Production Practices

Field  

Soil preparation 

Asian long eggplant performs best on sandy or sandy loam soils that provide good drainage and favourable soil temperatures. Transplants are most commonly planted onto raised beds covered with black plastic mulch. Two staggered rows are planted on each bed once the risk of frost has passed. Rows are spaced 30 cm apart with in-row spacing of 35 to 45 cm.       

Asian long eggplant is highly susceptible to Fusarium and Verticillium wilt. Growers are advised to have their fields tested for the presence of these pathogens prior to planting to determine the level of risk posed.

Fumigation is an effective measure to control both Fusarium and Verticillium wilt. At Vineland’s Research Farm, trials were set up to evaluate the impact of fumigation on the performance of Asian long eggplant. Under moderate disease pressure (Fusarium sp.) a 52 per cent increase in marketable yield was achieved when eggplant was planted on fumigated versus non-fumigated land (Figure 1).  

 Comparison of Long Purple F1 yield on fumigated compared to non-fumigated land

Figure 1: Comparison of Long Purple F1 yield on fumigated compared to non-fumigated land.

Fertility 

There are no specific recommendations for Asian long eggplant in Canada. In general, eggplant requires 120 to 140 kg/Ha of nitrogen. Fertility trials showed that non-grafted plants performed best when 125 kg/Ha of nitrogen was applied while grafted eggplant required up to 150 kg/Ha of nitrogen to achieve the highest yields (Figure 2).

Initially 50 kg/Ha of nitrogen was broadcast onto the field together with phosphorus and potassium as required per soil test recommendations. The remaining nitrogen was applied through weekly fertigation events starting two weeks after transplanting. Between 5 and 7.5 kg of nitrogen in the form of potassium nitrate is recommended per hectare per week through the summer.

 Nitrogen response curve illustrating eggplant yields at increasing nitrogen rates


Figure 2: Nitrogen response curve illustrating eggplant yields at increasing nitrogen rates.  

Variety selection 

Asian long eggplant can be divided into two categories: Japanese long and Chinese long. The Japanese long eggplant are characterized by a dark purple skin, while the Chinese-type showcase a lighter purple skin. Understanding market demands is crucial in selecting the appropriate varieties for production. In all trials, Orient Express F1 has consistently been the highest yielding variety of Japanese-type long eggplant. 

Season extension 

Row covers are a useful tool to enable early planting of Asian long eggplant and extend the field season. The covers protect young transplants from weather damage (frost, rain) early in the growing season. Planting occurred two weeks earlier with row covers compared to no covers. The use of floating row covers increased eggplant yield by 30 per cent over a growing season compared to that obtained when no covers were used (black plastic) (Figure 3). No yield benefits were obtained when perforated plastic covers were used.

Marketable yield of eggplant when perforated plastic and cloth row covers were used, compared to no cover (black plastic) 

Figure 3: Marketable yield of eggplant when perforated plastic and cloth row covers were used compared to no cover (black plastic). All treatments were planted on raised beds covered with black plastic mulch.

Transplant production 

Asian long eggplant is most successfully established from transplants, started six to eight weeks prior to transplanting. Young seedlings are susceptible to frost damage, so unless protective row covers are used, no plantings should take place until the risk of frost has passed. When grafted plants are used in production, scions (varieties) are seeded 10 to 14 days before rootstocks so the same thickness of stem is achieved at the time of grafting.

At Vineland, we evaluated the effects of grafting Asian long eggplant on different rootstocks. Among the measures taken, we compared total marketable yields of four rootstocks over two growing seasons. There was a 72 per cent increase when Long Purple was grafted onto Maxifort rootstock compared to the non-grafted control (Figure 4). Similar yield increases were also observed for Asia Beauty. A 38 per cent increase in yield was also found between grafted and non-grafted controls of Long Purple on fumigated land, suggesting that rootstock not only protects against pathogens but also improves plant vigour and yield. Maxifort also adds a high resistance to Fusarium races 1 and 2, Fusarium root rot, nematodes, corky root rot, tobacco mosaic virus and Verticillium wilt. Disease resistance is not transferred to the scion.

