IPM Conference Call: May 1, 2012

On today’s call, John covered a lot of ground, giving us updates on the weather and pest situation across the region. Please download the recording, see the topic list, and read the transcript below. Also, be sure to check out the articles referenced in the call, especially the ones brought to us by grower Dennis Norton.

Recording

Download the recording of the May 1 call here.

Call Topics

  1. Introduction to our new Webinar
  2. Plant disease issues – Fire blight and George Sundin’s new research
  3. Plant disease issues – On Apple scab
  4. Grower question: Temperature readings at what elevation for scab model?
  5. On the poor fruit set / freeze damage related to pest control at petal fall and first cover
  6. Current arthropods activity, and what can we anticipate for the coming week of warm weather
  7. Codling moth update
  8. Grower question: On timing of thinning

Related Articles

The “Apogee effect” – examination of the mode of action of prohexadione calcium in shoot blight control - George Sundin

Applying Apogee in 2012 – Phil Schwallier and Amy Irish-Brown

Fertilizing frost-damaged fruit crops - Eric Hanson

Considerations for commercial apple orchards with reduced crop - Amy Irish-Brown, Phil Schwallier, Larry Gut and Bill Shane

“Chemical Thinning of Apples in the Response to Frost Damage to Flowers” - Ontario Ministry of Ag

“Early Season Frost Damage” - Ontario Ministry of Ag

Call Transcript, May 1, 2012

Introduction to our new Webinar

Alex: Next week, we will have our first webinar. That means that we will be broadcasting video as well as audio. In order to view the video, you will need access to a computer with an internet connection. However, you will still be able to listen into the audio and ask questions, even if you aren’t at a computer, because we will be using the same conference call line that we always have for the audio.

John: I anticipate that the subject I want to cover may take two consecutive webinars. Obviously, if the first webinar is a complete flop and everybody hangs up, we won’t do the second. But if it works well, then this topic may take two webinar sessions, and I would prefer to have them on consecutive Tuesdays.

Grower: Does this mean that the other format won’t go on at the same time?

John: You would call in on your phone just like you normally do for the audio, but you’d also use an internet-enabled computer to watch the video that I broadcast.  I will just do a Powerpoint on the screen, go over some pictures and text slides.

The idea is that if people cannot get to a computer, they will hopefully be able to get enough from the audio portion to be able to ask questions and know where to look for more information in the video recording that will be provided on the AppleTalk blog.

The webinar subject material has to do with two topics.

One, I’ve been talking about for the last couple months: that is, insecticide resistance and the phenomenon of the 20+ new classes of insecticides we’ve introduced in the last twenty years. It’s hard from our perspective, living in it, to realize how revolutionary it is to have such a wide variety of materials. But in retrospect, we see that in the 45 years after the introduction of DDT in 1945, we only had 4 classes of insecticides: organochlorines, organophosphates, carbamates, and synthetic pyrethroids. So, for the first 45  years, we only had 4 classes of insecticide, while in the last 20 years, we’ve added almost 20 more classes of insecticides. A lot of them are reduced-risk and more specific. Most of them are not neurotoxins, whereas the 4 oldest materials are all neurotoxins.

It’s pretty exciting, because we have a lot of options. But we have also found out that we’re getting pests with multiple classes of resistance around the globe to both old and new materials. So, although we in Wisconsin, Illinois, Minnesota, and Iowa don’t have big problems with resistance in fruit growing (that I know of), we certainly may have things brewing in terms of multiple-resistance pests. Even if we do not, though, it behooves us to be on the front side of that curve rather than the back side, waiting for something to happen.

This concern of mine coincides with a pretty lousy year for fruit pollination or fruit set in a lot of crops, so we’ll focus primarily on apples.

For growers, the immediate correlation with resistance is this: if you have a light crop or reduced crop of apples, you’re probably going to be trying to reduce your pesticide costs and other input costs as much as you can. That dovetails well with techniques for reducing resistance development in our complex of insect pests. So, we’re in a year that we don’t want to be spraying a lot of insecticides willy-nilly (even more so than in a normal year). I think this subject of multiple-resistance is timely and something that we can all take some responsibility for, I think – at least for being aware of it.

So, I’ll so some slides with just text things, but there will be some photographs of insects, as well, to illustrate some of the techniques for replacing insecticides or doing different things with insecticides other than just blanketing your entire orchard with several materials

Alex: Okay, back to logistics. The webinar will essentially be a live conference presentation, with the exception that you all will still be on the line, and we will encourage you to interrupt John with questions you have and make it as much of a conversation as you’re willing to make it.

