Cultural practices to improve fresh market onion quality and profitability

Final 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
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Project Information

Summary:

Small-scale diversified fresh market growers who grow onions intensively in the Northeast U.S. are constantly challenged by yield losses due to bacterial bulb decay, which greatly compromises 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 plant spacing decreased, plant size decreased, maturity hastened, marketable yield increased, bulb size decreased, and bacterial bulb decay decreased. In the NY trial, narrow 4” plant spacing with 3 and 4 rows per bed provided 63% control of bacterial bulb decay at harvest compared to the grower standard (8” plant spacing with 4 rows per 3 ft bed). The narrow 4” plant spacing with 3 and 4 rows per bed had 1.4 and 1.5 times higher yield and net $109 and $142 more per 100 feet of bed, respectively, than the grower standard. In PA, we were unable to evaluate the effects of plant spacing and mulch type on bacterial bulb decay, because incidence was extremely low. We shared our results with 394 and 238 small-scale growers in NY and PA, respectively, via 11 educational meetings and tours, a conference proceeding and a newsletter article. Internationally, our results were presented to 160 participants at the National Allium Research Conference, and published in the trade magazine, Onion World. We anticipate that 20 growers in NY and PA will experiment with narrow plant spacing and/or an alternative to black plastic in 2011. This NESARE award enabled us to get promising results in a single year of study that in turn leveraged us an additional $219,506 in research dollars to continue our studies of bacterial diseases of onions in both small- and large-scale production. Ultimately, we will have the research base to develop a comprehensive Integrated Pest Management program for bacterial diseases of onions that will sustain the profitability of this industry in the Northeast US.

Introduction:

The challenge for small-scale diversified fresh market vegetable growers who grow onions is that the profitability of this crop has become greatly compromised by increased losses due to bacterial bulb decay. If bacterial bulb decay cannot be managed, the profitability of this industry will not be sustained or expanded.

Small-scale fresh market production of onions is intensive:

Small-scale diversified vegetable growers sell their onions, mostly sweet onions, through wholesale, produce auctions and direct markets. These lucrative markets pay $1 and more for colossal sized bulbs (>4 inches in diameter) at about $0.50 per pound. To achieve such large bulb sizes, onions are typically planted as early in the spring as possible on black plastic mulch with trickle irrigation. Typical plant spacing is 4 rows of onions on a 3 foot wide bed with 2 rows of drip tape, and plant spacing ranges from 6 to 12 inches. The black plastic mulch increases soil temperature, and thus onion growth, early in the season. Onions are harvested by hand (Figure 1). In New York, the amount of onions grown on these small farms ranges from 300 to 1500 feet of plastic beds (4 rows of onions wide) with a value of $800 to $1600 per 100 feet of row. In Pennsylvania, the amount of onions grown on these small farms ranges from 3000 to 12,000 feet of plastic or 25,000 to 100,000 plants with a value of $10,000 to $40,000 per acre. Sweet onions are a new and expanding crop in Pennsylvania within the past few years. From 2002 until 2008, the number of growers increased 11 fold from 3 to 34 in Lancaster County.

Bacterial rots are draining the profitability of fresh market onions:

During the past 5 years it has been common for the incidence of bacterial rot to be 35 to 45% in both Pennsylvania and New York. In 2008 in Pennsylvania, 34 growers lost a total of $140,000 to bacterial rot.

The sweet onion market is expanding and there is a broker in PA who would like to sell 3 times the current volume. As the “Eat Local” movement gains force throughout the Northeast, consumers are searching for local vegetables throughout the year. Unfortunately, the extreme losses fresh market onion growers are experiencing due to bacterial rot is a major deterrent for growers to increase or invest in onion production. The bacterial rot problems also prevent growers from being able to store their onions and market them throughout the winter when prices are higher, preventing them from capitalizing on the renewed interest in buying local. If bacterial rots could be managed to economically acceptable levels, small-scale fresh market growers stand to acquire a potential $1.2 million dollar sweet onion market.

