Considerations in Using Cover Crops for Nematode
Management
Koon-Hui Wang and Robert McSorley
Univ. Florida, Dept. Entomology and Nematology, P.O. Box
110620, Gainesville, FL 32611-0620, U.S.A.
(Last updated on January, 2002)
Introduction
This
article is a summary of key considerations in using cover crops for nematode
management, based on information that had been published previously (McSorley, 2001; Wang and McSorley, 2001).
1.
Biological
information on nematode genotypes.
Continuous
planting or overuse of resistant cultivars in rotation schemes has caused
shifts among nematode populations to resistance-breaking genotypes (Table 1).
Therefore it is critical to know the response of a candidate rotation crop to
the targeted plant-parasitic nematode races or isolates present in a specific
site prior to the planning of crop sequences.
Table
1. Targeted nematodes with resistance-breaking genotypes (pathotypes, races,
and isolates) reported in continuous cropping systems.
|
Continuous crop |
Targeted
nematode |
Resistance-breaking
nematode |
|
|
Pathotypes |
|
|
Potato clones |
Globodera rostochiensis |
G. pallida |
|
|
Races |
|
|
Soybean |
Heterodera glycines wild types |
H. glycine resistance-breaking races |
|
Peanut |
Meloidogyne arenaria race 2 |
M. arenaria race 1 |
|
Jointvetch |
M. incognita race
1 |
M. incognita race
3 |
|
|
Isolates |
|
|
Peanut |
Belonolaimus longicaudatus Georgia isolates. |
B. longicaudatus Virginia and Carolina isolates. |
|
Sesame |
M. javanica (California and Hawaii populations) |
M. javanica Florida and Texas populations |
2. Crop germplasm (resistant,
susceptible, tolerant, intolerant).
Avoiding
shift to resistance breaking pathotypes: Different responses among
crop cultivars within a species occur commonly. For example, cowpea (Vigna
unguiculata) cultivars exhibit a range of responses to Meloidogyne
incognita (Fig. 1, Gallaher and McSorley, 1993).
|
|
|||
Fig. 1. Number of Meloidogyne incognita
/ 100cm3 soil (data from Gallaher
and McSorley, 1993). |
3.
Relationship
between nematode density and crop yield.
4.
Nematode
biology. These include:
identification of the nematode species,
isolates, races, pathotypes.
population densities present.
relationship between nematode population
densities and yield.
nematode biology, host range, and population
dynamics.
effects and economics of control treatments.
environmental conditions that favor the crops
or the nematodes.
5.
Nematode
host range.
Mixtures of multiple species of
plant-parasitic nematodes in a site are commonly found. A rotation crop
resistant to a particular plant-parasitic nematode might be susceptible to
another (Table 2). Therefore it is critical to focus management options on the
key nematode pest, and shift mixed populations toward one that is less
aggressive and more easily managed.
Table 2. Rotation crops resistant or
susceptible to plant-parasitic nematodes.
|
Cover crop |
Resistant |
Susceptible |
|
Sunn hemp (Crotalaria juncea) |
Meloidogyne spp., Rotylenchulus
reniformis
|
Pratylenchus spp. |
|
Sorghum (Sorghum bicolor) |
Meloidogyne spp. |
Paratrichodorous minor |
|
Rye (Secale cereale)
|
Meloidogyne spp.
|
Belonolaimus longicaudatus
|
|
Marigold (Tagetes patula)
|
R. reniformis, Meloidogyne spp. |
B. longicaudatus |
|
Marigold (T. erecta) |
Meloidogyne spp. |
R. reniformis |
6.
Nematode
population dynamics.
7.
Economical
consideration.
Economics,
rather than efficacy, will often determine whether a particular rotation crop
is used. Modeling nematode dynamics in cropping systems in conjunction with
obtaining data on damage functions, economic threshold, and control-cost functions
can be used to select the most profitable cropping sequences. Successful
modeling of cyst nematodes is developed with the consideration of mixtures of Globodera
spp. and pathotypes, as well as potato germplasm with varying degrees of
resistance or tolerance. However, models of nematode population dynamics are
challenged by several sources of error, including error in estimating initial
population of nematodes in soil samples, error associated with development of
regression equations, and seasonal variation. Stochastic elements incorporated
into models or simulation runs for a range of possible scenarios can provide
probability forecasts for a range of possible outcomes.
8.
Duration
of rotation.
9.
Environmental,
seasonal, and regional effects.
Temperature affects nematode reproductive rate, therefore,
some rotation crops may perform well only during cool seasons of the year.
Regional differences in climate, soil type, cultivars used, and nematode
genotypes or cultural practices may also affect nematode dynamics in cropping
systems.
10.
Interactions
with other organisms (Table 2).
Table
2. Examples of the impact of crop rotation system on nontargeted organisms.
|
Rotation Crop |
Interaction with other organisms |
|
Sorghum (Sorghum bicolor) |
Increased problems with wireworms (insecta:
fam. Elateridae) in a subsequent potato crop.
|
|
Sunn hemp (Crotalaria juncea)
|
Increased nematode-trapping fungal
population at early stage of a subsequent pineapple crop.
|
|
Cotton (Gossypium hirsutum)
|
Suppressed Meloidogyne arenaria
and Sclerotium rolfsii in peanut.
|
References:
Gallaher,
N. R. and R. McSorley. 1993. Population densities of Meloidogyne incognita
and other nematodes following seven cultivars of cowpea. Nematropica 23: 21-26.
McSorley,
R. 2001. Multiple cropping systems for nematode management: A review. Soil and
Crop Science Society of Florida Proceedings 60:132-142.
Wang, K.-H. and R. McSorley. 2001. Multiple cropping systems for nematode management. Phytopathology 91:S145 (Abstract).