A little preview of how you’re going to be able to log into the webinar:

For the audio, we will use the same conference call line that we have been using. You will call in however you want to (either with your regular phone or with Skype). Again, Skype is free if you call into the FreeConferenceCallHD username. It’s not free if you use Skype to call the regular dial-in phone number. If you have any questions about how to use Skype to call in for free, please send me an email or give me a call (armccullough@wisc.edu, 608-466-6206).

To view the video, you will need access to a computer and the internet. We will send out information about how to log into the video in the next couple days. The video portion will be completely free, no matter what, and logging into it should not be very complicated.

So, to sum up: the video will be free, and the audio will work just as it does now. If you’re paying for the long distance call right now, and you want to keep doing that, that’s fine. If you want into dial in with Skype and you need help, just let me know.

We will be sending out information and reminders about the webinar in the next few days.

The last thing: we will be recording the video and audio together, and then uploading the audio and video to the website. So, if you absolutely cannot get access to the video in real-time, you will be able to download it later. But, we’d like to encourage everyone who will have access to a computer to log into the video portion so we can have a meaningful discussion, and so that whatever John is saying has the right visual context to stimulate questions and discussion.

John: I’m looking forward to it. The anticipation is that while you guys as growers sometimes feel hesitant to interrupt a guest or even interrupt me, I hope the visual stimulation of photographs or even text files on a computer will increase the dialogue. That’s what we hope for, anyway.

Plant disease issues – Fire blight and George Sundin’s new research

John: First, I want to direct your attention to a FruitCat news item sent out late last week by George Sundin (see the article here), the plant pathologist from MSU who was a guest on our calls two weeks ago. His research is on Fire blight.

He sent out two emails late last week having to do with research that he had done. I don’t want to discuss the particulars of those items, but I want to applaud his research. Basically, he looked at the effects of Apogee – which is a plant growth hormone that is applied to trees for reduction of shoot growth, but has also been widely accepted as reducing shoot blight infections from Fire blight (Erwinia amylovora).

The research that he did is unusual in a couple of ways. First, it’s unusual to get through that FruitCat newsletter actual research results. Most of the time, what we get is extension notes about what’s happening with this pest or that pest, or things to look out for – very applied information. This isn’t a full research paper that would be submitted to a refereed journal (he doesn’t have the materials and methods in there), but he does go into the actual research that they conducted in studying how Apogee works in the plant and why it may work as an inhibitor of Fire blight.

I find it quite an elegant bit of research, even though I’m not an expert plant pathologist. He has a theory on why Apogee works. He went out and got the research money to investigate this, and made it a combination of basic research and applied research, that I think that we as growers should at least note if not celebrate – that is, when one of the researchers that we depend on is doing work that goes beyond giving us a simple recommendation to use this chemical or that chemical, and instead gives us information about the biology behind why Apogee works, and, consequently, why other aspects of Fire blight and Fire blight management work or don’t work.

Having this level of discussion and detail is especially important, I think, to people like organic growers who can’t use Apogee. For example, we know that the older a plant tissue gets, the more resistant to Fire blight infection it becomes. George’s research shows that that resistance is a result of cell wall thickness.

He also makes the point that growers (he’s talking mainly to growers in Michigan) should be aware that we’re not done with Fire blight.  Growers over there are done with bloom for the most part, and most of them didn’t have to put on any streptomycin because we didn’t have warm enough weather for the bacteria to grow. But just because the blossoms may be gone or ageing in these apple trees does not mean that the threat of Fire blight has subsided. In fact, it continues, and it’s going to grow this week with the warm weather that’s coming our way. In most orchards, we haven’t had open blossoms susceptible to blossom blight infections. But if anybody has Fire blight cankers in their orchard, the bacteria that inhabit those cankers will be growing like crazy over the next 4 or 5 days and will spread with rain and wind. All they need is microscopic breaks in plant tissue (in new leaf tissue, for example) in order to infect. So, in young tissue or new growth, the possibility for shoot blight infection will be high.

The research that George published demonstrates quite nicely why that is.

When shoot growth stops and the terminals are set, that’s when the Fire blight threat subsides. Anybody who is still pruning trees, for example, needs to be aware that we will have bacteria growing rapidly in the next few days, as well as rain to spread it. If you’re out making cuts in tissue, you’ll be at risk of infecting those cuts with Fire blight.

The one caveat in all this is, just like with Scab, that it’s a question of how much inoculum you have. If you’ve never had Fire blight in your orchard, or if it’s been incredibly minimal or absent for several years, maybe the danger of pruning is far less. But that’s an individual decision.

