Evaluation of Variety Selection and Chemicals for Nematode Control and Prevention of Hardlock in Cotton

Authors: Patrick M. Phipps, Professor, Tidewater Agricultural Research and Extension Center; J.D. Eisenback, Professor, Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech.

Publication Number 424-230, Posted August 2006

Table of Contents

Disease Incidence and Losses

Cotton yields in 2005 were projected to average 965 lb or 2.01 bales/A in Virginia. Only a few diseases caused significant damage in cotton production. Rhizoctonia damping-off, Pythium root rot, and other seedling diseases were estimated to cause a 1% loss of yield. Areas of poor stand were often associated with soil compaction by heavy rainfall immediately after planting and/or planting seed too deep. The optimum depth of planting is usually 0.25 to 0.5 inch deep. Below normal rainfall in 2005 was thought to suppress hardlock, caused by Fusarium spp. Some fields showed symptoms of hardlock in up to 16% of open bolls, but only 2 or 3 % of the total number of locks were affected. Crop damage by southern root-knot nematode, Meloidogyne incognita, was estimated at 15% in problems fields and continues to increase in plantings of cotton for 5 years or longer. No significant losses to reniform nematode, Rotylenchulus reniformis, were detected in 2005. Instances of stubby root nematode in cotton are among the most common in Virginia, but yield losses statewide are likely no more than 5%. Sting nematode continues to be highly damaging to cotton, but occurrences are usually confined to small portions of fields with coarse, sandy-textured soil. As in previous years, the Columbia lance nematode was not detected in the region in 2005.

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Seasonal Degree Days, Rainfall, and Crop Growth in 2005

Rainfall, air and soil temperatures, and cotton degreedays (DD₆₀) were recorded at hourly intervals by a Sensor Instruments Field Monitor at farm sites in Suffolk, Capron, Skippers, and Waverly. Cotton degree-days and weather summaries were reported each day for county Extension agents and growers to access at http://www.ipm.vt.edu/infonet. The data for Suffolk was collected at the Virginia Tech Research Farm at Hare Rd. in Suffolk, Va., and used to provide insight for understanding the effect of weather conditions on crop growth, development, and yield. These data and cotton growth stages were plotted on a timeline from May 1 until November 10 when the season was essentially complete (Fig 1). Normal rainfall on the timeline shows accumulations based on the 73-year mean of records from NOAA station no. 44-4044 at the Tidewater Agricultural Research and Extension Center (AREC), which is 4 miles northwest of the field trials.

Figure 1. Degree days, rainfall and crop development in 2005 at Suffolk, Va.

Rainfall in May, June, July, August, and September was 0.02, 2.18, 1.33, 3.44, and 1.86 inches below normal, respectively, and rainfall in October was 2.95 inches above normal (Table 1). Total rainfall from May through October 2005 was 21.77 inches, which was 5.88 inches below normal for the period. The summary of cotton degree-day (DD₆₀) units showed that the growing season in 2005 received a total of 2297 DD₆₀ units, which was 129 units above the average for the previous 10 years. The greatest excess of DD60 units in 2005 was recorded in July and August while other months, except May, had accumulations near or above the 10- year average. A seasonal comparison of plant growth, yield, DD₆₀ units, and rainfall since 1995 indicated that below-normal rainfall was the greatest limiting factor for cotton production in 2005 (Table 2).

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Table 1. Comparison of rainfall, peanut heat units, and cotton degree-days (DD60) over the period from 1995 to 2005.
Month	Rainfall (in.)
	1995	1996	1997	1998	1999	2000	2001	2002	2003	2004	2005	Normal1
May	4.92	4.00	2.54	2.78	1.04	5.52 4	.19	3.98	7.14	4.77	3.81	3.83
Jun	5.20	4.50	0.69	2.80	2.72	6.09	8.78	1.66	4.10	5.10	2.07	4.25
Jul	2.95	9.12	10.74	5.07	5.39	4.33	3.04	5.53	4.98	12.53	4.57	5.90
Aug	3.03	4.73	1.24	5.29	9.33	7.13	4.07	2.22	3.50	11.00	2.31	5.75
Sep	2.96	7.98	1.99	5.97	23.47	4.17	1.64	2.96	11.81	5.15	2.60	4.46
Oct	4.78	5.10	2.89	3.03	7.76	0.03	1.00	4.89	4.40	4.52	6.41	3.46
Total	23.83	35.43	20.09	24.94	49.71	27.27	22.72	21.24	35.93	43.07	21.77	27.65
1Normal is the 73-year mean of records maintained at the Tidewater AREC, Suffolk.
Month	Cotton degree-days (DD60)
	1995	1996	1997	1998	1999	2000	2001	2002	2003	2004	2005	Avg.2
May	257	246	195	274	254	318	255	271	216	395	169	268
Jun	419	459	330	442	359	466	472	513	421	426	433	430
Jul	537	502	493	544	546	451	484	645	543	523	587	521
Aug	462	423	435	509	479	442	568	564	536	427	557	485
Sep	286	320	309	398	295	311	304	373	334	320	393	323
Oct	200	118	139	136	123	144	172	162	116	100	158	141
Total	2162	2068	1900	2303	2056	2132	2255	2498	2166	2191	2297	2168
2Avg. for previous 10-year period (1995-2004).

