EVALUATION OF LOCAL AND EXOTIC BRASSICA COVER CROPS FOR
NEMATODE CONTROL ON SUBSEQUENT CANTALOUPE
J. A. J. Desaeger, A. S. Csinos
University of Georgia
Dept. of Plant Pathology
P.O. Box 748
Tifton, GA 31793
Introduction
Many plants produce compounds called allelochemicals that directly or indirectly
impact their biological environment. Glucosinolates (GSLs) are allelochemicals that
occur throughout the agronomically important Brassicaceae (Cruciferae) family. There is
sufficient evidence to suggest that glucosinolates contained in Brassicaceae tissues
produce a variety of allelochemicals that are effective pesticides. Glucosinolate
degradation products such as isothiocyanates (ITC's) have broad-spectrum biocidal
activity, including insecticidal, nematicidal, fungicidal, antibiotic and phytotoxic effects.
For example, methylisothiocyanate (MITC) is used as a soil fumigant and is the active
pesticidal agent produced from the degradation of synthetic dithiocarbamates (e.g.,
metam sodium) and diazines (e.g., dazomet). Because isothiocyanates have pesticidal
activities and are dominant products formed from glucosinolates in soil, the use of
Brassica species and other glucosinolate-producing species to control soilborne plant
pests could be a valuable component of a methyl bromide alternatives program.
In this test we evaluated the effect of local Brassica winter crops and some exotic
Brassica crops (selected for high concentrations of glucosinolates), to control soilborne
pests and diseases on a subsequent cantaloupe plasticulture crop.
Materials and Methods
The study was located at the Gibbs Farm, CPES, Tifton, GA. The area had a
history of corn and okra. The area was prepared using all current University of Georgia
Extension Service recommendations. The plot design was a randomized complete block
design with 13 treatments and five replicates. Each plot was 50 feet long and 6 feet wide
with 15 ft alleys.
Brassica crops were: two Australian mustard cultivars (B. juncea Fumus L71 and
Fumus E75), two mustard cultivars from the Pacific US (Sinapsis alba Pacific Gold and
B. juncea Ida Gold), Ethiopian mustard (B. carinata), turnip (B. rapa 'Purple Top White
Globe'), rutabaga (B. napus, cv. ‘American Purple Top’), radish (Raphanus sativus, cv.
White Icicle’) and collards (B. oleracae var. acephala cv. Vates) rapeseed (B. rapa, cv.
Dwarf Essex) and a rapeseed (cv. Dwarf Essex) + rye (cv. Elbon) mixture. Two more
treatments consist of a rye (cv. Elbon) cover, with and without a dazomet application
(250 lbs/A) prior to laying plastic.
Brassica seeds were broadcast applied on 22 October 2003 by hand using a homemade salt shaker. Sowing density was 5 kg/ha. As per the recommendation of the
University Of Georgia Extension service, all plots received 500 lbs of fertilizer (10-1010) prior to planting winter crops. On 3 March, 2004, Brassica covers were double-cut
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with a Flail mower, fertilizer (5-10-15) applied at 750 lbs/A and plots were rototilled
three times. Dazomet was applied on designated plots using the salt shaker and all plots
were irrigated with 0.5 in of water using overhead sprinklers. All plots were covered with
plastic mulch (1 mil black polyethylene) within 2-3 hours after flail mowing. Plasticcovered plots were 50 ft long by 15 in. wide. Pathogen/pest sachets were buried in the
plots immediately following plastic laying by making a small cut in the plastic, burying
the sachets and taping up the plastic.
Cantaloupe cv. Athena seedlings (4-leaf stage) were purchased from Lewis
Taylor farms in Tifton. A single plant was transplanted using a mechanical type
transplanter, which cuts holes in the plastic just ahead of the planters in the center of the
plastic bed adjacent to the drip tape on 31 March. Plant spacing was 24 in.
