Cultural practices to improve fresh market onion quality and profitability

2009 Annual Report for ONE09-102

Project Type: Partnership
Funds awarded in 2009: $9,969.00
Projected End Date: 12/31/2009
Region: Northeast
State: Pennsylvania
Project Leader:
Christine Hoepting
Cornell Cooperative Extension - Cornell Vegetable Program

Cultural practices to improve fresh market onion quality and profitability

Summary

Small-scale diversified fresh market growers who grow onions intensively are constantly challenged by yield losses due to bacterial bulb decay, which greatly compromise the profitability of the crop. If bacterial diseases cannot be managed, this industry will not be sustained or expanded. The focus of this project was to evaluate, demonstrate and encourage adoption of cultural tactics including plant spacing and mulch type. We worked with two grower cooperators and conducted three on-farm small-plot research trials in Pennsylvania and New York. Results showed that as planting density increased, plant size decreased, maturity hastened, bulb size decreased, and incidence of bacterial bulb decay decreased. In the NY trial, the grower standard (8” plant spacing with 4 rows per 3 ft bed) had 37% incidence of bacterial bulb decay at harvest compared to the narrow (4”) plant spacing treatments with 4 and 3 rows per bed, which had 13% and 14% bacterial bulb decay, respectively. In this trial, the colossal sized bulbs were prone to bacterial decay, and thus, the narrow plant spacing treatment with 3 and 4 rows per bed had 1.4 to 1.5 times higher yield than the grower standard. The narrow plant spacing treatment with 3 rows per bed yielded the same weight of colossal bulbs and 3.8 times more jumbo weight than the standard. In PA, we compared different mulch types and found that biodegradable black plastic had significantly lower yield than black plastic, reflective silver plastic and bare ground, due to this treatment having the lowest colossal bulb weight. We were unable to evaluate the effects of mulch type on bacterial bulb decay, because incidence was extremely low. We shared our results with 110 and 120 small-scale growers in NY and PA, respectively, via 6 educational meetings and tours, a conference proceeding and a newsletter article. We anticipate that 3-5 growers will decrease their onion planting density in 2010.

Objectives/Performance Targets

The focus of this project was to evaluate, demonstrate and encourage adoption of cultural tactics to reduce bacterial rots in small-scale intensive production of onions grown for fresh market. We evaluated the effects of plant spacing and mulch type on incidence of bacterial rot of onions, yield, bulb size and economic return.

Accomplishments/Milestones

Plant Spacing Study

Essentially, wider plant spacing produces larger plants with more leaves, thicker necks and delayed maturity. Large bushy plants are more conducive to holding water in the leaf axils and whorls, which can favor bacteria entering into the plant. Thick necks take longer to dry down and remain succulent and greener for a prolonged period of time, which provides ideal conditions for bacterial diseases to spread from the leaves into the bulb. Delayed maturity interferes with proper lodging and curing of the neck and bulbs, allowing for increased risk of bacterial infections in the leaves to spread into the bulbs. It is possible for a bacterial infection that is in a leaf to be stopped before it makes its way into the bulb, if the neck tissue is no longer conducive to its spread (i.e. the tissue is dry and not green and succulent). Since narrow plant spacing produces smaller plants with thinner, tighter necks that mature on time, theoretically, these plants would have less bacterial decay and improved storability. Two on-farm small-plot plant spacing trials were set up, one in New Holland, PA and the other in Interlaken, NY. The details of each are included in Table 1.

Results of Plant Spacing Study: Plant Size

In New Holland, PA, compared to the grower’s standard (6” plant spacing, 4 rows /bed), plants grown with narrow spacing (4” with 4 rows /bed) had significantly fewer leaves per plant by 1 and a thinner neck by 0.08” (Table 2). Treatments with wider plant spacing (10” with 3 rows per bed) had numerically more leaves per plant by 0.35 and significantly thicker necks by 0.07” (Table 2). A similar trend was observed in the trial in Interlaken, NY, where compared to the grower standard (8” plant spacing, 4 rows /bed), the treatment with narrow plant spacing (4” with 4 rows per bed) had significantly fewer leaves per plant by 0.3, 0.6 and 1.0 on Jun 1, Jun 22 and Aug 13, respectively, significantly shorter plants by 6.0 cm and 3.9 cm on Jun 1 and Jun 22, respectively, and a significantly smaller neck diameter by 0.1 inch on Aug 13 (Table 3). The wider plant spacing treatments (10 inches with 4 or 3 rows /bed) did not have significantly more leaves per plant and were significantly shorter than the grower’s standard. The lowest planting density (10” plant spacing, 3 rows /bed) had significantly thicker necks than the standard by 0.1 inch (Table 3). Oddly, the wide spacing (10”) with 4 rows per bed yielded plants that were generally smaller than the standard.