Table 2. Relationship of total rainfall and degree-days to growth and yield of cotton in 2005.
Year	Rainfallz (in.)	Degree-days (DD60)	Pinhead square	1st flower	1st Open boll	Linty (lb/A)
1995	23.83	2162	7-Jun	10-Jul	6-Sep	703
1996	35.43	2068	11-Jun	10-Jul	5-Sep	662
1997	20.09	1900	16-Jun	15-Jul	15-Sep	587
1998	24.94	2303	12-Jun	8-Jul	1-Sep	821
1999	49.71	2056	14-Jun	13-Jul	13-Sep	697
2000	27.27	2132	12-Jun	10-Jul	10-Sep	948
2001	22.72	2255	15-Jun	13-Jul	5-Sep	922
2002	21.24	2498	17-Jun	7-Jul	2-Sep	473
2003	35.93	2166	27-Jun	18-Jul	14-Sep	831
2004	43.07	2191	4-Jun	2-Jul	30-Aug	1159
10-yr mean	30.42	2173	14 Jun	11 Jul	7-Sep	780
2005	21.77	2297	27 Jun	13 Jul	6-Sep	965x
zRainfall records for May through October at the Tidewater AREC in Suffolk, Va. yLint yields are for the City of Suffolk as reported by the Virginia Agricultural Statistics Service. xYield in 2005 is based on an estimate of statewide yield by the Virginia Agricultural Statistics Service.

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Chemical Control of Southern Root Knot Nematode in Virginia

This trial was located at Kenny Edwards’ farm on The Hall Rd. near Branchville, Va. The field site was planted to cotton each year since 2000, except for 2003 when corn was grown. The soil type was loamy fine sand that was naturally infested with southern root-knot nematode. Land was prepared for planting by ripping and bedding rows in stale beds of cotton from the 2004 season. Treatments were applied to two, 30-foot rows spaced 36 inches apart. DP451RR seed was treated with the standard fungicide mixture of Baytan, Thiram, Allegiance, and Lorsban. Gaucho seed treatments were applied by Bayer CropScience. Treatments in the field were replicated in four randomized complete blocks. Temik 15G was applied to the seed furrow at planting on 9 May, and a 12-inch band over rows during cultivation on 29 Jun. Vapam (42% metam sodium) was applied 8 inches under rows with a single chisel and bed shaper at 13 days prior to planting. A foliar spray of Orthene 97 at 6 oz/A was applied to all plots at 5 weeks after planting for thrips control. Thereafter, standard practices were followed for cotton production in Virginia. A soil elutriator and sugar flotation method were used to determine nematode populations in soil samples collected on 12 Aug. Data collection during the growing season included stand, root-knot gall ratings, plant height, flower counts, open and total bolls, and yield. Yield was determined by hand harvesting seed cotton from 6-foot sections of each row or a total of 12 feet of row in each plot on 20 Oct.

Plant populations tended to be higher in plots treated with Temik alone and Vapam plus Gaucho (Table 3). All treatments except Gaucho alone increased plant height and flower counts significantly on 26 Jul. Low to moderate counts of root-knot nematodes were found in soil on 12 Aug, and counts tended to be lower in plots treated with Temik. The intensity of root-knot galls was suppressed most by treatments with Temik banded over rows on 29 Jun. Numbers of open and total bolls among treatments on 15 Sep were not significantly different (not reported). Treatments with either Temik in-furrow, a band application of Temik on 29 Jun, or Vapam at 13 days prior to planting produced yields that were significantly higher than the untreated check and Gaucho seed treatment alone.

Table 3. Effect of seed and soil treatments on nematode control in cotton in 2005.
Treatment, ratez	Plants/fty (15 Jun)	Plant height (in.) (16 Jul)x	Flower count/12 ft of row (26 Jul)w	Root-knot juveniles in 500 cm3 soilv	Root-knot gall index (0 - 6)u	Lint yieldt (bales/A)
Untreated check	1.94 b	23.6 d	34 c	1340	5.0 a	1.38 b
Gaucho 600 FS, 12.8 fl oz/cwt (S)	1.95 b	24.9 cd	43 bc	2030	4.9 a	1.55 b
Temik 15G, 5 lb/A (F)	2.03 ab	26.2 a-c	60 a	780	3.2 c	2.11 a
Gaucho 600 FS, 12.8 fl oz/cwt (S) + Temik 15G, 5 lb/A (F)	1.89 b	27.4 ab	62 a	2690	3.4 c	2.23 a
Gaucho 600 FS, 1.32 oz a.i./100,000 (S) + Temik 15G, 5 lb/A (B)	1.95 b	27.8 a	60 a	490	1.8 d	2.11 a
Temik 15G, 5 lb/A (F) + 5 lb/A (B)	2.11 a	25.9 bc	54 ab	550	1.9 d	2.08 a
Vapam 42%, 5 gal/A (C) + Gaucho 600 FS, 12.8 fl oz/cwt (S)	2.12 a	27.8 bc	60 a	930	4.2 b	2.20 a
LSD	0.10	1.7	13	--	0.5	0.35
z S=seed treatment, F=in seed furrow at planting, B=band application on 29 Jun, C=chisel application under rows at 13 days prior to planting. yDetermined from counts in two, 30-foot rows/plot. x Data represent measurements of four plants per plot. wCounts of flowers in 6-foot sections of rows in each plot. vData are counts in composite samples of four replications of each treatment on 12 Aug. u Roots of four plants/plot were dug after harvest and scored according to the percent of roots with galls: 0=none, 1=1-10%, 2=11-25%, 3=26- 50%, 4=51-75%, 5=76-90%, 6=91-100%. t Yield of lint was determined by ginning samples of seed cotton. One bale weighed 480 lb and lint averaged 38% of seed cotton weight. Means followed by the same letter(s) in a column are not significantly different (LSD, P≤0.05). -- = data are from a composite sample of four replicates which precluded a statistical analysis.

