Understanding and Minimizing Cold Damage in Fruit Crops

February 18, 2021

- [Mike] I'm an extension educator, IPM extension educator out of the Southwest Michigan Research and Extension Center based out of Benton Harbor. I'm one of your moderators today. The other one is Bill Shane also out of SWMREC. He's the tree fruit extension educator down here. Before we start with our first presenter for the afternoon, I'll go over a few housekeeping things and then I'll hand it over to Bill. So, first thing I want to do is thank all of our sponsors for this conference. This is a little bit of a different format than we're all used to this time of year. We think of Southwest Hort Days, Ag Action Day, Farmers Day, those sorts of things. This is because of the virtual format, we've had to do this combination. So we wanna thank the sponsors for being flexible and helping us out in this process. As part of that sponsorship, they have provided us with some funding to offer some scholarships. So there is a scholarship opportunity for high school students and for college students. So if you wanna learn more or you have anyone who is potentially interested, you can go ahead and find this through our MSU extension site as well as you can probably find it through the Michigan Ag Ideas to Grow With, website specific. One other thing is we do, there is an RUP credit, re-certification credit available for this particular session. In order to receive that credit, you need to participate or be here through the full session. We will offer an evaluation link at the end of the talk probably while the Q&A is still occurring for you to all to link to, to, you know, give your input on the conference as well as to receive your RUP credit. One thing that's a little different for this conference is we will be monitoring attendance through Zoom reporting. So therefore, what that means is at the end of each and every talk, what we're going to do is close down the Zoom link and then open it back up for the next talk. This creates those nice clean reports that we can use for confirming those people that are asking for that RUP credit. One other thing is this meeting is gonna be recorded so if there is anything of note that you're concerned about or if you, if anything that comes about this is recorded presentation that will be available for viewing later, It won't be available for a first few days, but if you wanna come back, you can get access to the presentation another time. One last thing I wanna do before I hand it off to Bill is we have a series of farm stress videos we're providing before each talk throughout the conference. So I will start that here in a second, but also to note if you're interested in learning more about farm stress there is a farm stress track tomorrow. I think it starts at 11:00, so if you wanna learn more. So I'll go ahead and start this one. - Hi, my name's Eric Karbowski and I'm a behavioral health educator with MSU Extension that focuses on farm stress and today I wanted to share a couple of farm stress tips with you. We all experience stress and stress can look different to everyone but here are some common signs and symptoms of people that are experiencing stress. Signs of stress on the body might include headaches, stomach aches, backaches, high blood pressure, high blood sugar, you may feel your heart racing or you may feel nauseous. Signs of stress on the mind could include feeling anxious, angry, sad, bitter, depressed or hopeless and oftentimes actions that we see for people that are experiencing significant signs of stress could include not being able to sleep, sleeping too much, overeating or not eating at all, increased substance use which might include nicotine, cigarettes, drugs or alcohol. People may act out and break things, we may hear them yell or scream or they may begin to withdraw and so if you are experiencing some of those signs, maybe recognize that this could be that you're experiencing significant amounts of stress and know that there are a lot of different supports and tools and resources that are out there to help support you in this. A number of those resources can be found on the MSU Extension Farm Stress website and know that there are a lot of people that are working very hard behind the scenes to help support you as you support us. So with that, thank you again for taking the time and have a great day. - So I'll hand it off to Bill. - Thank you, Mike. Bill Shane, fruit specialist, Michigan State. A reminder, if you want to ask questions, if you mouse down to the bottom edge of the screen, you'll see a Q&A and a chat is probably better if you wanna answer to put it in the Q&A. We'll be monitoring those and at the end we will turn the questions over to Mark. Some may be answered by texts back to you during the course of the meeting. So let's jump into today's presentations. Our speaker is Mark Longstroth. He's a long veteran for area of small fruit specialist of Extension. He'll be talking about understanding