Cucumber Diseases W21

Hinzugefügt: 2026-05-13

[00:00:01]okay so to continue from last week i want to talk about uh cucumber diseases uh and viruses really not disorders uh and touch on a couple of bacterial things but it's mostly fungal uh that fungal diseases that we're going to be talking about with cucumbers going down the list of fungal infections cucumbers are particularly susceptible to a lot damping off rhizoctinia botrytis black root gummy stem blight penicillium stem rod leaf spot uh we're going to touch on all of these in this class now this is the kind of document that you would want to keep as a reference i'm not going to have you memorize uh every little detail so what i would do is pay attention to the review questions for the midterm to have an idea of what you need to know from the midterm so rather than getting lost but let me walk you through it and then we'll discuss some common elements at the end and uh hopefully if you're less concerned about all the details you'll relax and learn a little bit okay so before we get into it um sometimes people will say well why do i have to be able to diagnose it we just know it's a fungal infection and that can be true but at the end of the day the methods of controlling fungal infections need to be targeted to the species so it is important that you do your best to identify the species now if it's really unclear then it was worthwhile paying the 40 or 50 bucks to mail the sample off to the university of guelph lab or to your agricultural extension to have them diagnose it using microscopes and eliza kids but just below here i've got an example right so i've got you know dakinil and it is effective against the two two diseases like rhizoctinia and anthracnose whereas if we have botrytis uh or powdery mildew or septoria then we actually want to go with something like pristine on this side so uh understanding what type of fungal infection it is you have is important so that's why we're going through some of the common symptoms things you'd look for when you're trying to decide what process to use to keep it under control so the classic sort of beginner's introduction to fungal infections is damping off right you probably learned this in some of your courses already i hope you have in fact i hope some of this is review but my past experience this has not always been the case but so pythium and phytophthora are real common fungal infections that target roots and cause what we call damping off and it's always starts with the root zone right is it too wet and also if you have cold conditions a wet root zone with cold conditions is always a recipe for disaster so obviously along this diagonal here on this side we have healthy roots for a cucumber block and in this side we have damping off pythium so and of course the classic hallmark with the diagnosing pythium is that if you take a root so say over here i've got a couple of lines here that are supposed to symbolize the uh where the root was so if you take these tissues and extend them along the idea is that this part this cylinder of root can slide off so if you grab a root so down here you can see there's a hard break if you grab this outer root and you pull it actually sloughs off and leaves the steel behind so in here this is the this is the vascular steel the uh phloem and xylem bundle so that's a quick way to diagnose uh pythium infection in your crop so can you slide off the outer cortex and leave behind the vascular steel or cambium uh if you were to look at cut a bag open and look at the roots inside you would see a combination of new uh new white growth nice white healthy roots right so we've got you know a root here a root here there's a room here there's a couple coming out but they're surrounded by sick looking uh roots and that is uh pythium so what you do is just grab one of those roots give it a yank and see if you can pull it off leaving the vascular steel behind then you're pretty sure at that point you have pythium and phytophthora looking at rhizoctinia this is a key critical difference here is that it is uh typically above the soil line so if you look at these these seedlings that have been harvested and cleaned post infection you'll see that the the fungal infection is around the stem at the soil level differing heights but it's at the soil level so that is one of the key differentiators for rhizoctinia in a cucumber plant you would look for a br brown or blackening stem at the soil level this is more common in the coir than it is in the rock wool um but effectively what happens is the fungal chokes off the vasculature and then you have sudden wilting so sudden wilt onset of wilt and then the plant just can't get water and nutrients and things go downhill pretty quickly so it's important to keep your your greenhouse clean and catch these infections quickly uh it does survive on dead plant material so it's important to to clean thoroughly not only between crops but obviously during crafts some farms are kind of messy they throw everything in the ground they wait take their time cleaning it up where other farms are very fastidious you know one way or another mother nature gets you right so you can put the money in up front and keep it clean with pay the labor or you can leave it and pay the money in chemical control and headaches down the road so you know where i stand on that rhizoctinia does tend to see to be more of a summertime problem so hot weather and it is associated with a wet dry cycle so what what is important is to watch your bag dry down at night make sure that you don't have excessive dry down at night uh it's that moisture oscillation that sort of predisposes the stem to rhizoctinia um botrytis so botrytis is