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The Response of Cotton to Seed and In-furrow Treatments for Control of Southern Root-knot Nematode

This trial was also located at Kenny Edwards Farm on The Hall Rd. near Branchville, VA. Soil at the field site was loamy fine sand that was naturally infested with southern root-knot nematode. Cotton was grown at the site each year since 2000, except for corn in 2003. Land was prepared for planting by ripping and bedding rows in stale beds of cotton from the previous season. Personnel with Bayer CropScience applied seed treatments. The treatment with Temik 15G was applied to the seed furrow at planting on 9 May. Treatments were main plots of four 30-foot rows spaced 36 inches apart and subplots were two rows planted to ST5599BR (partially resistant to southern root-knot) and FM989BR (susceptible to southern root-knot). All seed were treated with the standard fungicide treatment of Baytan, Thiram, Allegiance and Lorsban. A foliar spray of Orthene 97 at 6 oz/A was applied to all plots on 9 Jun for thrips control. Thereafter, standard practices were followed for cotton production in Virginia. Soil samples for determining nematode populations were collected on 12 Aug and a composite sample of replications was prepared for each treatment and variety. A soil elutriator and sugar flotation method were used to process samples. Data collection included stand counts on 15 Jun, node counts on 12 Jul, plant height measurements and flower counts on 26 Jul, open and total bolls on 15 Sep, root-knot gall ratings on 19 Jun and 10 Nov, and yield on 20 Oct. Yield was determined by hand-harvesting, 6-foot sections of two rows or a total of 12 feet of row in each plot.

Stand counts averaged 1.97 and 2.05 plants/ft of row for ST5599BR and FM989BR on 15 Jun, respectively (not shown). Temik resulted in stand counts that averaged significantly higher than other treatments. No significant differences in varieties or treatments were found in numbers of nodes on 12 Jul (not shown). Temik resulted in the greatest plant height and number of flowers on 26 Jul (Table 4). Root-knot nematode populations were generally higher in the root-knot susceptible variety (FM989BR) and lowest in both varieties when treated with Temik. The numbers of open and total bolls on 15 Sep were significantly higher for ST5599BR compared to FM989BR, but no significant differences were found in treatments (not shown). ST5599BR had lower root-knot gall indices than FM989BR. Root galling was suppressed significantly by seed treatment nematicide with L1489A at 0.53 oz a.i./100,000 seed on ST5599BR on 19 Jun, and FM989BR on 19 Jun and 10 Nov. The treatment with Temik was significantly more effective than any seed treatment in suppression of root galling on both varieties on 19 Jun. Temik also resulted in a significant reduction in root galling on FM989BR, but not ST5599BR, on 10 Nov. Overall, ST5599BR produced a yield that was significantly higher than FM989BR. Temik in-furrow alone or Gaucho plus experimental seed-treatment nematicides produced the highest yield in both varieties, but differences were not significantly higher than that of the untreated or Gaucho seed treatment alone.

