Production Practices

Field

Soil preparation 

Indian round eggplant performs best on sandy or sandy loam soils that provide good drainage and favourable soil temperatures. Seedlings are transplanted 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.       

Indian round 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 Verticililum wilt. At Vineland’s Research Farm, trials were set up to evaluate the impact of fumigation on the performance of Indian round eggplant. When fumigation is not possible, an effective method of control is through the use of disease-tolerant rootstock (see Transplant production section).

Fertility 

There are no specific recommendations for Indian round 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 1).

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

Season extension 

Row covers are a useful tool to enable early planting of Indian round 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 2). This response will vary depending on the growing season.

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

Figure 2: 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 

Indian round 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 Indian round eggplant on different rootstocks. Among the measures taken, we compared total marketable yields on four rootstocks over two growing seasons. Of the rootstocks tested, DR0141TX was the best performing one. In addition, when Chu-Chu was grafted onto the DR0141TX rootstock in non-fumigated soil, marketable yields of 78 t/Ha were as good as those achieved in fumigated soil (Figure 3), confirming the resistance of the rootstock to soilborne diseases. Indian round Chu-Chu was the highest yielding variety of eggplant tested.  

Yield comparison between Indian round Chu-Chu and Japanese long Orient Express on fumigated land, and the effects of rootstocks on performance on non-fumigated land

Figure 3: Yield comparison between Indian round Chu-Chu and Japanese long Orient Express on fumigated land, and the effects of rootstocks on performance on non-fumigated land.

Staking 

Indian round eggplant is a relatively compact plant compared to Asian long eggplant. Staking and trellising are necessary to prevent wind injury and plant uprooting. When grafted plants are used, trellising is absolutely essential as plants are generally taller and more prone to uprooting.

Two common methods of staking, fencing and Florida weaving, were evaluated (Figure 4). 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 on how to use the Florida weave technique, 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 4: Comparison of total marketable yields of Indian round 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. Indian round eggplant develops firm, round fruit with a high gloss purple skin, and should be harvested when the fruit reaches a diameter of 4.4 to 5.7 cm. Fruit that is scratched or marked is often considered 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 

Limited information exists on greenhouse hydroponic production of Indian round eggplant. The goal of this project was to determine whether the Chu-Chu Indian round eggplant variety was adapted to hydroponic production in a greenhouse, and to evaluate its performance alongside two Italian eggplant varieties harvested for the ‘baby’ eggplant category. In general, production techniques are similar to those used for tomatoes, with crop-specific adaptations for fertigation. Bees were 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. In 2015, we 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.

Yield of each variety tested between January and June, 2015 

Figure 1: Yield of each eggplant variety tested; production trial run from January to June, 2015.

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.

Only one variety of Indian round eggplant was advanced from the 2015 trials. Chu-Chu F1 was selected as it meets retailer requirements for fruit quality, shape, size and uniformity. Two Italian-style eggplant varieties, Fantastic and Taurus, were also included in the trial to determine the yield potential of Italian eggplant when harvested for the “baby” category.

Both Fantastic and Taurus greatly outperformed Chu-Chu, suggesting there is a need to further test the development of a round eggplant variety that can sustain high yields in the greenhouse. Although Chu-Chu has been the best performing field variety year over year, this variety is simply not suited to greenhouse hydroponic cultivation. When grafted onto Maxifort rootstock, Chu-Chu achieved a yield of 15.56 kg/m2 which is well below the 30 kg/m2 target (Figure 2).

Average yields of Indian round eggplant and Italian-style eggplant during the 2016 and 2017 growing seasons 

Figure 2: Average yields of Indian round and Italian-style 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

Plants were pinched to force two heads from the first fork of the eggplant scion. Thereafter, a different pruning technique was used for Indian round varieties (compared to the long varieties), where two heads were still maintained, but two flowers were left at each node to develop. There was no initial flower pruning to balance the plants.

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. To meet retailers’ specifications, Indian round eggplant must be harvested when the diameter of the fruit is 4.4 to 5.7 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. Of all the varieties tested, Orient Express (Japanese long eggplant) was the only variety that yielded more than 30 kg/m2.

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.