Cantaloupe was side-dressed with urea (34-0-0 @ 200 lbs/A) at 3 weeks after
planting. All plots were sprayed with Bravo 720 (2 pts/A on April 16, 28 and May 14),
Quadris (11 oz/A on May 7) for control of foliar diseases, and Avaunt (3 oz./A on April
16), Lannate (1.5 pt/Aon April 28 and May 7) and Asana XL (9 oz./A on May 14) for
insect control. Weeds, mostly Texas Panicum, were sprayed with Round-Up (1 Qt/A on
April 22), using a hooded sprayer between mulched beds and Poast Plus (1 pt/A on May
14).
Stand counts and plant vigor ratings of cantaloupe were done on 28 April and 12
May. Plant vigor was rated on a 1 to 10 scale, 10 representing live and healthy plants and
1 representing dead plants. Fresh plant weights were recorded on 20 May (at flowering
stage).
Twelve cores of soil, 2.5-cm-diam × 25-cm-deep, were collected from the center
of each plot before planting brassica’s (22 October), at harvest of brassica’s (3 March),
and at planting (March 31) and harvest (28 June) of cantaloupe. Nematodes were
extracted from a 150-cm3 soil sub-sample using a centrifugal sugar flotation technique,
except at planting when they were extracted in Baermann pans (to capture only active
nematodes). On 20 May (at flowering stage) an early root gall evaluation was done on
four plants per plot using a 0 to 10 scale, whereby, 0 = no galls, 1 = very few small galls,
2 = numerous small galls, 3 = numerous small galls of which some are grown together, 4
= numerous small and some big galls, 5 = 25 % of roots severely galled, 6 = 50 % of
roots severely galled, 7 =75 % of roots severely galled, 8 = no healthy roots but plant is
still green, 9 = roots rotting and plant dying, 10 = plant and roots dead. Again following
final harvest on 28 June ten plants per plot were evaluated for root galls using that same
scale.
All cantaloupe fruits were hand-harvested from the 30-ft center area of each bed
(15 plants per plot). Each harvest was separated into marketable and cull fruits, counted,
and weighed. There were a total of three harvests, on 14, 22 and 28 June.
All data collected was analyzed with an analysis of variance (P = 0.05) and means
were separated using Duncan's Multiple range test.
Summary
All Brassica winter covers crops showed excellent growth and high biomass
production (Table 2). Root-knot nematode pressure was high and root galls were
observed especially on radish and mustard IdaGold. However, no or very few root-knot
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nematodes were extracted from roots (Table 2). Highest build-up of root-knot nematodes
in the soil was observed following all mustard species, except Fumus L71, and following
turnip (Table 3). Ring and stubby root nematodes were found in low numbers and freeliving nematodes were largely similar among cover crops.
Root-knot nematode soil populations at plant of cantaloupe ranged from 10
(dazomet) to 214 root-knot nematodes / 150 cc soil (Table 4). Root-knot nematode
pressure on cantaloupe was high and root gall indices (GI) (0-10) ranged from 5.5 to 7.9
at 3 weeks after planting (WAP) and from 9.4 to 10 at 7 WAP (Table 6). At harvest rootknot nematode populations ranged from 534 (dazomet) to 2716 (turnip) root-knot
nematodes / 150 cc soil (Table 5).
Plant vigor at 1 WAP was significantly less following dazomet, probably due to
phytotoxicity (Table 6). At 2 WAP, plant vigor ratings were similar among treatments.
Cantaloupe yields were significantly affected by root-knot nematode. Lowest yields were
recorded following mustard Pacific Gold and highest yields following dazomet (fruit
number) and radish (fruit weight) (Tables 7, 8).
Acknowledgments
The authors wish to thank Jimmy Laska, Chris Williamson, Unessee Hargett, Don
Hickey, Lewis Mullis and Bryan Horton for technical support.
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Table 1. Populations of plant-parasitic and free-living nematodes at planting of Brassica’s, fall 2003, Gibbs Farm,
Tifton, GA.