very common in greenhouses it loves the humid environment of course cucumbers are the most humid of them all so botrytis is fairly common and what you're looking at here is a classic example of someone who's cut something off a plant maybe it was a leaf that was damaged or they were lowering the vine they cut it off and that wound became an entry point and the mold is growing up the petiole towards the stem so you have to be very careful that the tools you're using are kept clean so that they're dipped and sterilized periodically so you're not spreading disease um you also want to make sure your tools are sharp so they make a clean cut the plants more likely to heal properly and less uh will heal itself up quickly and not allow an entry point for a fungal infection um so it's botrytis is visible as a gray fuzzy mold so on a on a cucumber fruit you see this gray fuzzy mold that's botrytis or on developing flowers it's often associated with flowers there's a gray fuzzy that's that's not the best picture but a fuzzy flower can be seen so really critical to maintain a proper greenhouse environment that means we've got to make sure there's no condensation forming on leaves fruit or flowers at the end of the day and we need to make sure that we're not allowing the fungus to propagate by keeping our cuts clean not leaving ragged cuts and keeping dead tissues and what not cleaned up off the floor and then of course you know keeping your relative humidity below 85 percent which of course you would for other things like powdery mildew we've discussed many times gummy stem blight uh by the way i'm i'm not gonna ask you to memorize the genus species of any of these diseases that's something you can look up um so just you know don't worry about that in in the in the actual business they're going to talk about it as gummy stem blight that's what you're going to see but it is important to understand that you know these things are widespread and not not ignored so you should try to absorb this information it's pretty easy to see here where there's like sap and exudate coming out of the stem that's sticky whoops so you can so gummy stem blight here's another picture to help you uh see you can see the stem is actually split open revealing the inner cortex and there's some sort of black elements sometimes it's black mold that's growing on the sap that's leaking out so it's a secondary infection be careful with that if you're looking at the end of the fruit so in this case it's the end of the cucumber this is more advanced something to help distinguish between gummy stem blight and say botrytis is that here it's black and smooth right it is not the kind of thing that grows fruiting bodies out the exterior that are nice and fuzzy so there's no fuzzy gray mold like you would expect in botrytis okay looks like aladdin slipper uh this is cucumbers from a few years ago uh before i taught this course uh and these are actually cucumbers that developed gummy stem blight at the college and you can see how they all welted um they ended up ripping that crap out it's a common theme so gummy stem blade the infections occur at pruning wounds you've heard this before or injured sites uh often new growth like flowers and fruit or uh sometimes leaves but you want to look mostly with flowers and fruit and then of course ultimately in the stem uh they start as what's called a water-soaked lesion so that that would be sort of a wet dark green looking spot uh you're not gonna necessarily see yellowing right away it's just gonna look water-soaked um eventually they turn into tan colored lesions you know with sort of black structures um but hopefully you catch it before it gets too far some other things to help you look for if this is a on the top here is a cross section of a stem and you're looking at the pith so as you go further down the stem there's an empty pith as the the cambium pulls apart and if that's sort of brown in there that's another clue but as you'll learn from slides coming down this could also could also be fusarium so it could be any number of things so you have to sort of try to combine the different ideas or if you're trying to make a fungal a fungicide selection then if you've narrowed it down to two pick a fungus a fungicide that is going to be effective for the two types that you think it might be that's sort of how you cover your bases here you can see the necrosis on the leaves it really it's so hard to know you know what i do try to say is that nutrient deficiencies tend to show uniformly across the leaf so you'd expect that you know the whole leading edge or the entire perimeter of the leaf is demonstrating symptoms that would be more nutritional where here you're seeing a lesion on one side but not on the other and you're seeing a big lesion on this side but not on the other so it's asymmetrical that sort of is one of your clues that there may be something going on here that's not necessarily nutritional it's not always the case but is more often the case so and then of course the the fruit thing here yellowing it could look healthy but if you slice it open you might see that brown region in it so how do you prevent it maintain higher ecs if possible so we don't have uh too much root pressure causing split right so if you're looking at the stem here and there's root pressure it causes the stem to split and that opens up a lesion which then allows the spores to get in and establish themselves the other thing we can do is have elevated calcium in our fertilizer that strengthens the walls which again helps resist splitting um and then of course as always with fungal things prevent moisture from forming on our leaves so that there's no moisture to ignite the uh the