage
Grower: Iâ€™ve been looking at apple damage that looks like CM feeding. Itâ€™s a very small indentation in the fruit that looks superficial from the outside, but itâ€™s clear when you cut the apples open that something has moved into the apple. There are watery spots all through the apple. The problem is all over the place. No matter how many I cut open, though, I canâ€™t find any larvae. I donâ€™t know what the heck it is.
John: Are those in that area of the orchard where we suspected that CM were coming in from across the road?
John: So, I suspect that theyâ€™re CM.
Grower: But I donâ€™t see any frass or anything.
John: No, you donâ€™t see frass initially. The first instar normally doesnâ€™t even tunnel. It will go into the fruit, but wonâ€™t go very far. Thatâ€™s why youâ€™ll get delayed mortality on that first instar with a neonicatinoid or Imidan. But after the first instar, the worm will tunnel in. Itâ€™s in the later instars, when the worm is getting big, that it will start producing a lot of waste material or frass.
Youâ€™re not the only orchard where Iâ€™ve seen damage like that. The hole in the skin is very tiny; sometimes itâ€™s incredible inconspicuous. There is no darkening around the entry point, and sometimes you canâ€™t even see a hole unless you look at it under a hand lens.
If you sprayed for something, then I wouldnâ€™t worry. The problem is that if you missed a portion of that population, and the worms are on their way into the fruit, thereâ€™s nothing we can do about it now. Youâ€™re going to have to fight it in the second generation. Iâ€™m hoping that your initial application for part of the orchard will have killed some of those and that thatâ€™s what weâ€™re seeing: first instars that went into the fruit but died from the insecticide spray.
Grower: Thatâ€™s kind of what I thought it was, but I never noticed before how much internal damage there was under these tiny marks on the outside of the fruit. That just hasnâ€™t happened before, here.
John: The damage looks the same if itâ€™s OFW or LAW. Itâ€™s very inconspicuous and easily confused with either a PC bite or even an early stinkbug or Tarnished plant bug bite. Then, when you slice through it and find that itâ€™s going in, you know that itâ€™s not either of those. If it were stinkbug or TPB, you donâ€™t like to see it, but youâ€™d know that it wouldnâ€™t create a monster for you in August. But if itâ€™s CM, OFM, or LAW and you donâ€™t control it now, that second generation is going to be a real doozy.
Grower: This morning, I checked my traps and found a couple of CM in both the L2s and the CMDAs.
John: Have you checked across the road in the abandoned orchard? (The abandoned orchard doesnâ€™t have any fruit on it, so the CM are apparently being pushed out of that orchard into his, where he has mating disruption up.)
Grower: There were 9 of them there over two days.
John: Hopefully the effective period of the spray you put on will get you through this influx of CM from across the road.
Itâ€™s really a good point. I think that this week would have been a great time for a webinar with slides of some of these things. I think weâ€™ll do one two weeks from now, after Larry Gutâ€™s visit, where I show photos of some of this first-instar damage.