Pre-Emergent Sprays

• During the months of March and April, chemical sprays can be applied to blackberry bushes. At this time, there are no fruits and no blossoms, and in most areas the leaves are just starting to emerge from the bushes. The sprays that should be applied at this time are fertilizers, which will ensure absorption into the soil before the bush begins to develop flowers and fruits. Herbicide can also be applied, and these will kill any weeds beginning to grow around the base of the bushes that can compete for nutrients once older. Fungicides are applied during these months, and these are mostly a preventative.
  
  

Blooming Sprays

• The late spring and early summer months are the time when pests and insect infestations should be managed. During this time, the blooms on the bush will be budding or open; these blooms will turn into fruits if properly managed. Insects such as Japanese beetles, sap beetles, leafhoppers and spider mites can be controlled with pesticide sprays, insecticide sprays or powders during this period. Early detection of these insects is crucial, because during this period bugs will feed on the blossoms and kill them, severely damaging the bushes and negatively impacting the amount of blossoms that will survive to turn into fruits.
  
  

Post-Bloom Applications

• As the flowers drop and fruits develop, it is important to remove fruits as soon as they are ripe to discourage pests such as insects and birds. Spraying may be necessary in some cases, as eggs of insects like the tree cricket will hatch at the same time the fruits are ripening. Sprays such as insecticidal soaps can be effective when applied during this period, but it is also important to remember to thoroughly wash any berries that were on the tree at the time of application before they are eaten. Fungicides can also be applied at this time, but should only be used if there are signs of an infection.
  
  

Killing Wild Blackberries

• If wild blackberries are the problem, the application of spray herbicides can be effective in killing these weedy plants. The late spring and early summer months are the best time to apply herbicidal sprays. During this period when the growth rate for the bushes is the highest, the herbicides applied to the ground will be transported quickly to all points of the plant, along with the nutrients absorbed for growth. Healthy plants that are growing quickly will absorb and transfer the poison faster than plants that are starved or dry. Once the canes have died, they can be cut back and removed. Because wild blackberries reproduce via an extensive underground network of rhizomes, treating the ground with herbicide after the removal of dead canes can help prevent regrowth.