Table 4. Response of cotton varieties to seed and in-furrow treatments for control of southern root-knot nematode, 2005.
Variety, treatment, ratez	Plant height (in.) (26 Jul)y	Flower count/12ft of row (26 Jul)	Root-knot juveniles in 500 cm3 soil	Root gall index (0-6)w		Lind yieldv (bales/A)
				19 Jun	10 Nov
ST5599BR
Untreated check	31.3 a-c	38.5	2250	2.7 a	2.2	2.75
Gaucho 600FS, 1.32 oz a.i./100,000 (S)	28.9 c	47.0	2090	2.3 a	1.9	2.71
Gaucho 600FS, 1.32 oz a.i./100,000 (S) + L1489A 18 EC, 1.6 oz a.i./cwt (S)	32.3 ab	48.8	4430	1.5 b	2.6	2.88
Gaucho 600FS, 1.32 oz a.i./100,000 (S) + L1489A 18 EC, 0.53 oz a.i./100,000 (S)	31.8 ab	44.0	4140	1.0 b	2.1	2.46
Gaucho 600FS, 1.32 oz a.i./100,000 (S) + EXP60003B 382SC, 8 oz a.i./cwt (S)	30.6 bc	44.3	2920	1.6 b	2.0	2.78
BCROJO, 1.20 oz a.i./100,000 (S) + L1489A 18EC, 0.53 oz a.i./100,000 (S)	30.6 bc	36.8	3080	1.3 b	2.5	2.69
Temik 15G, 0.75 lb a.i./A (F)	33.6 a	52.3	1850	0.0 c	1.4	2.91
LSD	2.5	n.s.		0.7	n.s.	n.s.
FM989BR
Untreated check	22.7 d	21.5 c	3770	2.9 a	4.8 a	1.35
Gaucho 600FS, 1.32 oz a.i./100,000 (S)	24.4 bc	25.8 bc	8970	3.0 a	4.9 a	1.87
Gaucho 600FS, 1.32 oz a.i./100,000 (S) + L1489A 18 EC, 1.6 oz a.i./cwt (S)	25.2 bc	34.8 ab	2310	2.3 ab	4.5 a	2.01
Gaucho 600FS, 1.32 oz a.i./100,000 (S) + L1489A 18 EC, 0.53 oz a.i./100,000 (S)	25.9 b	32.3 ab	13,410	2.0 b	3.5 b	1.75
Gaucho 600FS, 1.32 oz a.i./100,000 (S) + EXP60003B 382SC, 8 oz a.i./cwt (S)	25.0 bc	29.8 a-c	12,290	2.4 ab	4.4 a	2.04
BCROJO, 1.20 oz a.i./100,000 (S) + L1489A 18EC, 0.53 oz a.i./100,000 (S)	23.8 cd	32.3 ab	9130	2.4 ab	4.5 a	2.20
Temik 15G, 0.75 lb a.i./A (F)	28.0 a	40.0 a	2680	0.0 c	2.4 c	1.99
LSD	1.5	10.4	--	0.7	0.6	n.s.
Variety Mean
ST5599BR	31.3	44.5 a	2966	1.5 b	2.1	2.74 a
FM989BR	25.0	30.9 b	7509	2.2 a	4.1	1.89 b
LSD	--	3.8		0.2	--	0.17
Split-plot Analysis, P (F)
Treatment	0.0306	0.3046		0.0001	0.0006	0.4735
Variety	0.0001	0.0001		0.0001	0.0001	0.0001
Treatment x variety	0.0243	0.3671		0.1335	0.0006	0.1850
zS=seed treatment, F=in seed furrow at planting. yData represent measurements of four plants per plot. xCounts are from a composite of soil samples collected across four replications of each treatment on 12 Aug. w Roots of four plants per plot were dug at each date and scored according to the percent of roots with galls: 0=none, 1=1-10%, 2=11-25%, 3=26-50%, 4=51-75%, 5=76-90%, 6=91-100%. v Yield of lint was determined by ginning samples of seed cotton. One bale of lint equals 480 lb. Means followed by the same letter(s) in a column are not significantly different (LSD, P=0.05). n.s. = not significant -- = statistical analysis not valid because of significant interaction of treatment and cultivar.

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Comparison of Avicta (A14006) on Seed to Temik 15G In-furrow for Control of Root-knot Nematode in Cotton

This trial was located at Rick Morgan’s farm on Deer Forest Rd., Suffolk, Va. Soil at the field site was Rumford loamy fine sand that was naturally infested with southern root-knot nematode. The field site was planted to peanut in 2000, and thereafter to cotton each year. Land was prepared for planting by ripping and bedding rows in stale beds of cotton from the 2004 season. Personnel with Syngenta Crop Protection applied seed treatments. Treatments with Vapam (42% metam sodium) were applied at a depth of 8 to 10 inches under bedded rows on 26 Apr. Temik 15G was applied to the seed furrow at planting on 10 May. Treatments were main plots of four, 30-foot rows spaced 38 inches apart and subplots were two rows planted to DP449BG/BR (susceptible to southern root-knot nematode) and ST5599BR (partially resistant to southern root-knot). A foliar spray of Orthene 97 at 6 oz/A was applied to all plots on 8 Jun for thrips control. Thereafter, standard practices for cotton production in Virginia were followed. Soil samples for determining nematode populations were a composite from each treatment and variety. A soil elutriator and the sugar flotation method were used to process soil samples. Data collected during the growing season included stand counts, root-knot gall ratings, plant height measurements, node counts, flower counts, and boll counts. Yield was determined by harvesting subplots with a John Deere two-row cotton harvester on 8 Nov.

Stand counts on 14 Jun were significantly different for variety, whereas the effect of treatment was not significantly different from the standard fungicide/insecticide treatments of Dynasty plus Cruiser or RTU Baytan-Thiram/ Allegiance (Table 5). No significant differences in varieties or treatments were found in nodes/plant on 27 Jul (data not shown). Differences in plant height were significant for varieties but not treatment, except for Dynasty plus A14006 seed treatment on ST5599BR. This reduction may be attributed to the absence of thrips control until the foliar application of Orthene 97 was applied on 8 Jun. Populations of root-knot nematode reached moderate to high levels in both varieties according to counts in soil samples collected on 27 Jul. Root galling was significantly higher on DP449BG/BR than ST5599BR. Treatments with Avicta (A14006) on seed, Temik in-furrow, and Vapam under rows resulted in significant suppression of root galling on DP449BG/ BR, whereas only Temik 15G in-furrow and Vapam suppressed root galling significantly on DP5599BG/ BR. No significant differences in yield were found in the comparison of varieties or treatments.

