Galls On Blackberries: Common Blackberry Agrobacterium Diseases


By: Amy Grant

To those of us in the Pacific Northwest, blackberries may seem beyond resilient, more pest than welcome guest in the garden, popping up unbidden. Resilient the canes may be, but even so they are susceptible to diseases, including several agrobacterium diseases of blackberries that result in galls. Why do blackberries with agrobacterium diseases have galls and how can blackberry agrobacterium diseases be managed?

Blackberry Agrobacterium Diseases

There are a few agrobacterium diseases of blackberries: cane gall, crown gall, and hairy root. All are bacterial infections that enter the plant through wounds and create galls or tumors on either the canes, crowns, or roots. Cane gall is caused by the bacteria Agrobacterium rubi, crown gall by A. tumefaciens, and hairy root by A. rhizogenes.

Both cane and crown galls may afflict other bramble species. Cane galls occur most commonly in the late spring or early summer on fruiting canes. They are long swellings that split the cane lengthwise. Crown galls are warty growths found at the base of the cane or on the roots. Both cane and crown galls on blackberries become hard and woody and dark in color as they age. Hairy root appears as small, wiry roots that grow either alone or in groups from the main root or the base of the stem.

While the galls look unsightly, it is what they do that makes them disastrous. Galls interfere with water and nutritional flow in the vascular system of plants, seriously weakening or stunting the brambles and rendering them unproductive.

Managing Blackberries with Agrobacterium Diseases

Galls are the result of bacteria entering into wounds on the blackberry. The bacteria is carried either by infected stock or is already present in the soil. Symptoms may not appear for over a year if the infection occurs when temperatures are below 59 F. (15 C.).

There are no chemical controls for the eradication of agrobacteria. It is important to examine canes prior to planting for any evidence of galls or hairy root. Only plant nursery stock that is free of galls and do not plant in an area of the garden where crown gall has occurred unless a non-host crop has been grown in the area for 2 plus years. Solarization may help kill bacteria in soil. Place clear plastic on tilled, watered soil from late summer to early fall.

Also, be gentle with the canes when training, pruning, or working around them to avoid any injury that will act as a portal to bacteria. Only prune the canes during dry weather and sanitize pruning equipment both before and after use.

If only a few plants are affected, remove them immediately and destroy them.

Commercial growers use a non-pathogenetic bacterium, Agrobacterium radiobacter strain 84, to biologically control crown gall. It is applied to the roots of healthy plants just before they are planted. Once planted, the control becomes established in the soil surrounding the root system, protecting the plant from the bacteria.

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How to Grow Blackberries in Central Texas

The blackberry is a biennial bramble plant that grows berries on 2-year-old canes. Blackberry plants grow well in Central Texas gardens that have a U.S. Department of Agriculture growing zone of 5 through 8. The southern tip of Texas is too hot and dry for many varieties of blackberries. The plants will being producing fruit three years after planting and are productive for approximately eight years before requiring plant replacement. Blackberry plants grow best in a well-draining sandy soil with adequate water supplements during the growing season.

Select a planting location that has a well-draining, nutrient-rich soil and full sunlight conditions for the blackberry plants. Full morning sunlight is preferred over the hot afternoon sun. Air flow through the planting area should not be blocked by buildings or large structures as air circulation is required for disease prevention.

  • The blackberry is a biennial bramble plant that grows berries on 2-year-old canes.
  • Air flow through the planting area should not be blocked by buildings or large structures as air circulation is required for disease prevention.

Prepare the planting soil the growing season prior to planting. Remove weeds from the area, and test the soil to verify that the pH is 5.5 to 7.0. Work ground rock sulfur into the soil to lower the pH number if needed.

Add a 2- to 3-inch layer of organic compost to the planting area to increase the nutrient value and moisture retention ability of the soil. Work the compost into the soil with a tiller to the depth of 8 to 10 inches.

Soak the roots of 1-year-old bare root canes by placing them in a bucket of warm water for several hours. Place the plants in a hole that is wide enough to spread the roots out and the same depth as the cane was previously grown. Gently cover the roots and pack the soil to hold the canes in place. Space the canes 2 to 3 feet apart in rows that are 8 feet apart.

  • Prepare the planting soil the growing season prior to planting.
  • Place the plants in a hole that is wide enough to spread the roots out and the same depth as the cane was previously grown.

