Managing Cover Crops Profitably - Valley Crops Home
Managing Cover Crops Profitably - Valley Crops Home
Managing Cover Crops Profitably - Valley Crops Home
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Once a nematode species is established in a<br />
field, it is usually impossible to eliminate it. Some<br />
covers can enhance a resident parasitic nematode<br />
population if they are grown before or after<br />
another crop that hosts a plant-damaging nematode<br />
species.<br />
If a nematode pest species is absent from the<br />
soil, planting a susceptible cover crop will not<br />
give rise to a problem,assuming the species is not<br />
introduced on seed, transplants or machinery<br />
(296). One Iowa farmer reports that researchers<br />
analyzing his fields have found no evidence that<br />
hairy vetch,a host for soybean cyst nematode,has<br />
caused any problem with the pest in his soybeans.<br />
This may be due to his use compost in<br />
strip-cropped fields with an oats/hairy<br />
vetch>corn>soybean rotation (346).<br />
You can gradually reduce a field’s nematode<br />
pest population or limit nematode impact on<br />
crops by using specific cover crops. Nematode<br />
control tactics involving covers include:<br />
• Manipulating soil structure or soil humus<br />
• Rotating with non-host crops<br />
• Using crops with nematicidal effects, such as<br />
brassicas<br />
<strong>Cover</strong> crops may also improve overall plant<br />
vitality to lessen the nematode impact on yield.<br />
But if you suspect nematode trouble, send a soil<br />
sample for laboratory analysis to positively identify<br />
the nematode species.Then be sure any cover<br />
crops you try aren’t alternate hosts for that pest<br />
species. Area IPM specialists can help you.<br />
Using brassicas and many grasses as cover<br />
crops can help you manage nematodes. <strong>Cover</strong><br />
crops with documented nematicidal properties<br />
against at least one nematode species include<br />
sorghum-sudangrass hybrids (Sorghum bicolor X<br />
S. bicolor var. sudanese), marigold (Tagetes<br />
patula), hairy indigo (Indigofera hirsuta), showy<br />
crotalaria (Crotolaria spectabilis), sunn hemp<br />
(Crotalaria juncea) and velvetbean (Mucuna<br />
deeringiana).<br />
You must match specific cover crop species<br />
with the particular nematode pest species, then<br />
manage it correctly. For example, cereal rye<br />
residue left on the surface or incorporated to a<br />
depth of several inches suppressed Columbia<br />
lance nematodes in North Carolina cotton fields<br />
better than if the cover was buried more deeply<br />
by moldboard plowing. Associated greenhouse<br />
tests in the study showed that incorporated rye<br />
was effective against root-knot,reniform and stubby<br />
root nematodes, as well (14).<br />
Malt barley, corn, radishes and mustard sometimes<br />
worked as well as the standard nematicide<br />
to control sugar beet nematode in Wyoming sugar<br />
beets,a 1994 study showed.Increased production<br />
more than offset the cover crop cost, and lamb<br />
grazing of the brassicas increased profit without<br />
diminishing nematode suppression. The success<br />
is conditional upon a limited nematode density.<br />
The cover crop treatment was effective only if<br />
there were fewer than 10 eggs or juveniles per<br />
cubic centimeter of soil. A moderate sugar beet<br />
nematode level was reduced 54 to 75 percent in<br />
about 11 weeks, increasing yield by nearly 4 tons<br />
per acre (184).<br />
Weed Management<br />
<strong>Cover</strong> crops are widely used as smother crops to<br />
shade and out-compete weeds. Cereal grains<br />
establish quickly as they use up the moisture, fertility<br />
and light that weeds need to survive.<br />
Sorghum-sudangrass hybrids and buckwheat are<br />
warm-season crops that suppress weeds through<br />
these physical means and by plant-produced<br />
natural herbicides (allelopathy).<br />
Cereal rye is an overwintering crop that suppresses<br />
weeds both physically and chemically. If<br />
rye residue is left on the soil surface, it releases<br />
allelochemicals that inhibit seedling growth of<br />
many annual small-seeded broadleaf weeds, such<br />
as pigweed and lambsquarters. The response of<br />
grassy weeds is more variable.Rye is a major component<br />
in the killed organic mulches used in notill<br />
vegetable transplanting systems.<br />
Killed cover crop mulches last longer if the<br />
stalks are left intact, providing weed control well<br />
into the season for summer vegetables. Two<br />
implements have been modified in recent years<br />
specifically to enhance weed suppression by<br />
cover crops. The undercutter uses a wide blade<br />
to slice just under the surface of raised beds, severing<br />
cover crop plants from their root mass.An<br />
attached rolling harrow increases effectiveness<br />
(69, 70, 71, 72). A Buffalo rolling stalk chopper<br />
32 MANAGING COVER CROPS PROFITABLY
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