Growth regulation F20

Ajouté : 2026-05-13

[00:00:01]okay so this uh class is on plant growth regulation or maybe more specifically plant height control um here's a picture so sometimes you might say well why bother what's what's the point of this what's the big deal um going back maybe 20 years buyers for plants didn't seem to really care as long as they had the right number of plants and then about 10 or more years ago buyers got more educated more specific on numbers and the size and shapes of plants especially flowering plants and that meant that growers had to pay attention to what the buyers wanted and the buyers didn't always have realistic expectations and they were adamant so growers had to adapt their growing to make the plants suit the requested needs now a lot of the times that was to make it more marketable right this is a lot like when i talk about you're going to the produce section and you pick something and by picking something you're voting for that right and so when a customer is going through a garden center and they pick a particular plant what they pick is their vote and that feeds back to the buyers which trickles back to the farmer and reinforces certain things and gets rid of other things so that's how this whole growth regulator market came to be um in this particular picture here you can see that the flowers are buried within the foliage and that's just not acceptable uh we need to have the flowers on top of the foliage as a as a bare minimum for something to look at right so this is something we can control um the other thing is trying to keep plants in a suitable format for a pot size right so if you look there's this tiny six-inch pot down here for this huge dahlia that's just not appropriate so a grower has to contain the plant in the most compact well-presented size for that particular size pot is it always reasonable no but markets dictate you take a dahlia for example most dailies would be pulled out of the pot and planted in the garden but what the buyers find is that the customers don't want to buy a daily a bulb they want to buy dahlia and then as the years went on they don't want to just buy daily they want to buy a daily that's in full bloom and that becomes increasingly challenging for the growers to do that it's not that they're asking for this this is what the market dictates that's when they vote when they go buy stuff all right um here's a pansy looking at different pansies uh if we if we let a pansy grow without any growth regulation it becomes very floppy and falls over especially you hit it with a water stream of water and then next you know they're all laying on their side so growth regulators are used extensively for that production so in today's lesson i want to talk about different methods for controlling plant height and these are the major categories we'll talk about lighting and climate chemical methods and then some nutritional methods and i'll squeak in uh one other method in there so let's start with lighting um to review from your plant science one your red to far red light ratio right this is your red to far red light that ratio dictates plant stretch stretch and a lot of that's to do with plants competing for light so remember when a plant overlaps another plant it's filtering light and far red light gets to the plant not as much red triggering uh elongation so that that plant can stretch past the other one of course the plants just keep trying to compete past each other they get taller and taller and skinnier and skinnier as they're reaching for the light so we can influence light uh in the greenhouse and we can do here's just that picture reminding of how that works um and we can do that by playing with spectrum uh so blue light specifically is used extensively uh to inhibit auxin production so a high blue uh and in a sense remember auxin stimulates shoot and root growth right so oxen is something that is produced at the chute or the apex of the plant travels down and causes all kinds of growth and blue light has been shown to inhibit oxygen production so that would keep plants a little more compact it might slow them down as far as the spectrum of blue we can also increase the component of blue in our spectrum if you see in this impatience plug we have sort of a tall yellowy impatience plug all the way down to sort of uh interesting growth formats now the 100 blue has fewer leaves it's a bit odd looking but definitely 50 blue seems to be a sweet spot so that's an example of where the spectrum of light is used to control growth one of the other things we can do is play with the overall color spectrum so remember red far red impacts growth right so when we look at leds versus hps we can use led lights that have lots of red elements to override that ratio with the pfr so that the plants stay a little more compact and the led led grow lights we installed over our propaganda bench have quite a few red elements so they'll be very good for keeping our our plugs more compact when we start doing bedding plant cuttings and seeds in the winter so these pictures here show hps led and ambient and the the differences are subtle but hps is still good you know in the past i've talked about how there's nothing wrong with hps in fact we get radiant heat from it but some plants like this dianthus under the hps is a little more stretched a little leggier