Cover crop
Mustard Fumus L71
Plant-parasitic nematodes / 150 cc soil
Free-living nematodes / 150 cc soil
Root-knot
B’vores
Ring
2
Stubby
Total
156
446
F’vores
O’vores
Total
864
100
1098
64
166
146
1130
1308
Mustard Fumus E75
120
356
8
18
12
Mustard Pacific Gold
132
4
22
190
564
84
88
736
Mustard Ida Gold
262
10
22
330
510
80
90
680
Mustard Ethiopian
307
18
10
403
916
86
128
1130
Turnip Purple Top White Globe
122
2
12
186
532
66
144
742
Rapeseed Dwarf Essex
222
8
22
322
672
56
168
896
Rapeseed + Rye
236
10
18
322
942
52
164
1158
Rutabaga
118
24
24
202
660
106
154
920
Radish White Icicle
350
8
12
410
728
80
138
946
Collards
222
10
26
264
672
72
136
880
Rye
322
10
18
398
638
72
145
1043
Root-knot nematodes (Meloidogyne spp.); Ring nematodes (Criconemoides); Stubby root nematodes (Trichodoridae); Free-living
nematodes = non-parasitic nematodes; B’vores = bacterial-feeding, F’vores = fungal-feeding, O’vores = predatory and omnivorous
nematodes. Data are means of five replications. Means in the same column followed by the same letter are not different (P = 0.05)
according to Duncan’s multiple range test. No letters indicate non-significant difference.
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Table 2. Biomass productivity and root-knot nematode infection of Brassica’s, March 2003, Gibbs Farm Tifton, GA.
Fresh Biomass (lbs/acre)(x1000)
Root-knot nematode infection
Shoot
Root
Gall index (0-10)
Mustard Fumus L71
57.03 abc
24.20 c
81.23 bc
2.5 b
0.2
Mustard Fumus E75
Mustard Pacific Gold
Mustard Ida Gold
Mustard Ethiopian
Turnip Purple Top White Globe
Rapeseed Dwarf Essex
Rapeseed + Rye
Rutabaga
Radish White Icicle
Collards
Rye
65.74 ab
41.22 cde
17.83 g
52.19 bcd
26.70 efg
37.19 def
45.34 cde
30.33 efg
73.57 a
27.83 efg
21.74 fg
14.44 cd
15.65 cd
6.21 d
7.83 d
64.53 a
12.91 cd
16.13 cd
46.55 b
45.58 b
5.57 d
5.89 d
80.18 bc
56.87 cde
24.04 f
60.02 cd
91.23 b
50.09 def
61.47 cd
76.88 bcd
119.15 a
33.40 ef
2.1 b
1.8 b
4.3 a
0.2 c
1.6 b
0.2 c
0.3 c
2.8 b
5.4 a
0.1 c
0
1.0
0.2
0
0.3
0
0
0
0
0
0.0 c
0.8
Cover crop
Total
29.22 f
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J2/g root
Table 3. Populations of plant-parasitic and free-living nematodes at harvest of Brassica’s, spring 2004,
Gibbs Farm Tifton, GA.
