The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
site maintained by the Florida
Cooperative Extension Service.
Copyright 2005, Board of Trustees, University
pFG6 University of Florida
CFS AGRICULTURAL RESEARCH AND EDUCATION CENTER
83- Sanford, Florida
Research Report SAN 83-4 --- September 1982
UM / i ~~~-
EFFECTS OF COVER CROPS AND FALL L! ,' /
ON NEMATODES AND SUBSEQUENT CROP FIELDS I
H. L. Rhoades
&.A.S. i U
Fields that are used for winter vegetable production in Florida are usually
either clean fallowed, cover cropped, or allowed to grow up in weeds during the
summer months. Clean fallow reduces nematode populations as well as other soil-
borne pests and is used extensively. However, this practice is considered to be
destructive to soil fertility and physical properties and is not normally recom-
mended by soil scientists. Because of the abundance and diversity of species of
plant nematodes in Florida, the success of cover cropping depends largely on the
relationship of the cover crop to the nematodes. Since hairy indigo (Indigofera
hirsuta) has been shown to be resistant to population increase of the sting nema-
tode, Belonolaimus longicaudatus, and the root-know nematode, Meloidogyne
incognita, experiments are being conducted to compare the effects of this and
other cover crops with fallowing on nematode populations and subsequent yields of
Summer cover crops of hairy indigo, California Blackeye No. 5 cowpea, and
Grazer A (sorghum-sudangrass hybrid) were seeded on July 7, 1981. A natural in-
festation of weeds was allowed to grow as one treatment and another treatment
* consisted of clean fallow with periodic disk harrowing. The experiment was ran-
domized complete block with five replicates and was conducted on Myakka fine sand.
Plot size was 20 X 40 ft. The hairy indigo and sorghum-sudan grass were broadcast
seeded but the cowpeas were planted in 30-inch rows and cultivated during early
growth. The hairy indigo plots were mowed at a height of 4-5 inches on August 14
to prevent heavy weed growth since seedlings of this crop grow slowly at first.
All plots were mowed on September 24 and plowed September 29. On October 13, one-
half of each plot was treated with 2 Ib ai/acre of Nemacur applied in 15-inch
bands in-the-row, then 'Gourmet' cabbage was transplanted. Normal cultural
practices were followed and the cabbage was harvested three times (January 28,
February 12, and February 26). Soil samples were collected on September 14 be-
fore mowing the cover crops and from the cabbage plots on January 5, 1982, for
ectoparasitic nematode population determination. The plots were plowed on March 3,
then cucumber ridges were prepared and 'Poinsett' cucumbers planted on March 25.
On April 8, a severe rain and hail storm completely destroyed the cucumbers, conse-
quently the beds were reformed and planted on April 15. These were harvested seven
times during June 1-21, 1982.
Sting nematodes built up to high populations on sorghum-sudan grass and re-
turned to moderate levels on weeds and cowpea where the previous vegetable crop
had not been treated. Where the previous crop had been treated populations remain-
ed low. Populations remained low on hairy indigo and in fallow plots regardless of
whether the previous crop had been treated. Lance nematodes built up on sorghum-
sudan grass, weeds, and hairy indigo but remained low on cowpea and for fallow.
Populations were somewhat lower where the previous vegetable crop had been treated.
Stubby-root nematode populations built up to the highest level on sorghum-sudan
grass and remained lowest following cowpea and fallow. In general, treatment of
the previous crop of vegetables had little affect on return of this nematode.
Both cabbage and the succeeding crop of cucumbers were reduced in yield
from the high populations of sting nematodes following sorghum-sudan grass with-
out nematicide treatment. Yields were very similar for all other treatments
indicating that the populations of nematodes were too low to injure the crops.
Table 1. Effect of cover crops and fallowing on nematode populations.
Sting Lance Stubby-root
Treatment Check Treatedb Check Treated Check Treated
Sorghum-sudan grass 174 2 211 82 103 115
Cowpea 20 1 15 3 18 27
Weeds 33 1 202 103 41 34
Hairy indigo 6 1 176 65 75 32
Fallow 2 0 29 0 8 3
aAverage number of nematodes per 100 cc of soil at end of cover crop period.
bRefers to nematicide treatment of previous vegetable crops.
Tabld 2. Effect of cover crops on yield of subsequent vegetable crops
(cabbage, first crop; cucumbers, second crop).
Cabbage Nematodesb Cucumber
Treatment yield Sting Lance Stubby-root yielda
Sorghum-sudan 43 219 290 116 80
S + Nemacur 69 1 207 65 117
Cowpea 72 41 3 73 97
+ Nemacur 72 0 2 12 99
Weeds 65 61 339 122 89
+ Nemacur 69 0 167 52 99
Hairy indigo 74 18 147 200 120
+ Nemacur 76 0 68 75 118
Fallow 67 12 17 59 88
+ Nemacur 72 0 1 20 80
LSD .05 12 N.S.
pounds per plot (cabbage, 95 sq. ft.; cucumbers, 190
bAverage number of nematodes extracted
from 100 cc of
cabbage 12 weeks