most likely because there's a larger infrared component in hps versus the led elements um rooting looks a little better for the marigolds under hps for peppers it seems comparable but under all situations it's better than under ambient which is interesting um they don't tell us the time of year here so but you know um lettuce something we mentioned in one of the classes in root zone uh red lettuce especially in the winter when the sun is low in intensity led lights are used to help make red lettuce red in fact this green lettuce here is a red lettuce variety and it's grown in the winter months and so when they start putting led lights over the lettuce as you increase the blue percentage of the led elements in the light array you get a more red lettuce now from a practical perspective from an energy consumption perspective this is your better choice because uh red leds use less electricity and drive more photosynthesis so this this particular lettuce is going to finish sooner and has acceptable color so in case you're wondering about led lights on on lettuce specifically and blue again triggers the blue elements trigger that anthocyanin sunscreen pigment i talk about uh that gives you that purple color um so that's light let's look at climate um one of the biggest things that's used in controlling plants with climate is something called diff that's an abbreviation for difference and you calculate it by taking your day temperature and you subtract your night temperature so here we've got a 20 degrees c during the day 18 at night that's a positive two diff so the day is two degrees different from the night positively a negative diff right this is where we produce short plants with short inner nodes we a negative diff means it's the other way around right which means your nighttime temperature is warmer than your day temperature now that's a bit of a mind bender uh most crops the typical delta is about six degrees celsius so if your nighttime temperature is six degrees warmer than your daytime temperature you're going to have greatly uh compacted plants um warmer nights versus well basically what happens is you have higher respiration rates at night that means you're consuming sugars that might otherwise be used for growing and so the plant has a little less available for elongation in the morning on top of that there's reduced flow of oxen around the tissues in the morning during the day especially but with warm night temperatures we're typically looking at a cooler morning primarily right the this part here i wanted to highlight plant stems grow mostly in the morning uh that's probably the most important thing to remember in this little section so remember if plant stems grow mostly in the morning hours so we're talking from 5am to 8am is when a lot of the stem growth happens um it sort of introduces a new opportunity right so i talked about how a negative diff so having a warmer entire night versus a whole day will disrupt the flow of sugars and cause more compact plants but if the principal time of day is the morning where stem elongation actually happens we can actually adopt a different technique called a drop or morning dip and that basically what happens is that the greenhouse is cooled rapidly in the morning by about 5 to 10 degrees celsius so the first two to three hours of your day this is done and that effectively elicits the same response as having a full negative diff so where you have to maintain a warm night temperature for the whole night here all you're doing is creating this differential so the plants will look at this really cold morning as the sun's coming up the air temperature is quite a bit colder and it thinks man the night time was a lot warmer and that shock disrupts the flow and in the time when the plants trying to mobilize sugar and cause rapid stretching and move water so it's a it's a powerful tool um again the optimal diff is around delta six uh every crop's a little bit different and that requires some experimentation um this is something i've been trying to encourage some uh cannabis growers to adopt to cut down on labor and shaping their plants right strengthening their stems for holding flowers um one thing to keep in mind here that's important with this and that is this requires cool seasons so typically if you got your greenhouse right you got your your greenhouse right and you've got remember we talked about energy curtains that close at night to keep the heat in so night time you've got warm air in your greenhouse floating around and you have cold air above your energy curtain because the windows are up there right it's cold and then when you open your curtain this cold air dumps down onto the crop immediately and you get sort of a really abrupt shock in temperature and that's enough to elicit a diff drop morning effect so that only works in cool seasons so we're talking uh early spring winter and late fall so your daytime temperatures are still fairly warm and you can do this now summertime you know maybe depending on the crop it's a really heat-loving crop you could do it but generally speaking it's not applicable um so you're limited with your seasons for applying this right that's just one of the things we can't get around this is a little diagram i made to help you understand a positive diff so nighttime is a normal cool temperature we raise your