Onions are plagued by a number of bacterial pathogens that cause both bulb and leaf decay in NY and PA. Sour skin, caused by Burkholderia cepacia is the most common bacterial disease of onion in NY, while the Center Rot pathogen, Pantoea agglomerans and Soft Rot pathogen, Pectobacterium caratovora, are the most common in PA. Other Soft Rot (Pseudomonas marginalis), Center Rot (P. ananatis), leaf disease (Xanthomonas axonopodis and Pseudomonas viridiflava) and Enterobacter cloaceae have also been identified.

Bacterial diseases generally first appear as leaf blights on the youngest center leaves of the plant and result in yellowing or bleaching and wilting of these leaves. The infection progresses down the leaves and neck, and eventually into the bulb. Affected bulb scales become soft and water-soaked and are yellow-brown in appearance (Figure 2). In PA, growers often harvest two or three weeks before maturity and sacrifice bulb size in an attempt to prevent leaf-borne bacteria from moving into the bulb and causing rots and storage losses. At harvest, the foliage often tears away from the bulb when pulled. At first, and often even out of storage, the decay can be hard to detect, because the outer unaffected scales remain firm, and decayed bulbs are mistakingly marketed to detriment.

Chemical tactics have failed to control bacterial rots:

Attempts have been made by several growers, to control bacterial decay in onions with copper bactericides and other chemicals such as Oxidate. For example, it has been reported in PA that weekly sprays of various bactericides starting as early as the second week in May when onion plants have just 5 leaves and continuing until the pre-harvest entry interval of the bactericide resulted in unacceptably high incidence of bacterial rot (i.e. > 30%). Some farmers face losses of over 50%. Although, bactericides may play a role in the management of bacterial rot of onion, they need to be part of an integrated management system that incorporates various cultural tactics such as plant spacing or alternatives to black plastic mulch.

Using plant spacing to reduce bacterial rots:

Small-scale fresh market onion growers use wide plant spacing (i.e. 6 to 12 inches) to produce onions with large bulbs. When plant spacing is too wide, this encourages the onion plant to produce leaves at the expense of bulbing. This growth habit results in plants with very large, bushy foliage and thick necks. It also can delay or inhibit normal maturity. Such growth habit could be favorable for development of bacterial diseases for the following reasons:

  • Large bushy leaves are more conducive to holding water in the leaf axils and whorls, which can favor initial bacterial infections.
    Thick necks take longer to dry down, thus 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, and reduced storability in general.

It is possible for a bacterial infection spreading down a leaf to be stopped in its tracks 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). Our proposed solution is to narrow plant spacing, which will produce smaller plants with thinner, tighter necks that mature on time, which are less conducive to development of bulb rots and have improved storability.

High planting density has been questioned by small-scale fresh market onion growers as a contributing factor to bacterial rots, because they wonder if planting 4 rows per bed (= 8 inch row spacing) is too dense for adequate air circulation through the canopy. It is a well known fact that leaf wetness, and water congested tissue is conducive to development and spread of bacterial diseases. Our proposed solution is to trial onions grown with 3 instead of 4 rows per bed with different plant spacings, which will increase between row aeration, minimize periods of water pooling in leaf axils and whorls, and make conditions less favorable for development and spread of bacterial diseases.

Using alternatives to black plastic mulch to reduce bacterial rots:

Black plastic absorbs sunlight, thus increasing soil temperature, which in turn, promotes early crop development of onions. However, during the heat of June and July, the warmer soil temperatures provided by the black plastic may actually be creating a more favorable environment for bacterial diseases to develop and spread. Preliminary temperature data collected by Reid in NY in 2007 showed that the daily high soil line temperature during July was approximately 10 ?F cooler under reflective silver mulch than it was under black plastic. This could be the difference between optimum and below optimum temperatures for bacteria to grow. Bare ground may also provide a cooler microclimate that is less favorable for bacterial diseases to develop, and biodegradable black plastic may provide a growth push early in the season, but then give way to cooler bare ground as the mulch degrades.