Results of Plant Spacing Study: Maturity

In New Holland, PA, compared to the grower standard, the narrow plant spacing (4”, 4 rows /bed) matured significantly earlier (% lodging on Jul 16: narrow – 86.4% vs. standard – 44.3%) while the wide plant spacing (10 inch with 4 and 3 rows/bed) matured significantly later (% lodging on Jul 16: wide – 7.5% (4 rows), 7.0% (3 rows) vs. standard – 44.3%) (Table 2). In Interlaken, NY, there were no significant differences among treatments with respect to lodging. Numerically, the treatments with wide plant spacing matured later than the standard (% lodging on Aug 13: wide – 14.2%, 24.5% vs. standard – 37.5%) (Table 3). However, the narrow plant spacing treatments also appeared to have delayed maturity compared to the standard (% lodging on Aug 13: narrow – 20.7%, 15.2% vs. Standard – 37.5%) (Table 3). The reason for this was that there was higher incidence of bolting in the narrow spacing treatments (% bolting on Aug 13: narrow 4 row – 16.4%; narrow 3 row – 7.6% vs. standard – 2.8%). The wide plant spacing treatments had very low incidence of bolting (4 row – 1.0 %; 3 row – 0.9%) (Table 3). Bolting occurs when a plant produces a seed stock, which does not lodge.

Bolting is triggered by a cold spell during a susceptible stage of development, when the diameter of the neck is about 0.25”. Our theory is that the plants in the narrow plant spacing treatments would have been smaller in size than those in the standard and wide spacing treatments at the time of a cold shock, and were susceptible to the cold, while the larger plants were resistant. Whether bolting is more likely to occur in narrow plant spacing requires more experience, however, it is suspected that the reverse could happen just as easily: larger plants grown in wide spacing may be susceptible to a cold shock that smaller plants grown in narrow spacing are resistant to.

Results of Plant Spacing Study: Bacterial Diseases

In New Holland, PA, incidence of bacterial bulb decay was extremely low, 2.2% and less, and there were no significant differences among treatments (Table 4). In Interlaken, NY, on Aug 13, there were no significant differences among treatments with respect to above ground symptoms of bacterial canker (Table 3). At harvest, the grower standard (8” plant spacing, 4 rows /bed) had 37.3% bacterial decay. The treatments with the wide plant spacing (10”) were statistically the same as the standard, although had numerically higher incidence of bacterial bulb decay with 41.5% and 53.6% in 4 and 3 rows per bed, respectively (Table 5). Incidence of bacterial bulb decay at harvest was significantly only one third as much as the standard in the narrow plant spacing treatments with 13% and 14% with 4 and 3 rows per bed, respectively (Table 5).

Results of Plant Spacing Study: Yield

In New Holland, PA, the narrow plant spacing with 4 rows per bed had the highest total marketable yield (530 lb per 100 ft bed), which was not significantly different than the narrow plant spacing with 3 rows per bed (480 lb per 100 ft bed) and the grower standard (6” plant spacing, 4 rows per bed) (Table 4). The treatments with wide plant spacing had significantly lower total marketable yield (4 rows: 350 lb per 100 ft bed; 3 rows: 330 lb per 100 ft bed) than the grower standard. In Interlaken, NY, the narrow plant spacing with 4 rows per bed also had the highest total marketable yield (510 lb per 100 ft bed), which was not significantly different than the narrow plant spacing with 3 rows per bed (460 lb per 100 ft bed) (Table 5). These yields were similar to those in New Holland, PA. In Interlaken, NY, the total marketable yield of the grower standard (330 lb per 100 ft bed) was less than it was in New Holland, PA and also significantly lower than the narrow spacing treatments, a likely reflection of 6 vs. 8 inch plant spacing in New Holland vs. Interlaken, respectively. In Interlaken, NY, the treatment with wide plant spacing and 3 rows per bed (160 lb per 100 ft bed) was significantly lower than the grower standard, and the treatment with wide plant spacing and 4 rows per bed was numerically lower (220 lb per 100 ft bed) (Table 5).

