Update About the Guava Root Knot Nematode

In Sept. 2018, a short article titled “Guava Root-Knot Nematode: A Potential New Pest for Midsouth Soybeans?” was posted on this website. Portions of that article are repeated here, along with updates provided in articles that have been published since then.

The following information is provided so that producers, consultants, and other agricultural practitioners will become aware of this relatively new invasive pest that can affect soybeans and be involved in its detection and evaluation of possible remedies should they be necessary.

•    An article by Dr. Charles Overstreet and colleagues at LSU provides valuable information about the Guava Root Knot Nematode [RKN] pest.

•    The Guava RKN is considered one of the most damaging nematodes in the world because of its wide host range, aggressiveness, and ability to overcome current RKN resistance in crops such as soybean.

•    Presently, it has very limited distribution in the Midsouth.

•    Soybean is one of several commodity crops that are susceptible to this pest.

•    Weeds such as morningglories and Palmer amaranth are good hosts to the Guava RKN as stated in the Nov. 2, 2022 Farm Progress article titled “Invasive guava root knot nematode is a problem”.

•    Several cover crop species are susceptible to this pest (e.g. some vetch species). Therefore, know whether or not a site is infested with Guava RKN before selecting a cover crop species to grow on that site.

•    The Guava RKN is very similar to the Southern RKN (a close relative) that has been and still is a prevalent pest of soybean in the Midsouth as indicated by data cited here.

•    Distinguishing between Guava and Southern RKN’s can be difficult because both can produce rather large root galls.  It can be distinguished from the Southern RKN only by molecular techniques described here.

•    Its presence can be recognized when plants that are resistant to Southern RKN have large galls on their roots and suffer serious damage.

•    It is recognized as being more difficult to manage than Southern RKN, and its symptoms are more severe. It has the potential to cause heavy yield loss.

•    Sandy-textured soils with large pore spaces promote nematode movement through the soil since RKN’s move through water films.

•    The best defense against this potential nematode pest is to prevent its incursion into uninfested fields where susceptible crops are or will be grown.

Pertinent articles about the Guava RKN (in addition to those linked above) include the following.

•    Guava root knot nematode, world’s most aggressive

•    Root Knot Nematode of Soybean

More information about the spread of this damaging pest will be provided by state Extension specialists if and when it does become a problem for Midsouth soybeans.

Composed by Larry G. Heatherly, Nov. 2022, larryh91746@gmail.com