and minimizing cold damage in fruit crops. Mark, I turn it over to you. - [Mark] Thank you, Bill. So I've had an awful lot of experience with cold damage here ever since I came to Michigan. My first year, we had an extremely cold winter, and so I'm gonna talk about that and hopefully tell you what's going on. So exactly how does freezing kill the plants? Well, essentially, normally, especially during the summertime or the springtime, ice forms inside the cell and just breaks the cell apart. As we go into winter, the plants that will make it through the winter managed to harden themselves off and they do that by lowering the freezing point of the cell sap, the constituents of the cell membrane chains so that they don't, you know, freeze up and become solid like, they're like bacon grease, you know, after you finish cooking the bacon, the grease in the pan is liquid, you walk away and you come back half an hour later and it has congealed. So it changes the constituents of the cell membrane so it stays liquid when it gets really cold and also the cells let water freeze outside the cell. In between the cells, water will freeze and that will pull water out of the cells and lower the freezing point of the cells. And they'll supercool and for an awful lot of our crops, they can go down to minus 10, minus 20, minus 25 degrees before the cell finally freezes and then they're killed. So most of the Michigan fruit industry is located on the west side of the state for the moderating effect of Lake Michigan. You know, in the winter time the open lake prevents extremely cold temperatures. We get a lot of snow here which protects the vegetation close to the ground. You might get three to nine feet of snow. We often have one or two feet of snow on the ground and relatively seldom do we get below minus five but we do get down oftentimes to minus 10 or we might have minus 15 a couple of times. In my career, actually four times, we've gotten down to minus 20, which causes an awful lot of winter injury. But what we're also seeing as the climate begins to change and there's more CO2 in the atmosphere, the seasons are just becoming warmer and so we're getting earlier springs, you know, the plants green up earlier and the time between when they first green up and bloom is about constant. So we're seeing plants being susceptible to cold temperatures earlier and earlier in the year and the spring freezes still come as random events in the spring. There's no telling if you're gonna get one in late April or early May when our fruit crops are blooming. So here's a graph that just shows for Peach Ridge up by Grand Rapids. They've kept track of green tip from 1975 into the mid 2000s. And you can see that in general, a green tip of apples is occurring about 13 days earlier. Here's another graph that looks at, the red line is the length of the growing season, the blue line is the first 32 degree day in fall and the green line is the last 32 degree day in the springtime and so this is earlier than normal above the line and later, pardon me, later than normal above the line and earlier than normal so you can see over time our spring has become earlier, our fall extends a little bit longer and our growing season has become just a little bit longer. So we talk about dormancy and winter hardiness in the winter time and we also talk about chilling. And so dormancy is when the plant is dormant and won't grow even if the conditions are right. I mean, if we get a really warm day in January, normally the plants don't grow too well and it's because they have a way to monitor the cold during the winter and that's called chilling or the chilling requirement and what they're really looking at is the temperatures that are not below freezing but just above freezing, temperatures in the range of 35 to 50 degrees and they accumulate so many hours of these chilling units and then when it warms up again in the springtime, they'll start to grow. Now, so plants become relatively hardy and can withstand cold temperatures during the winter time and if we have a relatively warm winter, then they're not very hardy 'cause they're not used to seeing cold temperatures and if we have a very cold winter and the temperature's below freezing for long periods of time, the plants will actually acclimate and their amount of cold hardiness will increase and they'll be able to withstand colder and colder temperatures. So, unlike spring frost, when I can tell you what temperature will kill a blossom, in the wintertime that's a moving target depending on what the temperatures and conditions were for the previous two weeks or so. And generally, if things are actively growing then they don't have any hardiness, they can't withstand temperatures below freezing very far. And so in order to get into, to acclimate the plants, notice that the days are getting shorter and they begin to get ready for winter. And as the temperature falls, we get to have temperatures below freezing, that's a real clue to the