Biofumigants in Commercial Onion Production to Enhance Soil Nutrient Availability, Soil Quality, and Control of Weed, Nematode, and Disease Pests

Biofumigants in Commercial Onion Production to Enhance Soil Nutrient Availability, Soil Quality, and Control of Weed, Nematode, and Disease Pests

Summary

This progress report is for the year January 1, 2004, through December 31, 2004. Information contained herein is the compilation of data for the third and final year of this project on biofumigants in commercial onion production. The project is a three-year study. We are anticipating a no-cost extension of funding into a fourth year being available in January of 2005.

Summary 2004, third year:
Biofumigant biomass and P uptake increased with higher residual P in all years. Idagold P concentrations did not always increase from the higher P but the radish P concentrations were markedly increased with previously added P. Colonel (radish) appears to be less tolerant of low residual P than Idagold. Biofumigants did not increase P and N concentrations in onions and this was the case in most years. Mineralization of N was infrequently increased with biofumigants. Thus, they appear to have limited value as green manures for N and P nutrient cycling. Fumigation stunted early- and late- season onion growth at low soil P levels. Biofumigants had little effect on early- or late-season development, but stands and yields were reduced with biofumigants in some years. Biofumigants did not affect pink root infection early or late in the season in 2004, similar to previous years. Consequently, these biofumigants have limited potential for onion disease control.

In high lime fields, biofumigants did not raise P and N onion concentrations and had little effect on early development. Fumigation stunted early growth and tended to reduce stands. Metam sodium lowered Mycorrhizae colonization, root length and pink root severities. In low lime soils, onion yields were not significantly different. Weed control differed only among weed management programs. Fertilizer effects and interactions between fumigation and fertilization were rare, indicating that the compensation by P fertilizer for a lack of Mycorrhizae was only partial. Soil quality measurements showed no improvement except for Colonel, which improved aggregate stability over the check.

In 2002, the oilradish and mustard volunteered averaging 1.0 and 0.25 plants/yd2, respectively. In 2003, the oilradish volunteered producing a significant number of plants (35 plants/yd2). The mustard also volunteered but not in significant numbers. In 2004 the oilradish (Colonel) again volunteered. The hot mustard did not volunteer in any year. In each year volunteer biofumigants were removed by hand. Without the use of hand labor, the biofumigants would not have been effectively controlled by herbicide applications and would have been as competitive with the onion crop as many of the weeds. There were few effects of fumigant treatments on visual weed control (Table 1) or weed biomass (Table 2). In 2002, Vapam and the oil radish had higher redroot pigweed control than the fallow treatment, Vapam and the hot mustard greater common lambsquarters control than the fallow treatment, and Vapam provided greater annual grass control than all other treatments except for the mustard. The high-input herbicide program provided increased control of all species in two out of three years, although differences were significant for each species for different years. Redroot pigweed and common lambsquarters biomass data were combined across all three years. Hairy nightshade, kochia, and total weed biomass were combined across 2002 and 2004. Annual grass biomass could not be combined across years. In all years weed biomass was reduced by the high-input herbicide treatment compared to the untreated check. In most cases, the low-input herbicide treatment also reduced weed biomass compared to the untreated check. The exceptions were in 2003 where kochia, annual grass, and total weed biomass in the low-input herbicide plots was equal to those in the untreated plots.

Soil physical properties had very little improvement, and the use of biofumigants in a commercial field seemed to be detrimental to the onion crop. Commercial onion bulbs grown in 2.5- acre plots where Idagold and Colonel had been grown and incorporated had very high plate rot infections. The infections were so severe that the grower did not harvest the onions and disked them into the soil. Studies are needed to determine if the plant biomass maintains or increases the pathogen responsible for plate rot. It appears from this study that the biofumigants did support pathogen populations in some way, which then resulted in unacceptable levels of plate rot infections.

Objectives/Performance Targets

Project Background:
The objectives of this project are designed to determine if biofumigants are a viable option in rotation with commercial onions when compared to chemical fumigants. In the fall of 2001 wheat was planted in fields where this project took place. Following the wheat harvest in July and August of 2002, the ground was tilled and prepared for seeding with different biofumigants. Two fields were selected on the University of Idaho Parma Research and Extension Center. Both fields were necessary to meet the objectives of this project.