Plant disease issues – On Apple scab

John: The other disease I wanted to mention is Apple scab and the scab model. Whereas my discussion of Fire blight was based on George Sundin’s elegant research, my thoughts about Apple scab will be based on the kinds of “field research” that I’m more used to.

When we had Dave Rosenberger, the scab expert from Cornell, on the line a few weeks ago (see Dave’s conference call here), he answered a question about using the degree-day model for ascospore development versus doing squash mounts of actual perithecia (on diseased leaves from the previous year that have overwintered in your orchard).

His response was this: he thought that the degree-day model was more accurate than the squash mounts. What I’m going to talk about here is some field evidence that seems to support Dave’s view.

Ordinarily, in a normal year, the time that growers will see scab blow up out of nowhere is around the time of thinning toward the end of the thinning. Somewhere in that first, second, third cover period of time, scab will go from being unknown to being, all of a sudden, a very widespread problem. This is consistent orchard to orchard and year to year.

When the degree-day model was developed 20-30 years ago, it said to start that degree-day model ticking at green tip on Macintosh. There has been a considerable amount of research in the last 30 years that suggests that Apple scab will develop on leaves on the orchard floor before green tip on Macintosh if the conditions are right – that is, if you didn’t have a lot of snow cover and if you got warm weather in February and early March.  Dave suggested that very fact. This year, we were probably quite far along early in the year, and probably should have started the model prior to green tip on Macintosh.

So, here we are on May 1. Most people, if they started their weather stations on March 1, are in the 900+ degree-day range at base-32. In theory, that means that all the ascospores should be fully-developed. As soon as you hit that 99% maturity level on your model, then the following rain should theoretically release all of the ascospores, and 10-14 days after that – waiting enough time for the infections to become visible – you’re at the end of scab season and can assess the damage.

HOWEVER, this year, if we start the scab model not at green tip on Macintosh – which would be something like March 17 or March 20 – but on March 1, instead, then most orchard sites would be well over that 99% threshold. Again, that threshold tends to coincide with this normal explosion of scab showing up in people’s orchards.

Over the last few days, I’ve found a number of orchards where the scab has become widely visible. These orchards may still be at petal fall, and there may still be blossoms on a lot of varieties.  But we’re considerably earlier than the thinning period, which normally coincides with that big wave of scab showing up in people’s orchards. If, as Dave Rosenberger suggested, scab started developing sooner because of the warm winter and lack of snow, then it makes sense that this “explosion” of symptoms should occur earlier.

Indeed, what I’m arguing here is that this is the case: scab has exploded earlier than normal. I’ve seen it at quite a number of orchards in the last few days.

What does that all mean? It means it’s a fantastic time to go out and look for scab. Depending on when you started your data logger, if you’re at 99% and you’ve had a rain shower since then and released the last of the spores, the question is: how worried should you be about the thunderstorms and rain that are predicted over the next 4 or 5 days (some of which may initiate an infection period)?

Well, if you’ve been at 99% for a week or so and have released all of your spores in previous showers, the question is this: do you currently have any lesions out there? If you search your scab-susceptible varieties this week and you don’t find scab lesions out there, and you’re beyond this 99% and you’ve had a rain shower, then you don’t need to get really worried about having infection periods at this point. Pay attention to how much rain you’ve had and keep a protectant on there. If you’re conventional, you’re going to be doing Captan, at this point. I’m not recommending that people slack off fungicide protection. I’m just saying that now is the time to check for evidence about whether your scab protection program worked or didn’t work, at least in the southern part of our region. It’s a good time to assess, and then to plan what your control (or lack of control) is going to be for the rest of the year. Obviously, the level of your fruit load will have a big role in how much effort you’re going to put into controlling scab from here on out. If you have a variety that has scab lesions on it right now but is not going to have fruit on it, then maybe you don’t need to worry about it too much. But I’ve seen some blocks of some varieties that seem to be pretty well set and seem to have quite a bit of scab. Under those conditions at this time, when you have incredibly small apples, the trees are incredibly susceptible to scab. Controlling that amount of leaf scab and keeping it off the fruit for a season is going to be tough.

Grower question: Temperature readings at what elevation for scab model?

Grower: We noticed during these frost events that there is a significant difference in temperature across small differences in elevation. The temperature can vary up to 10 degrees between the ground and 6 feet off the ground. What is the height of temperature measurements that the Mills table was designed to be used with?

John: That’s a great question.  I know what you mean, but I don’t know the answer. In the early part of the year, when we had 50-degree temperatures in February, it’s warmer at the ground than it is at 3ft above ground in the tree. But in these frost events that we’ve had recently, the reverse is true. In those cases, the temperature difference can be as high as 10-15 degrees between 3.5ft and ground level. But I don’t know what height the Mills table was designed for. My presumption is that they probably would have been measuring the temperature on the ground floor as well as in the canopy. I suspect that they probably chose data sets that did not include extreme frost events, because they were probably controlling for some of those variables and excluding outliers.