temperature during the day and then we cool off again for the night we're a negative diff we have a warm night and then we cool off for the day assuming that's possible and then we warm up again for the night now of course a full diff means you're heating the greenhouse at night when there's no sunshine so maybe you can close your energy curtain but you have no benefit from the sun so this is a more expensive way to control heat but sometimes it is the only way available to us because of some plants are just not sensitive enough to a morning dip and so we have to do a much longer diff treatment but the morning dip would look like this you have a normal nighttime temperature and a normal daytime temperature right but just before the morning starts we drop the temperature massively for a couple hours and then we let it come back up and that gives us uh the same as if we were doing a negative diff oh i missed that just terrible accuracy there now some of you may remember that i have talked about an evening dip with tomatoes right for steering sugars into the fruit the same thing applies but this is not about being compact remember stem growth happens in the morning sugar mobilization to the fruit happens in the evening so we can do a dip at the end of the day and that drives sugars to the tomatoes because they're staying warm we'll talk a bit about more about that again as we do the vegetable course in the winter but i'm just going to keep repeating it subtly so you remember um so again diff for height control so we need only treat plants for a few days sometimes we get confused by this when i'm teaching this lesson and students think that oh it's the entire crop no anywhere from uh two days to maybe 14 days depending on the crop is all you need um another important factor to keep in mind is that it only works when the plant's in an active vegetative growth phase so remember your juvenile vegetative reproductive phases so only when it's really actively vegetatively growing will you get a good response to diffing there is a species-dependent response so there are some species not many but there are some that just are not sensitive to this so that requires you to do some homework to figure that out and again i mentioned you need a cool climate right so you're not it's not gonna work in the tropical climate um and on a side note uh for certain crops let's say you're doing a fall mom maybe a late mom say you're a weekly pot mom grower and you're trying to dip your mums to keep them compact but you're using incandescent bulbs for photoperiod control to keep it vegetative the light that comes off these bulbs produces infrared right and that infrared has been known to reverse the effect of diffing because it sends such a strong stretch signal to the plants it just means you got to be really careful that you don't use those incandescent law lamps longer than necessary some farmers have it dialed down to maybe 15 minutes in the middle of the night 20 minutes some might leave the lights on for four hours just you know insurance they might say but they don't realize that that four hours of incandescent light is stretching their plants so keep that in mind looking at the difference between both diff and drop remember drop is the morning temperature drop just to keep things clear where the diff is the full night uh diff works best on slow growing plants so we're talking uh you know herbaceous non-herbaceous plants perennials plants that just are slower to grow right they need a bigger push as i say here one of the downsides of diff is that it can slow the entire crop down so that you might even miss a ship date so it takes longer to finish a crop when you're doing a full dip because you're treating for the whole night you're using up sugars for the whole night so it takes longer for that plant to mature so you take it takes longer which costs you money uh it also causes smaller and more horizontal leaves but smaller is probably the bigger thing here uh so keep that in mind as far as the drops that's the morning dip it saves energy because you're not doing the entire night uh a real bonus is that by cooling the air off you can open the curtains like i suggested but you can also open your vents right so cold air drops and hot air escapes which means that you are dehumidifying wait which is always a good thing for reducing disease a morning drop has less of a delay on your crop so your ship dates more or less stay pretty close [Music] not to mention when you're shipping especially shipping to garden centers that morning drop that wild swing actually hardens off the crop makes them a little tougher so that there's less of a shock when they leave the greenhouse and get shipped to some other location where they don't know what they're going to see so a couple of pros and cons um this slide is just reviewing something i taught in the first part of the term but you know just remember that cool temperatures with high light we get uh compact growth with thick leaves so that's kind of a what i was trying to say that it might improve the quality a little bit but the downside is that you know cool temperatures with low light causes thin small growth and uh warm temperatures with highlight we get rapid with uh thick growth this is your sort of your your turbo fast possible but you may get stretch and of course warm light with