plant that winter's coming and they focus all their efforts on acclimating to the cold and once we get a good hard freeze then they begin to acclimate to the cold and they're no longer gonna grow, they have entered their dormancy. And so here's an idealized picture of what cold hardiness looks like in fruit trees and many of our perennial crops. The first clue is that we've got short days coming and that begins to occur in August and then we typically have a killing frost sometime in October, lately it's been in November and that's the real clue that tells it, okay, winter's coming, and they will sit there until they accumulate enough chilling hours, and for things like wine grapes, raspberries and peaches, they need about 700 chilling hours. For apples and blueberries and cherries, it's more like 1,000 to 1,200, maybe even 1,500, or pardon me, chill units before they'll start growing. And then when they've completed their chill units and it begins to get warm, they'll start growing again and we'll see growth. So here's what the chill units look like at the Southwest station this year. I arbitrarily start these things in October and the wavy blue line are the hourly temperatures from the SWMREC weather station and then this red line is just chill hours and that is just the number of hours between 35 and 45 degrees, it's just a rough measure. The upper blue line is what we call the Utah model and this was a model that was put together in Utah that actually looks at peaches specifically and it's got, rather than just assigning a unit of one or zero to an hour, it might be half a unit or a full unit or a half unit, depending on whether it was between 35 and 45, between 45 and, or between 35 and 45 would be one, between 45 and 50 be a half and so it can go up and down because it even has negative numbers. So you can see, we really didn't have a hard freeze at the Southwest station until about the middle of November, so perhaps I should be starting this over here but here are the daily temperatures and this red line is freezing and you can see that we had a relatively warm October and November, December became colder and colder and colder and by the time we got to the end of December and we went into, pardon me, January and February, it got really cold and for the last couple of weeks, it's been really cold indeed and we've gotten down to well at the Southwest station they haven't gone below zero, but in some places we've gone below zero and even down to minus 10, minus 15, minus 20 in some places. So you can see this axis over here is the number of chill units and for something that needed 700 hours, we would have been completing chilling right here, halfway through December. If we move that back, we probably still haven't completed chilling and they're gonna be able to go through this warm spot without any further additions. So I was speaking with Bill and this cold snap here that we've had the last couple of weeks has increased the hardiness of the peach flower buds, which are normally killed, I tell people they're normally killed between 12 and 16 degrees. Two weeks ago they were up around zero to minus seven and then Bill tells me that here, these last couple of days, it was more like 11 to 14 would have killed the flower buds, minus 11 to minus 14. So we don't expect to see an awful lot of injury to most peach varieties and I would expect the same holds true with wine grapes and most of those are grown in really nice sites. I'm gonna skip this slide and so what are the factors that can reduce winter cold hardiness? Well, early loss of the leaves. So if I'm a cherry grower and I get cherry leaf spot and my trees are defoliated in July, those trees aren't gonna be very hardy in the winter time. They just don't have the strength to build up their reserves. Another thing that happens is people will go out and prune in the fall because they have labor and they have time and that stimulates the plants to grow and that will lower the winter cold hardiness as well and it keeps it low the whole season. I also recommend against, you know, any late fertilization, you know, giving the plants a real jolt of fertilizer late in the season. I generally don't like to fertilize after July but there is some work that's been done that shows that light fertilization in the late fall, I mean we're talking like in late October, you know, while you still have leaves, but after the crop's off. It's only about five pounds of nitrogen per acre, sprayed on the leaves will increase the winter cold hardiness by several degrees. So here's an example that was done, some research that was done at MSU in the early 70s, comparing the winter cold hardiness of tart cherries that had been defoliated by cherry leaf spot and those that carried leaves all the way through the season til the leaves were killed by frost and so the upper red line is the temperature that it took to kill the flower buds in the cherries for the defoliated ones and the blue line below is the