Table 5. Comparison of Avicta (A14006) on seed to Temik 15G in-furrow for control of root-knot nematode in cotton, 2005.
Variety, treatment, ratez	Plants/ft of rowy (14 Jul)	Plant height (in.)x (26 Jul)	Root-knot juveniles/ 500 cm3 soilw	Root gall index (0-6)v (14 Nov)	Lint yieldu (bales/A)
DP449 BG/BR
Dynasty CST 125FS, 0.03 mg + Cruiser 5FS, 0.34 mg/seed (S)	1.95 ab	27.4	570	4.4 a	2.65
Dynasty CST 125FS, 0.03 mg + Cruiser 5FS, 0.34 mg + A14006, 0.15 mg/seed (S)	1.91 ab	29.1	670	3.5 b	2.69
Dynasty CST 125FS, 0.03 mg/seed (S) + Temik 15G, 4 lb/A (F)	1.89 ab	28.0	520	3.2 bc	2.73
Dynasty CST 125FS, 0.03 mg/seed (S) + Temik 15G, 5 lb/A (F)	2.10 a	28.1	600	3.3 bc	2.68
Allegiance-FL, 15 g + RTU Baytan-Thiram 1.76FS, 211 g/100 kg seed (S) + Temik 15G, 5 lb/A (F)	1.78 b	27.1	1760	3.3 bc	2.38
Dynasty CST, 0.03 mg/seed + A14006, 0.15 mg/seed (S)	1.96 ab	26.6	770	3.3 bc	2.63
Vapam, 5 gal/A (C) + Dynasty CST 125FS, 0.03 mg + Cruiser 5FS, 0.34 mg/seed (S)	2.15 a	28.6	340	2.7 c	2.58
LSD	0.32	n.s.	--	0.7	n.s.
ST5599 BR
Dynasty CST 125FS, 0.03 mg + Cruiser 5FS, 0.34 mg/seed (S)	1.65	30.6 a	320	2.5 a	2.71
Dynasty CST 125FS, 0.03 mg + Cruiser 5FS, 0.34 mg + A14006, 0.15 mg/seed (S)	1.45	30.9 a	700	1.9 a-c	2.55
Dynasty CST 125FS, 0.03 mg/seed (S) + Temik 15G, 4 lb/A (F)	1.45	31.0 a	1140	1.8 bc	2.69
Dynasty CST 125FS, 0.03 mg/seed (S) + Temik 15G, 5 lb/A (F)	1.61	30.7 a	1300	1.5 c	2.83
Allegiance-FL, 15 g + RTU Baytan-Thiram 1.76FS, 211 g/100 kg seed (S) + Temik 15G, 5 lb/A (F)	1.57	30.4 a	400	1.4 c	2.80
Dynasty CST, 0.03 mg/seed + A14006, 0.15 mg/seed (S)	1.63	28.6 b	230	2.2 ab	2.53
Vapam, 5 gal/A (C) + Dynasty CST 125FS, 0.03 mg + Cruiser 5FS, 0.34 mg/seed (S)	1.63	30.1 a	250	1.3 c	2.72
LSD	n.s.	1.1	--	0.6	n.s.
Variety Mean
DP449 BG/BR	1.96 a	27.8 b	--	3.4 a	2.62
ST5599 BR	1.57 b	30.3 a	--	1.8 b	2.69
LSD	0.11	0.4	--	0.2	n.s.
Split-plot Analysis
Treatment	0.1938	0.2617	--	0.0024	0.9381
Variety	0.0001	0.0001	--	0.0001	0.1482
Treatment x variety	0.6706	0.1007	--	0.6077	0.0647
z S=seed treatment rates are active ingredient, F=in-furrow treatments are formulated product applied at planting. C=chisel application rates are formulated product applied under rows. yDetermined from counts in two, 30-foot rows/plot. xData represent measurements of four plants per plot. wCounts are from a composite of soil samples collected across four replications of each treatment on 27 Jul. vRoots of four plants per plot were dug after harvest and scored according to the percent of roots with galls: 0=none, 1=1-10%, 2=11-25%, 3=26-50%, 4=51-75%, 5=76-90%, 6=91-100%. uYield of lint was determined by ginning samples of seed cotton. One bale of lint equals 480 lb. Means followed by the same letter(s) in a column are not significantly different (LSD, P≤0.05). -- = denotes no statistical analysis was performed because counts were from a composite sample of soil from four replications.

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Response of Cotton Varieties to Southern Root-knot Nematode and Application of Temik 15G in the Seed Furrow

This trial was located in the same field as the Avicta trial at Rick Morgan’s farm on Deer Forest Rd., Suffolk, Va. A split-plot design with four, randomized complete blocks was used to assess the susceptibility of 14 varieties of cotton to southern root-knot nematode. Varieties were planted in main plots. Subplots were two, 30-foot rows treated with and without Temik 15G 5 lb/A in the seed furrow. Rows were spaced 38 inches apart. All plots were planted on 10 May. A foliar spray of Orthene 97 at 6 oz/A was applied on 8 Jun for thrips control. Thereafter, standard practices for cotton production in Virginia were followed. Yield was determined by harvesting subplots with a John Deere two-row cotton harvester on 20 Oct.

Variety and nematicide treatment significantly affected plant stands on 14 Jun, but the range was thought to be small enough to minimize any effect on other parameters measured (Table 6). Temik 15G in-furrow caused a small but significant reduction in plant stand compared to the check, but increased plant height on 13 Jul compared to the check. Populations of southern root-knot nematode were not significantly different for variety on 19 Aug, but the effect of Temik treatment was significant (P<0.0589). The incidence of root-knot galls was affected significantly by variety and nematicide treatment, and the interaction of variety and treatment was also significant. The mean root gall index for varieties was 3.4 when untreated and 2.7 with Temik in-furrow. Varieties with a root-knot score of 3 or higher without Temik in-furrow were considered susceptible, and varieties with a root-knot score of 2.5 or lower were considered partially resistant to southern root knot. Rootknot susceptible varieties included DP444BG/RR (3.1), ST4892BR (3.4), DP555BG/RR (3.9), DP445BR (3.9), DP455BR (4.1), PHY310R (4.3), ST4575BR (4.3), and DP432RR (4.3). The only variety to have a root-knot score that was indicative of partial nematode resistance was ST5599BR (2.3). Overall, Temik increased yield of lint by 0.2 bales, but the interaction of treatment and variety was also significant which indicated that varieties differed in their response to Temik. ST5599BR ranked in the high-yield category of varieties treated with and without Temik 15G.

