Join us as we talk with Dr. Adrienne Gorny, N.C. State University Assistant Professor in Nematode Epidemiology and Management about the Guava Root Knot Nematode (Meloidogyne enterolobii). We discuss where it came from, why it is such a problem and how to deal with it.
Welcome to Crop Sense presented by North Carolina Cooperative Extension I’m Jacob Morgan a field crops agent with North Carolina Cooperative Extension today we have Dr. Adrian Gorny from North Carolina State University Assistant professor in nematode epidemiology and management good morning Dr. Gorny can you tell us a little bit about yourself good morning thank you very much for having me today um yes so I’m Adrian Gorny I’m originally from Michigan sort of southeast Michigan i grew up there and i did my undergraduate in plant biology at Purdue University so I’m a boilermaker at heart and then from there I went to graduate school at Cornell University where I studied the northern root knot nematode Meloidogyne hapla in Irish potato, white potato, we were looking at ways to manage this nematode in potato production and quantify levels that would lead to considerable crop damage from there I came to North Carolina State University in August of 2019 so I’m excited to be here. So today we're talking about the Guava root knot nematode so can you just start off with where did it come from. Sure, so the guava root knot nematode we believe is a tropical species of nematode it was first identified in China and from there it has spread to several countries around the world. In the United States it was first introduced into Puerto Rico in the 1980s and then from there it was introduced to the mainland in Florida. We believe that it has been introduced to North Carolina from Florida. It has also been identified in South Carolina as well. So we've had root not nematodes in North Carolina for years and years so why does this seem to be such a big problem. That's a great question so indeed we've had root not nematodes in North Carolina for quite some time, however these nematodes are a different species. The most common and prevalent nematode is the southern root not nematode incognita so this guava not nematode is a different species it's called Meloidogyne enterolobii
and it is unique in that it is able to overcome a lot of our host plant resistance genes so these host plant resistance genes essentially make the plant immune to infection by the nematode but in the case of the guava nematode these genes don't appear to be working and the nematode can easily overcome them which is very concerning because host plant resistance is a very powerful tool when it works. Gotcha so let's back up can you explain exactly what a nematode is for those that may have heard of it but they might not know exactly what it is or what it looks like. For sure, that that's a great question so it's a microscopic roundworm these worms live in the soil and they feed on plant roots. So in the nematode world there's actually good guys and bad guys. The good guys are sort of free living nematodes ,they they're very important in a lot of nutrient cycling activities but then the bad guys are parasites of plants and they they feed on the plant roots they can compromise root growth and function lead to a decrease in water uptake and nutrient uptake and in the case of crops such as sweet potato or carrot or white potato where the marketable portion of the plant is grown underground it can cause damage to that marketable plant portion and make it unsaleable. So how do we know if we have them. If we got root knot we're going to pull the roots up and we'll be able to see some signs of those nematodes can you describe what we would look for in that situation if a farmer's out in this field looking to see if he has root knot nematodes. Also how do we know if we have the guava root knot nematode versus like southern root knot. Great, yeah, so this is very important. One way to tell if there's a root knot nematode issue in the field is to go out and dig up a plant or two and actually look at the roots of the plant. The damage will appear as small galls or bumps along the root of the plant and this is very indicative of root knot nematode. In the case of soybean where the plant forms the rhizobium nodules one way to tell the difference between a potential root knot nematode gall and those rhizobium nodules is to actually cut one in half. The rhizobium nodules will have a light pink color inside whereas a nematode gall will be white or gray throughout. But then soil sampling is very important for nematode analysis collecting the soil sample from a field and sending this in to the NCDA nematode essay laboratory. This will provide you information with the types of nematodes that might be present in the field and their population levels from those population levels that will offer a risk assessment. Essentially how much risk of damage is there to a subsequent crop okay so what there's a hundred counties in North Carolina what percentage of counties do we know it's in and what percentage do you think it's probably in that we're not aware of quite yet. Great yes so it has been confirmed in approximately 13 counties in sort of the central part of the state unfortunately in the heavy sweet potato growing areas have been confirmed positive for the guava root not nematode. I should mention that the way to tell the difference between the guava root not nematode and the say southern root not nematode or the few other species of root not nematode this has to be done through a DNA molecular test that the ncda nematode lab performs. When we look at these nematodes under the microscope it looks super similar it's very difficult to tell them apart but using this dna test we can get a definitive identification of the guava root knot nematode versus other species. Okay so what other crops so we talked about sweet potatoes what other crops does it affect and what exactly types of symptoms? In sweet potatoes we talked about the marketable portion of the crop is obviously not visually appealing so that's going to affect the marketability but what other effects would it have on some of the other crops. Sure so unfortunately the guava root not nematode has a very broad host range. Host range refers to the number of different crops that it can infect and cause damage on. So the guava root knot nematode is able to infect sweet potato, tobacco, cotton, soybean, many different vegetables like peppers and tomatoes and watermelon many fruit crops as well at the moment. We've discovered that the non-hosts of the plants that it is not able to infect include small grains like rye and oats and wheat, peanut and corn so these may be good rotational crop options. How do we control this thing? Sure, yep so there are several options um first and foremost starting with the soil sample and positive identification as to whether or not it is in the field is the critical first step if a report comes back indicating that the nematode is present we would then recommend a chemical option so fumigation or a non-fumigator and then rotating to non-host crops such as those small grains or corn or peanut we have found in our NCSU research trials that a telone fumigant performs quite well and also some non-fumigant nematicides such as vellum prime can be very beneficial for controlling this thing. How long do we need to rotate out of susceptible crops and for us to feel like we've done a good job of kind of suppressing it. Indeed so um the root knot nematodes in general they can survive a couple of years in the soil without a suitable host crop so we recommend rotating out of a host crop for at least two to three years. Okay so what are so what are some ways we can prevent it from going maybe we have some fields that obviously have it some fields that don't have it what are some sanitation or some other methods to kind of prevent it from becoming a bigger problem in more of our fields? Indeed, so in the case of the guava root knot nematode prevention is the best medicine we don't want to move infected soil into clean fields. So if we are doing our regular soil sampling and we know where the nematode is we can quarantine these fields on the farm and be careful not to move infected soil out of those fields. So being conscious of equipment that is coming out of fields that have the nematode, washing off that equipment, washing off shoes, and truck tires. Also being very conscious about planting certified slips so slips that are free of the nematode including sweet potato slips that are free of soil and roots because this is how the nematode is frequently transferred into new fields. Anything else that we haven't covered that you want to talk about as far as the nematodes? I would encourage you if anybody has questions I’m always happy to answer those and please feel free to reach out. Alright, if you'd like more information on the guava root not nematode you can find a best management practices sheet that Dr. Gorny put together by googling
n-c-s-u-g-r-k-n best management practices or as always call your local cooperative extension agent. With that we appreciate your time Dr. Gorny and if you like this podcast please share it with your friends. If you've got friends that have sweet potatoes or tobacco some other of the susceptible hosts for guava root nematode please share this with them and as always thanks for listening to crop sense because if it's not making money it's not making sense.