temperature that it took to kill the ones that were healthy going into the winter. So you can see that there about four or five degrees hardier than the ones that were defoliated. And here they are coming out of winter dormancy and you can see that the plants that had leaves the whole season were very cold hardy while the plants that didn't have the carbohydrate reserves to go through the winter were less cold hardy and work that was done several years ago in Pennsylvania with peaches where they prune peaches in November, going into the winter time, showed similar results where the reduction in winter cold hardiness was there all season long. So generally I tell people when they say, when's the best time to prune, I tell 'em take a look at the weather and if it looks like it's gonna get real cold, stop pruning before that date, you know, give them time to settle down. And so generally I know commercial growers don't have the opportunity, but I tell people with small acreages and small plantings, wait until the coldest part of the winter goes by and then you can prune like crazy. So let's talk about spring freezes. So spring freezes, if you're a fruit grower you need to think about spring freezes all year round, not just the day before the freeze. There are passive measures that you can do. You can improve air drainage on your farm, you can manage the ground cover and besides the active measures that we all think about, things like wind machines or sprinklers or orchard heaters, things like that and so those are the things we can do beforehand but if we do some planning, we should be better able to handle the spring freezes. So let's think about the way heat moves and so there's radiation and so that's the way the sun warms the earth. At this time of year, if we don't have curtains over our windows, we can hold our hand up and we can feel that it's colder outside the window than if we held it up to an interior wall or we hold it up to a heater or a fireplace. We can feel the heat coming off that fire. That's radiation and that's the way most heat moves. Another way is by conduction and that's when the heat moves through an object like if I put a cast iron skillet on the stove and I cook my dinner in it and then I touch that cast iron skillet, it's the same temperature all over and I burn my hand when I touch it and the skillet was heated up by conduction and my hand is burned by conduction. And the last way heat moves is by convection, so something is warm and it's heated up. Like we have air that's sitting over a warm piece of ground and it heats up, it expands, it becomes lighter and that warm air rises up into the air. Have a radiation freeze and that is characterized by clear skies, clear, calm conditions or we advective freeze which we've had take place here recently where we just have a cold air mass comes in and it's really windy and so now that's quit and yesterday we had a really, or two days ago we had really clear conditions and that's when we got these low temperatures where people were going down to four or five degrees above or below zero and in the low spots it got really, really cold, minus 10, minus 15, even minus 20 in some places here in Michigan. Or we might have a combination of the two. So with radiation freeze, the heat just radiates away from the ground and the clear sky lets it all go up into the open sky. We have no mixing of the air and so cold air collects close to the ground and we may get a temperature inversion with a warmer air layer above the cold air at the ground. So here's a diagram of what a radiation freeze looks like where we're just losing heat to the air. If we had clouds, those clouds would catch some of that heat and radiate it back down to the ground. If we have windy conditions then we don't get any inversion forming and so the temperature is pretty much the same temperature all throughout the column of air. So typically in a radiation freeze we have winds that are less than five miles an hour, we have a clear sky and the cold air might be just, you know, 30 feet or maybe 100 feet peak and we get a warmer layer above it and that warmer layer might be three, four, five, even eight degrees warmer than the cold air close to the ground and the cold air will just move downhill because it's heavy, will go into all the low spots, which is why oftentimes we have fruit trees and fruit crops growing on the sides of hills so the cold air will drain away. And it's relatively easy to protect against those because what we're trying to do is just heat up the crop. We're not losing an awful lot of heat only by radiation. With an advective freeze, it's windy and it's blowy and the cold air will extend for a long ways. We don't have any inversion, it usually gets real cold and freezes the plant and there's really no effective way to protect against that other than grow your crop indoors. So here's an example of the cold air just moving downhill and it will collect in all the hollows and cold areas and any