On today’s call, John discussed a wide range of issues, starting with the most urgent: frost and freeze protection. Download the recording and supplemental references, see the full topic list, and read the full transcript below.

Recording

Download the recording of the April 10 call here.

Call Topics

Resources Mentioned in the Call

1)      An article on canker problems in apples: http://www.nyshs.org/pdf/fq/2007-Volume-15/Vol-15-No-4/Canker-Problems-in-Apple-Orchards.pdf

2)      Dave’s presentation on glyphosate’s effect on apple tree canker problems: http://shaponline.org/wp-content/uploads/sites/343/2012/03/Rsnbrgr-Thus-glyphosate.pdf

3)      Dave’s presentation on the use of copper sprays in tree fruit: http://shaponline.org/wp-content/uploads/sites/343/2012/03/Rsnbrgr-Wed-945am-copper.pdf

4)      Organic Tree Fruit Network mailing list: http://organictreefruit.org/?110210000000

5)      KDL freeze protection product from Agro-K: http://www.agro-k.com/index.php?option=com_content&view=article&id=68:kdl-frost&catid=3:newsflash&Itemid=18

6)      Scaffolds issue from April 9, 2012, with Dave Rosenberger’s article on fruit russeting: http://www.scaffolds.entomology.cornell.edu/2012/SCAFFOLDS%204-9-12.pdf

Full Transcript, April 10, 2012

Articles by Dave Rosenberger

John: Alex posted three articles by Dave Rosenberger on the AppleTalk website. One has to do with copper, its different forms, and issues with the different formulations – an article that is probably a little bit dated for us this year, but could be a good resource in the future.

The other two have to do with canker-forming fungi. The first is just a 4-page PDF article that you can print out. If you just want to learn about canker-forming fungi, it is an excellent resource. The second is a slide presentation that Dave gave earlier this spring out east, in which he also discusses glyphosate’s effect on canker.

They’re pretty simple, and they’re nice resources to have on your desktop. Thanks to Dave for sending those along to us; he’s a great resource.

An article on canker problems in apples: http://www.nyshs.org/pdf/fq/2007-Volume-15/Vol-15-No-4/Canker-Problems-in-Apple-Orchards.pdf

Dave’s presentation on glyphosate’s effect on apple tree canker problems: http://shaponline.org/wp-content/uploads/sites/343/2012/03/Rsnbrgr-Thus-glyphosate.pdf

Dave’s presentation on the use of copper sprays in tree fruit: http://shaponline.org/wp-content/uploads/sites/343/2012/03/Rsnbrgr-Wed-945am-copper.pdf

On the weather

John: So, everybody’s got the same issues to deal with – cold temperatures. Although tonight, it looks like everybody east of Madison is going to be pretty safe. And everybody west and north of Madison is going to have potential problems. It looks like the temps are supposed to be in the 25-26-27 range.

On the science behind frost and freezing

John: I wanted to talk about a couple things.

First, I want to talk about the science behind what’s going on in frost formation and freezing. I need to talk about this because I spoke to quite a bit about this to quite a few growers in the last week and gave them wrong information. So I will explain what that was and why I was confused. Since this is a fairly meaty topic – you might not think so, but a lot of research has gone into it – I emailed Alex a couple of articles that he will post on the AppleTalk website [FOLLOW – SEE THE FAO ARTICLES]. Both go into the physics behind frost formation and frost protection.

What I told people last week that was incorrect was this:

When you look at your dew point in the early-morning hours when your temperature drops below freezing, usually the dew point is somewhere below the actual temperature. What that means is that you don’t have dew – you don’t have frost if the dew point is below the actual temperature. So you can get down to 27 or 26 degrees in actual temperature, but if your dew point is 22, you won’t see a lot of frost in most places.

I told people it would be better if we did have frost, because I was thinking about the latent heat of fusion when water turns to ice. When water turns to ice, there is a release of heat called the latent heat of fusion. I told people, if we had the dew point up near where the actual temperature was and we had frost, the latent heat of fusion would confer a little heat to those blossoms and prevent fusion.

Well, that was wrong.

It’s better not to have the frost. It might be a little counterintuitive at first, because everyone knows about irrigating for the purposes of frost protection. But the differences between irrigating your crop – whether it’s strawberries or trees – to prevent freeze damage, is that you have to put on a lot of water, far, far, far more than is condensing on those things when you have a frost. What happens ordinarily when the temperature drops below freezing and you don’t have frost? The cells inside the leaves and the flower petals don’t freeze – they will supercool. Because of the solids that are in those cells, they won’t freeze at 28 or even 27, so they don’t have damage.

If the dew point is high, however, water vapor will condense and freeze right away and create frost. What that will do is prevent the normal transfer of heat between the leaf surface or flower petal and the surrounding air. Basically, it insulates it from the normal movement of heat coming from the ground or from the plant itself out into the atmosphere.