low light is not good so the key thing here what i'm i guess what i'm trying to say is that uh if you're using cool temperatures supplemental lighting may not be a bad idea um you know because you don't want to have this situation where you get thin growth all right one last thing i'm going to put it in the climate category but technically it's not climate but it i suppose it is because it's external to the plant and that is mechanical motion i don't know if you can see in this picture this is just a gray pvc conduit pipe that's being dragged across these these mini mums or many roses sorry this mechanical stimulation i mentioned this in plant science too uh actually causes the plants to react and because their stem is flexed they can sense the flex which is pretty amazing and in response they actually thicken their stems and stiffen their stems which means there's less energy to stretch so they become more compact and more sturdy um the big ten dollar word let's see if i can do ten oh man i cannot write with a mouse maybe it's because i'm i'm left-handed but i mouse with my right hand that's really unfortunate the ten dollar word um is thigmo morphogenesis there you go you can tell that to someone you you love and they'll be really impressed uh thigmo morphogenesis there's a link on that if you click on your powerpoint version of this you can take you to the i think it's just an abstract but that's probably all you'll read anyways um which talks about this uh there is a greenhouse in burlington and aldershot it's actually called aldershot greenhouses ironically uh that grows many roses and they do this throughout their greenhouse you know how i talked about how we have an irrigation boom at the college they hang a pipe like this on the boom and they just as the boom goes it drags across the crop and their irrigation booms actually rarely spray water all they do is drag these pipes over their their roses and they've almost eliminated their use of growth regulators as a result which is pretty cool um they have had a fair number of boom breakdowns though because they are moving like a hundred times more than the average farm uh so we get thickened stems and delayed flowering uh which means flowering oftentimes in the case of this we want to hold it off until the plants fully develop so that is a win-win that's not always a win but with many roses it's a win-win another thing i'll touch on it's not used a lot in ornamental but i have seen this in cannabis is extreme wind or airflow but if you think about it it's really no different than what i just talked about up here you're causing the plants to sway and that swaying motion causes them to react by stiffening their stems what i will say and i've seen this and i would discourage it is that the fans are left on all the time that's not important you're better off actually having gentle airflow for an even climate and if you are trying to cut back on labor and stiffen your plants you would put the fan on high speed maybe only about half a dozen times a day that's it so you could have a second fan on a timer on full speed and then one that's on all the time at low speed that would be your best bet otherwise your plants wasting too much energy responding to the motion um okay let's look at chemical methods for height control i know uh some of you will be uncomfortable with this because it's chemicals but keep in mind a lot of these things are are mimicking natural uh chemicals but that's that's all to be safe i'll say you know what you're right they are chemicals i wouldn't go putting them in my coffee when you rented a cream but uh you know they should still be treated respon responsibly um this is a long list this is i'm going to cover some of these i'm going to try to skip through this fairly quickly because i'll just put you to sleep but there are some things i got to highlight because you know if you do end up in the ornamental world i promise you you will run into this stuff so we have to cover it okay um for the most part if you go back to plant science one you remember learning about gibberellins okay remember the i hope uh they're using the picture i love that picture of the cabbage where you've got like a regular cabbage that's a nice big ball like a soccer ball size and then there's a guy in a stepladder holding a cabbage that's like 20 feet tall that's what happens when you apply gibberellic acid it's potent just like this arabidopsis uh picture here is showing boom stretch tall when you apply gibberellic acid so and plus it promotes flowering uh gerbilic acid it breaks dormancy remember you can soak your seeds if you've got you know seeds that are supposed to be winterized and you didn't do it just soak them in gibberellic acid anyways the key here is stretch that's the hormone that plants use for the most part to cause stretch so what do we do we use pgr's plant growth regulators and they act primarily by inhibiting gibberellins so they bind it or they block it so the plant can't sense the presence of the gibberellin so you don't get the gerbilic acid effect right so you don't get cellular elongation and division you don't get stretch that was hidden did you even see that possibly not sorry i had a really tough day focusing i don't know i was just maybe all the excitement of uh you know plant growth regulators anyways um it's just not a