fungal growth so gummy stem blade remember how i mentioned blossom end rot so here's a bunch of stems and tricky but if you look these growth seems to be in the center you can trace it right to the point on each cucumber so this is more an example of blossom enrot than it is of a gummy stem so it gets tricky to diagnose so again you got to look at at all the conditions but it doesn't it doesn't hurt of course to help with calcium to elevate it because that's also one of the ways of avoiding gummy stem blight as well right so and then of course if you're suspicious watch your vpd's make sure they're in acceptable targets so that the plant is transpiring enough okay moving on black root probably simple to diagnose in the sense that the roots look black uh but if you look carefully especially younger roots with the with a magnifying glass the the epidermis of the root looks splotchy and if you looked under a microscope you would actually see that what's going on here is the fungus is living in individual cells in blocks like lego blocks so there's you know a cell here a cell here but there's nothing around it so you get this sort of patchy uh growth of the fungus and the epidermis black root is uh there this is a nice close-up right over here you can see sort of how it's a rectangular it's bounded by the actual plant cell so they grow and then they burst this direction and release their spores so what are things to look for slightly darker foliage that can help weak growth if your yields are down they don't look right you should cut the bags open and look at the roots that's probably one of the first things you want to do when things don't seem right if you see wilting that does not recover so you see some couple of rows that have wilted and you think oh there must be a problem with irrigation check maybe there isn't if there isn't then you may have another issue cut a few bags open uh maybe cut a lateral stem if you can find something and see what's going on see if you have uh black root forming typically with black root it forms at the what's called the tide mark or the soil level so if it is black root you're looking at the stem as it goes into the bag or the rockwool block and if you're seeing dark at the top based on what we've talked about so far it could be rhizoctinia or it could be black root so you're going to open up the bag look at some of the young roots with a microscope or magnifying glass and see if you can identify the epidermis this classic structure um in the root epidermis that's why i've highlighted it it's an important distinguishing feature so black root rot is a soil borne disease that means that you got to make sure your staff are properly sanitized uh most vegetable greenhouses have shoe and foot baths that you have to walk through before you go on the greenhouse so you don't take your shoes off but what happens is you walk through a machine and it has wet brushes that brush the undersides of your shoes with a sanitizing agent and then you move into the greenhouse uh if you have poor sanitation not only for tools but also between crops or under your crop rows that can contribute but because it is soil that's most common in soil we don't really see it in rockville rockwell very much we see it more in the organic producers that are growing in you know soil and compost mixtures if you are reusing rockwool it can be a risk and if it's coir later in the crop cycle coil starts to break down then it's more susceptible uh cold root zones we've mentioned this a couple of times it is not uncommon to see a thermo thermometer like a like a cooking thermometer style thing like a stainless steel shaft you just pierce it into the bag and as a grower you go around and you would check the temperatures in the bags make sure they're not too cold this is most important in the winter time especially around the perimeter where the sidewalls are if you're these are your outside is -20 your crops are growing along here this outside edge is going to be cold and cold air is coming down impacting your crop so you have to keep an eye on those corners especially to make sure that you're not getting cold root zone temperatures because that's where problems start to ignite penicillium stem rot so yeah that's where penicillin comes from by the way this is an antibiotic derived from this mold this fungus penicillium oxalicum i got some better pictures what you're looking for here remember penicillium is actually the classic mold you grow in your fridge with a wet piece of bread if you remember anything like that from elementary school this sort of blue gray fuzzy mold that's your classic penicillin penicillium on cucumbers it erupts as blue gray fuzzy patches often near the ends you can also get it in the middle of a stem or along a cut off petiole from a leaf or a sucker that was not completely removed so it's often in soil and decaying matter so again if you're reusing bags which is not uncommon in cucumber houses uh if you're looking at water soaked translucent areas along the inner nodes of your stem then you have to be concerned that penicillin's growing in there if you see the blue gray blue mold it's it's already late right it's it's already erupted um those lesions become pale and then your mold sort of erupts um these are on your stem these cankers as they're called where the fungus sort of erupts they usually are above and below the the leaf node on the stem it can look very similar to botrytis uh botrytis especially because of the gray fuzziness um so it's tricky you can actually make if you catch some of the scrape some of the mold into a microscope slide if you have a little microscope at your farm you can actually look for these i call them