UC Ag Experts Talk: Management of Plant-Parasitic Nematodes in Citrus Orchards


Good afternoon, and welcome everyone. Hello, I’m Heather Johnson. I’m a graduate student intern with the UC Statewide IPM Program. Welcome to the UC Ag Expert Talk on plant-parasitic nematodes in citrus orchards. Cheryl Reynolds is also here, and will be running the polls and troubleshooting any technical problems. Now I’d like to introduce our speaker for today. Dr. Ole Becker is [a] Cooperative Extension Specialist and nematologist at UC Riverside. Today he’s speaking on the management of plant-parasitic nematodes in citrus orchards. And now I’d like to pass this over to Ole. So Ole, you can share your slides. [Ole]: Thank you, Heather. Here we go. Well, welcome to my webinar. This is my first in this series, so if something goes wrong, just blame me. I’ve been a nematologist [and] plant pathologist for almost 30 years now, I’ve been here with UC Riverside for 25. Before, I worked as a researcher in industry. And so today we will talk about nematodes. We [will] start out a little general. I like to always have a introduction to nematodes so we all know what we are talking about, and then I will go over to specifically citrus nematodes and we will see what else is going on. Okay, so what are nematodes? You know, nematodes are unsegmented aquatic roundworms. They are a special phylum that’s probably 500 million years old, and these worms are very abundant. They occur everywhere in the world; if you go to the highest mountain or the deep ocean floors, the sediments of the ocean, you find nematodes. And if you pick up or a handful of soil, several hundred or thousand individual nematodes are there. And so we consider them the most abundant animal on earth. Typically they are very small, they are microscopically small. You need at least [a] dissecting scope, sometimes a microscope, to really see them. They are transparent, and therefore very difficult to see in soil. You need special methods, and I’ll come to that during my seminar here— how to analyze soils for these nematodes. The plant-parasitic nematodes are only a very small part of this gigantic phylum. We have human pathogens among the nematodes, we have animal pathogens— and well, parasites I should say— and we have plant-parasitic nematodes. But [they] are maybe less than five percent of all the nematodes. However, they are economically very important. Especially in warmer climates, it’s estimated [that] about a hundred billion dollars each year are lost because of their feeding, and in California, my personal estimation is that we are maybe in the range of 1.8 [or] 1.9 billion dollar loss. So… This guy here on the right is one of the most famous nematologists, one of the first in the U.S., Nathan Cobb. And Nathan once said that if you move all the matter of the universe except nematodes, you would still see our world. You would see trees, plants in general, you see animals, you see a lot of humans, and so these guys are have been very successful in conquering almost any habitat. The really minimum requirement for nematodes is that they need some moisture. But I have a friend that works in the Dry Valleys of the Antarctic; and she finds nematodes there. And I mentioned already, the oceans… At the bottom of the ocean, in the sediment, [there are] lots of nematodes, and almost any any higher animal is parasitized by nematodes. So on the left side, you see a picture of [microscopic] soil extraction. And I would say there are at least five [or] six different species of nematodes, perhaps more, and when you look at them, they all are kind of worm-like, but they have different features, and [you need] a trained nematologist, a trained taxonomist I should say, [to] really distinguish those. And of course today we have some more modern methods, molecular methods, to distinguish this organism, but we are still working on it. There are estimates that there might be a million species, and we have probably identified and described maybe maybe 40,000 of them. But there are also, or I should say, there there are many good guys, and some of these are here, represented as entomopathogenic nematodes. These nematodes can attack grubs and weevils and fleas, and inside those organisms they release specialized bacteria, and the bacteria and the nematodes together can kill these crops. On the right side you see one of those big white grubs that is now filled with nematodes, and the bacteria— they basically degrade all the inner organs, and then the nematodes can feed on this substrate, and once they run out of food in this grub— by then, the grub is long dead— they they can move out of it and then find another insect. And if you go to a one of those nursery stores they often have commercial products, commercially available nematodes. These nematodes are good [for] using in home gardens and on turf, and in specialized situations. It’s an expensive way of controlling [insect pests], but it is safe and it’s a very neat process of biological control. Now, here I have listed six mug shots of nematodes: head, faces of various nematodes. And I [would] like you [to] guess here for a second or two which one is the plant-parasitic nematode because plant-parasitic nematodes have one specific feature that distinguish them from all the other nematodes. And no, I don’t want to make it too difficult here, so