Project Objectives:

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

Cooperators

Click linked name(s) to expand
  • Amos Lapp
  • Judson Reid
  • Eli Stolzfus
  • Jeff Stolzfus

Research

Materials and methods:
Plant Spacing Study

Project Design: Two small-plot on-farm trials were conducted, one in New Holland, PA and the other in Interlaken, NY. One wider and one narrower plant spacing was compared to the grower cooperators’ standard plant spacing, which were each evaluated with 3 and 4 rows per bed (Table 1). The standard spacing was evaluated with the standard row spacing of 4 rows per bed (Figure 3). The trials were set up as a randomized complete block design with 5 treatments and 4 replications. Each treatment replicate was 1 bed wide (3 feet) by 15 feet long. In each location, the grower cooperators’ standard mulch type (PA – black plastic; NY – reflective silver plastic) and variety (PA – Candy; NY – Nebula) were used. Hole poking tools were fabricated for 4”, 6”, 8” and 10” spacings and the different planting configurations set up by hand with the holes between rows at right angles to each other (Figure 4). In PA, the transplants were bare roots imported from Texas, and in NY, they were greenhouse-grown plug plants. The trials were planted by hand, one plant per hole, on April 16th and 17th , 2009 in PA and NY, respectively.

Plant size: In PA, 10 randomly selected plants per replicate were measured for neck diameter and number of leaves per plant counted at harvest on July 16, 2009. In NY, the number of leaves per plant from 10 randomly selected plants per replicate were counted on June 1st, 22nd, and August 13th. Plant height measurements of the tallest leaf were also taken on June 1st and 22nd and neck diameter measured on August 13th. Incidence of bolting was calculated on August 13th by counting the number of plants that had bolted and then dividing by the total number of plants per replicate.

Maturity: Percent lodging was visually estimated per replicate on July 16th and August 13th in PA and NY, respectively.

Yield and bulb size: All of the onions within the inside 10 feet of bed were pulled, topped, sized, counted and weighed on July 16th in PA. In NY, all of the onions within the 15 foot replicate were pulled on August 25th and windrowed. On September 14th, they were topped, sized, counted and weighed. The different harvest techniques reflect the differences in grower practices in the two locations. Bulb size distribution included small (< 2.5”), medium (2.5 to 3”), jumbo (3-4”) and colossal (> 4”).

Bacterial decay: On August 13th in NY, incidence of foliar symptoms of bacterial disease was determined by counting the number of plants showing symptoms and dividing by the total number of plants per replicate. At harvest, all bulbs with bacterial decay were graded out and weighed in both locations. A few representative bulbs were sent to Dr. Steve Beer’s lab, Plant Pathologist at Cornell University, for identification of pathogens present. In NY, all sound bulbs at harvest were put into the grower cooperator’s cold storage, and graded for bacterial decay after 3 months in storage on December 16th, again, to represent local grower practices.

Statistics: Statistical differences among treatments was determined by General Analysis of Variance (ANOVA) with mean separation by Fisher’s Protected LSD test, ? = 0.05.

Economic analysis: For each treatment, the only variable input cost was the cost of transplants, because higher density plantings with the narrower plant and row spacing had more plants. All other input costs were fixed. We asked the growers to provide us with their costs for transplants and the average price that they receive for each bulb size. We used our yield and bulb size distribution data from the research trials and the prices that our growers provided to determine gross income and then deducted the cost of transplants for the net economic return. In PA, growers sell their onions wholesale through a cooperative and receive higher prices for larger sized bulbs, and they cannot sell more than 30% of their marketable weight as small and medium sized bulbs. In NY, our grower cooperator sold his onions through a roadside stand and received a fixed price for all bulb sizes, but could not sell any small bulbs (< 2.5”).