The first field (A1 site 3) was identified because the soils were calcareous and high in lime. Onions have trouble growing in these soil conditions because phosphorus availability is sometimes limited. In addition, the chemical fumigants that growers use to control pests also reduce Mycorrhizae populations, which make it harder for onions to acquire P from the soil. Two biofumigants, an oilradish cultivar “Colonel” and a mustard cultivar “Idagold,” were sub-treatments along with no chemical or biological fumigants (fallow) and chemical fumigated (metam sodium) plots. The main treatments were differing rates of P and N. Under these treatments it could be determined if biofumigants help to improve P and N availability.

The second field (M6) had calcareous silt, loam soils that were low in lime. Onions tend to grow and produce better in these soil conditions. This field was identified to determine if biofumigants could suppress weed competition. Main treatments in low lime soil were: 1- fallow, 2- metam sodium, 3- “Colonel,” 4- “Idagold,” and 5- “Sunrise,” a canola cultivar that is low in glucosinolates. It has been suggested that glucosinolates reduce pest problems in the soil. Therefore, “Idagold” and “Sunrise” were compared in this field because “Idagold” contains 245 micromoles/g and “Sunrise” contains 6 micromoles/g.

Both field locations were planted with biofumigants in August. In November of each year, the biofumigants were worked into the soil by mechanically chopping the green tissue and then rototilling the tissue 6 inches into the soil. The chemical fumigant metam sodium was also applied at this time. Two weeks following the treatment applications, the field was disked and prepared for onion planting. On March 25 the fields were planted with the yellow Spanish sweet cultivar “Vaquero.” Both fields were lifted early in September. Following two weeks of curing, the onions were topped and harvested. All onions were sorted by size with a Kerrigan onion sizer.

Accomplishments/Milestones

Results:

Objective 1 – Evaluate a mustard and oilradish cultivar for the ability to reduce onion production problems, and compare them to soil fumigated with metam sodium and not fumigated.

Evaluation and comparison of the biofumigants, fallow and chemical fumigant on onion production is best described in objectives 2 – 7 and will not be repeated here in objective 1.

Objective 2 – Evaluate summer-fall biofumigant crop effects on both P and N availability to subsequent onions.

The biofumigants, especially the oilseed radish (Colonel), tended to have higher P and N concentrations when no P was previously applied as compared to the highest P rates, probably due to greater biomass and nutrient dilution with adequate P. “Colonel” had significantly higher P and N concentrations than “Idagold” at higher P rates, but “Idagold” tended to have higher total P and N content due to greater biomass (Table 1). Mineralized N increased as the growing season progressed, and net N mineralization tended to be higher with higher available P in most years. Increased biomass with previously applied P at 225 lbs/A did not significantly affect mineralized N when compared to the same fumigation treatment at 0 lbs/A of P. The biofumigants “Idagold” and “Colonel” tended to release more N before onions were planted and in some years during the onion season than the fallow or fumigated plots (Tables 2 and 6). Onion stands were largely unaffected by biofumigants in 2004 or available P as compared to the fallow treatment. Stands were generally highest where the soil was fall fumigated using metam sodium. Early-season onion growth was stunted by the previous fall fumigation and nutrient contents were reduced. Onion plant P concentrations in June and frequently in August were significantly higher with previously applied P. Biofumigants did not affect early-season onion growth or nutrient concentrations. Previously applied P did not affect dry biomass of onions near maturity nor N and P content, except for the fumigated treatment where previous P increased plant P concentrations. Marketable yield was significantly reduced with fall fumigation at the lowest P rate in all years.