this nematode on the bottom has a mouth stylet, and this mouth stylet is very similar to a needle, a hypodermic needle, where it has a hollow shaft, and a very pointy tip, and with this spearlike instrument, it can poke holes in plant cells and then it can actually inject compounds, enzymes, and low molecular compounds— some of those we just don’t really know— into the cells, and can help to withdraw the contents of the cell. That’s the way plant-parasitic nematodes feed. And I want to emphasize [that] they feed only on the living cells. This is quite important when you are bombarded with articles, or products that claim they kill the nematodes in the soil, and the nematodes can take up these compounds from the soil water with these particular compounds. This is just not true. Plant-parasitic nematodes do not feed just in the soil; they have to feed on plants or in plants. All right, and I don’t want to go into all the details of the others, but those are mainly bacterial feeders, and fungal feeders, and and the one on on the right is actually one of my favorites. It has this big tooth, and it can rip into other nematodes or other prey, and and then feed on them. All right, so another a large group of nematodes [that] are very important for the food web, the soil food web, and I have here a schematic drawing from Sterling. We see the plants on top. A lot of root exudates come out of the roots, plant assimilates go to the roots, and and some of those are then excreted out of the roots, and they feed bacteria and fungi. And these bacteria and fungi, they are again [a] nutrient source for protozoa, for mites, and springtails and other critters, but also for fungal-feeding nematodes and bacterial-feeding nematodes. They [often] occur in large numbers in soil and and they compete [for] space with the plant-parasitic nematodes. But what is important is that all three groups— and there are other scientists [who] distinguish actually more [of] the omnivores that can feed on various substrates— but all three groups here, they are subject to attacks by parasitic fungi— fungi that can destroy their eggs, or actually attack [the] nematode itself. And there are some [people that] are trapping these fungi. And I’ll show you some of these fungal antagonists. But there [are] also the predatory nematodes, [such as the] example with the tooth, and there [are] mites; mites also feed on these nematodes. Now you could say, “well, why don’t we just grow these guys and throw them out [in the orchard]?” Well, they occur almost everywhere, and just by number, they prefer— or I should say, not prefer, but I mean by number, they just take out bacterial feeders because those are typically the most abundant ones, and fungal feeders. But if a plant-parasitic nematode comes along, they will also attack that nematode. Alright, so that [was] about the beneficial [nematode]s. Now let’s come to the lifestyle of plant-parasitic nematodes. We can distinguish, really, two large groups. One, the ectoparasites, [or] ectos, are feeding on the outside of roots. And the endoparasites live in the plant tissues. And unfortunately the labeling here is a little bit small, but on the left side this one here, the Meloidogyne, that’s a root-knot nematode. Those belong to the endoparasites. And here’s another one on there, the Heterodera— those are cyst nematodes. They are also, for most of their life, inside the root. And on the other side, we have Trichodorus, a [plant-parasitic nematode] that spends all its lifetime in soil, and [never goes] into the roots, so it’s an ectoparasite. Here, we have Xiphenema, that’s a dagger nematode, a very large nematode, also exclusively an ectoparasite. And then there are some that can go into the root, but can come out again [migratory]. And so we distinguish sedentary and migratory nematodes. Sedentary— those are the root-knot [and] the cyst nematodes, because they stay in one spot for the rest of their life. But the lesion nematodes, those are migratory nematodes. They can penetrate the root surface [and] go into the root, but if the conditions are not [ideal] enough [for them], they can come out again and find another spot, so those are migratory. And here [what] we have now are Tylenchulus, Tylenchulus semipenetrans. That is the citrus nematode, and that will be my main topic for today, because in California, we have very few other nematodes of importance that can feed on the citrus root. And Tylenchulus is the only one, really, that can create considerable damage on citrus. But Tylenchulus is called “semipenetrans” because half of their body remains outside of the root. Only the head feeds inside the root. And so why do I show this building now? This is a picture maybe from the 1920s, when the Citrus Experiment Station was founded in 1907. They eventually moved to our location, what is today UC Riverside. And it was it was built and created because the citrus industry faced several pathogens and pests in those days, and [the citrus industry] demanded some support. And the legislative bodies in Sacramento created this station. In 1956 it became [a part of] the UC Riverside campus, but we still have a very large experimental station, not only for citrus but also other crops, and we are one of the world leading authorities on various diseases and other issues on these crops. Now, when we— and oh, I should say [this]. So