Aronia

An Old Fruit Crop, New to Maryland Farms

A new alternative crop is being studied by University of Maryland Extension for organic fruit production. The Black Chokeberry or Aronia, to which it is commonly referred, is an eastern U.S native with a long history of fruit production in Eastern Europe. The Aronia fruit is about the size of a large blueberry and comes in clusters of about 10 to 20, making them relatively easy to pick. A mature plant (about 7 to 8 years) can yield over 15 lbs, but they start fruiting (averaging 3 or 4 lbs of fruit per plant) within two growing seasons after planting.

Interestingly, the fruit itself is more closely related to an apple and is dark purple in color. The color is attributed to high concentrations of flavonoids including anthocyanins. Due to health-promoting effects, there is great interest in fruits and vegetables containing high concentrations of flavonoids and polyphenols, which are considered potent antioxidants. Recent studies have shown that Aronia has a very high Oxygen Radical Absorbance Capacity (ORAC) compared to other foods.

However, mounting evidence is showing that values like ORAC, as indicators of antioxident activity, have no relavance to the effects of specific compounds that are considered bioreactive in the body. Many of these "bioreactive" compounds like polyphenols and flavonoids including anthocyanins, may have beneficial effects on the body unrelated to antioxident capacity.

The Aronia fruit has very high concentrations of polyphenols, including anthocyanins which may relate to potentially strong beneficial properties for health with regards to the function of coronary arteries. Other studies suggest antimicrobial properties for urinary tract health, colon cancer-fighting properties and possibly aiding in the management of diabetes. To date, no major human health studies have been published, so these potential benefits are only inferred from in vitro research.

Several food products can be made from the Aronia fruit including juice, juice extracts, jelly, and wine. It is true that some processing of the fruit is necessary to overcome some of the fruit’s astringent qualities which probably stem from the flavonoid or tannin content. However, these qualities, considered nutraceutical, heighten Aronia’s marketability and sales potential as a value added product for Maryland farmers.

Aronia tolerates a variety of soils and pH’s, however to optimize growth a soil test should be performed before plants and soil should be amended following the recommendations for fruit trees. The plants should be placed in full sun.

When planting, consider how the fruit will be harvested and what quality of fruit you want. If there are no plans for mechanical harvesting, the Aronia plants should be planted at a spacing of no less than 4 feet on center or greater to improve canopy light penetration in mature plants. Maximizing sunlight interception may improve sugar content in fruit.

At Wye REC, the original Aronia orchard plot was planted at a spacing of 3 feet on center. This spacing has become very tight since planting. Light penetration is low and picking fruit is difficult. However, this is the spacing that is recommended if using a side-row harvester. Two other orchard plots were planted in 2010 and 2011 at spacings of 4 and 7 feet on center.

Mulching is a concern for Aronia growers and there are many options. At Wye REC, we used 3 foot-wide nursery fabric and planted down the center. Holes were made in the plastic and should be large enough so the black plastic does touch the plant so as to not burn the young stems during hot and sunny summer months. The distance between the holes is dependent on the planting density you wish to have.

Other mulch options may be composted organic matter or wood mulch. However, the use of wood mulch will require supplemental nitrogen. This is to overcome bacterial competition for nitrogen in the soil due to the increase of carbon from the mulch. Between rows can be managed several ways, but should be planted with some vegetation to reduce erosion. Grass is one low management option, but some Aronia growers are using legumes like alfalfa or clover between rows. Blister beetles are known to feed on alfalfa flowers. Certain pests can be harbored by the plants one chooses to maintain in between rows. Consider doing some research before making that choice.  Weed management is a concern.  There are no pre-emergent herbicides labeled for Aronia at this time. 

Irrigation through drip is a good method for improving initial survival and establishment, especially during the first two growing seasons. The amount and method of irrigation to apply will depend on your soils. In sandy soils, irrigation should be applied several times during an irrigation day for durations of 15 minutes to 30 minutes. In clay soils, a single application or two applications at 15 to 30 minutes will suffice.

Organic nitrogen fertility studies at the Wye Research orchard have shown that after three years, fruit yield was influenced by high rates (above ¼ oz nitrogen per plant) in the new orchard plots. However, soluble sugar and phytochemical content was unaffected by these high nitrogen rates. Other studies have shown that high nitrogen increases yield but lowers anthocyanin content in the fruit.

While Aronia is a hardy plant, it does have a number of potential pest species that can have a large affect on plant health and fruit yield.  Throughout the year, growers are encouraged to monitor their Aronia orchard to stay on top of possible insect, disease and other pest problems. For now, there are few control options that can be applied to Aronia, because of labeling.  Some exist, but please inquire with the developers of this website to know which are available for Aronia. Aronia has been placed in the IR4 Group 13, subgroup 07B: Bushberry and Small Fruits. If a pesticide has this group labeled and the pest labeled, it is legal to use on Aronia.