Table 1. Biofumigant production P and N content as affected by P rates. Field A1, Parma, 2004.
Fresh Dry P Content N Content
P205 Weight Weight
lb/A T/A ppm lb/A % lb/A

Idagold 0 12.8 2.65 2533 13.2 2.8 149
Mustard 50 15.4 2.65 3533 19.4 3.1 167
100 15.8 2.91 2633 21.3 3.0 172
150 16.2 3.08 2833 23.7 3.1 186

Colonel 0 9.9 1.53 2367 7.6 3.3 109
Radish 50 22.5 2.48 4867 23.8 3.6 178
100 20.0 2.93 5633 34.8 3.3 200
150 23.9 2.79 5467 29.8 3.1 172

LSD.10 8.6 0.89 1675 13.8 0.4 52
CV 37 38 17 51 14 43

Table 2. Net mineralized N in buried bags as affected by biofumigant and P rates. Field A1, Parma 2004.
March April May June July Aug. Sept.
17 14 12 9 7 4 1
P205 ppm
lbs / A
Fallow
0 24 23 29 33 43 53 52
150 23 24 28 34 45 53 60

Fumigated
0 21 26 29 33 42 49 55
150 23 25 30 35 44 53 59

Idagold Mustard
0 29 29 38 41 53 62 67
150 32 35 41 47 57 56 74

Colonel
0 28 29 34 38 47 59 64
150 37 36 45 49 58 65 79

Table 3. Early-season onion development, pink root ratings, P and N content at bulb initiation in June. Field A1, Parma, 2004.
Stand Pink Dry P Content N Content
P205 Count Root Weight
lb/A lb/A ppm lb/A % lb/A

Fallow
0 79 0.07 337 4033 1.34 3.78 12.4
150 79 0.02 863 5467 4.70 3.40 29.0

Fumigated
0 100 0.02 155 3433 0.63 3.88 6.0
150 95 0.10 1097 5033 5.52 3.57 39.1

Idagold
Mustard 0 82 0.01 375 4217 1.65 3.83 14.3
150 81 0.02 1026 4867 4.96 3.33 34.5

Colonel
Radish 0 80 0.01 449 4100 1.87 3.90 17.6
150 75 0.00 795 5367 4.24 3.50 27.9

LSD.10 12 0.08 185 586 0.9 0.5 7.5
CV 20 187 25 10 26 10 28

Table 4. Late-season onion development, pink root ratings, P and N content at tops down in August. Field A1, Parma, 2004.
Pink Dry P Content N Content
P205 Root Weight
lb/A Tons/A ppm lb/A % lb/A

Fallow
0 1.98 5.06 3883 38.8 1.95 193
150 2.02 5.98 6200 73.4 2.07 247

Fumigated
0 0.15 3.49 4183 30.3 1.80 128
150 0.75 6.38 6033 75.9 2.03 259

Idagold
Mustard 0 1.81 5.13 4083 42.6 2.02 206
150 1.79 5.70 5700 64.6 1.93 215

Colonel
Radish 0 1.81 4.70 4117 39.6 1.98 185
150 1.64 6.31 5600 71.2 2.07 261

LSD.10 0.54 1.62 1,195 12.1 0.4 55
CV 19 23 18 18 16 20

Table 5. Onion stand, yield, and grade as affected by bio-fumigant, N and P treatments. Field A1, Parma, 2004.
Stand Small Mediums Jumbo Colossal Marketable Total
P205 N Count <2" 2-3.25" 3.25-4" 4-5"
lb/A lb/A ———————————–Cwt/A———————————-

Fallow 0 0 79 12 67 337 122 459 561
0 80 80 11 104 321 80 400 523
50 0 68 7 77 292 171 462 554
50 80 86 10 66 398 264 663 761
100 0 88 9 86 394 274 668 786
100 80 89 7 76 398 280 678 797
150 0 96 6 77 375 303 678 774
150 80 61 8 45 291 267 558 635
mean 81 9 77 351 220 571 674

Fumigated 0 0 104 32 90 186 80 266 395
0 80 97 43 140 178 20 198 319
50 0 102 16 104 403 243 645 783
50 80 111 17 115 501 249 750 902
100 0 107 13 110 460 297 757 894
100 80 105 15 98 492 324 816 947
150 0 98 8 92 402 289 691 812
150 80 93 10 66 393 371 764 871
mean 102 19 101 381 239 620 740

Idagold 0 0 80 8 57 322 184 506 573
Mustard 0 80 84 15 124 339 81 420 572
50 0 61 6 50 283 205 488 558
50 80 86 9 84 411 254 665 775
100 0 70 6 57 318 295 613 703
100 80 77 8 69 319 283 602 719
150 0 95 5 66 384 352 715 822
150 80 67 3 32 254 290 544 604
mean 77 7 67 326 243 569 666