the citrus nematode was actually discovered in 1910 in Southern California, and by 1912 or so, it was described by [Nathan] Cobb. And in the late ’50s, our own Seymour van Gundy described the life cycle of the citrus nematode. But where can you find the information about citrus pests? If you go to the UC IPM [Pest] Management Guidelines— and I’ll come [back to this] at the end, but I just want to show you that— there is pretty much [a] consensus that the citrus nematode is the important one, and we have listed also the sheath nematode, but I must say, in the next edition, I’m inclined to take this one out because it so rarely occurs and and we haven’t seen any major damage in recent years. Alright, let’s talk about the life cycle of the citrus nematode. Because that’s always important. When does this nematode become active, and how long does it take, [and] what is the reproduction? Let’s go into this [picture] here, which is all at one of our UC IPM [Pest Management] Guidelines. We have a second-stage larvae down here; it’s a very typical worm form, and it will feed the first ten days after hatching out of the egg, on the outside of the root. And it will go up and down the road and feed on the epidermal cells. And then it moves deeper in, toward the cortex, and eventually it goes through several molts. All plant-parasitic nematodes, or almost all plant-parasitic nematodes, have these stages from the egg…in the egg, the first-stage nematode develops, the first-stage larvae, then the second. And the second then emerges out of the egg; it is the infective stage, it goes into the root, and then molts another time to the third stage, and another time to the fourth stage, and [then the] final molt. We have the the female here, and the female [is] in between these last molts. The rear end there basically [is] the half that sticks out of the root, enlarges, and in this last molt it becomes sedentary— it will not move away from its position again. The female there— the males stay outside of the root; they don’t feed, They play hardly any role. Most of the reproduction is asexual. Mating occurs, but it’s rare. And it takes about five to six weeks to complete the life cycle. The female lays eggs— about a hundred of them— in a gel matrix. This gel is a kind of gummy substance that protects their eggs against drying out, and perhaps also against microbial attack. But we have about two periods in Southern California where the reproduction phase is at its peak. It coincides with the root flush, and when you think back, I already mentioned that the nematode needs a temperature of at least 65 to 70 degrees before they hatch and become really active, so right now they are all very much dormant, and if you were to treat the soil with nematicides right now, it wouldn’t make much sense. By the time the nematodes become active, that material would be long gone. So here I have some some pictures. It shows the second stage on the left side, and then this [second picture] might be already a third stage, and you see the nematode is way down here in the cortex. And what it does here, it chooses some cells around its head, and in these cells serve them as nurse cells and there is probably some signaling going on to the upper part, and nutrients [that] are preferred [are] directed to these nurse cells. And then here on the third one, of course we’ve stained these nematodes; otherwise, they would be very hard to see. But with the stain, you can see its head; the region is somewhere here, very near to the central cylinder, but the posterior end of the nematode is exposed to the right. And here we have actually a really nice picture from my colleague from Taiwan it shows again the rear end of the female sticking out of the root. Now I said that they lay the eggs in this gummy gel…it actually produces something like an almost nigh diagnostic symptom. On the left side is a work that was grown without citrus nematode. And it looks nice— long roots, whitish, really healthy root system, but on the right side, this was out of an orchard that was heavily infested with the citrus nematode. And as you seen you can, I hope, see [that] the roots are much shorter and they appear to be thicker. Now, I said “appear” because if you would wash these these roots, a lot of dirt would come off and this dirt, this soil, sticks to this gel that the nematodes have produced. And so you have the impression that there is some thick layer but it’s just soil that sticks to it. And here is a series of pictures that demonstrate the disease. Citrus nematode causes what we call a slow decline, so from the healthy tree to basically a dead tree. Now, this takes years. The nematode is not a very aggressive pathogen; it causes this starvation and it leads to poor root health. And often the nematode is not alone; there are many fungi that can take advantage of the damaged root, and can penetrate the root, and accelerate the senescence. So there have been many studies [on] whether there is some direct interaction between nematodes and Fusarium solani, for example, or Phytophthora, but [the] evidence is not really clear-cut on whether there is a synergism. But definitely both, especially Phytophthora, and in the citrus nematode they often go together, and their target are the feeder roots. The nematodes really prefer the young feeder roots and so does Phytophthora. Okay, let’s