Insects

Aphids are noted throughout the growing season feeding on the growing tips of the plant, but are usually controlled by predators like ladybird beetles and lacewings.

Blister beetles (Lytta sp.) have been found eating Aronia flower buds one week before flower peak. Since flowers are set the previous fall season, this equates to a loss of yield.  In the past blister beetles have left within 4 days after arrival, leaving about a 5% loss in yield.

Cherry Fruitworm (Grapholita packardi), a lepidopteran (butterfly/moth) larvae has been noted for the past two years feeding inside the fruit. Less than 5% of the fruit has been damaged annually. The life cycle of this insect is known and organic control should be possible. If adults are noted in May, spray for larvae during the first week of June. The larvae reside inside the fruit throughout the growing season and emerge about about harvest time. This picture was taken after washing the fruit. The larva was coming out of the fruit.

Brown Marmorated Stink Bug (Halyomorpha halys) was seen feeding on fruit as early as June. Since 2011, damage from BSMB occured on less than 5% of the fruit. Ongoing research is looking at control options, but until now, few exist.

Japanese Beetle (Popillia japonica) is present from mid-June through July.  Monitor orchard throughout this time period as often as possible. Beeltles rapidly consume foliage and fruit and can have a major detrimental affect on yield. Organc control methods are available.

Spotted Wing Drosophilla is a relatvely new fruit fly pest. This fruit fly is difficult to identify, and only males have the spotted wings.  Females have an ovipositor (egg-laying mechanism) that can cut through fruit flesh, so fresh fruit can be infested. Some anecdotal evidence and some unpublished research has shown Aronia to be susceptable. The Aronia orchard at Wye REC has been monitored since 2013 for this fly. No infestations were noted.

Lace bug is a pest that occurs occasionally on Aronia. It can be controlled with dormant oil in the spring while the first generation is developing. Better control in the spring means less pesticides in the summer.

Japanese Maple Scale has been noted in several orchards last summer. This pest needs to be controlled early and should not be allowed to infest orchards. Control by dormant oil before bud break in spring when temperaitures are above 55 degrees F and above freezing for at least 3 days after application. Several sprays are required throughout spring.

Disease

At present, only one disease, Gymnosporangium spp. (e.g. Quince Rust or Cedar/Apple Rust) is has infected plants at the Wye Research orchard.  In the past, infections are minimal and fruit that are infected are usually aborted. In the past years the infections have matured before fruit abortion and have moved into stem tissues. Infections however, continue to be minimal and all are removed from the plants by hand. 

Powdery Mildew is a group of fungi that cause white or gray powdery spots or patches on leaves, flowers and fruit. It usually occurs when temperatures and humidity are high. Infected leaves will drop off and near complete defoliation can occur. This is detrimental for fruit production. Monitor at beginning of June, throughout summer. Control can be with various fungicides and organic controls like potassium bicarbonate.

During the 2016 growing season, a new and potentially destructive fungus was identified on aronia orchards at Wye Research and Education Center. Fusicladium, a scab disease was identified on fruit and leaves.  Pictures below show infections in July progressing to harvest time. A brown lesion is seen on fruit which later, cause skin cracking, completely damaging fruit and making it unsalable. At this time cultural management is through sanitation during the fall. Leaves, containing spores that may infect fruit next season.  Fallen leaves should either be collected or mulched for quick decay. No recommendations for chemical sprays can be made until the species is identified. 

Other Pests

Deer are one of the larger problems associated with grower Aronia. The most effective deterent is a fence. Deer primarily eat dormant flower buds in winter, but damage has been noted throughout the year.  Rabbits will cut stems off of small plants but as plants grow past 24" in height, problems discontinue.  In the mid-west, bird predation on the fruit has been suggested but this has not been a problem in the Mid-Atlantic to this date.

Depending on your location, Aronia will flower between late April and mid-May. Flowers will persist for about 3 to 7 days. Many species of bees pollinate the flowers but Aronia is apomictic and does not require fertilization for fruit production.

Fruit begins setting and developing throughout June to August. Fruit progressively turns from green to red to purple during this time period. For the most part, the fruit ripens at the same time, with some stragglers.

In Maryland, harvest is usually between the middle and end of August and can be based upon the increasing Brix content of the fruit. There can be a large variation in the Brix (soluble sugar content) of each fruit due to presently unknown factors, possibly environmental. When checking Brix, use several fruit throughout the plant. Check individually or extract juice from several (10) fruit together. Expect between 15% and 18% Brix. Most importantly, the fruit should be harvested before it starts to wrinkle and dry, oftentime this is before maximum brix is attained in the Mid-Atlantic.