kind of obstruction we have like here on the, can see we have a tree line so cold air will pool on that tree line and generally an obstacle will obstruct the flow of air to about three times its height. So we'll get a big layer of air built up here before it starts to spill over that obstacle and goes down to the lowest areas and collects in the low areas. And so we often get really cold air in the low areas in the landscape and here's a picture of it. I get to see this quite a few times in Southwest Michigan where we had a freeze when the buds of the grapes were about as big as the end of your little finger and temperatures just below freezing will kill the bud at that time and so you can see that there's a line across the hill there where there was relatively no damage above the line and almost complete damage below the line where the temperature was above 32 degrees in the inversion, but below 32 degrees below. So one thing you can do is increase your air drainage. Anytime you have any kind of obstruction, you can open up an opening to let the cold air come down and that opening should be at least 60 feet wide and the wider it is the better, the more air that can come through that. You can see that the grower would have had a huge reservoir of cold air on cold, calm mornings in that orchard up on the hill but now the cold air can come down and empty into this lower area that's too low really to raise fruit because it freezes quite often and so that works out well for him. Another thing you can do is try to store the heat in the ground before a freeze and a mowed cover crop in my mind is a warmer than an unmowed cover crop. Clean cultivated is warmer than grass and packed soil is warmer than loose soil and wet soil is warmer than dry soil 'cause it has water in it and water can hold an awful lot of heat. There was some research done in California that actually looked at different types of soil treatment and they found that bare, firm, moist soil was the warmest temperature at four feet above that soil surface. If the crop, if the cover crop was shredded over more soil, that was half a degree colder than the bare soil. If it had a low cover crop that was one to three degrees. Dry soil as opposed to wet soil was two degrees colder than the moist soil and freshly disked soil didn't provide you with anything and growing your cover crop higher didn't really afford any protection either. So generally I tell people to clean cultivate if they're not on a hilly site or whatnot early in the spring so that that ground has a chance to settle down and be firm. Sometimes before a freeze I'll tell people to irrigate and get the ground wet so it'll store more heat if the ground is dry and the last thing in the world you wanna do is go out there and disk everything in the orchard the day before a freeze because you're not gonna accomplish anything. The best thing to do probably is to mow your cover crop down. Another thing to think about in the springtime is the humidity. And so moist air and, holds, holds more water and the water is what holds the heat. Dry air can cool down really quickly and so relative humidity is a measure of how much moisture is in the air now, as opposed to how much moisture it could hold if it was saturated. So the warmer the air is, the more water it can hold and generally the more water it has, the warmer it is. And so relative humidity means the air's saturated, it can't hold anymore. If it's 100% relative humidity and it gets cooler then we see fog, we see dew and if the temperature's below freezing, we see frost forming on any surface. Talk about the dew point and for a volume of air that has moisture in it, the dew point is as I cool that air down to the point where the relative humidity goes down, down, pardon me, comes up as temperature goes down because the cold air can't hold as much water and the dew point is where we get 100% relative humidity and so dry air without much water vapor and it can go down really quickly and if there's not much water vapor in it, we might have a very low dew point below freezing and so generally once we get to the dew point and we get to 100% relative humidity, the air has to freeze or the water in the air has to either condense as dew or freeze out as frost at that point in time and so the temperature will drop really quickly to the dew point but once it hits the dew point, the temperature will actually bump up a little as that heat is released from freezing or condensing the water out of the air and it will fall much slower after it reaches the dew point and oftentimes when it gets to the dew point it stops falling very quickly at all and pretty much stays right around the dew point for the rest of the morning. And I already talked about that, yes. And so for the temperature to fall, you either have to condense more water out of the air and that will release more heat. So here's a example of the springtime, the critical temperature for apples. So when we're at silver tip to green