Limitations to Chemical Control
Limitations to Chemical Control
Limitations to Chemical Control
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<strong>Limitations</strong> <strong>to</strong> <strong>Chemical</strong> <strong>Control</strong><br />
May not be effective based on environmental<br />
limitations = soil conditions, weather, etc.<br />
May not be economical.<br />
May not be any products registered for that crop.<br />
Product may be in short supply.
Cultural Strategies for Nema<strong>to</strong>de Management<br />
Nema<strong>to</strong>de Management With Plants<br />
- No plants – fallow<br />
- Nonhosts – crop rotation<br />
- Green manure cover crops<br />
- Timing of planting and harvest <strong>to</strong> avoid damage<br />
= “escaping in time”<br />
- Antagonistic plants<br />
- Trap crops<br />
- Resistant cultivars
Dry Fallow<br />
An extreme form of crop rotation where<br />
no crop is planted -> starve the nema<strong>to</strong>des<br />
Works best in areas with high soil temperatures and<br />
low rainfall or highly seasonal rainfall so that six<br />
months or more of hot, dry weather exist.<br />
Many nema<strong>to</strong>des are dead after six months of dry<br />
fallow and most are dead after one year.<br />
Others, such as cyst nema<strong>to</strong>des, remain viable for<br />
5-10+ years under fallow, but these are extreme cases.
<strong>Limitations</strong> <strong>to</strong> Dry Fallow<br />
1. Can you afford <strong>to</strong> take land out of production for a<br />
long enough period that fallow will be effective?<br />
= reduction in revenue<br />
2. Requires periodic disking, or harrowing <strong>to</strong> remove<br />
weeds or volunteer plants and <strong>to</strong> bring viable<br />
nema<strong>to</strong>des from below the surface <strong>to</strong> the harsher<br />
conditions at the surface. = operational cost<br />
3. There is also the problem of potential soil loss due <strong>to</strong><br />
erosion while there is no plant cover on the field.<br />
= environmental cost<br />
The bot<strong>to</strong>m line is that fallowing is not cost free!
Cultural Strategies for Nema<strong>to</strong>de Management<br />
Nema<strong>to</strong>de Management With Plants<br />
- No plants – fallow<br />
- Nonhosts – crop rotation<br />
- Green manure cover crops<br />
- Timing of planting and harvest <strong>to</strong> avoid damage<br />
= “escaping in time”<br />
- Antagonistic plants<br />
- Trap crops<br />
- Resistant cultivars
Crop Rotation<br />
Most common method of nema<strong>to</strong>de control.<br />
Plant crops that nema<strong>to</strong>des cannot feed/reproduce on.<br />
Population density is reduced by starvation.<br />
Host range for the target nema<strong>to</strong>de must be known.<br />
Rotation sequence selected depends on what<br />
nema<strong>to</strong>des need <strong>to</strong> be controlled and what crops can<br />
be grown and marketed in the area.<br />
Alternating graminoids such as corn (maize) or wheat<br />
with nongraminoids, like pota<strong>to</strong> or soybean effective.
<strong>Limitations</strong> of Crop Rotation<br />
The first limitation is that it only works for nema<strong>to</strong>des<br />
with a narrow host range like:<br />
- stem nema<strong>to</strong>des<br />
- cyst nema<strong>to</strong>des<br />
- and some root-knot nema<strong>to</strong>des<br />
but is less effective for nema<strong>to</strong>des with wide host ranges<br />
like:<br />
- root-lesion nema<strong>to</strong>des and<br />
- most migra<strong>to</strong>ry ec<strong>to</strong>parasites including virus<br />
vec<strong>to</strong>rs although this<br />
- can work for virus diseases if the crop is host<br />
for the nema<strong>to</strong>de vec<strong>to</strong>r but not for the virus.<br />
(TRV and alfalfa example.)