palm trees uh penicillium is it always looks like a big tree or a palm tree under a microscope where all the other uh fungi look sort of more generic or like lollipops on a stick but not everyone has that equipment so um typically penicillium is very aggressive which means it progresses faster and the stems actually become squishy and collapse faster so it is a very aggressive one so you got to be on top so conditions for penicillium high humidity wet this is a very common theme outer rows like i mentioned where it's cool and damp insufficient ventilation again all generic controls for controlling fungus wounds again you're starting to see the themes here right excessive nitrogen fertilizer i haven't talked about this one before but it does happen if you're pushing the crop and it's overly vegetative right so you're going you're really vegetative the tissues become soft the leaves become very pliable and the cell walls are weak which makes the plant more susceptible to spores germinating and establishing themselves on the plant so don't overdo the nitrogen if you have too many fruit on the plant it's kind of similar to this problem right uh you're it you're essentially stressing the plant out and it can't defend itself from the fungal infections because it's got these plants that are parasitic on the the nutrients uh penicillin is one that is more common in rock well as opposed to soil which is usually the other way around but this is one we see probably because rockwool is quite wet this is a challenge there's so far penicillin there's no resistance between cultivars so you can't choose you know different cultivars to try to prevent it from happening you have to just deal with it and unfortunately does survive between crops so you have to make sure you sterilize the greenhouse properly in effect you know before you plant a new crop as far as what it might look on look like on leaves if you see the leaves are puckered like the surface of the leaf is bumpy not smooth that main indication that you have penicillium uh it usually starts on the veins underneath the leaf and eventually the veins become actually brown first uh and on the leaves it'll be somewhere near where it is in the stem so if you see it on the stem check leaves nearby for confirmation alternaria this is another one there's two kinds of alternary but effectively it doesn't really matter you end up with these yellowing blotchy spots across the entire leaf they start at a small little point and they just get bigger and bigger it's important to note that thrip damage can look very similar to altenaria if you look here you'll see there's sort of a rectangular bounded spots between the veins patches here and here these are actually thrip damage on cucumbers and it can be confused between alternate areas so we have some white spots forming on our cucumbers at the college and we weren't sure if they were thrip or not because we didn't see evidence of frass or their poop but it is important to understand that cucumber leaves are very there's not much to them if you ever look at them they're light the cells are massive they're mostly water which means that as thrip or feeding there's not much to poop out in terms of solids so we don't see as much grass on them so we're gonna have to keep an eye on the thrips at the college to see if that is our issue on the older leaves um we had hypothesized that there was maybe a bit too much iron and it was iron toxicity but it's really not clear if you've seen what's going on but generally the crop looks really good it's just the really old leaves have these kind of exact same spots that look like alton area another one is anthracnose always sounds scary because you know i think ooh anthrax like deadly deadly deadly disease anthracnose is very common uh i'm only talking about the fungal version in this lesson but there is actually a bacterial so you have to understand which one you've got usually bacterial uh this is a raised black smooth bump on the leaf so those would require uh like a a copper in a fungicide it's actually bactericidal as well to spray so that's oftentimes anthracnose they spray with a kind of a copper to control it and it works both fungal or bacterial but in the case of the cucumbers it's most often fungal and we see these sort of legions and what's important to recognize is they start as pinpoints and they kind of have concentric rings that flow outwards with a yellow margin on the edge of it so that's how you diagnose anthracnose um again very common well it means the leaf is wet in my experience this is often where there's water dripping regularly so check your greenhouse structure maybe there's a leaky window or even a pipe that's dripping frequently on that that particular part of your crop and that's where you'll see the anthrax now so you can treat it all you want but you're better off to deal with the dripping obviously high relative humidity is a factor it does show up everywhere on the fruits the leaves the stems it's most predominant on leaves but you will see it on fruit too i know that in the fruit farmers in the niagara region get anthracnose on their peaches and nectarines apricots and plums and apples so anthracnose is definitely a broad reaching fungal thing and that's important to keep in mind because sometimes these fungal infections are coming into your greenhouse from outside well they are but they might be coming from a crop really close to you like peaches or apples and stuff like that where botrytis for example blows in from grape farm so just be aware of where you might be getting your problems from it usually shows as a pale green water soaked spot to begin with long before you start getting these brown