Limitations to Chemical Control

Limitations to Chemical Control
May not be effective based on environmental
limitations = soil conditions, weather, etc.
May not be economical.
May not be any products registered for that crop.
Product may be in short supply.

Cultural Strategies for Nematode Management
Nematode Management With Plants
- No plants – fallow
- Nonhosts – crop rotation
- Green manure cover crops
- Timing of planting and harvest to avoid damage
= “escaping in time”
- Antagonistic plants
- Trap crops
- Resistant cultivars

Dry Fallow
An extreme form of crop rotation where
no crop is planted -> starve the nematodes
Works best in areas with high soil temperatures and
low rainfall or highly seasonal rainfall so that six
months or more of hot, dry weather exist.
Many nematodes are dead after six months of dry
fallow and most are dead after one year.
Others, such as cyst nematodes, remain viable for
5-10+ years under fallow, but these are extreme cases.

Limitations to Dry Fallow
1. Can you afford to take land out of production for a
long enough period that fallow will be effective?
= reduction in revenue
2. Requires periodic disking, or harrowing to remove
weeds or volunteer plants and to bring viable
nematodes from below the surface to the harsher
conditions at the surface. = operational cost
3. There is also the problem of potential soil loss due to
erosion while there is no plant cover on the field.
= environmental cost
The bottom line is that fallowing is not cost free!

Cultural Strategies for Nematode Management
Nematode Management With Plants
- No plants – fallow
- Nonhosts – crop rotation
- Green manure cover crops
- Timing of planting and harvest to avoid damage
= “escaping in time”
- Antagonistic plants
- Trap crops
- Resistant cultivars

Crop Rotation
Most common method of nematode control.
Plant crops that nematodes cannot feed/reproduce on.
Population density is reduced by starvation.
Host range for the target nematode must be known.
Rotation sequence selected depends on what
nematodes need to be controlled and what crops can
be grown and marketed in the area.
Alternating graminoids such as corn (maize) or wheat
with nongraminoids, like potato or soybean effective.

Limitations of Crop Rotation
The first limitation is that it only works for nematodes
with a narrow host range like:
- stem nematodes
- cyst nematodes
- and some root-knot nematodes
but is less effective for nematodes with wide host ranges
like:
- root-lesion nematodes and
- most migratory ectoparasites including virus
vectors although this
- can work for virus diseases if the crop is host
for the nematode vector but not for the virus.
(TRV and alfalfa example.)

Limitations of Crop Rotation
Second, often a limited number of cash crops in any
given area that can be grown in a rotation sequence
effectively.
Often the most valuable crop is the most damaged.
Grower must grow less profitable crop to suppress
nematodes to nondamaging levels.
For example, it may be necessary to grow wheat in
order to suppress populations of northern root-knot
nematode Meloidogyne hapla which damage more
valuable crops like potato, carrot, or sugarbeet.

Limitations of Crop Rotation
Growers and their bankers may be reluctant to
rotate from a high cash value crop to one of lesser
value just to control nematodes.
Often, it is still more economical to use nematicides
and continue to grow the high value crop.
In subsistence agriculture systems, farmers may have
to grow crops that feed their family whether they are
hosts for nematodes or not. May have little chance to
rotate.

Limitations of Crop Rotation
Third limitation is that some nematodes, like cyst
nematodes, can exist in soil as eggs for several years
without a suitable host (= nematode persistence).
Grower may have to rotate away from a high cash
value crop, like sugarbeet, for five or more years
before nematodes decline to a nondamaging level.
Often, it is still more practical to use nematicides and
continue to grow the high value crop.

Limitations of Crop Rotation
Fourth problem with crop rotation can occur if two or
more nematode pathogens are present in the same
soil, each with different “alternative” hosts.
An example of this problem exists in the Pacific
Northwest where both M. hapla and M. chitwoodi may
exist together. Both nematodes damage potato but
each has a different range of alternative hosts as well
as nonhosts.

Limitations of Crop Rotation
Growing wheat reduces M. hapla, which cannot
reproduce on wheat, but maintains or increases
M. chitwoodi, which reproduces well on wheat.
Growing alfalfa reduces M. chitwoodi race 1 but
maintains or increases M. hapla.
This situation is further complicated since rotations
with alfalfa to control M. chitwoodi appear to have
selected for a second race of this nematode that is
capable of reproducing on alfalfa.

Limitations of Crop Rotation
Volunteer plants from the previous host crop and
weeds must be strictly controlled during the rotation.
Although it is often overlooked, weeds can be good
hosts for nematodes that damage crops.
Of course, rotation is only practical for annual crops
or short-term perennials like alfalfa or strawberry
and is of no value to long-lived perennials.
So, there can be several considerations to address
before implementing crop rotation for
nematode management but it can still be effective.

Crop Rotation
Nematode Management With Crop Rotation
May Be Enhanced with Green Manure Crops

Cultural Strategies for Nematode Management
Nematode Management With Plants
- No plants – fallow
- Nonhosts – crop rotation
- Green manure cover crops
- Timing of planting and harvest to avoid damage
= “escaping in time”
- Antagonistic plants
- Trap crops
- Resistant cultivars

Cultural Strategies for Nematode Management
See Green Manure Cover Crop File