Plant-parasitic nematodes / 150 cc soil
Free-living nematodes / 150 cc soil
Root-knot
Ring
Stubby
Total
B’vores
18 ab
Mustard Fumus E75
58 b
394 ab
2b
32
12
118 b
456 ab
Mustard Pacific Gold
422 a
10 ab
26
474 ab
Mustard Ida Gold
Mustard Ethiopian
434 a
394 ab
4b
12 ab
40
40
Turnip Purple Top White Globe
408 ab
0b
Rapeseed Dwarf Essex
242 ab
84 ab
Cover crop
Mustard Fumus L71
Rapeseed + Rye
Rutabaga
Radish White Icicle
238 ab
F’vores
O’vores
Total
872 ab
60 ab
786 ab
46 ab
128
122
1060 ab
954 ab
1110 a
56 ab
168
1334 a
516 a
460 ab
1144 a
996 ab
46 ab
22 ab
138
112
1328 ab
1130 ab
42
478 ab
928 ab
46 ab
154
1128 ab
0b
18
266 ab
592 b
40 ab
172
804 ab
8 ab
26
136 b
714 ab
44 ab
152
910 ab
38
316 ab
814 ab
46 ab
158
1018 ab
24 a
80 ab
8 ab
12
104 b
654 ab
34 ab
102
790 b
Collards
176 ab
8 ab
30
226 ab
882 ab
78 a
174
1134 ab
Rye
225 ab
2b
36
273 ab
598 b
43 ab
151
792 b
Root-knot nematodes (Meloidogyne spp.); Ring nematodes (Criconemoides); Stubby root nematodes (Trichodoridae); Free-living
nematodes = non-parasitic nematodes; B’vores = bacterial-feeding, F’vores = fungal-feeding, O’vores = predatory and omnivorous
nematodes.
Data are means of five replications. Means in the same column followed by the same letter are not different (P = 0.05) according to
Duncan’s multiple range test. No letters indicate non-significant difference.
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Table 4. Populations of plant-parasitic and free-living nematodes at planting of cantaloupe following incorporation of
different Brassica cover crops, spring 2004, Gibbs Farm Tifton, GA.
Cover crop
Plant-parasitic nematodes / 150 cc soil
Free-living nematodes / 150 cc soil
Root-knot
Ring
Stubby
Total
B’vores
F’vores
O’vores
Total
18
17 ab
154 ab
1
6 ab
178 ab
85 ab
1912 ab
Mustard Fumus E75
136 ab
68 ab
2388 ab
148 abc
82 abc
64 abc
2148
2600
Mustard Pacific Gold
56 ab
30
19 ab
115 ab
1690 b
60 bcd
102 ab
1852
Mustard Ida Gold
120 ab
10
36 a
172 ab
1692 b
110 abc
134 a
1936
Mustard Ethiopian
106 ab
12
8 ab
133 ab
1756 b
78 bcd
110 ab
1944
Turnip Purple Top White Globe
68 ab
20
5 ab
104 ab
2046 ab
64 bcd
99 ab
2209
Rapeseed Dwarf Essex
80 ab
8
16 ab
104 ab
1978 ab
Mustard Fumus L71
182 a
64 abcd
126 a
2286
116 ab
2166
Rapeseed + Rye
218 a
4
10 ab
252 a
1956 ab
Rutabaga
106 ab
30
19 ab
161 ab
1806 ab
126 abc
100 ab
2032
Radish White Icicle
132 ab
4
6 ab
150 ab
2164 ab
50 cd
44 bc
2258
Collards
94 ab
6
10 ab
110 ab
1654 b
70 bcd
Rye
30 b
2
20 ab
52 b
1958 ab
92 abcd
Rye + Dazomet
10 b
0
0b
10 b
3238 a
8d
138 a
1862
79 abc
2129
13 c
3259
Root-knot nematodes (Meloidogyne spp.); Ring nematodes (Criconemoides); Stubby root nematodes (Trichodoridae); Free-living nematodes = non-parasitic
nematodes; B’vores = bacterial-feeding, F’vores = fungal-feeding, O’vores = predatory and omnivorous nematodes.
Data are means of five replications. Means in the same column followed by the same letter are not different (P = 0.05) according to Duncan’s multiple range test.
No letters indicate non-significant difference.
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Table 5. Populations of plant-parasitic and free-living nematodes at harvest of cantaloupe following incorporation of
different Brassica cover crops, spring 2004, Black Shank Farm Tifton, GA.