legions it would be like a dull green sort of soaking wet spot like someone kind of crushed a part of the leaf it they do spread quickly so you want to be on top of that powdery mildew now we've spent already quite a bit of time talking about powdery mildew so i don't want to get into it too much but uh with cucumbers it does not seem to infect the fruit it's rare uh but it will make your fruit smaller because all these hyphae growing on this leaf and i've seen some pretty bad cucumbers in my day uh that impacts the you the photosynthetic efficiency of that leaf so if you're not making as many assimilates there's not as much sugar for you to make fruit right so you have slow smaller yields and smaller fruit uh it also shortens the shelf life of your fruit because it doesn't have enough sugars to to give it the the fuel to stay alive once it's cut off the plant and flavor may deteriorate as well and again just a closer look at powdery mildew it's usually on the surface of the leaf it's fuzzy to look at so i'll re review this we have talked about this last bit but i'll review it dry conditions caused it to sporulate i probably will ask this on the midterm in humid conditions cause it to increase its growth or grow hyphy or germinate the spores so typically we do have tolerant varieties so you can actually choose varieties or cultivars that are resistant to powdered mildew and if you can choose it you should do that in the meantime we can improve our climate to reduce the incidence of the disease by for example increasing air movement but not too much uh using favorite temperatures you know not having wild swings where our vpd goes outside that danger zone make sure the leaves don't get wet and remember we talked about the boundaries on right the idea that we need enough error movement that it will influence the surface area of the leaf so if it's 80 relative humidity up here it's pretty safe to say that it might be 90 at the leaf surface right so we have to make sure we understand that there's this boundary layer that we're trying to influence and so what we have in our actual climate may not be what the leaf is experiencing at the epidermis in that boundary layer now often confused with powdery mildew is downy mildew and one of the best ways with cucumbers especially to diagnose it is if you look at the upper surface of the leaf there the fungus is bounded by these sort of cell structures of the of the epidermis of the leaf so it looks rectangular it's kind of like that black root where you see the black spots on the epidermis of the root downy mildew it looks like this it starts off as a lighter green like you'll see there's some lighter green uh blocks here here here and then eventually they transition to yellow or darker or even full out necrotic spots so down mildew is something that affects all q-corbids so not just cucumber it's common against you know melon squash pumpkins so if you have a pumpkin farmer that's within a couple of kilometers of your farm there's a good chance downy mildew's in the air so you got to be on the on the ball um it is a worldwide broadly uh available fungus so it's there's no escaping it for the most part it's foliar right so it doesn't really go after the fruit just like powdery mildew but you do have smaller yields and fruit size again because of lost leaf area right but unlike powdery mildew where there's you know oscillations between high and low humidity this is strictly a cold temperature high humidity fungal infection that's it so it likes cool temperatures now we try to keep cucumbers on the hotter side but in the winter especially around the perimeter of the greenhouse again this is something i mentioned but it will come up right on the perimeter of the greenhouse or that those two exterior walls it's cold on the outside and that causes damp cool conditions inside the greenhouse in the corners especially so watch those corners when you're scouting your crops always check the corners um in addition to epidermal structures to look for with downy mildew if you flip the leaf over and look underneath you'll see that there is a fuzzy sort of hypo and fruiting body growth they are usually white to purplish in color uh and sometimes very dark almost black uh its older leaves are affected primarily uh that that those are the key things that you would use to diagnose downy mildew so now as far as downy and powdery mildew the key to define to identifying which is is which one you have in your crop is to as i jokingly say where's the fuzz uh if the fuzz the fuzzy moldy growth obviously these are not correct biological terms but they're to help you remember if it's underneath the leaf it's downy if it's both on top and under it's powdery mildew okay that's that's your key simple derek way of identifying the difference between downy and powdery mildew how can you tell if they're dead say you spray fungicide it's hard to know sometimes well the key thing to look at with your loop is to make sure that the hyphal or canadian or reproductive structures structures are laying flat that they've matted down that means they're dead because they're they've leaked out their solution and they've wilted so if they're still standing up proud and fuzzy they are not dead so be aware of that use your magnifying glass if you can at the farm maybe they have a stereo microscope look at it carefully make sure the fuzz is laying down then you know it's dead as far as preventing downy mildew again common with all fungal things good air circulation making sure your leaves are dry especially around the perimeters not being greedy with your plants and spacing them appropriately you know sometimes people think more plants is more yield well it