So, tree tissues can survive better for longer if they don’t have frost.

If you’re irrigating to prevent frost, you have to put on upwards of ¼” per hour, and you have to continue that while the temperatures are below freezing. That’s problematic for a lot of obvious reasons. Ice buildup, for example, will shut off the convection and radiation of heat energy coming out of the ground and impinging upon the plant tissues. It will insulate the tissues just like frost. The only difference between irrigation and frost is that when you irrigate, you’re putting so much water on that it’s a significant addition of heat (from the latent heat of fusion) that radiates into those plant tissues.

I don’t know if that’s any help, but I had to mention it because I told people the opposite, and I don’t want you going to early mass to pray for a frost.

See the FAO articles for more detail, if you want to study it in your spare time.

More on frost protection

John: Everybody knows about air drainage. But my feeling is that while everybody knows about it, nobody does anything about it. What am I getting at? This is a year that you start looking around at your orchard and really analyze where the airflow goes and what obstructions there may be for that air to continue to flow through. I can think of a lot of orchards where they want might to take out part of a hedge row on the edge of the orchard, or an overgrown fence, that would function basically as a windbreak and stop that cold air from being able to escape the orchard. It’s something to think about for the future.

John: What I really wanted to talk about were these foliar sprays that people have been discussing.

If you’re on the Organic Tree Fruit Network mailing list, you’ll know there have been about 30 emails about frost protection and things you can spray on your trees to prevent plants from being damaged. Growers have provided questions and suggestions for things you can spray, and there haven’t been any serious objections.

I’m going to talk about a few materials; one of them, I’m going to flat-out recommend that people might want to try – even though there isn’t an Extension bulletin in the land that suggests these things actually work. But my feeling is that you guys aren’t going to go out and buy wind machines or heaters, and you can’t do a whole lot about the slope that your orchard is planted on. And if we’re looking at another 3 weeks of potential freeze weather, you could at least try these sprays.

One of the sprays is urea. I’m not going to recommend this, because the only study I’ve seen that showed a positive has never been duplicated. I don’t know if it wasn’t duplicated because nobody has attempted to duplicate it, or because other Extension people don’t want to promote something like this if they don’t understand what happened in a particular research trial.

Another material I won’t recommend is from a company called Liquid Fence. They put out a product called FreezeProof. It’s basically propylene glycol with several surfactants in it, and they claim that it confers 5 or 6 degrees of additional protection. I didn’t look into a whole lot because I didn’t like some of the surfactants that were in it. Also, it was incredibly expensive, at least in small quantities. Look into it if you want to.

The material I looked into a little more is a product called KDL from the company AgroK. (Thanks to Lauro for this recommendation.) The K stands for potassium, and the D and L stand for a couple sugars – dextrose and lactose, I think. It’s a potassium ion that’s bound to these two sugars. You spray it on as a foliar nutrient, and it is supposed to do some good. If you go to their website, they have a number of grower testimonials. One of them is from John Jacobson up in White Bear Lake. He’s a grower that a lot of people know, and he works a sizeable orchard. He seems to think that the product does some good. The product is a nutrient that the plants use quite a bit of anyway, so I can’t see it hurting anything.

If you’re interested, go to AgroK’s website, then call them up. It costs about $20/acre to apply. That’s at a 2% mix, a gallon per 50 gallons of water. And they really don’t want more than 50 gallons of water to be sprayed on, because they don’t want you to apply it to run-off. The protection is supposed to last up to 2 weeks, depending on how much growth you have.

I’m not saying that this product would certainly make a huge difference, but we don’t have many other alternatives. If my forecast was for the low 20s, if it were me and I had no other options, I would get a hold of some and apply it.

The one caveat!: if you try this stuff, use it with a check. I can’t stress enough how important it is that if you’re going to spray this stuff, leave just a few trees in a couple places unsprayed. Whether it works or doesn’t work, you want to be able to differentiate so that you know what to do in the future.

On fire blight

John: We’re going to be in bloom for a fairly extended period of time, particularly the guys up north who aren’t very far into bloom yet. Fire blight will be on peoples’ minds for a while. If we’re going to apply streptomycin, we need to take resistance development into account.

NOTE: George Sundin from Michigan State will be on next Tuesday, April 17, to discuss this issue. He has studied streptomycin resistance in fire blight. I want him to come share what he knows so that you guys can decide what the risks are if you’re going to continue to use it. I know that are growers that have never used it, and other growers that use it very selectively. But there are a number of growers who apply it as a complete cover, as well.

What I will say, from what I’ve heard of George’s work, is that the best way to avoid conferring resistance to streptomycin is to:

1)      Don’t apply it on an orchard-wide basis.