Table 6. Susceptibility of cotton varieties to parasitism by southern root-knot nematode, and the response to application of Temik 15G in-furrow, 2005.
Treatment, rate, varietyz	Plants/ft of row (14 Jun)y	Plant height (in.) (13 Jul)x	Root-knot juveniles/ 500 cm3 soilw	Root gall Index (0-6)v	Yield (bales/A)u
Untreated
DP 434 RR	1.89 ab	21.1 ab	3615	2.6 de	2.34 cd
DP 444 BG/RR	1.68 c-e	21.5 a	3595	3.1 cd	2.49 a-d
ST 5599 BR	1.72 c-e	20.6 a-c	1868	2.3 e	2.70 a
ST 5242 BR	1.66 de	20.8 ab	4245	2.9 c-e	2.59 a-c
DP 451 B/RR	1.70 c-e	20.9 ab	3205	2.8 c-e	2.53 a-c
DP 5303 R	1.45 f	18.6 c-e	2685	2.6 de	2.25 d
DP 455 BR	1.78 b-e	19.7 a-e	3073	4.1 ab	2.43 a-d
DP 445 BR	1.82 a-d	21.5 a	3945	3.9 ab	2.64 ab
ST 4892 BR	1.45 f	19.9 a-e	3175	3.4 bc	2.41 b-d
PHY 310 R	1.73 b-e	19.9 a-e	7015	4.3 a	2.40 b-d
FM 989 BR	1.72 c-e	18.0 e	6168	2.8 c-e	2.37 b-d
DP 555 BG/RR	1.97 a	18.4 de	5343	3.9 ab	2.36 b-d
ST 4575 BR	1.64 e	19.4 b-e	4983	4.3 a	2.64 ab
DP 432 RR	1.84 a-c	20.4 a-d	1883	4.3 a	2.62 ab
LSD	0.2	2.1	n.s.	0.8	0.28
Temik 15G, 5lb/A (in-furrow)
DP 434 RR	1.65 a-c	25.8 a-c	4113	1.6 ef	2.80 a-c
DP 444 BG/RR	1.55 b-d	27.0 a	5113	1.9 d-f	2.85 ab
ST 5599 BR	1.47 c-e	24.6 bc	3925	1.3 f	2.90 a
ST 5242 BR	1.43 c-e	24.8 bc	3328	2.4 cd	2.76 a-c
DP 451 B/RR	1.53 b-d	25.8 a-c	4883	1.9 d-f	2.38 de
DP 5303 R	1.36 de	24.6 bc	5673	2.6 cd	2.19 e
DP 455 BR	1.34 de	24.3 c	3918	2.5 cd	2.43 de
DP 445 BR	1.73 ab	25.6 a-c	3393	3.0 bc	2.97 a
ST 4892 BR	1.28 e	25.9 ab	3823	3.7 ab	2.63 b-d
PHY 310 R	1.60 bc	25.6 a-c	7233	3.6 ab	2.81 a-c
FM 989 BR	1.45 c-e	22.3 c	7083	2.1 de	2.47 d
DP 555 BG/RR	1.86 a	24.7 bc	4850	3.9 a	2.55 cd
ST 4575 BR	1.44 c-e	24.7 bc	2203	3.7 ab	2.85 ab
DP 432 RR	1.72 ab	24.9 bc	3383	3.9 a	2.93 a
LSD	0.2	1.5	n.s.	0.7	0.26
Treatment Mean
Untreated	1.72 a	20.1 b	3914	3.4	2.48
Temik 15G 5 lb/A	1.53 b	25.0 a	4494	2.7	2.68
LSD	0.05	0.4	n.s.	--	--
Split-plot Analysis, P (F)
Variety	0.0001	0.0991	0.1063	0.0001	0.0001
Treatment	0.0001	0.0001	0.0589	0.0001	0.0001
Variety x treatment	0.4882	0.1263	0.7087	0.0022	0.0444
zTemik 15G was applied to seed furrow at planting. yData based on counts of plants in two, 30-foot rows/plot. xMeasurements of four plants/plot. wSoil samples were collected on 19 Aug. vRoots of four plants per plot were dug after harvest and scored according to the percent of roots with galls: 0=none, 1=1-10%, 2=11-25%, 3=26-50%, 4=51-75%, 5=76-90%, 6=91-100%. uYield of lint was determined by ginning samples of seed cotton. One bale of lint equals 480 lb. Means followed by the same letter(s) in a column are not significantly different (LSD, P≤ 0.05). n.s. = not significant. -- = statistical analysis not valid because of significant variety x treatment interaction.

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Control of Hardlock with Foliar Fungicides

Effect of Headline (BAS 500) fungicide on hardlock. The soil type was Nansemond fine sandy loam that was planted in a corn/peanut/cotton rotation at the Tidewater AREC in Suffolk, Va. Land was prepared by strip tillage into a cover crop of wheat and plots were four, 30-foot rows spaced 36 inches apart. A randomized complete block design with five replications was used. The field was planted on 4 May to DP555BG/RR at 3.5 seed/ft of row and 0.50 to 0.75 inch deep. Fungicide treatments were applied at 30 psi and 16.5 gal/A with a LeeSpider sprayer using a 12-foot spray boom and 8002VS nozzles spaced 18 inches apart. The first application was made at pinhead square (5 Jul), followed by additional sprays at early to mid bloom (21 Jul) and 10 to 50% full size bolls (15 Aug).