Colonel 0 0 80 10 62 357 176 534 612
Radish 0 80 79 10 77 311 155 466 562
50 0 72 8 48 271 303 574 641
50 80 92 10 79 424 284 707 828
100 0 81 5 72 363 345 708 814
100 80 72 7 61 292 294 586 685
150 0 84 6 61 303 362 666 757
150 80 67 7 61 251 340 591 579
mean 78 8 65 323 281 604 685

LSD.10 11 7 29 95 88 120 129
CV 20 70 39 29 37 21 20

Table 6. Buried bag nitrate-N as affected by biofumigant and sampling date. Field M6, Parma, 2004.
Treatments Mar 23 April 20 May 18 June 15 July 14 Aug 10 Sept 7

Fallow 38 24 29 38 44 39 58
Net change -13 5 9 6 -5 19

Fumigated 44 35 37 44 55 65 72
Net change -9 2 7 11 10 7

Colonel 45 24 30 41 55 60 62
Net change -21 6 11 14 5 2

Sunrise 47 22 24 38 43 58 60
Net change -25 2 14 5 15 2

Idagold 46 18 24 34 51 61 56
Net change -28 6 10 17 10 -5

LSD.10 6 6 5 8 16 18 8
CV 12 20 15 17 26 26 11

Objective 3 – Evaluate and compare soil properties.

Soil quality measurements were made in the weed-free treatment of the study. The addition of plant dry matter contributes to the organic matter in the soil. Organic matter is a principle component of soil structure and contributes to water-holding capacity and porosity. The organic matter was measured in each treatment to determine the contribution that the addition of green manure made to the soil. Bulk density measurements were made early in the season when the onions were 25 cm tall. The bulk density was measured on the surface 15 cm of soil using the standard core sample method. Aggregate stability was also measured using a dry sieves method. Soil aggregates were collected from the surface of the soil sieved to determine the number of aggregates at each size. Each of the samples was then sieved again to determine the difference among the sieved weights.

The addition of the green manure did not significantly influence soil bulk density or organic matter (Table 7). Soil nitrogen levels at 7-30 cm depth were significantly lower in the biofumigant treatments than the fallow treatment, likely due to the extraction of nitrogen by the biofumigant plants and the majority of nitrogen deposited in the 0-7 cm depth with the plant biomass. Colonel had significantly more phosphorus at the 0-7 cm depth than the metam sodium or fallow treatments. There were no significant differences in phosphorus levels among the treatments at the 7-30 cm depth. Potassium levels were significantly higher for Colonel and Idagold than metam sodium or fallow at 0-7 cm. Sunrise had significantly higher potassium than all other treatments at 7-30 cm depth, suggesting that biofumigants had a benefit in increasing soil potassium. Cation exchange capacities did not differ significantly among the fallow, metam sodium and the biofumigant treatments (Table 7).

Continuous green manure applications may indeed increase %OM over time. Nutrient recycling appears to occur with incorporation of the plant biomass back into the soil, both of which are, and will be, beneficial to the soil and onion production if the practices continue. However, it may take many years for the soil organic matter to increase and other beneficial soil properties to be observed.

Table 7. Soil analysis of treatments for bulk density and nutrients.
Treatment Bulk Density OM 0-7 cm N
0-7 cm P
0-7 cm K
0-7 cm CEC 0-7 cm OM 7-30cm N
7-30 cm P
7-30 cm K
7-30 cm CEC 7-30 cm
Idagold 742 2.2 58 32.5 367 30.8 1.9 17 23.8 240 30.4
Colonel 759 2.0 61 38.8 371 29.5 2.1 15 23.5 242 29.7
Sunrise 772 2.0 56 31.0 341 28.8 2.1 17 23.8 263 31.4
Metam Sodium 755 2.1 78 28.8 318 30.2 2.0 24 24.3 243 30.0
Fallow 728 1.9 63 28.5 306 30.7 2.2 29 23.8 241 31.1
LSD 46.1 0.23 25.2 7.3 37.1 1.8 0.25 8.9 2.2 16.2 1.6
OM = soil organic matter
N = soil nitrogen
P = soil phosphorus
K = soil potassium
CEC = cation exchange capacity

Objective 4 – Determine if a biofumigant crop positively or negatively impacts root populations of Mycorrhizae and Phoma terrestris (pink root).