The temperatures that we use that are established at 3.5ft off the ground are probably the ones that they used.

I would suspect, though, that if you were to monitor the cumulative degree-days at the ground level vs. 3.5ft from January 1 to now, you’d probably find that the totals wouldn’t be incredibly different because of that inverted temperature differential between winter and spring.

On the poor fruit set / freeze damage related to pest control at petal fall and first cover

John: The reading I did over the weekend on the relationship between frost damage, tree stress, and yield leaves me with the distinct impression that there are lots of variables that play into whether a tree holds its fruit or not. It’s more complicated than whether we simply have good thinning weather or bad thinning weather.

The #1 variable is: stress to the tree. Last week, Phil Schwallier spoke about tree stress. What I’m seeing in orchards, and what I’m concerned about, is that, in some orchards, there are a lot of varieties that look nitrogen-stressed. There are clearly apples in virtually every orchard with brown centers. Now, there are growers who say that any apple that is starting to swell but has a brown center will become a June drop, and there’s no saving it. There are other people that disagree.

From my reading over the weekend, it appears that the amount of stress that the tree goes through over the next four weeks will play a huge role in how many of those fruit are held and how many drop in June, thinner or no thinner.

So, I want to reiterate: if your trees look light green, if they have reddish-tinged leaves, and if you’re concerned about the fruit load or freeze damage on those trees, then you should do something to boost that tree to alleviate that stress. That basically means applying a small amount of nitrogen. Whether you’re organic or conventional, it’s relatively easy and relatively cheap to throw on two to three of actual N per acre in a foliar spray (whatever formulation that comes in). It’s not a lot of nitrogen, but it could make a big difference, particularly as the weather picks up and the trees start to respond to the warmth.

The most significant stresses to a tree are weather-related. In particular, warm weather that is cloudy. The warmer the weather is, the more the tree is going to metabolize. It’s a function of temperature. So, the warmer that tree is, the more processes are going to be going on in that tree. But if it’s cloudy and that tree can’t make sugars to feed those metabolic processes, then that tree is going to be stressed. If it’s cold and cloudy, it’s far less stressed, because the metabolic processes have slowed down.

The other factor besides temperature is whether it’s daylight or dark. The ideal situation to alleviate stress would be warm, sunny days and cool nights. (At night it doesn’t matter whether it’s clear or not, obviously.) In warm, sunny days with no clouds, the tree will crank up and maximize its sugar production. Then, cool nights will slow down the metabolism when the tree can’t be making sugars because there’s no sunlight, meaning the tree won’t be burning up the sugars at night. That’s the best situation to alleviate tree stress.

A second stressor related to fruit is the crop load. We all know about biennial bearing, and about trees’ response to having too many fruit on the tree post-bloom.

What we don’t know, here, is this: if a bunch of those fruit have frozen and you’re able to cause an entire cluster to fall off just by flicking it, then that tree has begun to seal itself off from the fruit stems because it can sense that the fruit are already gone. But if the fruit are sizing and you can’t flick them off easily, then that tree knows that that fruit is there. Whether it knows that the fruit are damaged or not, I have no idea.

My contention is that if we have a significant amount of these flowers that are just falling off and there is not a lot of fruit sizing on the trees, and if 100% of the fruit on these lightly-fruited trees have some brown in the center, the tree is more likely to retain those fruit if the tree is not stressed – that is, not stressed over the course of the next 3 or 4 weeks.

So, it makes sense to do anything we can to decrease the stress of the tree. That’s why the nitrogen makes sense.

Other than that, I don’t know of much we can do.

A warning: there’s one technique related to organic production that might come up: spraying the plant with kaolin clay, or Surround. Spraying Surround at petal fall for the prevention of Plum curculio is a standard practice. I’m warning people who are organic not to do that if they have any concern about their fruit set. They’re going to have to play off Plum curculio threat versus additional stress to their trees. My expectation is that as we get into warm weather in the next few days, the trees will come out of their stressed appearance to some degree and will start growing again, and will probably be a lot happier. To put Surround on the tree when it is unstressed will have less of a stress effect in terms of dropping the fruit than it would to put it on now when the tree is stressed.

I know that those variables vary quite widely from orchard to orchard and from variety to variety. But just as a general principle to keep in mind: if you’re going to use Surround for PC control over the next few weeks, know that it does have a similar effect on the tree to cloudy weather and reduces the amount of sugars that can be produced.