tip, that bud goes from being able to stand about two degrees Fahrenheit to about 15 degrees Fahrenheit without any damage. As we get the half inch green and tight cluster, 15 to 23%. And those numbers that I'm given, those are numbers that were determined in Washington State for Red Delicious apples and the lower number is about 10% surviving or yeah, 10% surviving and 90% being killed at 15 for tight cluster as opposed to 10% being killed at, or yeah, 10% being killed at 23 and 90% being alive. So that's the range between some damage and almost complete damage. And you can see as we get closer and closer to bloom, that temperature goes up and by the time we get to bloom temperatures in that, you know, we will see some damage at 28 degrees during full bloom and we'll see almost total damage at 25 degrees. That's very similar for lots of other crops. I worked a lot in blueberries and here are the same numbers for blueberries, where we get when the bud is breaking and the flower buds are first exposed, 15 to 20 degrees is gonna hurt them, where at bloom it'll be 25, 28 degrees and for green fruit, it's probably around 29, 30 degrees that will cause green fruit to freeze. So let's go back, let's talk about how can we put heat into the orchard? Can we radiate heat? Can we put heat in by conduction? There's really no way to put it in by convection. We worry about if we put too much heat into our fruit planting, the heat will rise by convection, so we'll lose that. So I used to work a lot with smudge pots and essentially I can tell you those things work by. And you can feel the heat radiating off of it and it radiates all trees around it and they get to soak that heat up and then. And so what we're trying to do is heating the, keep heating the orchard. If it gets too hot, you have too many smudge pots in an area, you create this huge chimney and all your warm air is rising up and it's pulling in cold air from the sides so you can defeat yourself by having too many heaters but very few people can afford to heat anymore with diesel or gas or natural gas. What we see an awful lot of times are overhead sprinklers in strawberries and blueberry fields, apple growers used to use it a lot but they're moving away from what I call ice incasement and what we're doing is we're using the heat that water gives up when it changes from a liquid to a solid. And so you can think of this, that it takes energy to melt ice. You know, when I put ice in my drink, it cools that drink because it's pulling heat out of the drink and when you sweat in the summertime and that sweat, when it evaporates, cools you back down. So conversely when water freezes, it has to give up heat or when water condenses, it has to give up heat when it changes from a gas and condenses as dew, becomes water, it gives up heat or if it condenses as a frost, it gives up even more heat. So generally if we're using the sprinklers, we'll turn them off before it gets to freezing and we need, we will drop the temperature when the sprinkler comes on and so we'll turn it on, say like at 35 degrees and we will run the sprinklers and as long as we keep the ice wet, it will give up enough heat that it will keep everything in the ice right at 32 degrees. It won't get down to that 28, that magic number of 28, 29 degrees that causes any damage. If we have a wind, we have to put even more water on and so most of our irrigation systems here in Michigan put on like a 10th to an eighth of an inch of water, that's a, here's a 10th and there's an eighth, so if there's virtually no wind and we're irrigating with an eighth of an inch of water an hour then we can protect down to 24 degrees. But if we wanna protect down to 22 or 18, we have to put on a fifth of an inch of water and that really requires you to design a special system be able to put on that much water. When you're using this system, you gotta keep the ice wet. If the ice begins to dry out then the evaporation of water vapor from the ice will cool the ice down colder than the air itself. So here's the starting point for sprinklers. And so depending on the dew point, you can go out and determine the dew point. Here's an example of overhead sprinklers in blueberries and about, oh gosh, almost 70% of Michigan blueberry fields have the ability to frost protect their blueberries because blueberries are almost always grown in the lowest areas in the landscapes so they're fairly cold, even though they bloom usually the second week of May, freezes are a big problem for them. And so here's a picture of some blueberry blossoms encased in ice and when the ice is clear, you know your system's working well. If the ice is cloudy then you know that there's periods of time when it's dry and there's some evaporation. So when you use sprinklers for frost control you have to apply the water fast enough to keep the ice wet all the time, you have to be able to apply enough water and you need high system uniformity. You need to be able to put the same amount of water