Alternatives to black plastic mulch study

Project design: This study was set up as a small-plot on-farm research trial in PA only, because in NY, previous work by Hoepting and Reid (2006) showed higher yields with silver reflective mulch, which has become the growers’ standard in this area. Treatments included black plastic mulch as the grower standard, reflective silver plastic mulch, biodegradable black plastic and no mulch (bare ground). Herbicides, Prowl H2O (8 fl oz) and Goal Tender (24 fl oz) were applied once to the bare ground treatment for control of weeds. The grower cooperator laid the mulches using their standard equipment. We used the grower’s standard planting configuration of 6” plant spacing and 4 rows per bed and the grower planted by hand bare root sweet transplants (cv. Candy) that were imported from Texas on April 7th. Each treatment was replicated 4 times. Each treatment replicate was 1 bed wide (3 feet) by 15 feet long.

Plant size: Height of the tallest leaf of 10 randomly selected plants per replicate was measured on May 5th and 22nd.

Yield and bulb size: All of the onions in the entire 15 feet of bed per replicate were pulled and topped by the grower cooperator prior to July 16th when we sized and weighed them, as described for the spacing trial.

Bacterial decay: During sizing, all bulbs with bacterial decay were graded out, counted and weighed.

Statistics: As described above for plant spacing project.

Economic analysis: For each treatment, the only variable input cost was the cost of plastic mulch and herbicides for the bare ground treatment, while all other input costs were fixed. We asked the growers to provide us with their costs for mulch and herbicides and the average price that they receive for each bulb size. We calculated net economic return by subtracting the variable input costs of mulch and herbicides.

Research results and discussion:
Plant Spacing Study

Plant Size: In general, as plant spacing decreased and planting density increased, plants had fewer leaves and thinner necks that matured earlier. 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 1 fewer leaf per plant and a 0.08” thinner neck (Table 2). Treatments with wider 10” plant spacing had numerically more leaves per plant and 10” plant spacing with 3 rows per bed had 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” with 4 or 3 rows /bed) did not have significantly more leaves per plant, but 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).

Maturity: In general, as plant spacing decreased and planting density increased, maturity hastened with increased risk of bolting. 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” 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.

Bacterial Disease: In general, as plant spacing decreased and planting density increased, bacterial disease decreased. In New Holland, PA, at harvest, incidence of bacterial bulb decay was extremely low, 2.2% and less, and there were no significant differences among treatments. Numerically, the narrow plant spacing provided 62% and 67% control with 4 and 3 rows per bed, respectively (Table 4). In Interlaken, NY, on Aug 13, there were no significant differences among treatments with respect to above ground symptoms of bacterial canker, although numerically, the narrow plant spacing treatments had 2.4 (4 rows) and 3.5 (3 rows) times less foliar symptoms of bacterial canker than the standard (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, representing 63 to 64% control (Table 5, Figure 5).

Yield: In general, as plant spacing decreased and planting density increased, marketable yield increased. 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 marketable yield in the wide plant spacing with 3 rows per bed (160 lb per 100 ft bed) was significantly lower than the grower standard, and wide plant spacing with 4 rows per bed was numerically lower (220 lb per 100 ft bed) (Table 5).

Bulb size: 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 wide spacing with 3 rows per bed had significantly the lowest jumbo yield in the trial (Table 4). The wide plant spacing with 3 rows per bed had significantly the highest colossal weight (152 lb per 100 ft bed) of all treatments. 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 narrow plant spacing with 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 and had 4.4 and 2.2 times more small and medium bulbs, respectively than the standard (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 narrow spacing with 3 rows had the highest colossal yield (270 lb per 100 ft bed), which was not significantly different than the wide plant spacing with 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 narrow spacing and 4 rows per bed. We suspect that the reason for this difference was because it is the large colossal bulbs that succumb to bacterial bulb decay. In the jumbo class, 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 small and medium bulb weight than the standard by 10 times and 6 times, respectively (Table 5).

Storage: 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 out of storage 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 weight, 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 weight out of storage than all others. Only narrow spacing with 4 rows per bed had significantly higher medium weight than the standard (Table 6).

