I'm concerned about lots of fruit and no leaves on my 5-year-old blueberries
I'm concerned that after a wonderful bloom and fruit set my 5-year-old blueberry plants don't seem to be leafing out. We applied ammonium sulphate at the beginning of May (through bark mulch) at the rate of 8 oz. per plant spread around the drip line. The plants are beginning to issue new shoots and that is about the only place we're seeing leaves. Many of the plants are completely bare except for the huge crop of green berries. We're also experiencing our second year in a row of a large rose chafer infestation. We sprayed the plants with Sevin on June 11 when we noticed the beginning of the chafer emergence and have been hand-picking them since. We have about one acre of berries (about 700 plants). Thanks.
Yes I am seeing a lot of this and it is a cause for concern. I think we had an excellent fall for setting flower or fruit buds and many shoots have nothing but fruit buds on them. Since blueberries only have flowers or leaves in a bud this means there are very few leaves on the plant. The leaf buds produce new shoots which will fruit next year. Flower buds only produce flowers and fruit, so there is no more growth from those buds. We are seeing this over abundance of flowers a lot in Bluecrop and Elliott. How much new growth did you get last year? I like to see 8 to 12 inches of new growth in the top of the bush and shoots about twice as vigorous coming from the crown. Do you irrigate? Plants in poor vigor often set a heavy crop of flower buds.
The plant will start only a few new shoots from the branches but most of the new shoot growth will come from the base of the plant and the few shoots from leaf buds above. The berries will be able to do some sizing and growth by doing photosynthesis themselves but without leaves to feed the fruit the fruit will be small.
One of the things that has probably happened is that you have not done any pruning on these young plants and all the canes are getting old. You need to start pruning the plant by removing the older canes. This stimulates new growth from the base of the plant. You need to take out several of the older canes each year. We recommend two larges cuts removing the whole cane at ground level. The ideal is to have a range of canes in the bush aged from one to 6 or 7 years old. We think the most productive canes are 3 to 6 years old. As the canes age the number of new shoots from the cane increases but the shoots become smaller with few buds.
This is probably not what caused the specific over production of flowers versus leaves on the shoots this year but if you had had a number of new shoots from last year they would not have set many flower buds as your older canes.
There is not much you can do to change the situation. You may decide that you need to remove some of the shoots or even whole canes soon if the fruit on is all small and there is no leaf growth. I think you will see a lot of the stressed canes die but the bush will survive. I would not do any pruning after August as this will stimulate the plant to grow and reduce the winter hardiness of the shoot this coming winter. Next spring, I would remove the shoots that did not put out any leaves this year.
Putting a little more fertilizer on now in June will help with the growth of new shoots and leaves. You put on 8 oz. of Ammonium Sulfate (21-0-0), which would have been 2 oz. of actual nitrogen on a wood mulch. I expect that not much of that nitrogen made it through the mulch. I would apply another 8 oz per plant and water it in as soon as you can. Dumping more fertilizer on the plants might damage the roots and hurt them even more.
You should irrigate to keep the leaves health and productive so they can support the growth of the shoots. Irrigation will also help size the fruit but most of the fruit sizing occurs soon after bloom.
I attach a picture of Bluecrop from a variety trial to show you what the extreme case look like. As you can see there was no growth last year from the crown. As I looked at these plants last week I thought they should have been pruned last year.
You might want to read my essay on blueberry shoot growth.