Mycorrhizae counts were collected by taking a core of soil 6 inches deep by 2.5 inch diameter with the onion at the center. Each sample was washed on a 500 micrometer sieve to remove soil. Then the roots were washed again on a 25 micrometer sieve. The onion roots were then placed in 70% ethanol. The root density / gram of soil was calculated and the Mycorrhizae were stained and counted according to vesicular colonization and hyphal colonization. Mycorrhizae sampling dates will be given when the mycorrhizae analysis is completed.

Mycorrhizae colonization of onion roots

Mycorrhizae analysis is currently underway on the results from 2004.

Mycorrhizae results from 2002 and 2003
Vapam significantly reduced root length and Mycorrhizal colonization. Vapam fumigation also reduced shoot P concentration and shoot dry mass at various harvests, and the combination of these effects significantly reduced shoot P content at the last two harvests. Fertilizer effects and interactions between fumigation and fertilization were rare, indicating that the compensation for lack of Mycorrhizae in onion offered by P fertilizer was only partial. These results show that chemical fumigation reduces Mycorrhizae of onion and that P fertilizer is only partly effective to offset this effect in the early season. Further, the biofumigant treatments do not inhibit the growth of Mycorrhizae and are associated with early-season growth and P nutrition of onion that was essentially indistinguishable from that of the fallow treatment.

Pink Root
Pink root samples were collected on June 2 and July 26, and were estimated by placing the onions in 6 classes based on the infection of the roots. Class 1 was 0%, 2 = 1-3%, 3 = 4-6%, 4 = 7-10%, 5 = 10-15% and 6 = 16-30%. In low lime plots (field M6), pink root severity was not significantly different among the treatments (Table 8). Idagold and metam sodium had significantly less disease severity than the Colonel and Sunrise treatments. However, Idagold and metam sodium were not significantly different from the fallow treatment. In the high lime field (A1), the metam sodium (fumigated) treatment was significantly lower than the other treatments. Idagold and Colonel were not significantly different from the fallow treatment (Table 4).

Table 8. Pink Root severity on “Vaquero” onion roots in field M6.
Treatment Disease Severity Index Significance
Colonel 3.4 A
Sunrise 3.3 A
Fallow 2.8 A B
Idagold 2.4 B
Metam Sodium 2.3 B
LSD (0.05) 0.87

Objective 5 – Determine if the use of biofumigant crops in onion production has potential to reduce the use of synthetic fumigants and herbicides applied for weed control by reducing weed germination and growth.

Methods
Weed control programs included a weedy check, low herbicide inputs, high herbicide inputs, and a weed-free check. The low-input herbicide program consisted of Buctril (0.19 lb ai/acre) plus Goal (0.094 lb ai/acre) applied to 2-leaf onions on May 23, 2002, May 16, 2003, and May 3, 2004, Buctril (0.25 lb ai/acre) plus Goal (0.125 lb ai/acre) plus Poast (0.19 lb ai/acre) applied to 3- to 4-leaf onions on May 31, 2002, May 27, 2003 and May 20, 2004 and Goal (0.25 lb ai/acre) applied to 4- to 6-leaf onions on June 12, 2002, June 9, 2003 and June 3, 2004. The high-input herbicide treatment was the same as the low-input but included a preemergence application of Roundup (0.375 lb ai/acre) and Prowl (1.0 lb ai/acre) on April 2, 2002, April 7, 2003, March 26, 2004, and the addition of Prowl (0.5 lb ai/acre) to the last postemergence application on June 12, 2002, June 9, 2003, and June 3, 2004. Herbicide applications were made with a CO2-pressurized backpack sprayer calibrated to deliver 40 gpa at 30 psi pressure in 2002 and 2004. In 2003, herbicides were applied with a 4-wheeler mounted sprayer calibrated to deliver 30 gpa of water at 30 psi. Plots were 6 rows wide by 25 feet long. Weed control was evaluated using weed counts, visual weed control ratings, and weed biomass samples. Weed counts were taken from 10 feet of rows 2 and 4 in each plot on May 6, June 3, June 11, June 25, and July 24, 2002, May 13, June 8, and June 23, 2003, and April 20 and June 1, 2004. On July 29, 2002, July 11, 2003, and July 20, 2004, weed control was evaluated visually. Weed biomass samples were harvested from 5 feet of one row of each plot, separated by species, dried, and weighed on July 29, 2002, July 16, 2003, and July 19, 2004. Following sampling, weeds were removed from all plots to allow for harvesting in September. Onion stand was determined for each plot by counting the number of onions in 10 feet of rows 2 and 4. Onion yield was determined by harvesting 25 feet of the center 4 rows of each plot. In 2003, a reduction in onion stands in the first replication that was unrelated to treatment required the first replication to be removed from the analysis of onion stand and yield data.