Results of Plant Spacing Study: Grade

In New Holland, PA, the majority of the yield fell into the jumbo size class, where the grower standard yielded the highest (360 lb per 100 ft bed), which was not significantly different than the narrow spacing treatments (4 rows: 300 lb per 100 ft bed; 3 rows: 340 lb per 100 ft bed) (Table 4). The treatment with wide spacing and 3 rows per bed had significantly the lowest jumbo yield in the trial (Table 4). The treatment with wide plant spacing and 3 rows per bed had significantly the highest colossal weight (152 lb per 100 ft bed). The colossal weight of the grower standard (34 lb per 100 ft bed) was not significantly different than any treatments except the wide plant spacing with 3 rows. The highest small and medium bulb weight occurred in the treatment with narrow plant spacing and 4 rows per bed (small: 83 lb per 100 ft bed; medium: 130 lb per 100 ft bed), which was significantly higher than any other treatment (Table 4).

In Interlaken, NY, colossal bulb yield was the highest in each treatment except for the narrow plant spacing with 4 rows per bed, which had the highest weight in the jumbo class (Table 5). In the colossal size class in New Holland, PA, there was a general trend that as planting density decreased, colossal bulb size increased (Table 4). This was not the case in Interlaken, NY where bacterial bulb rot occurred; instead, the grower standard and the treatment with the narrow spacing and 3 rows had the highest marketable colossal yield (270 lb per 100 ft bed), which was not significantly different than the treatment with wide plant spacing and 4 rows per bed (200 lb per 100 ft bed) (Table 5). The lowest density planting (10” plant spacing, 3 rows /bed) had significantly the lowest marketable colossal yield (130 lb per 100 ft bed), which was the same as the treatment with narrow spacing and 4 rows per bed. We suspect that the reason for this difference is because it is the large colossal bulbs that succumb to bacterial bulb decay. In the jumbo class, the narrow plant spacing with 4 rows per bed had significantly the largest yield (330 lb per 100 ft bed) in the trial, which was 6.6 times higher than the grower standard. The narrow plant spacing with 3 rows per bed yielded the same marketable colossal weight as the standard, but had significantly 3.8 times more jumbos (Table 5). Similar to the New Holland, PA site, the narrow plant spacing with 4 rows per bed had significantly higher marketable small and medium bulb weight than any other treatment (Table 5).

Results of Planting Study: Storage Evaluation

Onions were evaluated after 3 months in storage at the Interlaken, NY site. Out of storage, there were no significant differences among treatments with respect to incidence of bacterial bulb decay (Table 6). The standard had 39.5% loss due to bacterial bulb decay. Numerically, the narrow plant spacing treatments had less bacterial bulb decay (4 rows: 35.6%; 3 rows: 27.4%), while the wide plant spacing treatments had higher incidence of bacterial bulb decay (4 rows: 46.1%; 3 rows: 42.1%). The majority of the bacterial bulb decay in the narrow plant spacing treatments was secondary to these bulbs having hard necks, which was a function of these treatments bolting. Had bolting not occurred the narrow plant spacing treatments would have had virtually no bulb decay at all.

The highest marketable yield occurred in the narrow plant spacing treatments with 321 and 338 lb per 100 ft bed in 4 and 3 rows, respectively, which was significantly higher than all other treatments, and almost twice as much as the grower standard (183 lb per 100 ft bed) (Table 6). The grower standard and the wide plant spacing treatments had higher colossal weight than jumbo, while the narrow plant spacing treatments had higher jumbo weight than colossal. The highest marketable colossal weight out of storage was in the narrow plant spacing with 3 rows per bed (119 lb per 100 ft bed), which was statistically the same as the grower standard (116 lb per 100 ft bed) and wide plant spacing with 4 rows per bed (75 lb per 100 ft bed). The narrow plant spacing with 4 rows per bed had the lowest colossal weight (33 lb per 100 ft bed). The narrow plant spacing treatments had significantly more jumbo and medium weight out of storage than all others, and all but the grower standard, in the jumbo and medium bulb classes, respectively.

Mulch Type Study

An on-farm small-plot research trial was established in New Holland, PA. The grower standard consisted of black plastic with 6” plant spacing and 4 rows per 3 ft bed. It was suspected that black plastic may be creating hot temperatures that favor the development and spread of bacterial diseases. Reflective silver plastic mulch, biodegradable plastic mulch and bare ground were trialed against the standard black plastic mulch as a cultural practice to help reduce incidence of bacterial bulb decay in onions. In a previous study, it was found that the temperatures under reflective silver mulch were approximately 10?F less than under black plastic, which could be less favorable for the development of bacterial diseases. Similarly, bare ground would be expected to offer cooler soil temperatures than black plastic. Biodegradable black plastic would offer an early push to the growing season just like black plastic, but would give way to cooler soil temperatures in July as the plastic degrades.