go to the management. So we have sanitation, or exclusion, resistance— I should really replace resistance with maybe tolerance— the citrus orchard management, fumigation [is] almost gone, contact nematicides, new ones are on the horizon and I’ll spend a little while on biological control and natural enemies. So, sanitation starts with nematode-free planting material I’ve looked up [on the] CDFA web site; they have this Citrus Nursery Stock Pest Cleanliness Program. I could not remember the whole title! Here it is. And so under their code, section 5803, it is unlawful for any person to bud, graft, or otherwise propagate any citrus [in violation of the pest cleanliness program] and this is of course really important; it’s one of the key elements of our management program. If you buy [a] certified tree from a nursery, it’s supposed to be nematode-free. And those nursery plants, or at least a start for the nursery plants, comes from our Citrus Clonal Protection Program at UCR, that for many years has been run out of the Plant Pathology Department. And it is really the key for [the] successful growing citrus. Sanitation also means a nematode-free planting site. Now, that is more difficult. Especially if we go back into an old citrus orchard. I mean I don’t want to give it a percentage, but many, many orchards are infested with citrus nematodes, and if old roots are hanging around, they are they are also our source for infestations— not only by the nematode, but also by the fungi I mentioned. And so if you can remove or destroy some of these old roots, you’re ahead of the game. In the past we used methyl bromide or Telone. That can penetrate the root tissues very deeply and kill anything in there. Now that has become either not available, or very expensive. And metam, for example, does not penetrate well into roots, so that is not not a great choice there. You should certainly determine, is there a potential of [a] nematode infestation, take samples, and run them by one of our commercial labs. And if you have a very high infestation, you might want to wait to replant, and plant something else. Sanitation also means [cleaning] machinery and tools and just washing your tractor tires and in other machinery with water will do great good. Rootstock resistance is the second key of of growing healthy, nematode-free, or at least nematode-tolerant [citrus]. Now, originally there were four biotypes of Tylenchulus semipenetrans; now there are only three. The fourth was a grass nematode, and it turned out it does not really attack citrus, but we have the Mediterranean which really occurs only in the Mediterranean area and in Africa, South Africa for example, and but the other two; citrus [nematode] and Poncirus are in North America and definitely also in California. They differ in the ability to infect, or reproduce on various citrus and related plants, but this form for all practical purposes that we have, these two cultivars— or I should say biotypes— that that attack citrus. And here is a chart out of a publication by Niles, Freckman, and Michael Roose, where they looked at various rootstocks and their susceptibility to the citrus nematode. And it’s pretty much the same way you might recognize…you know these names down here, for tolerant rootstocks and they’re still very much available. So how do we sample for soil and root analysis? So, the goal is that we can predict the damage risks, and we should take soil and root samples from under the canopy. And the citrus feeder roots, they are fairly shallow, so we don’t have to go three, four, or five feet deep as we have to do with some of the other tree crops, but take samples from several trees in the orchard, go in kind of a waving form between the trees and sample, and do a composite sample. Mix it nicely up, and also if you have diseased trees, maybe have them separate. Separate the diseased one or the unhealthy looking ones from the healthy ones. And then treat the samples with lots of care. Don’t let the plastic bag sit in the sun, [that will] solarize the soil and you will kill all the nematodes in there. And that is important because many of us use extraction procedures that require the nematodes to be active. And then include as much info as possible so that the lab may actually give you some kind of a recommendation. I have a lab result here; it’s not from a citrus orchard, but this is the only thing I found. This one separates plant-parasitic nematodes from those that are bacterial feeders and fungal feeders, but what’s important is that it shows that the extraction method. This one is sieving and flotation— [the form] has it down here, sieving, sugar flotation— that means they use sieves to first get rid of the larger parts— soil parts— and then they use gravity of centrifugation process that can separate the nematodes from the soil. And this is important because it tells you a little bit about the extraction efficacy, but in this particular lab they actually mention here that [the process has] 68 percent extraction efficacy. That means if you put 100 nematodes in the soil— 100 healthy nematodes, and then extracted with this method, you will get 68 out of it. So if you have a number that is— let’s see here— yeah here it’s a hundred, you can you can say you have have probably another 60 to 68 percent in addition, so you have a real population of maybe 170 nematodes