<strong>Limitations</strong> of Crop Rotation<br />
Second, often a limited number of cash crops in any<br />
given area that can be grown in a rotation sequence<br />
effectively.<br />
Often the most valuable crop is the most damaged.<br />
Grower must grow less profitable crop <strong>to</strong> suppress<br />
nema<strong>to</strong>des <strong>to</strong> nondamaging levels.<br />
For example, it may be necessary <strong>to</strong> grow wheat in<br />
order <strong>to</strong> suppress populations of northern root-knot<br />
nema<strong>to</strong>de Meloidogyne hapla which damage more<br />
valuable crops like pota<strong>to</strong>, carrot, or sugarbeet.
<strong>Limitations</strong> of Crop Rotation<br />
Growers and their bankers may be reluctant <strong>to</strong><br />
rotate from a high cash value crop <strong>to</strong> one of lesser<br />
value just <strong>to</strong> control nema<strong>to</strong>des.<br />
Often, it is still more economical <strong>to</strong> use nematicides<br />
and continue <strong>to</strong> grow the high value crop.<br />
In subsistence agriculture systems, farmers may have<br />
<strong>to</strong> grow crops that feed their family whether they are<br />
hosts for nema<strong>to</strong>des or not. May have little chance <strong>to</strong><br />
rotate.
<strong>Limitations</strong> of Crop Rotation<br />
Third limitation is that some nema<strong>to</strong>des, like cyst<br />
nema<strong>to</strong>des, can exist in soil as eggs for several years<br />
without a suitable host (= nema<strong>to</strong>de persistence).<br />
Grower may have <strong>to</strong> rotate away from a high cash<br />
value crop, like sugarbeet, for five or more years<br />
before nema<strong>to</strong>des decline <strong>to</strong> a nondamaging level.<br />
Often, it is still more practical <strong>to</strong> use nematicides and<br />
continue <strong>to</strong> grow the high value crop.
<strong>Limitations</strong> of Crop Rotation<br />
Fourth problem with crop rotation can occur if two or<br />
more nema<strong>to</strong>de pathogens are present in the same<br />
soil, each with different “alternative” hosts.<br />
An example of this problem exists in the Pacific<br />
Northwest where both M. hapla and M. chitwoodi may<br />
exist <strong>to</strong>gether. Both nema<strong>to</strong>des damage pota<strong>to</strong> but<br />
each has a different range of alternative hosts as well<br />
as nonhosts.
<strong>Limitations</strong> of Crop Rotation<br />
Growing wheat reduces M. hapla, which cannot<br />
reproduce on wheat, but maintains or increases<br />
M. chitwoodi, which reproduces well on wheat.<br />
Growing alfalfa reduces M. chitwoodi race 1 but<br />
maintains or increases M. hapla.<br />
This situation is further complicated since rotations<br />
with alfalfa <strong>to</strong> control M. chitwoodi appear <strong>to</strong> have<br />
selected for a second race of this nema<strong>to</strong>de that is<br />
capable of reproducing on alfalfa.
<strong>Limitations</strong> of Crop Rotation<br />
Volunteer plants from the previous host crop and<br />
weeds must be strictly controlled during the rotation.<br />
Although it is often overlooked, weeds can be good<br />
hosts for nema<strong>to</strong>des that damage crops.<br />
Of course, rotation is only practical for annual crops<br />
or short-term perennials like alfalfa or strawberry<br />
and is of no value <strong>to</strong> long-lived perennials.<br />
So, there can be several considerations <strong>to</strong> address<br />
before implementing crop rotation for<br />
nema<strong>to</strong>de management but it can still be effective.
Crop Rotation<br />
Nema<strong>to</strong>de Management With Crop Rotation<br />
May Be Enhanced with Green Manure Crops
Cultural Strategies for Nema<strong>to</strong>de Management<br />
Nema<strong>to</strong>de Management With Plants<br />
- No plants – fallow<br />
- Nonhosts – crop rotation<br />
- Green manure cover crops<br />
- Timing of planting and harvest <strong>to</strong> avoid damage<br />
= “escaping in time”<br />
- Antagonistic plants<br />
- Trap crops<br />
- Resistant cultivars
Cultural Strategies for Nema<strong>to</strong>de Management<br />
See Green Manure Cover Crop File