Yields of grafted Long Purple and Asia Beauty on four tomato rootstocks and native roots in 2016

Figure 4: Yields of grafted Long Purple and Asia Beauty on four tomato rootstocks and native roots in 2016.

While the selection of varieties that have the right specifications to meet market demand is crucial, the selection of the rootstock to support the chosen variety is also important, as interactions between variety and rootstock can vary. Figure 5 illustrates the yield of different eggplant varieties as influenced by rootstock. 

Marketable yield of Asia Beauty, Long Purple and Orient Express on four tomato rootstocks


Figure 5: Marketable yield of Asia Beauty, Long Purple and Orient Express on four tomato rootstocks.

Staking 

Staking eggplant is necessary to help protect plants and fruit from wind damage, which in turn will yield higher quality marketable fruit. When grafted plants are used, trellising is essential as plants are generally taller and more prone to uprooting.

Two common methods of staking, fencing and Florida weaving, were evaluated (Figure 6). Results indicate that the use of the Florida weaving method can increase marketable yield by up to 23 per cent over plants where no trellising was done. To learn more how to use Florida weave, click here.

Comparison of total marketable yields of eggplant when using fencing and Florida weaving trellis methods to support plants compared to a no trellis system (control)


Figure 6: Comparison of total marketable yields of Asian long eggplant when using fencing and Florida weaving trellis methods to support plants compared to a no trellis system (control).

Pest control 

A regular scouting program should be used throughout the summer to detect, identify and treat (if necessary) pests quickly to avoid economic loss. It is important to examine both the upper and lower sides of leaves when looking for pests such as aphids, thrips, leafhoppers, two-spotted spider mites, Japanese beetle, Colorado potato beetle, cutworms, flea beetle, whitefly and tarnished plant bug. Verticillium wilt, damping-off and root rots, anthracnose, early blight and Phomopsis blight are also the most commonly found eggplant diseases in Canada. Monitoring involves the examination of 10 to 15 plants per hectare in four random locations evenly distributed throughout the field ensuring that the plants at the edges and in the middle of the field are included.

For specialty eggplant, consult the Ontario Ministry of Agriculture, Food and Rural Affairs’ Publication 838, Vegetable Crop Protection Guide — 2014-2015. This crop is in Crop Group 8-09: Fruiting Vegetables Group and subgroup 8-09B: Pepper/Eggplant Subgroup and subgroup 8-09C: Non-bell Pepper/Eggplant Subgroup. For a full list of registered pesticides for eggplant click here. 

Harvest and postharvest handling

It is essential to harvest eggplant regularly, as fruit quickly become overgrown and unmarketable. Ideally, eggplant should be harvested every second or third day. Both Japanese and Chinese long eggplant are harvested when fruit reaches a length of 23 to 35.5 cm and a diameter of 4.4 to 5.7 cm. Fruit with scratches and excessive curving are not marketable through most retail outlets.

Eggplant is susceptible to chilling injury and should be stored between 10 and 12oC. For more information on postharvest handling of eggplant, click here

Greenhouse  

Introduction 

Asian eggplant varieties are mostly produced in the field and limited information exists on greenhouse hydroponic production. The goal of this project was to assess various varieties of Asian long eggplant and determine their suitability for hydroponic production in a greenhouse. In general, production techniques are similar to those used for tomatoes, with crop-specific adaptations for fertigation. Bees are used to pollinate the crop, and should be used at the same release rate/acre as recommended for tomatoes. 

Variety selection 

Careful considerations must be given to selecting the right type and variety of eggplant for production in a greenhouse. Asian eggplant can be grouped into three types: Japanese long (dark skin), Chinese long (light purple) and Indian round.

In this study, a target was set to achieve a yield of at least 30 kg/m2. Only the Japanese-style long eggplant variety Orient Express consistently achieved this goal, and even surpassed this target in trials that were run in 2016, where yields of greater than 35 kg/m2 were achieved (data not shown). 