Alternatives to black plastic study

Plant size: On May 8th, the black plastic had significantly the tallest plants (11.5”), followed by biodegradable black plastic (10.8”), which were significantly taller than the reflective silver (9.7”) and bare ground treatments (9.5”) (Table 7). This is likely a function of the black plastics absorbing more heat from the sun and giving these plants a slight growth push early in the season. On May 22nd, black plastic still had the tallest plants (20.6”), which were not significantly taller than the biodegradable black (20.3”), but were significantly taller than reflective silver plastic (16”). Bare ground had significantly the shortest plants (13.7”) (Table 7).

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. However, in a trial conducted in 2010 at this site, reflective silver plastic, biodegradable black plastic and bare ground provided 59%, 71% and 75% control of bacterial bulb decay, respectively (Figure 6). in this same trial, the onions grown on reflective silver mulch and biodegradable black plastic had significantly higher yield than those grown on black plastic (data not shown).

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 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). These results are curious to us, because it is not known why the biodegrable black plastic had the lowest yield and the bare ground treatment had one of the highest yields, because our plant data suggests the opposite. It would have been beneficial to have plant size information closer to harvest.

Research conclusions:
  • In this study alone, in Interlaken, NY, we reduced incidence of bacterial decay at harvest 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 our grower cooperator.

    As a result of exposure to our presentations and newsletter articles about this project, two small-scale diversified fresh market vegetable growers in NY indicated to Hoepting that they were going to grow their onions on silver plastic in 2011. Both of these growers were previously growing their onions on bare ground, which yields less than when onions are grown on silver plastic. In 2011, in PA, 15 growers plant to experiment with silver mulch on their farms.

    Promising results from this study led to Hoepting, Reid and Stoltzfus to team up with Research and Extension Plant Pathologist at Penn State, Beth Gugino, to successfully receive a Northeast-IPM Partnership grant ($39,718) to continue this project in 2010 and 2011 in both NY and PA. In 2010, spacing trials were repeated in PA and NY with some modifications to the NY trial, and the mulch trial was repeated in PA. The spacing trials consistently showed that narrow 4” plant spacing controlled bacterial bulb decay by 53 to 64% compared to the growers’ standards, which increased the net economic return by $43 to $258 per 100 feet of bed. The alternatives to black plastic (reflective silver, biodegradable black plastic and bare ground) reduced bacterial bulb decay by 59 to 75%, which resulted in an increased net return of $96 to $215 per 100 feet of bed compared to black plastic.

    While working on this project in PA, we observed a significant block effect where the block located at the bottom of a slope had 83% bacterial bulb decay at harvest, while the block located at the top of the slope had only 17%. The field was heavily manured, which is common practice on plain-sect farms. Presumably, nitrogen leached to the bottom of the slope where it favored the development of bacterial disease. This observation and several others lead to the suspicion that there is a relationship between high fertility, especially nitrogen, and increased bacterial disease that warrants further investigation. Consequently, Hoepting and Gugino teamed up with Cornell University Plant Pathologist, Steve Beer, and were successfully awarded a Northeast IPM Competitive grant ($179,788) to investigate this relationship and to identify other factors that favor bacterial diseases in onions in 2011 and 2012.

    The trade magazine, Onion World, which has international distribution, published an article on this project. As a result, we received much interest from large-scale commercial onion growers regarding the effects of plant and row spacing on bacterial disease in their operations where onions are predominantly directly seeded at much higher planting densities. It became clear that the feasibility of using narrow plant and/or row spacing as a management strategy for bacterial diseases in large-scale onion production also needed to be investigated. Consequently, Hoepting and Beer recently applied for a USDA Pest Management Alternatives Program grant to address this very issue.

    The $9,969 that we were awarded from NESARE enabled us to get promising results in a single year of study that in turn leveraged us an additional $219,506 ($443,863 if we get the PMAP grant) in research dollars to study bacterial diseases of onions in both small- and large-scale production. Essentially, for every $1 of NESARE money that we received, we leveraged an additional $22($44 if we get the PMAP grant) in additional research dollars to study bacterial diseases of onions.