Weed Control
In 2002, the oilradish and mustard volunteered averaging 1.0 and 0.25 plants/yd2, respectively. In 2003, the oilradish volunteered producing a significant number of plants (35 plants/yd2). The mustard also volunteered but not in significant numbers. In 2004 the oilradish (Colonel) again volunteered. The hot mustard did not volunteer in any year. In each year volunteer biofumigants were removed by hand. Without the use of hand labor, the biofumigants would not have been effectively controlled by herbicide applications and would have been as competitive with the onion crop as many of the weeds. There were few effects of fumigant treatments on visual weed control (Table 9) or weed biomass (Table 10). In 2002, Vapam and the oilradish had higher redroot pigweed control than the fallow treatment, Vapam and the hot mustard greater common lambsquarters control than the fallow treatment, and Vapam provided greater annual grass control than all other treatments except for the mustard. The high-input herbicide program provided increased control of all species in two out of three years, although differences were significant for each species for different years. Redroot pigweed and common lambsquarters biomass data were combined across all three years. Hairy nightshade, kochia, and total weed biomass were combined across 2002 and 2004. Annual grass biomass could not be combined across years. In all years weed biomass was reduced by the high-input herbicide treatment compared to the untreated check. In most cases, the low- input herbicide treatment also reduced weed biomass compared to the untreated check. The exceptions were in 2003 where kochia, annual grass, and total weed biomass in the low-input herbicide plots was equal to those in the untreated plots.

Onion Stand and Yield
While onion stand was not affected by fumigant treatment in 2003, onion stand was significantly reduced by all biofumigant treatments compared to the fallow or Vapam treatments in both 2002 (Table 12) and 2004 (Table 11). Correspondingly, onion yield was not reduced by fumigant treatments in 2003, but was significantly reduced by the three biofumigants in 2002 and 2004. It appeared that onion stand and yield were reduced because of the biofumigants that volunteered. However, the hot mustard did not volunteer in any year and yet onion stand and yield were reduced in the hot mustard plots in 2002 and 2004. This result suggests that the biofumigants are affecting the seed bed in some way that is reducing onion stand. Reductions in onion stand almost always result in reduced onion yields. Herbicide treatment did not affect onion stand in any year. Herbicide treated and hand-weeded plots yielded greater than untreated plots in all three years. Onion yields were increased with both the low- and the high-input weed control treatments compared to the untreated plots, and in 2003 onion yields were similar between the herbicide treatments and the hand-weeded check. In most comparisons in 2002 and in 2004, herbicide treatments yielded lower than the hand-weeded check. This was likely due to less-than-complete weed control in herbicide treated plots in 2002 and 2004.

Overall, the use of biofumigants did not positively affect weed control. However, the biofumigants did reduce onion stand and yield in two of the three years. Additionally, the mustard and the oilradish volunteered at varying levels in all three years becoming weeds themselves. Onion growers can not accept the negative affects caused by the biofumigants without any positive affect on weed control or suppression.