on everywhere so overlap is extremely important and generally the higher the wind gets, the less likely this is to work, even though virtually every strawberry grower in Michigan uses this system to protect their strawberries. - [Bill] Mark, five minutes before question and answer. - [Mark] Okay, I think I'm pretty close to the end here. So we see tree fruit growers have moved away from overhead sprinklers to under the tree sprinklers, these micro sprinklers, and so they release that heat diffusion of water underneath the canopy and it doesn't matter if it freezes down there on the grass, no big deal, they're releasing heat below the orchard and these are real compatible with wind machines. You know, if you were, if you had unlimited amounts of money you could preheat the water, but it's not gonna damage the crop if the system fails, you know, you just, you know, the ice over the flowers, it's not there so they're not gonna get super cool. So here's an example from 2012 where micro sprinklers were being used in an orchard to provide heat at the orchard floor and warm the orchard. So we have wind machines and they become more and more common and these systems will work anytime you have a radiation freeze and you have an inversion. And so typically we get an inversion, you might have a layer of cold air that's formed close to the ground with a layer of warm air up above it. And so the wind machine will mix that air and as it rotates around, it will mix the warm air above with the cold air below and we're actually heating the whole planting by bringing that warm air down. You hear about people hiring helicopters to fly over their crop in a freeze situation. That is essentially what they're doing. Do these systems work all the time? No. But like I say, when you have a good, strong inversion they will work. I remember asking one grower, you know, "Did that thing pay for itself the first year you had it put in?" He said, "Nope, but it's paid for itself several times over since I put 'em in." So these are becoming more and more common because they work at a lot of different times of the year, not just right around bloom time like the sprinkler systems. So the advantage is they work well enough if the inversion is low enough, three feet, you know, that should be 30. They can protect a large area, if the inversion's real strong they can protect a large area. If the inversion is not very strong, they protect a fairly small area. They can provide six to nine degrees of protection in the grape ideally, but they won't work if the winds are over five miles per hour, they simply, the air is being mixed up, there is no inversion. So you have limited control over, you know, no single freeze protection technique works all the time. Most work well in the right conditions but not at all in others. So proper siting of the crops you have, planning ahead. Don't plant stuff that's susceptible to winter cold or spring freezes or blooms early in frost susceptible sites. Put them in high, less vulnerable sites, otherwise you're gonna lose a crop. I tell people there's no reason to grow peaches, you know, very far from Lake Michigan, because you're only gonna get a crop every one or two out of three years. And so, so choose the crops that grow well in your region and spread your risk by growing multiple crops. All right and I can say, you know, basic thing is to most tree fruit growers is do everything you can to improve your air drainage so that you don't have any cold air impoundments. So I'm ready for questions, Bill. - [Bill] Hey, great. Thanks, Mark. First question is, so why does Michigan use March one as the starting point for growing degree days? - [Mark] Because in general, in the past, we didn't have an awful lot of growth before March one. Bill and I, you know, I mean and they're sitting in East Lansing or Grand Rapids so they don't see much growth. Early on in my career, I saw several Februarys where the last week of February was really warm and so Bill and I will often use January one for the start of our growing degree days and generally the difference is pretty small. We're only talking like, you know, 30 to 100 growing degree days and that might only be a day or two in June or July. - [Bill] Yeah, I also, in the old days they had to put out these old wooden weather stations out in the fields and (laughing) that was a pain to take care of 'em when you still had snow on the ground - [Mark] Yeah, when you still had three feet of snow on the ground. - [Bill] Okay, another question, with overhead irrigation system, do they blow their lines after they overhead spray? Trying to envision how this works and the economics. - [Mark] No, generally the overhead systems, they're only being used in the springtime and so that generally the only time they're worried about it freezing is during the early morning hours and so they'll run the sprinklers. I didn't say, what you have to do is you have to run the sprinklers, you start before it gets to freezing and