depends on the time of the year and how much control you have over your climate if you end up with fungal disease you make a lot less yield so it doesn't help you in the long run overhead irrigation is kind of irrelevant with hydroponics but it's there that might apply more if you're growing uh young cucumber seedlings for you know supplying greenhouses they usually sub irrigate they use flood floors they don't top irrigate and then of course there is resistant cucumbers to downy mildew just like powdery mildew so if you can select it do it it doesn't mean that they're always the most desirable variety so some farmers are forced to not grow resistant varieties even as much as they would like to okay moving on to fusarium root and stem rod so fusarium solani this is a very common one in cucumbers in a lot of plants to be honest and for the most part it lives in the central cambium of the stem that's where we often find it when we're diagnosing it so what the person's done here is they've sliced this stem open and peeled it back and they've looked inside and they're seeing all sorts of light yellow brown lesions and that's telling them that they have fusarium in the cambium or the central pith um if your cucumbers wilt and there doesn't seem to be good explanation you don't see black at the soil horizon there's no ooze coming from the stem so it's not gummy stem you're going to start wondering if it's fusarium so whether you can sacrifice a plant and cut the stem open and have a look might be worth it if you see that brown then you know you're off to a good start for diagnosing it so again here you can see there's sort of a yellow this is an earlier stage in the cambium kind of yellowy brown typically this is a hot weather summertime thing when plants are stressed that yellow stem eventually turns white you get sort of white quirkiness um plants can kind of grow through fusarium they'll still yield and produce but they are choked off they're not getting the nutrients in the water they need so the yields drop so if you're trying to finish a crop it may be not the end of the world you might be in a couple of weeks out of it maybe you'll pull some more cucumbers off and then you rip it all out another interesting thing about fusarium if you cut the bag open the roots are still firm so the roots are not like pithium and phytophthora and rhizoctinia or mainly those first two where the roots get soft and slough off with fusarium the roots stay firm so when you cut the bag open to look at the roots you're going to see that the roots look relatively you know full of water and maybe even happy fusarium one of the critical aspects for fusarium because it is very common is sanitation and commercial greenhouses all use a lot of sanitation staff often have uniforms maybe even hair nets not always depends on the farm it's probably more more common for visitors but staff themselves they may go through what's called an air shower to blow off any spores and bugs they often go through a foot bath here to wash their shoes and they quite often have a staff uniform that they wear and that's that clothing is laundered by a service so that the staff are not bringing their own clothes in um so fusarium is one that really got that started i mean farms are always worried about food safety but honestly a lot of this uh cleaning that you see in farms is primarily for biosecurity and of course sanitizing tools is really important scissors and knives that are used for trimming the plants need to be dipped in sanitizer often at the end of the rows they can dip them or they put them into a bucket on a cart and pick a fresh pair so what are some common elements in controlling fungal infections these are the things that i'm going to want you to remember for the midterm for sure so definitely know this list um excellent sanitation critical that means not just your your hands right i'm talking the greenhouse structure and floor your staff and your tools the staff need to make sure they have clean tools that are sharp that leave clean cuts so we're not leaving ugly messes this isn't particularly cucumbers now remember sometimes with tomatoes you can snap the leaf off at the opposition point and it leaves a nice clean break because that abscission layer is kind of contoured and to let the leaf off but always in all plants you could apply a lot of this to any crop that we've talked about so far clean cuts is definitely helpful keep your relative humidity under control that's a critical one for your powdery mildew your downy mildew your phytophthora your rhizoctinia all of them um choose resistant varieties oh yeah and i did mention this right microclimates exterior walls corners anything dripping all those things really important sorry back to this one so choosing resistant varieties when possible absolutely we're looking at you know both virus powder mildew downy mildew resistance in our varieties um consistent consistent moisture control in the root zone right that means how are you irrigating are you letting it dry out increasingly and then giving it lots of water or are you being subtle so it's important to make sure that our root zones are not experiencing massive yoyos space plant spacing right and air flow that's critical controlling your insects so things like thrip and white fly in aphids when we talk about virus coming up next those are critical if you keep them under control you reduce the spread of virus tremendously obviously constantly scouting and then culling or removing plants that are suspicious immediately don't waste time just deal with it and of course if you start with a clean greenhouse you're less likely to have problems alright i got a few slides left to talk about