    After two years of very encouraging research results, we are now encouraging grower adoption of our plant spacing recommendations. In 2011, we anticipate to have at least 15 small-scale onion growers experiment with narrow row spacing on their farms in NY and PA.

    We anticipate that within the next five years, we will have the research base to develop a comprehensive Integrated Pest Management Program for managing bacterial diseases in onions. Grower adoption of our sound recommendations will dramatically reduce losses from bacterial bulb decay and increase profitability, acreage of intensively managed sweet onions will increase, more locally grown produce will be available to the consumer and the small-scale onion industry will be sustained.

Participation Summary

Education & Outreach Activities and Participation Summary

Participation Summary:

Education/outreach description:
Publications
  • 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.
    Hoepting, C.A. 2010. Onion spacing to reduce bacterial rot of fresh market onions. Veg Edge, 6(2): 12-14. Distribution approximately 500.
    Hoepting, C.A. 2010. onion spacing to reduce bacterial rot of fresh market onions. Muck and Mineral, May 2010L 1-3. Distribution approximately 500.
    Hoepting, C.A., K.E. Klotzbach, J.E. Reid and B. K. Gugino. 2010. Using cultural practices to manage bacterial diseases and increase profitability of fresh market onions in the Northern United States. In Program and Proceedings of the 2010 National Allium Research Conference, Reno, NV. USA. December 8-10, 2010: http://www.unce.unr.edu/adhoc/narc2010/files/pdf/2010NARCConferenceProgram.pdf.
    As a result of exposure at the National Allium Research Conference, this project was picked up by the trade magazine, Onion World: Using cultural practices to manage bacterial diseases and increase profitability, January 2011, pp. 10 – 14. (Hoepting, Klotzbach, Reid and Gugino). Distribution: international.
Outreach

Outreach – Pennsylvania:
  • Summer Field Day, New Holland, PA, June 30, 2009: approximately 50 growers toured the onion mulch and plant spacing trials (Stolzfus, Gugino)
    Fall Onion Grower Meeting, October 14, 2009: preliminary results were shared with approximately 50 onion growers (Stolzfus).
    New Holland Vegetable Meeting, New Holland, PA, January 18, 2010: “Onion disease management”; 70 growers (Gugino).
    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”. 54 growers in attendance (Hoepting).
    Spring Onion Grower Meeting, New Holland, PA, March 4, 2010: final results were shared with approximately 70 onion growers (Stoltzfus).
    Summer Onion Grower Twilight Meeting, New Holland, PA, June 28, 2010: spacing and mulch trials (not funded by NESARE) were viewed by approximately 50 growers (Stolzfus).
    Fall Onion Grower Meeting, New Holland, PA, September 29, 2010: combined results of 2009 and 2010 trials shared with approximately 50 onion growers (Stolzfus).
Outreach – New York:
  • Summer Twilight Meeting in Penn Yan, NY, July 24, 2009: 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 (Hoepting).
    Winter Produce Auction Meeting in Penn Yan, January 20, 2010: “Controlling bacterial rot in onions via planting density”; 110 growers in attendance (Hoepting).
    Capital District Vegetable and Small Fruit Growers Winter Meeting, Albany, NY. March 10, 2010: 66 growers learned about growing onions on plastic mulch including how plant spacing and mulch type can reduce bacterial bulb decay (Hoepting).
    Onion/Produce Twilight Meeting, Panama, NY, August 24, 2010: 12 growers learned about managing bacterial rot using narrow plant spacing and mulch type (Hoepting).
Outreach – International:
  • 2010 National Allium Research Conference, Reno, NV. USA. December 8-10, 2010: Using cultural practices to manage bacterial diseases and increase profitability of fresh market onions in the Northern United States. 160 attendees (Hoepting).