Results of Mulch Type Study: Bacterial Disease

Fortunately, for our grower cooperator, incidence of bacterial disease in this trial was extremely low (i.e. less than 0.3%) (Table 7). Unfortunately for us, we were unable to make any conclusions from our trial with respect to using mulch type to manage bacterial diseases of onions.

Results of Mulch Type Study: Yield and Grade

The biodegradable black plastic treatment (470 lb per 100 ft of bed) had significantly lower total marketable yield than all the other treatments (Table 7). Numerically, the bare ground (523 lb per 100 ft bed) and black plastic (522 lb per 100 ft bed) had the highest total marketable yields. Numerically, the largest marketable colossal weight occurred with the reflective silver mulch (136 lb per 100 ft bed), followed by black plastic (118 lb per 100 ft bed), bare ground (94 lb per 100 ft bed) and biodegradable black plastic (77 lb per 100 ft bed) (Table 7). No significant differences occurred among treatments with respect to jumbo weight. The bare ground treatment had the highest medium weight (38 lb per 100 ft bed), which was not significantly different than black plastic (30 lb per 100 ft bed) (Table 7).

Outreach

Pennsylvania:
• Summer Field Day: approximately 50 growers toured the onion mulch and plant spacing trials
• Fall Onion Grower Meeting: preliminary results were shared with approximately 50 onion growers
• Mid-Atlantic Fruit and Vegetable Convention, Hershey, PA. February 2-4, 2010. “Onion spacing and mulch type to improve quality and profitability of fresh market onions”. (Hoepting); 54 growers in attendance.

• Hoepting, C.A. 2010. Onion spacing and mulch type to improve quality and profitability of fresh market onions. In Proceedings of the Mid-Atlantic Fruit and Vegetable Convention, Hershey, PA. February 2-4, 2010, pp. 57-59.
• Spring Onion Grower Meeting: final results will be shared with approximately 70 onion growers

New York:
• Summer Twilight Meeting in Penn Yan: approximately 50 growers heard a presentation about the research that was underway in NY and PA to use cultural practices to help reduce bacterial bulb decay in onions.
• Winter Produce Auction Meeting in Penn Yan, January 20, 2010: “Controlling bacterial rot in onions via planting density” (Hoepting); 110 growers in attendance.
• Hoepting, C.A. 2010. Onion spacing to reduce bacterial rot of fresh market onions. Veg Edge, 6(2): 12-14. Distribution approximately 500.

Impacts and Contributions/Outcomes

  • In this study alone, in Interlaken, NY, we reduced incidence of bacterial rot from 37.3% to 13-14% on 120 feet of row, which increased total marketable yield by 186 lb for a total value of $167 for Eli Stoltzfus. He is considering a slight increase in his planting density in 2010.

    In Pennsylvania, approximately 70 onion growers will consider using an alternative to black plastic mulch. In addition to the results of this study (which provide yield data only, not bacterial decay control), they will take into consideration their own experience and that of their neighbors.

    Promising results from this study led to this Research and Extension team (Hoepting, Reid and Stoltzfus) to team up with Research and Extension Plant Pathologist from Penn State, Beth Gugino, to apply for an IPM Partnership grant to continue this project in 2010 and 2011. As of March 1, 2010, this proposal is still under review. The plan is repeat the plant spacing and mulch field trials again, with some modifications to the NY trial in 2010. Then, in 2011, mulch and plant spacing interaction studies will be conducted; Extension Educators will assist growers with implementing these new cultural practices and grower adoption will be documented.

Collaborators:

Jeff Stolzfus

jeff_stoltzfus@elanco.k12.pa.us
Extension Educator
Pennsylvannia Cooperative Extension
126 Eastern School Rd
New Holland, PA 17557
Office Phone: 7173541522
Amos Lapp

Vegetable grower
139 Amishtown Rd
New Holland, PA 17557
Office Phone: 7173545178
Judson Reid

jer11@cornell.edu
Extension vegetable Specialist
Cornell Cooperative Extension Vegetable Program
417 Liberty Street
Penn Yan, NY 14527
Office Phone: 5853138912
Website: http://blogs.cce.cornell.edu/cvp/
Eli Stolzfus

Vegetable grower
3175 Munson Rd
Interlaken, NY 14847