Cultivation

• Proper cultivation helps keep blackberries healthy, which boosts their resistance to disease and pests. Plant blackberries in deep, well-drained soils. Blackberries are adaptable to many soil types. Soil pH should be between 4.5 and 7.5. If soil pH goes higher than 8.0, iron chlorosis will result and leaves will become yellow and discolored. Blackberries should be pruned regularly to keep bushes neat and healthy. Cut the canes back when they grow longer than 48 inches to encourage new branching.
  
  

Fungus

• The fungal disease anthracnose is particularly devastating to blackberries, especially if it spreads. The shoots and leaves will be affected first, Eventually, the fruits will become shriveled and dry. Fungal growth is more likely on plants with poor air circulation. Use copper spray to prevent and control anthracnose.
  
  

Pests

• Small plant insects, including stink bugs, feed on the berries of the plant as they begin to mature and ripen. Affected fruits will become damaged or disappear entirely as they are eaten. Other insects, including leafminers, eat the foliage of the plant and cause wilting, yellowing and other discoloration of leaves. Use pesticides to chemically control insects that feed on blackberries. Prune away all damaged areas of the plant when pests are present to prevent their spread.
  
  

Weather

• Too much hot, dry air has a negative effect on blackberry plants. Weakened by scorching winds, fruits begin to turn white and discolored in the UV rays from sunlight. The problem, identified as white drupelet, occurs when temperature raises quickly and humidity drops. Lack of cooling moisture scorches the berries and may make them unfit to eat. When dry wind and high temperatures are expected, shade blackberry plants to protect them from white drupelet.