Plants averaged 22 inches tall with 12 nodes and 7 squares on 6 Jul when the first fungicide sprays were applied (Table 7). Flower counts/plot at the 2nd and 3rd fungicide application averaged 55 and 138, respectively. Fungicide treatments did not have a significant effect on the total number of locks/plant, the incidence of hardlock, or the number of open bolls (Table 8). Yield was not affected significantly by any treatment.

Table 7. Height, number of nodes, squares, and flowers in untreated plots at the time of application.
Rep	6 Jul			No. of flowersy
	Plant height (in.)z	No. of nodesz	No. of squaresz	21 Jul	15 Aug
I	24	11	6	48	139
II	21	13	10	90	126
II	19	10	5	18	137
IV	25	13	8	64	149
Mean	22	12	7	55	138
zDetermined from measurements of six plants per plot. yData represent total number of flowers per plot.

Table 8. Effect of foliar sprays on incidence of hardlock, earliness, and yield of cotton on 4 Nov.z
Treatment, rate/A (application date)	Total number of locks	% hard lock	Open bolls	Yieldy
				lb/A	bales/A
No fungicide	47.5	12.6	10.6	3570	3.3
BAS500 00F, 6.14 fl oz (7/5, 7/21)	55.1	10.7	12.3	3573	3.3
BAS500 00F, 9.2 fl oz (7/5, 7/21)	43.0	7.1	9.6	3657	3.4
BAS500 00F, 3.07 fl oz (7/5, 7/21, 8/21)	51.2	10.1	11.4	3781	3.5
BAS500 00F, 6.14 fl oz (7/5, 7/21, 8/21)	55.4	10.9	12.3	3615	3.4
BAS500 00F, 9.2 fl oz (7/5, 7/21, 8/21)	48.4	8.8	1.8	3642	3.4
LSD	n.s.	n.s.	n.s.	n.s.	n.s.
z Counts represent the mean of four plants/plot, and percentage of hardlock is based on the number of open bolls with one or more locules showing symptoms of hardlock. The mean number of locks was 4.5 per boll. y Weight (lb/A) includes lint + seed; bales/A are weight of lint only. Lint was 45% of total weight and 480 lb/bale. Plots were harvested on 7 Nov 2005. n.s. = not significant at P=0.05 according to Fisher’s Protected LSD.

Effect of Quadris fungicide with and without Pix Plus on hardlock. This field trial was located adjacent to the Headline fungicide trial. The soil type, variety, experimental design, and method for application of treatments were the same except four replications were used in this study. Applications of fungicide began at 1st bloom and were repeated at 14-day intervals. The study employed two rates of Quadris 2.08SC applied alone or tank-mixed with Pix Plus. When sprayed alone, Pix Plus was applied 3 days before or after the application of Quadris to minimize any potential interactions of the two products. Flower counts were made in untreated plots at the time of applications.

Flower counts at the 1st, 2nd and 3rd, application of treatments averaged 24, 63, and 146/plot, respectively (Table 9). Fungicide treatments did not have a significant effect on the total number of locks/plant, the incidence of hardlock, or the number of open bolls (Table 10). Yield was not affected significantly by any treatment.

Table 10. Effect of foliar sprays on incidence of hardlock, earliness and yield of cotton on 7 Nov.z
Treatment, rate/A (application date)	Total number of locks	% hard lock	Open bolls	Yieldy
				lb/A	bales/A
Pix Plus, 10 fl oz (7/21, 8/4) Quadris 2.08SC, 6.2 fl oz (7/18, 8/1)	43.6	9.6	9.7	3896	3.7
Pix Plus, 10 fl oz + Quadris 2.08SC, 6.2 fl oz (7/18, 8/1)	36.6	16.5	8.1	3733	3.5
Pix Plus, 10 fl oz (7/18, 8/1)	46.4	10.9	10.3	3869	3.7
Pix Plus, 10 fl oz (7/21, 8/4) Quadris 2.08SC, 9.2 fl oz (7/18, 8/1)	47.3	11.4	10.5	3954	3.7
Pix Plus, 10 fl oz + Quadris 2.08SC, 9.2 fl oz (7/18, 8/1)	40.5	9.2	9.0	3784	3.6
LSD	n.s.	n.s.	n.s.	n.s.	n.s.
z Counts represent the mean of four plants/plot, and percentage of hardlock is based on the number of open bolls with one or more locules showing symptoms of hardlock. The mean number of locks was 4.5 per boll. y Weight (lb/A) includes lint + seed; bales/A are weight of lint only. Lint was 45% of total weight and 480 lb/bale. Plots were harvested on 7 Nov 2005. n.s.= not significant at P=0.05 according to Fisher’s Protected LSD.

Response of cotton to foliar applications of Topsin fungicide for control of hardlock. This field trial was located adjacent to the Quadris/Pix Plus trial. The soil type, variety, experimental design, and method for application of treatments were the same as used in the Quadris trial. Applications of fungicide began at matchhead square or 1st bloom and were repeated at 14-day intervals. Flower counts were made in untreated plots at the time of applications.

