Development of disease management, fertility, and weed control best practices for northeast garlic production

Materials and Methods:

Hypothesis 1: Improving cultural practices to optimize nutrition and limit competition will result in increased quality and/or yield of garlic. This hypothesis was tested with a fertility trial and a weed control trial.

 Introduction: Rates and timing of fertility applications on garlic vary greatly due to a lack of definitive     recommendations. Nitrogen needs are of particular interest because of the concern that mistimed nitrogen   applications will not be available to the garlic when it needs it. This study focused on finding the nitrogen   levels that optimize yield and determining what percent of nitrogen should be applied in the spring versus in the fall.

About the trials: Three organic farms on Long Island, in the Hudson Valley, and in the Mohawk Valley   Region were selected for trialing. The soils on these farms ranged from sandy to gravelly loam with a high organic matter content. Soil tests were taken using Agro-One testing laboratory in September of 2012 to guide fertility recommendations. Fertilizer was then applied to thirty-foot plots as a banded application in-furrow at planting. Phosphorus and potassium were both brought to the optimal levels as indicated by the soil tests and based on current recommendations (Table 1), and nitrogen was applied at 6 different levels (Table 2). Nitrogen recommendations were reduced based on the percent organic matter in the soil. Recommendations were reduced by 10 lbs/A for every percentage of organic matter in the soil.

  Table One: Rates of P and K based on soil testing. Source: Agro-One Soil Labs

Table 2: Six experimental fertility treatments

Slow release forms of nitrogen including alfalfa meal and pelletized chicken manure were applied in the fall. All nitrogen applied in the spring was in the form of fish emulsion, which was considered quick release. Care was taken not to fertilize excessively with phosphorus or potassium in order to reach optimal nitrogen levels. For example, pelletized chicken manure might supply half the needed nitrogen, but once phosphorus was     optimized the remainder of the nitrogen was applied as alfalfa meal.

Existing recommended call for splitting the spring nitrogen applications. However, research by Angela   O’Callaghan indicates that splitting the application does not increase yields. Therefore, we applied spring   nitrogen in one application, as close to when garlic begins growing as possible.

Results:

Two of the farms showed clear trends related to the fertility treatments: Farms 1 and 3. Farm 2 did not show clear trends, which might be explained by the high weed pressure on this farm. The weeds might have both consumed most of the nitrogen and competed with the garlic, suppressing yields. When this farm is removed from the data, it becomes clear that 50 lbs of nitrogen is not enough to maximize yield, regardless of timing. What is not as clear is what the effects of timing and rates are once we jump to 100 lbs of nitrogen. According to the data, 100 lbs of fall nitrogen leads to better yields than 100 lbs of nitrogen split between the fall and spring. 150 lbs of nitrogen yields better than 100 lbs both in the fall and as a split application, but the difference is fairly small—if a grower produced 1000 pounds of garlic using the 100 lbs of N in the fall rate compared to the 150 lbs of N in the fall rate, he or she would only increase yield by about 50 lbs, or 5%. Comparing the 100 lb rate to the 150 lb rate with a split application increases the yield gain to 139 lbs, or about 14%.

Discussion: Although it is clear that more work needs to be done to determine the best relatively high rate of nitrogen to use to maximize garlic yield, it is clear that applying at least 100 lbs of nitrogen is necessary to maximize yield. Whether all of the nitrogen is applied in the fall or some is held back until the spring is a question we will continue to examine. In the meantime, growers are encouraged to look at their cropping systems and make decisions based on the expense of   additional nitrogen application in the spring versus the possible returns. If a spring nitrogen application is relatively easy to accomplish through drip or by side-dressing, I would not hesitate to split the nitrogen application between fall and spring. If making a spring application is extremely difficult, using a higher fall application rate can nearly make up the difference. To make your own complete comparisons, please see Table 3, which has the average weight bulbs from each treatment, averaged over the trials at farms 1 and 3.

Table 3: Fertility treatments and average bulb weight.

Weed control trial:

Garlic trial was conducted on the lower quality garlic, all variety German White. 13 treatments were devised for the trial. The first treatments were applied in the fall shortly after planting (11/15/12). Herbicide was applied using a C02 sprayer. Each plot was calculated to be 50 square feet, or .0012A. Applications were mixed with the equivalent of 40 GPA of water.

Applications:

• Control
• Hand Weeded Check – as needed
• Prowl H20 - Fall
• Chateau (6 oz) - Fall
• Chateau (3 oz) - Fall
• Goal 2xl
• Hay mulch
• Select Max
• Outlook
• Poast
• Goal + Select Max @ rate limit
• Outlook + Select Max
• Dual Magnum + Goal

Long Island Herbicide trial treatments. The applications were treated similarly.