Cover crop
Plant-parasitic nematodes / 150 cc soil
Root-knot
Ring
Free-living nematodes / 150 cc soil
Stubby
Total
B’vores
F’vores
O’vores
Total
Mustard Fumus L71
1534 ab
2b
6 ab
1542 ab
472 ab
24
86 ab
582 ab
Mustard Fumus E75
1672 ab
2b
2 ab
1690 ab
422 ab
18
44 ab
484 b
Mustard Pacific Gold
1330 ab
18 b
6 ab
1356 ab
640 ab
16
72 ab
728 ab
Mustard Ida Gold
1916 ab
42 a
4 ab
1962 ab
658 ab
46
80 ab
748 ab
Mustard Ethiopian
660 b
12 b
0b
676 b
538 ab
18
58 ab
614 ab
2716 a
2b
4 ab
2728 a
478 ab
26
36 ab
540 ab
678 b
2b
2 ab
684 b
502 ab
18
46 ab
566 ab
Turnip Purple Top White Globe
Rapeseed Dwarf Essex
Rapeseed + Rye
2024 ab
0
0b
2028 ab
516 ab
20
64 ab
600 ab
Rutabaga
1534 ab
2b
0b
1544 ab
562 ab
14
82 ab
658 ab
Radish White Icicle
1596 ab
4b
0b
1600 ab
528 ab
18
96 ab
642 ab
844 ab
4b
8a
858 ab
854 b
20
1162 ab
2b
4 ab
1168 ab
746 ab
24
56 ab
826 ab
0
0b
536 b
396 b
16
14 b
426 b
Collards
Rye
Rye + Dazomet
534 b
126 a
1000 a
Root-knot nematodes (Meloidogyne spp.); Spiral nematodes (Helicotylenchus spp.); Stubby root nematodes (Trichodoridae); Free-living nematodes = nonparasitic nematodes; B’vores = bacterial-feeding, F’vores = fungal-feeding, O’vores = predatory and omnivorous nematodes. Data are means of five replications.
Means in the same column followed by the same letter are not different (P = 0.05) according to Duncan’s multiple range test. No letters indicate non-significant
difference.
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Table 6. Plant vigor and root-gall indices of cantaloupe following incorporation of different Brassica cover crops,
spring 2004, Gibbs Farm Tifton, GA.
Cover crop
a
Plant vigor a (1-10)
Stand count
At 1week
At 2weeks
Plant weight (fresh)
At 3 weeks
Gall index b (0-10)
At 3 weeks
At 8 weeks
Mustard Fumus L71
20
8.6 bac
8.8
12.6
6.4 ba
9.9
Mustard Fumus E75
20
7.5 bdac
8.3
10.7
7.6 ba
10.0
Mustard Pacific Gold
20
8.3 bac
8.5
9.1
6.0 ba
9.9
Mustard Ida Gold
20
7.9 bdac
8
9.5
7.9 a
10.0
Mustard Ethiopian
20
8.2 bac
8.3
9.7
7.1 ba
9.6
Turnip Purple Top White Globe
20
9.2 a
9.2
12.5
6.7 ba
10.0
Rapeseed Dwarf Essex
20
8.3 bac
8.7
12.9
5.5 b
9.7
Rapeseed + Rye
20
8.6 bac
8.8
10.9
7.5 ba
9.7
Rutabaga
20
9.1 ba
9.1
11.2
6.6 ba
9.8
Radish White Icicle
20
8.7 bac
9.3
12.9
7.7 ba
9.9
Collards
20
8.3 bac
8.6
11.0
6.2 ba
9.7
Rye
20
7.5 dc
8
9.6
6.5 ba
9.4
Rye + Dazomet
20
6.8 d
11.2
5.8 ba
9.7
8.4
bb
Vigor was done a 1-10 scale with 10= live and healthy plants and 1=dead plants; Root Gall Index 0-10 scale whereby, 0 = no galls, 1 = very few small galls, 2
= numerous small galls, 3 = numerous small galls of which some are grown together, 4 = numerous small and some big galls, 5 = 25 % of roots severely galled, 6
= 50 % of roots severely galled, 7 =75 % of roots severely galled, 8 = no healthy roots but plant is still green, 9 = roots rotting and plant dying, 10 = plant and
roots dead.