October or early March

– Fertilize 0.25 oz N per plant

– Prune; remove dead/diseased tissue

Mid to Late April

– Plant will begin bloom

– Watch for Blister beetles

May

– Evaluate Yield

– Look for Lace Bug and Aphids

– Look for Cherry Fruit Worm Adult

– Watch for Rust symptoms

June

– Spray for Cherry Fruit Worm

– Evaluate disease (Rust Scab)

– Look for aphids on fresh growth

– Watch for Japanese Beetles

– Watch for Brown Marmorated Stink Bug

July

– Watch for Rust and scab symptoms

– Watch for Japanese Beetles

– Watch for Brown Marmorated Stink Bug

August

– Begin Harvest mid-to end of August based on a stabilized BRIX target of between 16 and 18%. However, your fruit may not achieve that soluble sugar content. Sample many fruit and pick before fruit wrinkles on plant (before end of August in Maryland).

October

Sanitation of orchard including removal or mulching of leaves 

At Wye Research and Education Center an active orchard has been maintained and studied for over 9 years. During that time, several interesting conclusions have been drawn.

• Aronia can be grown organically because of few pest species
• Relatively low fertilizer rates can be use to maintain yield and fruit quality
• Plants yield within the second year after planting
• Can be grown at densities similar to blueberries
• Plants tolerate a variety of soil conditions
• Can be easily propagated from cuttings or seed
• Plants are apomictic, meaning they self pollinate.

Results from Recent Research

Most recent results from new orchard plots show differences of yield between high and low nitrogen rates of 14 grams (1/2 ounce) nitrogen and 3 grams (1/8 ounce) per plant. The higher nitrogen rate doubled yield. While this information may not be surprising, organic fertilizers are expensive and minimal fertilizer rates were tested to see what the yield differences would truely be. Brix or soluble solids where not different between rates. 

Average fruit yield for plants by harvest year (age of plants) in plots B (planted in 2010) and C (planted in 2011), given either 1/8 oz (3 grams) or 1/2 oz (14 grams) nitrogen per plant per year. Plants given 1/2 oz nitrogen yielded more fruit. Plants in plot B were spaced 3 feet (1 meter) on center and plants in plot C were spaced 6.5 feet (2 meters) on center. While plants spaced further apart yielded more fruit per plant, more fruit was harvested per acre after the 5th harvest year from plants grown in higher densities (776 vs 426 plants acre).

Other studies being conducted in new orchard plots at Wye REC have evaluated the use of conventional fertilizers compared to organically based fertilizers on yield and fruit quality. Results are showing no differences in fertilizer source, but again greater yield has been noted in plants receiving 14 grams (1/2 ounce) nitrogen compared to 3 grams (1/8 ounce) nitrogen. These results are contrary to the earlier results in the older orchard plots. Nitrogen application recommedations should be between 1/4 and 1/2 ounce per plant per year.

Further studies being conducted in new orchard plots at Wye REC will evaluate irrigation technology to determine irrigation needs for Aronia. These Wireless Network Systems will be operating in the near future.

Since Aronia has a chill requirement for break winter dormancy, not all locations in the U.S. are suitable for fruit production. Breaking winter dormancy requires that dormant buds receive a minimum of chill time before they can open in the spring. Since all the varieties are of similar genetic stock, they have very little if any differences in their chill requirements. Chill zones are not related to climate zone maps.

Chill hours are calculated several ways, depending on the model used. The single chill hour model calculates the accumulated time that temperatures are below 45 degree F. For every hour below 45 degrees, a chill hour is accumulated. Similarly, a dual temp model calculates time between freezing and 45 degrees F. Another model assigns weighted temperatures, giving a full chill unit between 36 and 48 degrees F, a half unit to temperatures between 34 and 36, and 48 and 54 degrees F. Temperatures lowers than 36 degrees F and between 54 and 60 receive no chill units. Interestingly, temperatures between 60 and 65 subtract a half unit while temperatures above 65 subtracts a full chill unit, actually reversing the chill accumulation. 

Several years of dormancy studies at the University of Maryland have revealed preliminary estimations on the southern range of all Aronia varieties which is around 1000 chill hours (using the dual temperature model). The map below shows the average yearly accumulation hours in the contiguous for the dual temperature model. The blue represents the northern most average range of 1000 chill hours. A blue circle on the border of Georgia and Tennessee is an expanded area below the line due to the high elevations. The large blue circle in North Dakota indicates that this region does not accumulate over 1000 hours of temperatures between freezing and 45 degrees. Temperatures of obviously much lower. There seems to be no problem with growing Aronia in that region.

This is an estimation only. Yearly changes in temperatures can affect what regions consistently get the appropriate chill hours. Some years along that blue line may not receive the needed chill hours. If you are near these blue lines, testing a few plants in your location for several years may be necessary.