coincidence that i'm starting with a but let's start with a a rest or arrest uh i think in the states that sold under the label abide it is a anti gibberellin no surprise we just talked about that um let me back up for a second when when we zip through these growth regulators there's a few things that i want to highlight that you know you might want to know for example um does it move through the plant if it moves to the plant that means that if you apply it on one part it will diffuse through the entire tissue now let me back this up because some of you probably panicked when i said you might want to know this i'm not going to ask you any kind of question on a quiz or a final that says what is the mode of action of a rest but i might ask you what does it mean when a growth regulator is mobile in a plant so that's what i want you to know that kind of stuff the broader more thematic stuff anything you can look up like this so what you can look it up what do i need to know you know that you know it off the top of your head so make sure you understand uh what anti-gibralic means or anti-gibberin uh understand what it means to be mobile in the plant right where can you apply it uh keep in mind if it's mobile you can actually drench it to the roots right if there's your soil line if you put it in the water that it will go in the roots and it'll travel up the plant from the roots so you can drench it as well so being mobile in the plant is really really useful at times um a-reft is probably one of the more broadly effective uh growth regulators uh it's it's fairly expensive so it's you know if you have crops that are not where other ones are not working or not effective you might try your rest um but yeah bulk crops are a good example although not many bulb growers get into growth regulators that's getting pretty extreme but it's possible uh phytotoxicity right that means that it causes burn on a crop some growth regulators if you're not absolutely correct with your math you can burn crops you can burn the edges of leaves where the droplets form and concentrate so a rest being a low toxicity growth regulator growers that grow plugs juvenile plants for sale to other people these are high value high dense plants there's a lot that can go wrong it can be a stressful thing to do as a grower very rewarding financially but stressful so a lot of times plug growers will stick with something tried and true that they know is not going to cause toxicity um in the sense it's also safer right in that this is another important thing to remember like mobility is residual activity i got all these lines everywhere highlighting things but residual activity is really important right so if something has a really extensive residual activity that means that if you spray it it's going to act on the plant for quite a long time that could be anywhere from uh a week to two months so you have to be very cognizant of what the residual activity is some growth regulators are a lot more extreme than others and so a reds arrest is one that is somewhat limited and if you think about it from a growing perspective the more transient the the pgr is the more control the grower has because they can pulse in some growth regulator for a slot to control the growth without fear of shutting the crop down for three four weeks so they go in they give it a shot slows it down then they let it grow again then they might have to give it a shot a couple weeks later they're pulsing in the control right and you can only do that when you have uh limited residual activity um this is uh another dahlia a dahlia trial with different rates of arrest and trying to figure out what the best rate was a lot of farms end up doing these kinds of trials in-house because it's not always the same you know where one milligram worked for this person you know maybe two milligrams works better at your farm that can often be related to something as simple as the ph of your water but at the end of the day a lot of farms have to do these sorts of trials to figure out what rates to use that are suitable these are excessive the plant is overly compact for the pot where these would both be possibly even this one would be acceptable so you have a fairly wide range you get 0.5 all the way to 2 milligrams would be acceptable so the nice thing about that is that there's a fairly wide margin for error right um cycle cell matt's talked about this because it's the most commonly ones used in poinsettias uh it is a foliar for the most part main reason why we fully apply it is because we can pulse in smaller rates it has a limited residual effect if you drench another common theme issue yes you can foliar but you can also drench but when you drench you put quite a bit more in the soil so it has a longer acting effect on it a longer uh grown-on effect so be careful with drenching in terms of giving up some control so yes uh b9 which is a another very common growth regulator used partly because it's inexpensive it's uh it breaks down very rapidly this is probably one of the shortest uh residual effect growth regulators very mobile you spray one part of the plant it moves around the entire thing and here in this cosmo you can see the control on the left and what a 3000 ppm spray of b9 did on the right um fyi 3000 ppm ppm is actually fairly concentrated uh but remember b9 is cheap so uh it is