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Prune back your blackberries, but only the canes that had fruit this year. If they did not, prune lightly. Fruit is borne on canes only in the second year of growth. If you prune hard on new canes that didn't bear fruit this year, you won't have new fruit next year.
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Remember to water deeply. A brief squirt with the hose won't get down to the roots that you want to encourage to grow deeply.
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Remove all leaves that show signs of fungal problems. Between plants, clean your pruners with rubbing alcohol or Lysol.
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Keep an eye out for spider mites and blast your plants with the water hose (including under the leaves) a few times a week.