On arthropod activity, and what can we anticipate for the coming week of warm weather

John: I have a couple of things to say, here.

One: even though it’s been very cold, and sometimes you can barely find a living insect in the orchard these days, know that there are a lot of insects active in the orchards right now. With warm nighttime temperatures over the next 4-5 nights, insect populations are going to explode, of course. But don’t think that there isn’t already a lot of activity.

Most of this activity is from beneficial insects that are involved in biocontrol. For example, there are parasitic wasps (Hymenoptera) that have already completed their life cycle on Wooly apple aphid and now flying around peoples’ orchards. The wasps have already emerged from the mummies.

There are quite a number of predatory mites in peoples’ orchards. There are other mite predators like Stethorus, the black “Mite destroyer” (common name) active in orchards.

So even though we haven’t had Codling moth, we haven’t had Plum curculio, the Tarnished plant bug have been mostly quiet, and we’ve had very little leaf roller activity – a lot of other things are going on.

The aphid populations – whether they’re Green apple, Spirea, or Rosy – are growing. And hopefully the predators and parasites of those are active. I’ve seen some activity with them, but I’ve seen very few colonies of Rosies and Green apple aphids that have been wiped out by beneficials, so far. I hope that that changes over the next couple weeks.

My take-home message about control at petal fall:

My suspicion is that Plum curculio moved at least to the perimeters of a lot of orchards in March when it was hot. They clearly have not done anything since. Over the next four nights, when the lows are in the 50s and the highs are in the 70s – and the nighttime temperatures are the most important, here – the Plum curculio will start moving out of their hibernating winter sites and maybe even up into trees.

So, that period of warm nights is a prime time to do a perimeter of insecticide. At a minimum, be watching those perimeters on a daily basis. You don’t have to spend an hour out on the perimeter to determine what’s going on. Spending 10-15 minutes per day on the perimeter of a 40-acre orchard will give you enough information to decide whether Plum curculio is threatening you.

HOWEVER, this would be a horrendous time to cover the orchard with a broad-spectrum insecticide. I know a lot of people aren’t at petal fall yet and still have bees in, so it’s not even a question for some. But there are plenty of others who are past petal fall. For those growers: I wouldn’t apply a broad-spectrum at all, unless you have another insect that is really causing you problems – and that’s been rare in my observations, so far. There are very few orchards that have lots of Oblique-banded leaf rollers in the terminals. And even those may or may not be a problem if you have a very light fruit load, because I don’t think they will be the difference between profit and loss this year. Putting a spray of insecticide on the whole orchard and eliminating a bunch of beneficials to control some Oblique-bandeds doesn’t make sense to me, but maybe it does to some people. I don’t think it’s worth it. You will be wasting most of that cover spray. And another downside is pertinent to our webinar next week: you don’t want to be eliminating a bunch of beneficials right now, beneficials that control secondary pests that we don’t want to have to spray for.

Codling moth update

John: I’m sure everyone has their Codling moth traps up or will get them up in the next few days. I just want to communicate an observation of mine, reiterating Larry Gut’s parameters for CM flight.

CM are going to fly in the evening – from 5 or 6pm to 10 or 11pm. In order to fly, the temperature must be above 61 or 62 degrees during that period, the wind must not be above 3mph, and it must not be raining. In the next five nights, we’ll probably have at least 4 nights that are above 61 degrees during that whole window. Whether we’ll have rain or wind, I don’t know.

But I’m anxious to see what happens this week, because I think that this will tell us what to anticipate for CM this year. For instance, I argued all spring that CM should be further ahead because they overwinter on the trees and don’t require the soil to come up to a certain temperature, etc, and they shouldn’t have been killed off in the winter because it didn’t get cold enough. My contention was that CM should be in higher numbers and should be a little earlier.

It’s clear at this point that they’re not early, because it’s been cold for a long period of time. But if we have conducive weather in the next week, and if all the CM didn’t die because of starvation over the last 3 weeks or because they froze, then there should be a pretty big backlog of adults ready to fly.

Keep an eye on the weather conditions for CM flight over the next few evenings. It may tell us an awful lot about what kind of summer we’re going to have in terms of CM pressure.

Grower question: On timing of thinning

Grower: I came across an article from Canada entitled “Chemical Thinning of Apples and the Response to Frost Damage to Flowers.” They had a similar incident back in 2008 with early heat and then frost. It’s a very short article, but it does discuss thinning, and when to thin.

Read the articles Dennis sent in:

-          “Chemical Thinning of Apples in the Response to Frost Damage to Flowers”

-          “Early Season Frost Damage”