Water the canes generously after planting by soaking the ground. Do not overhead water the canes as wet plants are susceptible to fungal diseases. Water the canes weekly with 1 inch of water during the spring season. Increase the water amount so each plant receives 2 gallons of water daily during the fruit production season. Decrease the water amount after harvest is complete.

Apply a 3-inch layer of mulch around the blackberry canes to assist with moisture retention. Refresh the mulch each year in the spring season to maintain a 3-inch layer.

  • Water the canes generously after planting by soaking the ground.
  • Water the canes weekly with 1 inch of water during the spring season.

Fertilize blackberry plants four weeks after planting by applying a 10-10-10 fertilizer once the canes shows signs of growth. Fertilize the plants each year in spring before flower buds appear on the canes.

Prune the blackberry canes be removing damaged and dead canes each spring. Top the canes in summer by pruning 3 inches off the top to stimulate new growth. Prune 2-year-old fruiting canes after harvest by cutting them off close to ground level.

Recommended blackberry varieties for Central Texas gardens are: Brazos, Rosborough, Womack, Shawnee, Choctaw, Brison, Arapaho, Navaho and Hull.


Fertilizing Brambles

Fertilize trailing blackberries, Dormanred raspberries and erect blackberries twice a year in most situations. Trailing blackberries and Dormanred raspberries should receive about 2 ounces of premium grade (containing micronutrients) 10-10-10 in April and July of the first year. Scatter the fertilizer evenly over a circle 2 feet in diameter centered on the plant.

Erect blackberries usually are planted closer together, so a banded fertilizer application can be made from the start. The first year, apply 1 pound of 10-10-10 per 18 feet of row in April and 1 pound per 36 feet of row in June.

For all three types in future years, apply 1 pound of 10-10-10 per 9 feet of row in February or early March and 1 pound of 10-10-10 per 18 feet of row in June. Spread the fertilizer evenly over the row in a band 2 feet wide. Take a soil sample to your county Extension office for custom fertilizer recommendations for your soil.


Recommended Varieties in Order of Ripening by Cane Type
Fruit Type Variety Cane Type Comments
Blackberries Apache Erect Large quality berries thornless.
Arapaho Erect Early- to mid-season thornless medium size fruit resistant to Rosette disease, but may have problems with leaf diseases and cane die-back.
Chester Trailing Late-season thornless premium fruit.
Chicksaw Erect Mid-season large fruit.
Darrow Erect Early-season sugar sweet fruit with great flavor.
Kiowa Erect Early- to mid-season very productive large fruit size. Moderately susceptible to Rosette disease. Probably the best home garden variety.
Natchez Erect Early-season thornless large fruit.
Navaho Erect Mid- to late-season thornless medium fruit size resistant to Rosette disease but may have problems with leaf diseases.
Ouachita Erect Mid-season thornless.
Shawnee Erect Mid-season medium to large fruit with good flavor.
Triple Crown Semi-Erect Early-season known for flavor, productivity and vigor. Disease-resistant. Large berries.
Raspberries Anne Erect Golden yellow fruit, tropical in flavor. Self-pollinating. Sets fruit on cane first year.
Autumn Bliss Erect Early-season everbearing large attractive fruit.
Cumberland Trailing Black raspberry one of the oldest cultivars.
Dormanred Trailing Fruit must be very ripe to be sweet good producer statewide better cooked than fresh. Makes good jam and pies.
Heritage Erect Possibly the easiest and heaviest producer.
Jewell Black Trailing Most disease-resistant variety highly flavorful fruit.
Nova Erect Early-season thornless.
Polka Erect Great companion for Heritage. Winter hardy, but heat-tolerant.


Q. Blackberry

Can you identify this growth in a wild blackberry patch

Crown gall is a common plant disease caused by the soil-borne bacterium Agrobacterium tumefaciens. It is found throughout the world and occurs on woody shrubs and herbaceous plants including grapes, raspberries, blackberries and roses.

Crown gall symptoms include round, wart-like growths — 2 inches or larger in diameter — that appear at or just above the soil line, or on lower branches and stems. Plants with several galls may be unable to move water and nutrients up the trunk and become weakened, stunted and unproductive. Young plants can be killed by developing gall tissue.
In many cases, existing galls can be removed with a sharp pruning knife. Destroy the infected plant tissue and treat the wound with pruning sealer. If the plant does not recover, remove and destroy it.


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