Table 9. Influence of fumigant and weed control program main effects on visual weed control, 2004. Fumigant main effects are averaged over low and high herbicide inputs. Herbicide main effects are averaged over all fumigant treatments.
Weed control
Redroot
pigweed Common lambsquarters Hairy nightshade Kochia Annual grass†
Main Effects 2002 2003 2004 2002 2003 2004 2002 2003 2004 2002 2003 2004 2002 2003 2004
——————————————————————————%——————————————————————————–
Fumigant
Fallow 72 98 80 79 100 93 78 100 95 87 90 85 72 91 84
Vapam 85 100 75 91 99 95 84 100 92 80 91 77 91 94 86
Hot mustard 78 99 86 89 99 94 87 100 95 72 89 76 79 94 83
Mustard 79 99 80 85 99 95 82 100 96 76 93 71 81 99 87
Oil radish 82 98 83 82 97 94 77 98 94 86 91 80 78 95 84
LSD (0.05) 7 NS NS 8 NS NS NS NS NS NS NS NS 11 NS NS
Weed Control
Weedy check – – – – – – – – – – – – – – –
Low input 74 98 80 76 98 91 77 99 91 65 85 72 67 92 81
High input 85 100 82 95 100 98 85 100 97 96 96 84 93 97 88
Weed free – – – – – – – – – – – – – – –
Pr >F ** * NS *** NS * * NS * *** ** NS *** ** NS
†Annual grass was a mixture of barnyardgrass and green foxtail.

Table 10. Influence of fumigant and weed control program main effects on weed biomass, 2004. Fumigant main effects are averaged over no-input, low input, and high herbicide input treatments. Herbicide main effects are averaged over all fumigant treatments.
Weed biomass
Redroot
pigweed Common lambsquarters Hairy nightshade Kochia Annual grass† Total
Main Effects 2002-2004 2002-2004 2003 2002+2004 2003 2002+2004 2002 2003 2004 2003 2002+2004
————————————————————————–lb/yd2———————————————————————————-
Fumigant
Fallow 0.14 0.12 0.24 0.06 1.10 0.34 0.23 0.43 0.32 2.05 0.99
Vapam 0.16 0.07 0.23 0.09 1.31 0.57 0.10 0.12 0.27 2.03 1.02
Hot mustard 0.13 0.13 0.22 0.04 1.30 0.23 0.07 0.41 0.42 2.26 0.77
Mustard 0.15 0.04 0.11 0.04 0.80 0.33 0.06 0.12 0.26 1.44 0.72
Oil radish 0.09 0.13 0.13 0.09 1.50 0.22 0.12 0.51 0.42 2.37 0.73
LSD (0.05) NS NS NS NS NS NS NS NS NS NS NS
Weed Control
Weedy check 0.34 0.21 0.52 0.17 1.55 0.70 0.25 0.26 0.76 3.07 1.90
Low input 0.04 0.03 0.04 0.01 1.84 0.28 0.08 0.56 0.14 2.59 0.47
High input 0.03 0.01 0.00 0.01 0.21 0.04 0.01 0.14 0.12 0.44 0.17
Weed free – – – – – – – – – – –
LSD (0.05) 0.09 0.10 0.26 0.05 1.02 0.22 0.08 0.32 0.19 1.25 0.26
†Annual grass was a mixture of barnyardgrass and green foxtail.

Table 11. Onion stand and yield as influenced by main effects of fumigant and weed control, 2002, 2003, and 2004.
Onion stand Onion yield
Main Effects 2002 2003 2004 2003 2004
—————————–no./acre—————————- —————cwt/acre————–
Fumigant
Fallow 105,064 106,920 134,541 386 717
Vapam 115,682 116,496 136,917 392 653
Hot mustard 85,165 99,650 107,588 324 570
Mustard 82,789 105,661 123,997 336 568
Oil radish 78,037 111,078 125,779 352 635
LSD (0.05) 20,754 NS 12,538 NS 80

Weed Control
Weedy check 87,853 110,354 120,522 74 0
Low input 87,437 111,387 127,175 426 788
High input 91,357 102,822 127,235 439 797
Weed free 89,725 108,286 128,126 494 930
LSD (0.05) NS NS NS 76 77

Table 12. Interaction of fumigant and weed control on total onion yields and influence of fumigant on onion stand, 2002.
Total onion yield
Fumigant Weedy check Low input High input Weed free
——————————cwt/acre—————————-
Fallow 17 555 614 737
Vapam 135 589 629 716
Hot mustard 48 345 529 579
Mustard 46 351 539 595
Oil radish 38 394 552 468
LSD (0.05) 72

Objective 7 – Disseminate information by conducting research on growers’ farms, presenting data at field days, workshops, and annual growers meetings.