in the soil. This is very important because some of our other methods the Baermann funnel method, has a extraction efficacy typically around 30–35 percent, and so we basically have to take the number and multiply by three, and you get the real number. Here are some other details mentioned: extraction efficacy, variance, soil texture and moisture, that is very true— but it will give you an idea [of] how large your population is. This is the Baermann funnel, where we put the soil or the roots on top, and the nematodes then move through a facial tissue and the wire screen, and they fall to the bottom. And here in the bottom, we can collect them and then count them under a dissecting scope. Our economic threshold is— these data go back 40 years or so, but it’s still a rule of thumb, and we’ve seen that our data from California pretty much agree with them from Florida and from South Africa, and from Israel. So a high population in early spring is about 12,000; later it’s maybe even more, 18,000 per 500 cubic centimeters, so approximately a pound of soil has that many nematodes. Then at this level, it would be advisable maybe to think about a treatment. Anything below, it’s like if you have a few aphids on a tree, you have a few nematodes on the tree…it wouldn’t make any sense, especially not any economic sense to treat them. A much better estimate we get with females, so this is per gram of root, if you get over 1000, or 1100, up to May, July, 1400 [or] 1500 then it is time to think about some [control] measures. But I realize that, you know, for citrus, the decision for a rootstock is not only done by susceptibility, tolerance, or resistance to a nematode, what you have here [is] a table by Michael Roose that shows you all these different types— we have viruses, we have Phytophthora, here is the citrus nematode, we have the soil type, we have salinity, the soil reaction to a lot of water, freezing tolerance, and so on and so on, and fruit quality. And so if you look at this and then the compatibility with the scion, this all needs to be taken into consideration. And so, if you have have questions about this, ask your farm advisor, especially if we have a citrus advisor, we’re a little bit down in [advisors] the last two decades, but hopefully you will get some fresh blood in there in the next few years again. Let me go to the chemical control; I have to rush a little bit now, I look at the watch [and] my time is getting down here, but we have a history of nematicides, and the different colors— I call them the first generation, the second generation, and we are now at [nematicides] 3.0. The first generation were fumigants, and we started in the 1870s in France and in Germany, then we went over [to] chloropicrin, methyl bromide…most of these are gone. We still have Telone and we have metam and related compounds. And then in the late ’50s and 1960s, mainly we have these organophosphates and carbamates that were the first nonfumigant contact nematicides; all of them had basically the same mode of action, and then now, since I would say, since 2000, I would say, yeah about 2000, 2006…here we have a new generation of nematicides, that were developed almost specifically with target of nematodes. All the previous ones basically were developments that came from the entomologists, they found this class of carbamates and organophosphates effective against the insects, and then they found also that they are usable for nematodes. But many of those are very toxic, and [get into] the groundwater, and [cause] all kinds of problems. Now we have these new compounds, and we are really hopeful that they bring in a new generation of compounds. Methyl bromide is gone, development costs are up, the carbamates And O.P.s are almost all banned, and per our public perception, everybody knows it was very negative towards nematicides. And so until recently, no new and effective postplant nematicides in almost 30 years. By the time…but it takes more than 10 years to develop a new product, and more than 200 million dollars. Many of the industries have have stopped their program, and only in recent years they have started up again. I just want to mention these three new nematicides that just recently came on the market for certain crops, and you will hear much more about these, I’m confident…so, Nimitz, from Adama, Velum One, from Bayer, and Salibro from… it was developed by DuPont, but now it’s Corteva; DuPont together with Dow joined forces. And what is amazing with these compounds is their low toxicity, low mammal toxicity. Here we have the oral rat LD50 [for] Temik, one milligram per kilogram, extremely dangerous. And even Nemacur at 15 milligrams. As you see, these these new compounds [are] all in the range of 1,800 to 2,000 milligram per kilogram. Aspirin or caffeine in comparison, has an LD50 of 200, so this is really a step in the right direction. And all these old chemicals had a “danger” or “poison” signal word on the label; the new ones will all have “caution.” Okay, so just a few words about biological control. There are many, many enemies of nematodes; also citrus nematode. We have here on the left, the trapping fungi that create these traps; nematodes go in there and in parts of a second, this lasso or this loop, will close in on the nematode, and eventually the nema— sorry, the fungus, will eventually grow into the nematode and