Data are means of five replications. Means in the same column followed by the same letter are not different (P = 0.05) according to Duncan’s multiple range test.
No letters indicate non-significant difference.
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Table 7. Marketable yield of cantaloupe (number of fruits) following incorporation of different Brassica cover crops,
spring 2004, Gibbs Farm Tifton, GA.
Number of marketable fruits
Cover crop
Yield 1
Yield 2
Yield 1-2
Yield 1-3
Culls
Mustard Fumus L71
5.8 abc
14.8 cd
20.6 bcd
29.0 abc
7.2 a
Mustard Fumus E75
2.8 c
22.6 ab
25.4 abc
27.8 bc
2.4 b
Mustard Pacific Gold
4.4 abc
11.6 cd
16.0 d
20.4 c
3.6 b
Mustard Ida Gold
3.4 c
17.0 bc
20.4 bcd
23.2 bc
2.6 b
Mustard Ethiopian
4.6 abc
17.2 bc
21.8 bcd
26.4 bc
3.0 b
Turnip Purple Top White Globe
Rapeseed Dwarf Essex
7.6 ab
7.2 ab
17.0 bc
14.4 cd
24.6 abc
21.6 bcd
30.0 ab
28.4 bc
4.0 ab
5.6 ab
Rapeseed + Rye
7.2 ab
14.2 cd
21.4 bcd
25.0 bc
2.8 b
Rutabaga
8.0 a
9.6 d
17.6 cd
23.2 bc
4.6 ab
Radish White Icicle
7.8 a
14.2 cd
22.0 bcd
28.4 bc
5.6 ab
Collards
7.4 ab
16.2 bcd
23.6 bcd
29.0 abc
5.0 ab
Rye
4.4 abc
21.6 ab
26.0 ab
30.8 ab
3.6 ab
Rye + Dazomet
5.2 bac
26.0 a
31.2 a
37.6 a
2.4 b
* per 30 ft bed length
Data are means of five replications. Means in the same column followed by the same letter are not different (P = 0.05) according to Duncan’s multiple range test.
No letters indicate non-significant difference.
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Table 8. Marketable yield of cantaloupe (weight of fruits) following incorporation of different Brassica cover crops, spring
2004, Gibbs Farm Tifton, GA.
Weight of marketable fruits (lbs)
Cover crop
Yield 1
Yield 2
Yield 1-2
Yield 1-3
Culls
Mustard Fumus L71
38.6 abc
83.8 ab
122.4 ab
155 abc
29 abc
Mustard Fumus E75
Mustard Pacific Gold
Mustard Ida Gold
Mustard Ethiopian
Turnip Purple Top White Globe
Rapeseed Dwarf Essex
Rapeseed + Rye
Rutabaga
Radish White Icicle
Collards
Rye
Rye + Dazomet
17.1 c
22.6 abc
19.5 bc
29.4 abc
47.5 a
43.2 ab
46.1 a
46.4 a
45.6 a
44.4 ab
27.7 abc
32.5 abc
131.1 a
59.8 b
92.9 ab
94.7 ab
93.7 ab
82.8 ab
79.2 ab
51.1 b
141.0 a
88.3 ab
120.6 ab
149.3a
148.4 ab
82.4 b
112.4 ab
124.1 ab
141.1 ab
125.9 ab
125.3 ab
97.4 b
186.6 a
132.7 ab
148.4 ab
181.8 a
159 abc
97 c
128 bc
139 abc
160 abc
155 abc
138 abc
119 bc
209 a
157 abc
166 abc
195 ab
28 bc
20 c
23 bc
26 bc
30 ab
28 bc
25 bc
23 bc
28 bc
29 abc
31 ab
38 a
* per 30 ft bed length
Data are means of five replications. Means in the same column followed by the same letter are not different (P = 0.05) according
to Duncan’s multiple range test
No letters indicate non-significant difference.
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