bacterial and viral problems with cucumbers bacterial wilts rots cucumber mosaic virus cucumber necrosis virus pseudo yellow virus watermelon there's all kinds of them uh viruses are particularly challenging um but starting with bacteria we did talk about this with their crops class with arwenia right with succulents especially how they like their stems well they like cucumber stems too and if you cut a stem or a petiole and you pull it apart and you see a stringy sticky sap between the tissues you may you most likely have arwenia so now if it's a healthy plant i don't know but if the plants showing symptoms like curled leaves and then you cut that and pull it apart and you see this you should be suspicious of bacteria living in the vasculature and they produce kind of a sticky substance that fills up the vasculature and chokes it that's why water is not flowing the leaves are wilting so erwinia the is transmitted through mostly cucumber beetles now in the summer a lot of greenhouses try to screen their events to keep beetles out they can become a big problem we don't have biologicals to go after these large heavy insects right they're like tanks so we have to use chemical controls and we don't want to do that so we put screens on the vents to keep them out um similar to other infections it starts as a dull green patch so when you see dull green patches good luck i don't know it could be anything uh if the if you see wilting uh then you need to consider it is arwenia so remember what i said cut that petiole pull it apart see if it's got stringy sticky uh sap then you have a you know you have an arminia problem um it does move very quickly and the entire plant will wilt very quickly including fruit because the entire vasculature is choked up with that gummy sap um but yeah erwin is a tricky one but cleanliness and identification moving on to viruses cucumber mosaic virus the key here viruses are very difficult to diagnose you almost always have to use agdia antibody strips which you can buy and take a leaf sample crush it into a tube add the solutions dip your your agdia kit and then identify it i'm pretty sure you talked about this in many other courses so i'm not going to repeat that but aphids are big vectors for cmv and you definitely got to manage your weeds because aphids don't really like cucumbers that much but they love weeds so uh greenhouses sometimes around the again again the exterior of the greenhouse you might get grass tufts growing those have to be removed you need a weed a weed-free barrier around the perimeter of your greenhouse to keep aphids at bay but with the cmv you want to look for this sort of light green sort of mosaic it looks almost uh well yeah it says mosaic but this is what it looks like like a convoluted structure of mottled light green almost like a fractal uh that is indicative of of cnv virus some more pictures i can see you might think it was a nutrient deficiency but the leaf is kind of modeled here that helps tell you that something else is going on and this is showing up more around the veins where usually we're looking at intervenal chlorosis with with nutrition although there are some micronutrient deficiencies like zinc which show up in the veins so um again you want those agnia kits to identify if it's a virus or not then cucumber necrosis virus this is a tough one these things are really brutal because this looks a lot like anthracnose so how do you know how do you know it's tough um so you can you can use those kits idea kits i'll put a link in the this week's folder for you to find so you can read up on them and if it comes out negative for any virus then you know it's probably anthracnose pseudo yellow virus this is a tough one because it looks just like a nutrient deficiency except for the simple fact that on older leaves typically is where it presents and when you see intervenol chlorosis like this it's always on the young leaves because we're dealing with iron if it was on the old leaf in yellow we would assume it was nitrogen but remember nitrogen is yellow evenly across the whole leaf the veins would be yellow as well so that sort of helps you identify pseudo yellow virus it is vectored by white fly so you definitely got to keep on top of white fly make sure it's not in your greenhouse lots of incarcera so general comments uh with viruses we want to control weeds because that controls our vectors and on top of that then we're going to control our aphids and our white fly and our thrip and as all of these things sanitation you can see is obviously huge whether it's fungal viral bacteria sanitation is absolutely critical that's why well-run greenhouses look like a hospital polished concrete walks white epoxy structures sanitation stations you name it if a plant is suspected remove it there's you know millions of plants in the greenhouse you're not going to miss one at the end of the world uh and by the way when you remove a plant you put it into a garbage bag at that location and seal the bag and then take it out you don't drag the sick plant through the entire greenhouse hanging behind you as you walk towards the dumpster in the parking lot that's not going to help you is it um obviously clean clothing and tools disinfection and of course disinfecting recirculating nutrient solutions now what's the one that impacts viruses well we know that ozone and uv will kill viruses not many are very effective at viruses after that bromine chlorine maybe but you can't use chlorine with cucumbers um so you're looking at mostly ozone and uv so you definitely got to keep things clean all right that brings us to the end of this i'll put the agdia link in this week's folder and i'll see you in the greenhouse bye