utilize it as a nutrient source. And of course, it kills the nematode. Here’s another fungus that has zoospores and then cysts on the nematode, and also that end effect is that [the nematode] is killed. What you see here is a one egg, one nematode egg, so it’s of course not to scale, but you see a fungal hyphae there, all wrapped around this egg, and the fungus then penetrates the egg and utilizes the nutrients. Down here is more one of my favorites, it is a fungus that parasitizes sedentary nematodes. You see here that in this case, its a cyst [nematode], but it could be also a root-knot or or perhaps Tylenchulus, citrus nematode, where it just parasitizes the female. Here we have a sting nematode; it’s an ectoparasite, and these blobs on the cuticle are bacteria, and the bacteria drill into the nematodes, and then multiply inside, and thousands and thousands of them are created and come out and attach to the next one. There’s also, for citrus nematode, there is one species that does this parasitism. And then, finally, I don’t want to forget [this] other organism, this is a mite that feeds on nematodes in the soil. Okay, so to wrap it up, well what other information do we have? There is an Integrated Pest Management [for] Citrus manual, and we have a more recent Citrus Production Manual, there are articles on nematodes in there, but as I mentioned at one point, to choose a tolerant or resistant rootstock, there are many, many other aspects that I couldn’t touch on and that I’m not the expert in that, but you find information in this production manual, it’s very handy, very useful. And for the everyday questions, for example, what kind of pesticides are registered? Or you know, what more do you want to know about the other citrus pests and diseases? There is of course the UC IPM website, really our premium website for pest management, and it is updated every few years by our experts. And these are the citrus nematode [management] guidelines; I’ve shown you this top part before, and [it] says the description of the pests, the damage, the symptoms and so on, and including other management suggestions. So with that I will close up, I think I’m pretty much on time. Let’s see. Anybody there? [Heather]: Okay, so now we can bring up the poll questions for the participants to answer and then, Ole, if you want to go over the answers after we show the results, that would be great. [Ole]: Okay. So, the first question is “what distinguishes plant-parasitic nematodes from almost all other nematodes?” and I have kind of silly answers here, but you just pick which one you think is right, and then I’ll comment on it. And the second question is “Which parasitic nematode is important in California’s citrus production?” We have the burrowing nematode, the sting nematode, or the citrus nematode. Okay, so, yeah know I was funny with the long and pointy tail, and hairs, and so it’s the mouth stylet. You know, all plant-parasitic nematodes have a mouth stylet. They need that to puncture the cells and then withdraw the contents out of the living cell. Okay, well eighty-one percent, that’s pretty good. And then, “which plant-parasitic [nematode] is important in California’s production?” It is the citrus nematode. And the burrowing nematode occurs, so far, not in California. It is a big problem in Florida, but not here. Sting nematode, same thing, is in Florida, but not in citrus in California. And lesion nematodes do not really play a role in citrus production. Okay, next. So “what is the disease called that is caused by the citrus nematode?” Citrus slow decline, citrus plant destructor, or citrus sour disease? And then the question number four, which is here number two, “what are the typical disease symptoms?” Yellow, small leaves, small fruits; tree canopies thinning out; “dirty” roots; galled roots; or all of the above? That’s a little tricky question. Okay, ninety-four percent are correct; it’s the citrus slow decline. And yeah, I knew that you guys would run into a problem with the second question. It is actually one, two, and three are correct. But not four, and certainly not five. So yellow, small leaves [and] small fruits, that could be a symptom of slow decline. Tree canopies thinning out could be an indication, and the dirty roots— I, you know, I kind of talked about that a little bit, but not galled roots. Galled roots occur with the root-knot nematode, and we don’t have root-knot nematodes on citrus in California. There are such pathogens in Asia— in China— but so far, we have not— you know, knock on wood— we have not seen them here in California. with one exception in the 1960s. Seymour van Gundy found a tree with galls, but it was destroyed, and we’ve never seen any again. And now, of course, then because number four was not correct, all of the above is not correct. Sorry. So, next questions: “what are the potential sources of field infestations?” Previous cropping to vegetables; citrus nematode infected rootstocks; soil from citrus orchards on tires, machinery, [and] tools; runoff from infested citrus orchards; or all of the above. And then the second one [is] “why is a soil and root analysis important for orchard management?” It makes growers aware of potential tree problems; it keeps commercial labs in business; analysis helps to predict damage risks; or all of the above? Okay, so…yeah 3% fell for the cropping to