Babycake blackberries planted last year devoured by Japanese beetles. I covered with fruit cage, and mosquito net to protect.I pru
ned, fertilized, water regularly, full sun and had lots of blossoms but only little nubbins that are not maturing into berries. I had ph tested 7.8. Why are there no berries? The plants are beautiful and have tripled in size.
Japanese beetles are frustrating and require daily vigilance to spot the start of their season. I wonder if the mosquito netting kept bees from pollinating the flowers. Although blackberries are self-fertile, pollen still needs to be transferred from stamens to stigmas. Wind might be sufficient but your experience this year indicates it might not be enough. Some people gently shake tomato stems to get pollen to move; I've even read of using an electric toothbrush against the cane near the flower stems. Since the plant was decimated by last year's infestation it may have needed a year to recover. If you have never tested the soil, that is another potential problem. If there is a deficiency in phosphorus and potash (potassium), fruiting is affected. Also, too much nitrogen favors leafy growth, not fruit.
If you test through your state extension service, recommendations to correct deficiencies and annual fertilizer needs are given.