2)      Don’t spray it unless you really need to.

Fire blight needs temperatures above 55 or 60, but if you look at some of the models out there, you’ll know that once the temperature is above 65, it doesn’t take even a day to run into a fairly serious infection. The warmer it is, the faster the bacteria multiply.

In the cold of this morning, after a 30-degree night, the number of bacteria in the cankers and on the blossoms would be very, very low, and they won’t grow very fast in the temperatures forecast over the next few days. But on Saturday, they’re forecasting highs in the mid-60s and some precipitation, meaning the bacteria have the potential to multiple very rapidly over the weekend.

Even though we haven’t had fire blight problems for a couple of years, most people have experience fire blight popping up and surprising them.

So, if you’re thinking about using streptomycin sometime during bloom, this weekend might be a time to use it – even though neither the Mary Blight model nor the Cougar Blight model are going to show much of a problem because the forecasted temperatures are so moderate.

On using Apogee to improve fruit finish

John: In the most recent issue of Scaffolds, Dave Rosenberger discusses at length different mechanisms by which russeting or skin problems on different varieties, including a yeast they’ve isolated that can cause russeting .

The article also has some good stuff on pollinators and mite management using new materials.

On apple scab

John: Most growers, if they’re conventional growers, have probably applied at least a couple of fungicides by this time. They’ve probably applied at least one or two covers at full rate, maybe even tank-mixed with a strobilurin or an SI with the protectant. At this stage, some people tend to get conservative and go back out 7 days later to spray. Other people go the other way and put things on hold.

I want to reiterate that right now, the apple scab should be right at its peak. We’re in the middle of bloom in most places. But, since growth has slowed so much and there’s no major rain in the forecast, I don’t think you have the need to rush back out and spend a bunch more money on fungicides 7 days after your last cover. There’s no reason to go back in 7 days after your cover spray if you haven’t had more than 1” of rain on the cover and your leaf expansion has been minimal (which it has).

However, if you move toward this weekend and those rain chances stay high, you might have reason to be concerned. These are the temperatures that apple scab likes. It’s right at home in the 40s, 50s, and 60s, and it doesn’t even like the higher temperatures. If this is the peak of its maturity and ascospore release, you sure don’t want to mess up now.

Another issue: Check up on whether last year’s infections have gotten away from you this year. Because of the early bud break, a lot of people were not able to put a fungicide on at green tip or silver tip. If a scab infection has occurred – either as conidia on the buds as they opened up, or with that early infection period that we had about 3 weeks ago – those lesions should be showing up right now.

If you had a block or a variety last year that had some leaf scab (it may not have even had fruit scab) – particularly if you had rainy weather in the Fall that would have helped those few lesions increase in number – you should probably spend some time out in that variety/block picking off clusters. Pick off five per tree. You really have to pick them off, because you have to look very closely at the undersides of the first two or three leaves that emerged. These lesions are small; they’re not what we’d see at thinning time, when you can see them from 2 or 3 feet away. Even I sometimes get confused as to whether they are even scab.

This will be very useful a few weeks from now; it might prevent a blow-up. You might have a few lesions right now and not know they’re there, and you’re paying attention to the ascospores, instead, and the rain that may cause those ascospores to be released – if so, your fungicides might not be timed adequately to protect against all these conidia that even these tiny lesions can put out. It seems to me that a lot of times, the worst scab years we have happen when people slack off right about now, and scab comes up in a major second wave around thinning time.

On powdery mildew

John: I’ve said before in calls and meetings that we usually don’t get too excited about powdery mildew. But because we should have more innoculum out there this year, we should not let our alertness for powdery mildew slide (like Dave Rosenberger said). So, consider putting one application of a material on for powdery mildew: it could be sulfur, a sterile inhibitor, or a strobilurin. Further, Dave Rosenberger strongly suggests that you go back in and repeat that application within two weeks. Last week, he even said that he would have people do it a 3^rd time, around petal fall. We will see later on whether you want to mess with it a 3^rd time.

I think I’ve mentioned that you need to be concerned mainly about the non-bearing and young trees that haven’t filled out completely.  That’s where the powdery mildew is really going to do its damage, by infecting those young shoots and shutting down their growth – which would normally happen in June, but this year it may happen in May, instead.

To reiterate:

• Sulfur works great for powdery mildew control. Also, strobilurin or sterile inhibitor.
• The conventional protectants (Captan and EBDCs) do not have any efficacy against powdery mildew.

On codling moth

John: I mentioned last week that you should be getting your codling moth traps and mating disruption out. The one caveat here is that the evening temperatures these days are below threshold for their flight, for the most part. So I’m not sure we will see a lot of CM flight in the near future, because it’s not going to be above 61, 62 degrees in that 7pm-to-midnight timeslot. That gives us some wiggle room for getting traps and mating disruption out. But I put traps out everywhere I go, because you’ll probably feel better having them out in case we do have a warm night.