Results: Please see attached data sheets and powerpoint with visual data. The top choice for herbicide use was Cheateau at the rate of 6 oz per acre. The top trialed organic choice was straw at a spring thickness of three inches.

Hypothesis 2: Optimizing post-harvest handling of garlic will reduce post-harvest loss and improve seed stock.

Post-harvest treatments: Post-harvest treatments were root and stem pruning, washing, and curing in high-tunnels. The trial was replicated at three sites and for two years in order to account for seasonal and site-based environmental variation.

Each treatment was applied to 10 linear feet of garlic. In year one there was no control for doubles, which added significant variation to the data. This was corrected in year two. After curing is complete, each treatment was trimmed to marketable form (no tops, roots), graded and weighed. Marketable weight and cull weight was noted, and diseases were identified and noted. Treatments were spot-checked in September to see if disease had developed since curing.

High tunnels at each site contained data loggers (we have them already, and they were not included in the budget) so that if had seen damage from temperature, we would able to determine how high temperatures got in the high tunnel. Temperatures did not reach damaging levels in any tunnel.

Treatments: A=Trim roots flush with basal plate         B= Trip tops to 6” long

                     C= Wash       D=cure in high tunnel           E=Cure in open-air structure

                     F= leave roots and tops un-cut

The following treatments were included at each site each year. If the 6” trimming is very promising, a 1.5” trimming may be added in year two.

Effects of treatments on bulb quality, disease incidence, drying time, and final weight

High Tunnel vs. Open Air: Across the trials garlic in high tunnels dried an average of three days faster than garlic in open air structures. Garlic dried in high tunnels had slightly better wrapper quality (tighter, less discoloration) than garlic dried in open-air structures at one site during both years. Garlic dried in tunnels also had slightly lower disease incidence (Aspergillus, Embellisia and Botrytis), though disease was not severe in any site or treatment in either year. No garlic treatments showed damage from being dried in the high tunnel.

The environment in the high tunnel needs to be carefully managed in order to be most effective. Technically temperatures can reach 121° F before waxy breakdown, the physiological disorder resulting from high temperatures, is initiated. However, to account for uneven heating in the high tunnel and possible delays in dropping temperatures through ventilation, the grower cooperators agreed that 110° F was a safer limit. Thermometers to monitor the temperature were located at the same height as the garlic.

Limiting temperature is just one aspect management. Maintaining air movement in the high tunnel through the use of internal fans helps even out the temperature and humidity, particularly if drying racks are stacked (Image 1). The grower cooperators also agreed running dehumidifiers at night and whenever the high tunnel was closed was beneficial, as it removed up to 20 gallons of water from the air during an eight-hour period and kept conditions closer to optimal. Without closing the tunnel and running dehumidifiers the humidity in the tunnel can reach up 100%, which pauses or reverses the drying process.

Roots trimmed vs. roots untrimmed: No statistically significant differences were observed between these treatments in regards to bulb quality, weight, or disease incidence in either year. Root pruning is considerably more difficult and time consuming on wet roots than dry roots.

Tops trimmed vs. tops untrimmed: Trimming the tops mechanically in the field using a sickle-bar mower greatly increased the speed of harvest and reduced the space needed for drying. Top trimming did not have a significant effect on disease incidence in dried bulbs, but there were differences in bulb weight at two of the farms in year one, with un-cut bulbs being slightly heavier (Table 1). It was unclear if this difference was due to weight loss or to double bulbs, since the number of bulbs is greater in the treatments with lower weights. Because of this question, relatively uniformly sized, non-doubled bulbs were chosen for the samples during year two instead of taking every bulb from a plot, including doubles, as had been done in year one. In addition to this change, additional cutting lengths were also added to determine if leaving some stem would affect weight or disease incidence. During year two, the pruning length did not affect the dried weight of bulbs significantly (Table 2). Furthermore, there were no significant differences in disease incidence across any of the trimming treatments.

Table 1: Treatments and average weights aggregated from three trial sites, each with three replications per treatment.

Table 2: Treatments, aggregated weights of treatments across replications, counts, and average weights per head from year two. Data was combined from all three sites.

Washed vs. unwashed: Washed garlic initially had very clean, tight wrappers, but became more discolored than the unwashed garlic during the drying and curing process. Most discoloration could be removed by removing 1-3 wrapper leaves, but this extra step is time consuming. Disease incidence, particularly Aspergillus and Embellisia, was slightly higher in washed garlic. This treatment was discontinued after year one of the study because the returns from the process were deemed too low.