Project Outcomes

Project outcomes:
Plant Spacing Study

Variable pricing: Using the PA Simply Sweet variable pricing structure, growers would receive higher prices for the larger sized bulbs and the standard spacing net an economic return of $164 per 100 feet of bed (Table 8). Significantly higher marketable yield and reduced bacterial decay in the narrow plant spacings had a net economic return of $229 (4 row) and $230 (3 row) per 100 feet of bed, which was 1.4 times and $65 to $66 more per 100 feet of bed than the standard (Table 8).

Uniform pricing: Growers selling to a road side stand in Interlaken, NY receive $0.90 per lb for all onions greater than 2.5 inch and the standard spacing had a net economic return of $277 per 100 feet of bed. Significantly higher marketable yield and reduced bacterial decay in the narrow spacings resulted in a net economic return of $386 (3 row) and $419 (4 row) per 100 feet of bed, which is 1.4 and 1.5 times and $109 and $142 more per 100 feet of bed than the standard for 3 and 4 rows per bed, respectively (Table 8).

Alternatives to black plastic study

Due to the extremely low incidence of bacterial bulb decay at harvest in this trial and some curious yield data, we did not conduct an economic analysis on this study.

Farmer Adoption

  • As a result of exposure to our presentations and newsletter articles about this project, two small-scale diversified fresh market vegetable growers in NY indicated to Hoepting that they were going to grow their onions on silver plastic in 2011. Both of these growers were previously growing their onions on bare ground, which typically yields lower than when onions are grown than when onions are grown on silver plastic. In 2011, in PA, 15 growers plan to experiment with solver mulch on their farms.

    After two years of very encouraging research results, we are now encouraging grower adoption of our plant spacing recommendations. In 2011, we anticipate to have at least 15 small-scale onion growers experiment with narrow row spacing on their farms in NY and PA.

    By 2012, we anticipate that at least 50% of the growers who experimented with narrow row spacing will expand narrow row spacing to their entire onion acreage and more growers will experiment with narrow plant spacing on their farm.

Assessment of Project Approach and Areas of Further Study:

Areas needing additional study

Feasibility of narrow plant or row spacing/increased planting density for managing bacterial disease in large-scale onion production:

The trade magazine, Onion World, which has international distribution, published an article on this project. As a result, we received much interest from large-scale commercial onion growers regarding the effects of plant and row spacing on bacterial disease in their operations where onions are predominantly directly seeded at much higher planting densities. It became clear that the feasibility of using narrow plant and/or row spacing as a management strategy for bacterial diseases in large-scale onion production also needs to be investigated. Consequently, Hoepting and Beer recently applied for a USDA Pest Management Alternatives Program grant to address this very issue.

Determine relationship between nitrogen fertility and bacterial disease:

While working on this project in PA, we observed a significant block effect where the block located at the bottom of a slope had 83% bacterial bulb decay at harvest, while the block located at the top of the slope had only 17%. The field was heavily manured, which is common practice on plain-sect farms. Presumably, nitrogen leached to the bottom of the slope where it favored the development of bacterial disease. In an on-farm small-plot trial located in muck soil in NY that was designed to investigate the relationship between nitrogen fertilizer and onion thrips, Hoepting collected data on the incidence of bacterial bulb decay at harvest. Results showed that the addition of only 2.0 lb/A of nitrogen had 0.7% bulbs with bacterial decay at harvest. When the recommended rate of nitrogen (125 lb/A) was applied, bacterial decay at harvest was 10.8% of the bulbs, which was 15 times higher than the 2.0 lb/A rate. When nitrogen was reduced to 62 and 94 lb/A, the incidence of bacterial decay at harvest was significantly reduced to 4.9% (less than half) and 7.3% (one third less) without any significant differences in yield. Clearly, additional studies are needed to confirm the relationship between nitrogen and bacterial bulb decay, because preliminary evidence suggests that growers might achieve reduced losses from bacterial disease by reducing nitrogen fertilizer inputs. Fortunately, Hoepting and Gugino teamed up with Cornell University Plant Pathologist, Steve Beer, and were successfully awarded a Northeast IPM Competitive grant ($179,788) to investigate this relationship and to identify other factors that favor bacterial diseases in onions in 2011 and 2012.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.