I’ve spoken to some groups about the probability that this year might have higher CM numbers than last year’s second generation. Why? Because for the first time in several years, our winter did not have low enough temperatures to kill them off. CM overwinter on the trees and on the floor of the orchard as fully-grown larvae. Right now, they’re pupating and turning into adults. In an ordinary winter, when we might get to -15 or -20 degrees, we lose a good chunk of the population.

However, the weather we’re having right now might reduce the population and reverse that prediction. Why? The CM came out of their diapause and started to pupate when it was in the 80s for those weeks in March. Now, the weather has cooled down again. With any insect, if they’re already started to pupate and then their development is stalled by cold weather, they generally suffer some mortality, if the cold period extends for a long period. It’s probably more pronounced in insects that are adults coming out of hibernation right now (plum curculio, for example), because they’re living on depleted reserves they had from the fall. However, in many moths, their biochemical defense against freeze drop out as soon as the larvae become activated by warm weather, making them much more susceptible to subsequent freezing than they would have been in November or December.

On codling moth lures

John: If you have the red lures that Krista from DATCP used to sent out: the red lures usually last about 3 weeks. But in this cold weather, I think they can safely be used for a month.

If you’re using a long-life lure (whatever brand), they will last 8-12 weeks. In this cold weather, they probably last until the end of that time frame. So that means we’ll still only be using two of them in the season. We’ll still be changing it July 1 like we normally do.

If you don’t have mating disruption, there’s no reason to use any other lure than the gray, long-life lures. They have a really nice design and are nice and reliable.

Finally, for people who are going to use mating disruption: When you go to purchase CM lures, you’ll find four basic types: 10x lures, mega-lures, CMDA combo lures, and long-life or “L2” lures.

I’ve argued for a number of years that nobody should be using the 10x lures. They don’t last more than 2 weeks in the summer time.

The mega-lures will last as long as these long-life lures, but they are a little harder to interpret if you have mating disruption. If you have those long-life lures out there, they should not catch anything, right? If your mating disruption is working 100%, no males should find any females, and your L2 (long-life) lure should not attract any males (because it should not be able to overpower the mating disruption). But if you find any males in your L2 traps, then some of the moths are finding mates. If they can find your traps, then they can find a female.

The question then becomes: how do you assess how well the mating disruption is working? Normally, you’d use the combo lure in addition to the L2 lure. You have to use both of them at the same time. The combo lure has pear ester (not sex pheromone) in it; it will attract both females and males. You should have more L2s than combo lures (maybe a 5-to-1 ratio, depending on the layout of your orchard).

BUT, if you know where your population of CM is highest (or where their outside source points are), then you should put a couple traps with combo lures around those areas, even if the mating disruption is working at 100%. Because they should always pick up at least some moths, you’ll be able to at least monitor when they’re flying.

On other insects

John: Now we get to talk about all the insects that you don’t see. And we might be doing this in vain, because they might all be dead by the time it warms up. However, it is pretty amazing how many things moved in earlier than they’ve ever moved into the orchards – that is, earlier not by calendar, but relative to the tree phenology.

For example, the MSU manual recommends beginning to scout for Tarnished plant bug adults at pink. I had never seen one at pink or even early in bloom, but this year, they’ve been around for at least a week, and probably longer. They’re not doing a lot right now; they could damage fruit clusters if they had warmer temps to do feeding, but I think we’ve lucked out with them.

The same goes for thrips. I’ve told quite a few people that the thrips flew in on the 19^th and 20^th of March in big numbers and were inhabiting flowers everywhere I looked. They’ve also shut down in the cold. They’re still there, but they’re not doing any significant damage to the blossoms.

There are also some leaf rollers. I haven’t seen any Oblique bandeds. They’re the worms with black heads and green bodies. They overwinter on the tree as small worms. They should be active now, and we should be able to seen them.

I’ve seen other species of Tortricid larvae (like Variegated leaf rollers, not Green fruit worm) in the fruit clusters. They’re tunneling through the clusters. I haven’t seen any Red banded leaf rollers. They’ve been flying like gangbusters for weeks, and you should be catching them in your traps, but it will probably be a couple of weeks before we start to see them hatch out.

Also, aphids. There are lots of Rosy apple aphids and Green apple aphids in places. There’s not much we can do about it now except monitor for it and know where they are. If you think it’s going to be an issue, you can address it right at petal fall instead of waiting until there is a lot of damage done.

There are also European red mites that have hatched out in those first leaves around the clusters. If you had mites in any part of your orchard last year, go to those spots now and check the clusters. If you used oil, you should be able to determine your oil’s efficacy.