This research project was presented to growers at three field days, to the Idaho Eastern Oregon Onion Research Committee, and twice at the Annual Onion Growers Meeting held in Ontario, Oregon.

As this is the third and final year of the project, the biofumigants were grown by two commercial onion growers in their fields. The first grower had extremely poor stands of the biofumigant Idagold. The seed was placed in a fertilizer cart and was only supposed to be spread over a 3-acre area. However, the fertilizer cart with fertilizer and Idagold seed was used on 15-plus acres of land. The Idagold plants were spaced too far apart for significant biomass returns to the soil and the whole field had Idagold in it, so there was no control portion of the field to compare the biofumigants.

The second grower chose to use two biofumigants, Idagold and Colonel, a non-treated section, and chemical fumigation on the remaining portion of his field. Each biofumigant and non-treated section of the field was approximately 2.5 acres. Biofumigants stands were good but growth varied according to soil fertility levels. Where the field had higher N fertilizer application, the biomass that was produced was significantly greater than other portions of the field, which had lower N application levels.

The amount of dry biomass that was worked into the soil in the fall was 1.5 tons / acre for the Idagold biofumigant and 1.6 tons / acre for the Colonel biofumigant. Stand counts, pink root, and nematodes for each of the four treatments within the grower’s field are given in (Table 13). Chemical fumigation had the highest stand counts followed by Idagold. Pink root severity data on onion roots was collected in June and July. Idagold was consistently lower in both sampling periods and was the lowest in June. Nematode counts were about the same except for Colonel (oilradish), which had a lot more pin nematodes than any other treatments.

Table 13. Onion stand counts and pink root ratings in a commercial field with biofumigants, synthetic fumigant, and no fumigation treatment.
Treatments Stand Count
05-24-04 Pink Root
06-15-04 Pink Root
07-28-04 Nematodes 06-23-04
Idagold (mustard) 118 4.8 4.5 85
Colonel (oilradish) 94 5.8 5.0 1290
No Fumigation 93 5.5 3.8 140
Chemical (metam sodium) 123 5.2 4.9 45

Whole plant tissue samples from the treatment areas were collected on June 15 and July 28, dried and weighed. Onions samples from the chemical fumigated plot had higher dry weights than the other treatments. Similar results were observed in yield of onion bulbs that were harvested on September 14 (Table 14). More plant material, onion bulbs, was collected from the fumigated plot, nearly 100 cwt more than the next best treatment (control).

Table 14. Yield and grade of onions from a commercial onion field with biofumigants, synthetic fumigant, and no fumigation treatment.
Onion Grade and Yield in cwt/acre
Treatment Medium Jumbo Colossal Super Col. Culls Total
Idagold 69.5 72.2 22.5 7 26.8 198
Colonel 51.6 94.2 26.2 10.5 17.9 200.4
No Trtmnt 82.5 73.2 28.7 4.2 28 216.6
Fumigant 37.3 85.6 132.9 43.4 13.4 312.6

Although plate rot data were not recorded, it was observed that onion bulbs from biofumigant treatments and the non-treated areas had much higher rates of plate rot than the onion bulbs grown in the fumigated soil. The fumigated onions also had more onions and larger onions with fewer culls. Plate rot was so severe that the grower did not harvest the onions from the biofumigant treatments and from the non-treated areas; instead he disked them into the soil because the problem was so severe.

The biofumigants tested in this study will not be a viable substitute for chemical fumigation in commercial onion production. Results from small plot research indicated that biofumigants did little in benefiting onion yield and grade. In fact, the yields were consistently lower, which was likely due to the poor onion stands experienced in biofumigant plots. When the study was taken into a commercial onion grower’s field, the problems persisted and new ones became apparent. Stands were again lower in the biofumigant-treated areas, and the biofumigants appeared to have increased the incidence and severity of plate rot.

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