actually a very common i consider it an old-school one but it is common and it's safe so it's still used a lot um it's effective in a lot of crops except the one key one is lilies but you know not many people grow easter lilies anymore a few buchenstein myers there's not many that that market is disappearing uh like literally probably cove is wiping out more of them but that generation is is not longer rounded so just think about it who do you know buys easter lilies not many um it is also very good for seedlings uh and that's the other place where i've seen it used a lot um you go in the ball grow book oftentimes it's just standard instruction b9 your seedlings at this stage they can encourage branching and makes a more compact bedding plant interesting most effective and cooler climates so again we live in a cooler climate for the most part so we're okay with that um i used growth regulators a fair amount when i grew uh potted sunflowers that was a long time ago but you had to keep them short to sell if they got tall on you people didn't want them so they are definitely b9 is definitely a powerful affiliator this is a really cool one it's called the chemical name is paclobutrisol but it's known as bonsai piccolo is just the cheaper version made by accompanying guelph same thing it acts on gibberellin but it i would say it's probably only recently become the most widely used because of its cost benefit ratio it doesn't take much and it's very effective it does have a fairly long control window so there's the difference between bonsai and a rest right so you're looking at season long control um this is one that where the betting plant producers often use it because you can't have bedding plants overgrowing at a garden center people don't buy they try taking the pots they can't get them apart the flowers rip off so by drenching them with bonsai once in the crop cycle those bedding plants kind of really stay compact the downside is that when someone buys those types of bedding plants they sit in their garden for three weeks four weeks not doing anything until the bonsai finally until they finally grow out past the bonsai on a side benefit it acts as a fungicide as well it seems to the growth of fungi a fungus on plants so your fungal infections are reduced very low rates remember i said it's a cost-benefit thing 0.1 to 1 ppm keep contrast that to 3000 ppm for b9 so this stuff is potent um on a on a uh unofficial side note from derek you know if you do get your hands on some bonsai and you're you know you don't really like mowing your lawn a lot in the summer spray your lawn with bonsai and it gets super dark green and it won't grow for weeks a little trick there um couple other brands out there concise to magic again let's look at it so what do we look for it's you can do foliar you can do drench that means it's gonna is it effective well in this case it does not move within the plant so why would you do a drench because you're going to limit growth of roots these are typically used with lilies and they lilies are interesting in that a lot of their sensory inputs are in the roots it's a bulb they grow roots the roots are really important root sense the temperature they sense the climate it's strange in that context it's not like that a lot of other plants yeah anyways sprenched which is a heavy spray long lasting at very low rates um one of the things that's worth noting about a lot of these things like these chemicals last ones i talked about bonsai uh some magic all these other ones a lot of them stick to plastic surfaces they're persistent on plastic surfaces and in soil now a lot of times in the ornamental world we don't reuse the soil we ship it it's gone but we do reuse things like seedling trays and cutting trays so if you ever use a growth regulator on anything plastic like that uh really you have to recycle it otherwise you have to understand that it's going to potentially impact the growth of what you put in that train next time so be very aware of that um other growth regulators that have interesting effects uh ethaphon this is sort of a non your non-standard uh gibberellic growth regulator this is one that actually causes plants to release ethylene so it actually causes butt abortion uh some bedding plants we need to make sure there are no buds for a while partly because if they flower too early the the flowers will bloom out and fall off and then rot and trigger botrytis uh on your plant which impacts the quality later so if you can keep them from flowering to for a little while uh and then let them flower at the right time you don't have all the labor of cleaning it up um hanging baskets are a really good example here like this lobelia they just drop stuff constantly and everything underneath gets covered with these pedals that rot um so yeah not all pgrs are about growing right there's branching there's flower there's ones that encourage stretch just like that ethaphon promotes flower butt abortion uh it also controls height but it does increase branching as well which is really a useful um trait if you're trying to get a broader plant that has more flowering sites right yes it's illegal to use that in cannabis i know someone's thinking that um oh ago this is another interesting one a fairly new one uh i've got a link on here i think i put the link on this week's folder as well if