The GARDENA gardening expert
1. Dear F. family, with regard to your highbush blueberry, at least 80 percent of the flowers should bear fruit for a full yield, as a rule of thumb. The question as to why the inflorescences have died is difficult to answer without actually seeing the problem. Your letter was sent at the beginning of June and in it you mention that the damage occurred in the "last two weeks". With this in mind, could the damage be attributed to a late mid-May frost?
You also said that your blueberry bushes bore plenty of fruit "in the last two years" (note: you were right to plant three varieties for better cross-fertilization.) With regard to this, there is another possible solution: Highbush blueberries need a very acidic soil (pH 3.5 to 5). Even if the required pH was initially observed when planting the bushes by inserting them into bare peat or similar, it usually changes within two to three years — as a result of neutralization with chalky irrigation water and coming into contact with chalky soils or even calcareous fertilizers. That is why most gardeners acidify the location of the plants around every two years by adding plenty of peat or acidic peat substitutes, such as bark humus or similar (compost is already too calcareous!). Attention should also be paid to fertilizers: Do not use any calcareous fertilizers; use acidic or physiologically acidic fertilizers, such as sulfuric ammonia or similar.
And finally: With regard to the bud rot you mentioned, this is usually caused at the time of flowering in wet years by the fungi Botrytis and Monilia. Both can be combatted through preventive spraying with environmentally friendly fungicides, such as those available from Neudorff.
2. Regarding the damage to the onions in your garden: If young bulb plants wither, if their leaves discolor to become yellowish-gray, or if they dry out and can be pulled out easily, it is likely that the damage has been caused by Delia antiqua — onion flies. You can often see the whitish maggots—i.e. the offspring of the fly—at the base of the plant. Completely covering the onions with a cultivation protection net for vegetables helps to prevent such damage. Incidentally, this also helps against carrot and radish flies, as well as aphids. The first round of your onions has clearly been lost. However, it is still worth covering any plants that have not been infected. After the first generation of flies from the end of April to the end of May, the second generation is in July/August.