you run the sprinklers as long as it's below freezing and once you can see the ice melting and you turn the sprinklers off, it's above freezing, it's usually above freezing for the rest of the day and if you have to run sprinklers again the next morning, you'll turn your sprinklers back on, recharge the line. So they don't have to winterize the system after running it in the spring. - [Bill] Another question, how cold, for how long does it have to be to kill newly planted trees, one to two years old, for apples or stone fruit? - [Mark] Newly planted, as in I planted them in the fall or newly, I would think that you, if you had a spring freeze, newly planted tree and you planted the trees and it, I would think it would have to get down to 10, 15 degrees to kill the tree. - [Bill] I think it depends on if there's green growth on the tree or if they're truly dormant makes a difference too. - [Mark] Right and if they were leafing out, you know, I can see where that it would certainly perhaps kill, you know, if it got cold enough to kill the leaves, if it got down into the low 20s. Usually a newly planted tree's pretty healthy and can put out new leaves. So I'm thinking cold enough to kill the cambium, kill the wood would probably be down around 10 to 15 degrees. - [Bill] Yeah, I've never really seen it a problem with early spring plant trees. - [Mark] Yeah it just doesn't get cold enough once we have time to get in there. - [Bill] What is your opinion of low trajectory frost irrigation in peach in the spring? Is this an effect way to create a heating effect and how much protection could you expect? - [Mark] Low trajectory, yeah. If I could keep it underneath the canopy I could probably put out a fair amount of heat but how many degrees is that? Probably two to three degrees Fahrenheit that you might be able to get if it's under calm conditions. So that might be the difference, you know. It's oftentimes, you know, you know, the difference as you can see, like the, you know, the difference between 28 and 25 degrees, if that was during peach bloom and I managed to raise the temperature from 24 to 26, I went from having virtually no crop to having a quarter crop. But if I had, if I managed to raise the temperature from 27 to 29, I'd go from like a half a crop to a full crop and then I'd have to thin so. It has an opportunity but you're really in these situations, you're dealing with pretty thin margins. - [Bill] We had an earlier question. I gave a partial answer but be interested in your input. My small one acre orchard, apples, pears and peaches is east of Battle Creek. Should I be concerned about cold hardiness? I do have good air drainage. - [Mark] Well, most of those crops can handle. So yeah, my rule of thumb is like for peaches as I mentioned, we worry about losing the flower buds in peaches when we get into the negative teens, but apples, pears, plums, generally we don't see flower bud loss until we get down around minus 20 and all these trees, when we get down to around minus 25, we might see some damage. Bill and I have seen damage to peach trees a couple of times in our careers and generally those were, it went down into the minus mid 20s and even though you're east of Battle Creek you're still in a relatively warm condition, to somebody in Minnesota or Wisconsin. But so, and to come back again, I wouldn't do practices that reduce winter cold hardiness, but judging by the mix that you've got, you don't need to spend an awful lot of time worrying about it. My growers generally don't get too concerned unless we get below minus 10. I'm done. - [Bill] Okay. You got a compliment, Mark. You've been great help to us all and the question's, what will we do without you? Who will we call? (Bill and Mark laughing) - I will be around for awhile. I've told the university that I'll come back part-time here this year until they hired a replacement for me and I'm under the impression that a replacement for me is about second on the list for the fruit replenishment. Thank you much. - [Bill] Yeah, thanks, Mark. Great presentation as always. Remember the, you need to, if you want recertification credits and certainly to give us feedback, click on that link that's in the chat there, the bit.ly and this is good for one, recertification credit for commercial 1C, for core and also for private. - [Mark] You have the question that are we gonna do the meetings, Monday night meetings and the answer's yes. So whether or not they will be at Coloma or virtual hasn't been decided yet - [Mike] And also a reminder for everyone, so that we can keep clear track of the RUP requests, we will be closing this session down here in just a minute or two and then reopening about five minutes or two for the next talk which will be Sushila Chaudhari, the weed specialist with MSU talking about weeds in fruit. So any last questions? If not, make sure you hit the link and then we'll be closing down here in just a minute.

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