In 2006, another agronomic pest was discovered in Tennessee. The pest was a cyst nematode found in corn production. Cysts were observed in stunted corn plants, in a field located in Obion County Tennessee. After careful inspection, it was determined that cyst nematodes were present on plant roots. Obion County is one of the major corn seed production counties of Tennessee. Funding was requested to survey corn fields to establish the distribution of this recently discovered cyst nematode and bioassays will be conducted to determine if the pest survives on other agronomic crops. Without proper information, severe crop losses could occur due to insufficient knowledge of the pest distribution and its feeding preferences on other crop hosts. Distribution of this cyst nematode is currently unknown and knowledge of distribution would allow further assessment of the impact this nematode and the effects it may have on current and future corn production in the US. A preliminary greenhouse study has suggested this nematode reproduces on corn and not on dicotyledonous crop roots. Identification of the cyst nematode is ongoing but the USDA Nematology Lab (contracted by APHIS) has confirmed that the nematode is not Heterodera zeae, the corn cyst nematode, which had previously been under federal quarantine. Molecular tests have confirmed that it is not any of the common monocotyledon cyst nematode species. However, specimens are identical to an undescribed cyst nematode found in west Tennessee on goose grass (Eleusine indica) in 1978. Goose grass is not an agronomically important crop, therefore the cyst samples found in 1978 remained undescribed, however, samples were available from USDA for morphological comparison purposes. Obtaining more information on distribution of this pest will allow researchers to determine the nematode’s economic importance in corn production and its potential to cause yield loss and/or spread to other corn and/or crop production areas within the USA.
A major concern of this species, is proper management of the SCN. A mixture of this pest species and SCN will give diagnostic labs an inflated number of cysts present. This could indicate that the SCN problem is more severe than actual number of SCN present. Two outcomes may occur due to inadequate knowledge cyst species present in soil samples. First, with a high SCN count, soybean producers are urged to rotate to corn or some other non-SCN host for several years. If the Cactodera species is present, the cyst count will increase (if corn is planted) rather than decrease, giving an impression that rotation is not working and a highly virulent population of SCN may be present in the field. Second, producers may be encouraged to utilize a highly resistant SCN variety, therefore SCN may adapt to the new resistance. The end result may provide producers with high cyst counts of either Cactodera or SCN. Awareness of the possibility of mixed cyst genera in the field will hopefully reduce the risk of making bad management decisions.
In mid-2007, two projects were awarded funding to determine distrobution of this pest. The first project included sampling within Tennessee and the second project inlcuded sampling other areas of Tennessee, as well as Kentucky and Mississippi.
In August of 2007, I spent several hours working on this newly discovered parasitic nematode (Cactodera spp.) of corn. I visited the USDA laboratory in Jackson, TN and I saw that you can not just look superficially at the roots of corn plants or cysts found within soil to determine if cysts collected are truely parasitic on corn or not. I had a very difficult time finding any cysts on corn roots. The majority of cysts found were obtained by washing plant roots in mesh screens. The shape and size of this cyst nematode is very similar to the shape and size of cysts of the soybean cyst nematode (Heterodera glycines). Soybeans are commonly rotated in areas where corn is produced in West Tennessee and it would be highly likely that both of these cysts could be present in soil samples collected. Specimens of this Cactodera species reproduced well (RF > 5) on all tested hybrid corn cultivars (Robert Heinz, University of Missouri). There was poor reproduction on other monocots and no dicot hosts have been found to date. Currently, for all purposes to differenciate between Heterodera or Cactodera is to examine the vulval cone. Bullae are absent, see figure E., on page 254 of Handoo's journal article listed below to see examples of bullae. Remember, vulva are circumfenestrate; bullae and an underbridge are absent in Cactodera. Ernest Bernard and Zafar Handoo are currently working on obtaining other morphological characteristics of this nematode.
Reference Material of Interest
Iowa State IPM Program
Genus Catodera - Krall' and Krall' 1978
1) Handoo, Z.A, 2002. A Key and Compendium to Species of the Heterodera avenae Group (Nematoda: Heteroderiae). Journal of Nematology Vol. 34(3):250-262.
2) Nematology Sturhan, D., 2002. Vol.4(7):875-882 Notes on the Genus Cactodera
Pat Donald, United States Department of Agriculture - ARS, Jackson, TN (Tennessee, survey).
Don Hershman, University of Kentucky, Princeton, KY (Kentucky, survey).
Trey Koger, Mississippi State University (Mississippi, survey).
Darrell Hensley, University of Tennesssee, Extension Service, Knoxville, TN (Tennessee, survey).
Melvin Newman, University of Tennesssee, Extension Service, Jackson, TN (Tennessee, survey).
Ernest Bernard,University of Tennesssee, Experiment Station, Knoxville, TN (taxonomy)
Zafar Handoo, USDA-ARS (taxonomy)
Robert Heinz, University of Missouri, Plant Sciences (host range)
This is a cooperative project with USDA-ARS, University of Tennesee Experiment Station, University of Tennessee Extension Service, University of Kentucky, Mississippi State University, Southern Plant Diagnostic Network (SPDN), and the Southern Region Integrated Pest Management Center (SR-IPMC).
For more information please contact individuals listed above.