In 2015, Vineland ran two six-month crop cycles in an older greenhouse and nine varieties across all three Asian eggplant categories were tested to identify those best suited to greenhouse hydroponic cultivation that also had the right retail specifications. Figure 1 illustrates the yield of tested varieties during a six-month crop cycle.

Three long eggplant varieties with the requisite consumer and production traits were identified for further testing in Vineland’s Collaborative Greenhouse Technology Centre: Orient Express (Japanese long), Asia Beauty and Long Purple (Chinese long) (Figure 1). Chu-Chu (Indian round) was also included for comparison (see section on Indian round eggplant for more details).

It was also determined that grafting has a positive effect on yield and without grafting, greenhouse production is unlikely to be successful.

Yield of each variety tested between January and June, 2015 

Figure 1: Yield of each eggplant variety tested in a six-month production trial run from January to June, 2015. Note the higher yields obtained from grafted versus non-grafted (on own roots) long eggplant varieties. Chu Chu (Indian round) did not show a similar yield response when grafted.

Seedling production 

Eggplant is grown hydroponically in a greenhouse using similar techniques to those used for tomatoes. Eggplant have to be grafted onto disease-tolerant rootstock to boost vigour and protect against root pathogens. Eggplant (scion) seeds are sown into sheets of rockwool to germinate. Tomato (or compatible eggplant) rootstocks are sown in the same manner seven to 10 days after the eggplant scions emerge and cotyledons have opened. Rootshield® WP (BioWorks) should be applied to tomato rootstock rockwool sheets seven days prior to grafting to aid in the healthy establishment of roots. Grafting is usually completed four weeks after sowing eggplant seeds as per instructions found in the Washington State University fact sheet (Washington State University Extension Fact Sheet FS052E, 2011). Immediately after grafting, Previcur® N (Bayer CropScience) is applied and seedlings are placed in a healing chamber at 20 to 21oC with 80 to 95 % RH. Fertilizer is not added during the germination and healing process. After healing, grafted plants can be removed from the healing chamber and planted in the greenhouse.

Rootstock selection 

Rootstocks not only help manage pathogens such as Verticillium and Fusarium wilt, but also boost plant vigour. The effect of rootstock on marketable yield of eggplant was studied in Vineland’s pre-commercial greenhouse.

Of the Asian long eggplant tested, Orient Express was the highest yielding variety and gave a yield of more than 30 kg/m2 when averaged over two growing seasons (Figure 2). Overall, the highest yields (for all varieties) were obtained when scions were grafted onto the general tomato rootstock DR0141TX.

Average yields of Asian long eggplant during the 2016 and 2017 growing seasons 

Figure 2: Average yields of Asian long eggplant during the 2016 and 2017 growing seasons.

Transplanting and plant maintenance

Grafted plants are transplanted into rockwool blocks immediately after healing. Once roots establish in the blocks, plants are placed on coconut fibre slabs with a plant density of 2.7 plants/m2. In 2017, a trial was undertaken to determine if a higher plant density (3.6 plants/m2) could drive up yields in the non-vigorous Orient Express eggplant. Planting took place nearly one month later than in 2016 and light levels were low compared to the 2016 growing season. As a result, yields were generally much lower. The highest yield of 24.57 kg/m2 was obtained when Orient Express was grafted onto DR0141TX rootstock at 3.6 plants/m2 (Figure 3).

Orient Express yield on three rootstocks at two plant densities 

Figure 3: Orient Express yield on three rootstocks at two plant densities (data from 2017 trials).

Plants were pinched to force two heads from the first fork of the eggplant scion. To balance the initial fruit set of Asian long varieties, flowers at the second node of the first head were removed. The first and third flowers on the second head were also removed. All flowers were pruned to leave one flower at each node after the plants were balanced.