you want to watch plants grow but it's pretty cool because they take a little spray bottle and they just barely spritz the plants right and it actually has quite an effect on the plants and we're talking just a few droplets landing all over the place it wasn't like a soaking spray but it does chemically pinch which means it's removing uh bud sites so that when it does flower there's more flowers see look at that this is without it this is with it that's pretty impressive so it promotes lateral branching which of course is the same as taking uh pinching the apical parts of your plants off like you did with your poinsettias i got a lot of circles here um so pinching requires labor if you you have 500 000 pots and you want to pinch the apical meristems of them all you have to hire an army of people right so depending on the crop like if it's hydrangeas you just mow them you go over with a mower basically and chop the tops off but they're going to grow so much bigger over the season that you won't see the damaged leaves whereas with like a bedding plant like a fuchsia you can't do that so you spray with a chemical pinching agent like wagio and that that gives you way more flower sites and gives you a fuller looking plant this is sedum it's hard to see here this is overdone this is probably the sweet spot here and this is with uh almost none so the the buds you can't really see them but they're buried and there's not many in the plant where in this one the buds are above the leaves remember what i said in the first slide and there are lots of them so this is going to present really nicely that's going to that's going to give your your product the kind of sales you need configure this is another one i include this also because it's timely we it's christmas time and you go to home depot and canadian tire i'm pretty sure that they've got christmas cactus sitting on the shelves now uh christmas cactus is photoperiodic but generally speaking what we do is we spray it with configure uh and it actually triggers flower and branch set uh so christmas cactus it's the it's the number one thing that's gonna get all these buds that form on the on the ends of the cactus by spraying with configure that's basically obsidic acid uh this is another one instead of like the other growth regulators where we're trying to block gibberellin the situations where you want to spray gibberellin and so things like pro gibb or floor gib are synthetic variants of gibberellins so it's like almost duplicate copy of the molecule and you're spraying it on your crop and what's interesting is that in as far as strawberry production something we do uh you actually increase your branching and promote runners uh so you can get a bigger fuller whoops fuller strawberry plant by spraying with something like progib um and then if you remember from [Music] your plant science one i don't know if you've talked about that but uh azaleas are sprayed with gibberellic acid because that makes them flower once normally in azalea they flower starting in the spring and it's sort of stretched out over a number of weeks when you grow azaleas ornamentally you want them to flower all at once and so by spraying them with a pro gib it triggers all the apical meristem buds to go into flour at the exact same time and you get this beautiful flush of flowers if you take it home and you carry it on and keep growing it you'll notice that never flowers like that again unless you spray it with pro-gibb it'll flower sporadically throw over through a longer period of time but you won't get that huge flush um another one fresco fascination probably fascination is one you'll run into uh this is when you're trying to avoid leaves from falling off so it avoids it stops lower leaf drop so this is one that's that's kind of that's blocking the effects of ethylene so to speak and it also prolongs flower life so you can if you this is can be used as a band-aid if you use too much of a growth regulator right so one of your gibberellin inhibiting ones if you got the number wrong you can correct that by spraying with fascination lastly uh ethyl block is kind of a cool one this is one that when you're shifting plants in a truck or if they're in a cooler for a long period of time you want to make sure that there's not too much ethylene with orchids what happens with organs is that if they're in a box for too long the flowers all fall off and that nothing more disappointing than growing a crop for you know as long as it takes to grow an orchid and and then when someone opens the box at the flower shop all the flowers are sitting at the bottom of the box so uh oftentimes the crop is sorted into a finishing area and then sprayed with ethyl block to keep the flowers from falling off the orchids um they also sometimes have sachets that hang in the box that will absorb ethylene to keep the flowers from falling off okay important considerations when applying plant growth regulators so the plant has to be the correct stage of growth right so for the most part that's the vegetative growth phase right the plant cannot be water stressed that's a good way to get phytotoxicity you want to make sure your plants are happy healthy growing not stressed and every piece your pgr should be tested you know even if you're just trying a different cultivar one you're not familiar with uh really important [Music] determine if your pgr is mobile or not don't just assume it is check that it is because if it's not mobile you have to spray to the point of runoff right that means that you cover the plant thoroughly so all the leaves are dripping if it's mobile you can get away with just spraying your crop willy-nilly and letting it move around the other thing is consider your growing media and what i mean by that is that for example bark based media so at times you see bark being used actually in nurseries i see this a lot at the college we've experimented with grow bark to with different growing media where there's wood fiber and bark in the media and uh recent evidence has shown that uh bark actually uh interacts with growth regulators differently so be aware that you may not get the desired effect with bark in the media so here for example this pansy is not responding to the paclobutrazole so not as much as pete and perlite so just be aware of that and then down here you can see this is out of control almost the same as the control here whereas the other two are are responding to the growth regulator i don't know what that is can't tell from here maybe a million bells or something like that anyways just know that bark interferes with a lot of growth regulators um i wanted to look at this this actually this case this is a link here if you click on that you'll see where i got this from uh this is effectively a growth chart so remember a lot of growers they track the height at different weeks of the growing season and that's how they know if they have to apply a growth regulator so what's happened here is that growth regulators were applied where all these arrows are and the crop responded accordingly and you can see right here the crop was off the chart a bit that's why we got these three brief cycle cell applications um then there was one more application here it didn't look like it needed it because it was on the chart and that kicked it into the middle zone uh but it looks like it was a heavy dose i actually haven't read the paper i'm just looking at this and there's too much control and the plants slow down way too much [Music] and here we have something another input where the crop just sort of took off and goes back into the the correct zone so i'm guessing what's happened here is that this is cycle cell there is a weak application here it slowed the crop but then it started to recover again because it's a transient growth regulator but i think they overdid it probably should have done a heavier dose here and then they could have skipped these two maybe one here and this one possibly not even needed anyways it's an interesting thing to look at so you can see how growth regulators have an impact on a crop lastly we have discussed this before so it should be review um nitrogen and phosphorus both impact height right if you supply a lot of nitrogen it discourages reproduction and you get lots of growth and large internodes and then of course phosphorus you can either have it in in excess which causes stretch or deficient which causes compact growth um so in these pictures there's some examples this is tomato uh without fa with phosphorus and without phosphorus and look at the extreme it's it's massive uh same thing as another tomato these are sun impatiens these are phosphorus deficient so um options for controlling growth this is my review slide i think yeah my last slide so first one right off the bat before you do anything choose the correct cultivar right choose ones that have the growth habit you need as close to it as possible eliminate shading so first of all that means don't be greedy don't have your plants so dense that they're overlapping each other the other thing often neglected is make sure the greenhouse is clean is it dirty inside are there shadows what what's impacting penetration of light to your crop and if need be use supplemental lighting yes it costs money but it can also save you money right in terms of diffing and spraying and labor for pinching and whatnot limit the amount of phosphorus so don't i'm not saying withhold it but you can definitely limit how much is supplied and maybe even limit your water right don't let them wilt though create mechanical stress we talked about that with uh mechanical as in like bending the plants through uh some object or with wind increase air circulation right so getting plants that they're they're uh getting good flow between the leaves that also means you're going to get good light what else led lights you're red to far red right make sure you get lots of red in the spectrum um cut back or pinch that's pretty old school looks like that's basically you give up you're just gonna go in and just do the lawnmower thing which works for hydrangeas um last but not least plant growth regulators yes what i spent the last ages talking about um pgrs uh like i said if you end up in the ornamental world this is this is just that's just life um you wear your proper ppe when you spray it typically growth regulators are not toxic or carcinogenic i don't recall seeing any that had major warnings on them um unlike some insecticides so but pgrs are are used quite a bit in the ornamental industry so can't avoid that okay don't forget that there is a quiz this week and every week till we're done this term which is coming fast really okay see you in the greenhouse