Flower counts at the 1st, 2nd, 3rd, and 4th applications of treatments averaged 26, 64, 166, and 153/plot, respectively (Table 11). Fungicide treatments did not have a significant effect on the total number of locks/plant, the incidence of hardlock, or the number of open bolls (Table 12). Yield was not affected significantly by any treatment.

Table 11. Number of flowers in untreated plots at the time of fungicide application.
Rep	Number of flowers
	19 Jul	21Jul	1 Aug	15 Aug
I	35	64	149	137
II	30	70	177	173
II	22	57	176	152
IV	28	75	181	157
V	32	74	180	142
VI	8	44	131	156
Mean	26	64	166	153
z Data represent total number of flowers per plot.

Table 12. Effect of foliar sprays on incidence of hardlock, open bolls and yield on 7 Nov.z
Treatment, rate/A (application date)	Total number of locks	% hard lock	Open bolls	Yieldy
				lb/A	bales/A
Untreated check	37.9	15.3	8.4	3981	3.8
Topsin M 4.5F, 16 fl oz (7/18, 8/1)	44.3	12.8	9.8	3868	3.7
Topsin M 4.5F, 16 fl oz (7/18, 8/1, 8/15)	46.7	15.8	10.4	3918	3.7
Topsin M 4.5F, 16 fl oz (7/7, 7/21, 8/1, 8/15)	47.8	12.6	10.6	3933	3.8
LSD	n.s.	n.s.	n.s.	n.s.	n.s.
z Counts represent the mean of four plants/plot, and percentage of hardlock is based on the number of open bolls with one or more locules showing symptoms of hardlock. The mean number of locks was 4.5 per boll. y Weight (lb/A) includes lint + seed; bales/A are weight of lint only. Lint was 46% of total weight and 480 lb/bale. Plots were harvested on 7 Nov 2005. n.s.= not significant at P=0.05 according to Fisher’s Protected LSD.

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Summary: Evaluation of Variety Selection and Chemicals for Nematode Control and Prevention of Hardlock in Cotton

1. Rainfall in May, June, July, August and September was 0.02, 2.18, 1.33, 3.44, and 1.86 inches below normal, respectively, and 2.95 inches above normal in October. Total rainfall from May through October 2005 was 21.77 inches, which was 5.88 inches below normal for the period. A total of 2297 DD60 units were accumulated in the 2005 growing season or 129 units above the 10-year average from 1995 to 2004.
   
   
2. Treatments with Temik 15G 5 lb/A in-furrow, Temik 15G 5 lb/A banded at pinhead square, or Vapam 42% 5 gal/A under rows at 2 weeks prior to planting increased yields an average of 2.15 bales/A in a field infested with southern root-knot nematode at Kenny Edwards’ Farm near Branchville. Nematode damage to roots increased significantly and yield was significantly reduced in untreated plots (1.38 bales/A) and plots planted to seed treated with Gaucho Grande (1.55 bales/A).
   
   
3. In a second trial at Kenny Edwards’ farm, root galling was suppressed significantly by the seed treatment nematicide L1489A at 0.53 oz a.i./seed on ST5599BR (root-knot resistant) and FM989BR (root-knot susceptible) on 19 Jun and 10 Nov. Temik 15G was significantly more effective in reduction of root galling on FM989BR, but not ST5599BR, on 10 Nov. Overall, ST5599BR produced significantly higher yields than FM989BR. Varieties treated with Temik 15G infurrow alone or Gaucho plus experimental seed treatment nematicides produced the highest yield.
   
   
4. A field trial at Rick Morgan’s farm in Suffolk evaluated 14 varieties with and without Temik 15G in-furrow for control of southern root knot-nematode. The severity of root galling was scored from 0=none to 6=all roots severely galled. Root-gall scores above 3.0 were used to recognize susceptible varieties which included DP444BG/RR (3.1), ST4892BR (3.4), DP555BG/RR (3.9), DP445BR (3.9), DP455BR (4.1), PHY310R (4.3), ST4575BR (4.3), and DP432RR (4.3). The only variety to have a root-knot score that was indicative of nematode resistance was ST5599BR (2.3). Overall, Temik 15G increased yield of lint by 0.2 bales/A, and ST5599R ranked in the highest yield category.
   
   
5. Another trial at Rick Morgan’s farm in Suffolk compared Avicta Complete Pak seed treatment to Temik 15G in-furrow for root-knot nematode control on DP- 449BG/BR (susceptible) and ST5599BR (resistant). Treatments with Avicta on seed, Temik 15G in-furrow, and Vapam 42% resulted in significant suppression of root galling on DP449BG/BR, whereas only Temik 15G in-furrow and Vapam 42% suppressed root galling significantly on DP5599BG/BR. No significant differences in yield were found in the comparison of varieties and treatments.
   
   
6. Foliar applications of Quadris, Headline, or Topsin in three field trials did not have a significant effect on incidence of hardlock, earliness, or yield of cotton in 2005.

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Acknowledgements

The applied research described in this publication was supported by grants from the Virginia Cotton Board and private industry. The authors thank Ames Herbert, Jr., IPM Program Coordinator, Virginia Tech; Joel Faircloth, Extension cotton specialist, Virginia Tech; and Glenn Rountree, Extension agent, Isle of Wight County, for reviewing this publication. The authors also recognize Steve Byrum, Barron Keeling, and Ed Hobbs for their help in carrying out each field trial and data processing.

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