Eggplant scions will continue to grow and it has been documented at Vineland that they can reach a height of above six metres (Figure 4) on DR0141TX rootstock. Plants therefore must be clipped or wrapped using twine, applying similar plant management practices as those used for tomatoes. When the growing tips of the scion reach the trellis wire, plants should be carefully lowered.

Plant heights recorded at the end of the 2017 season for each variety and rootstock 

Figure 4: Plant heights recorded at the end of the 2017 season for each variety and rootstock.

Fertigation

A fertigation schedule is required to maintain high eggplant yields in the greenhouse. Eggplant’s nutrient requirements are akin to those of tomatoes, and a similar fertilizer regime should be followed. It is recommended to hire a crop consultant to tailor a fertilizer recipe specific to individual greenhouse needs. At Vineland, we followed the fertigation schedule shown in Table 1.

 Fertilizer schedule for greenhouse eggplant during growth phases

Table 1: Fertilizer schedule for greenhouse eggplant during growth phases.

Pest and disease control

Scouting is an important practice to detect and identify pests quickly to avoid crop damage and economic loss. Both upper and lower sides of leaves should be carefully examined for commonly found insects including aphids, thrips, whiteflies, fungus gnats, shoreflies and spider mites.

Fungus gnats (Sciara sp.), shore flies (Scatella stagnalis), red morph green peach aphid (Myzus persicae), two-spotted spider mites (Tetranychus urticae), thrips (Frankliniella occidentalis), Echinothrips (Echinothrips americanus) and whiteflies (Bemisia tabaci, Trialeurodes vaporariorum) were found on the crop throughout the course of this project.

Biological controls such as Aphidius colemani, Orius insidiosus, Atheta coriaria, Delaphastus catalinae, Neoseiulus californicus, Amblyseius swirskii, Encarsia formosa and Eretmocerus eremicus were released regularly to prevent pest outbreaks. Chemical controls included applications of Floramite©, Shuttle©, Previcur©, Kontos©, Botanigard© and Fontelis© when pest populations or disease pressure increased beyond an acceptable threshold. Ensure compatibility of all products selected (including fungicides) with all the biocontrol agents being used to avoid negative side effects. Consult biocontrol companies' 'Side Effects Guides' for information to aid selection.

For additional information on pest management, please consult the Ontario Ministry of Agriculture, Food and Rural Affairs’ Publication 838, Vegetable Crop Protection Guide — 2014-2015. Click here for a complete list of registered pesticides for eggplant. Read each label thoroughly to determine if the pesticide is registered for greenhouse use.

Harvest

Eggplant were harvested three times weekly. It is important to have regular harvest intervals for Asian long eggplant cultivars, as fruit can quickly become oversized and unmarketable. To meet retailers’ specifications, Asian long eggplant must be harvested with a diameter of 4.4 to 5.7 cm and a length of 23 to 35.5 cm. 

The 2017 yields were considerably lower than those obtained in 2016. There were two reasons for this: planting occurred a month later in 2017 and growing conditions, especially light levels were not as good as in 2016. Orient Express was the only variety in the trials that yielded more than 30 kg/m2.

Of the rootstock tested, DR0141TX was consistently the best followed by Maxifort and Kaiser (Figure 5). In 2017 under adverse growing conditions, DR0141TX held up better then Maxifort. Additional work is required to further refine production recommendations for greenhouse eggplant.

Marketable yield of Orient Express eggplant on three different rootstocks 

Figure 5. Marketable yield of Orient Express eggplant on three different rootstocks.

Postharvest storage

To maintain a high quality of fruit, it is beneficial to harvest in the morning when it is cool, keep eggplant out of direct sunlight and minimize rough handling of the crop. By transporting eggplant quickly to a sorting facility, it is possible to remove damaged and diseased fruit to avoid the spread of postharvest pathogens that can render eggplant unmarketable.

Following harvest, it is important to bring down the eggplant temperature to between 10 and 12oC as quickly as possible to maintain quality. Temperatures below this range can cause chilling injury while temperatures above increase respiration rate leading to a shorter shelf life.