vegetables. Citrus nematode really goes only to citrus and related crops, not to vegetables. Citrus [nematode] infected rootstocks, yeah that is really— has been in the past, really the main cause. I probably did not mention it, but you know, citrus nematode occurs in all of the citrus-producing areas of the world. And they came all from China, and they came all via infected rootstocks. I would really guess that in California, they came with the missionaries in the 1700s, and then spread from there. And of course the third answer— soil from citrus orchards on tires, machinery…yes that’s another source, and runoff is correct too, but because I had the little tricky number one, number five is not correct. So then why is soil analysis an important for [orchard management]? Well, one and three [are] really the the main [answers]. Number two, I think it would be great if we always have business for commercial labs, but it’s not the correct answer. Okay? Alright. Citrus nematode samples should be stored in a freezer but not together with food. Actually, I realized I probably did not even address this question. But okay, let’s just go with it. So should you put it in a freezer, but not together with food; in a sunny spot as a nematodes cannot regulate their body temperature; or number three, in the shady, cool place? And there is really only one right answer. That’s my little hint. And number two, “if you send only one soil sample per acre for an orchard analysis, where do you collect?” One, from the sickest looking tree, to at least two feet depth; or [two,] combine soil and feeder roots from about a dozen trees, mix and send a subsample to the lab. [Heather:] We have another question, that says is there any systemic product that you can use? [Ole:] There is…well, registered, I think is oxamyl, and as long as you don’t have alkaline soil, that might be your, in the moment, might be your only choice. Oxamyl, [trade name] Vydate, is systemic. I must say in alkaline soils, I would not recommend it because it breaks down very fast, so it depends on your soil type. I would say, contact your local farm advisor; they know more about the local situation. Nimitz is— I think it might be registered now; I’m not totally sure, on citrus. Velum, I think is also [registered] now, but Velum, yeah it has minor systemic activity, but I think the key is not that the tree takes up this material, the key is that you basically eliminate the the females, which stick out of the root. And so it is not required to have a systemic nematicide for this. Because the female is always sticking out of the root. I showed you this picture of the rear end— at times, when you will apply it, [the female] will stick out [into] the soil. And the eggs are out in the soil, so there’s really no reason to have a systemic. Okay… Yeah, [a] shady, cool place. Yeah, that’s correct. I always have to remind even my farm advisors not to leave the plastic bags out in the sun, or in the car, in the trunk of a car. It will inactivate the nematodes or kill them, and that makes extraction more difficult. So that…it’s a really important thing to keep in mind. You could just stick it in a cooler, and then take it back into your office, if you can’t ship it out right away. Even at room temperature would be okay, right, that would be a little cooler, but don’t put them in the freezer, and then certainly not in the spot where you where you store your food. But…yeah, and then the second question, yeah it’s clear you want to have the soil, you want to have the feeder roots. The lab you will contact— they will tell you either they will analyze the soil for the second-stage juveniles, which is, you know, it’s an okay procedure. I would prefer that they look at the feeder roots, and and count the females, but it’s a little more laborious, that procedure. And not all the labs will offer that that service. But the variability is much lower than looking at the J2s. Okay, and this should be the final one— “what should you do when you want to apply a nematicide?” Read and follow the label; know your nematodes (soil or root analysis); consult with your farm advisor; and consult with your local agricultural commissioner’s office. And the number two here is, “where should you look for more relevant information about citrus nematodes?” The UC IPM website, UC citrus farm advisors, or the citrus production manual? And that’s it. Okay, well. Yeah I mean I’m sure you all got well-trained [to] read and follow the label, because that’s the law. Know your nematodes should also be very clear, you know. If you don’t have citrus nematodes you don’t really have to worry about it. And even if you have a very, very low population, I wouldn’t worry about it. But I would always recommend consulting with your farm advisor. It’s free, it’s a good idea. And even consult with your local agricultural commissioner. In any case, that’s free and good advice. Number two, again all three answers are correct, and and I think this is a pretty good quiz. [Heather:] Okay, and if there aren’t any more questions, just once again be sure to respond to the feedback questionnaire, and don’t forget to include your license number. Otherwise, thanks, Ole, and thank you all for attending. That can conclude this webinar, and enjoy the rest of your day. [Ole:] Thank you, all.

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