How and when should I prune my current bushes?
They should be pruned in late winter or early spring, before they start to leaf out. You mainly want to remove older canes as canes older than 3 years old do not produce fruit. You also may want to prune out dense areas to allow more light into the center of the bush, which promotes more growth and fruiting.
I have large black knobs on many of the branches. I cut them all off in the winter but they keep coming back.
Hopefully this article will help: https://www.gardeningknowhow.com/edible/fruits/currants/currant-pruning.htm
If I plant Consort currants next to my Nanking cherries, will they cross pollinate, changing the flavor of either?
They cannot cross, so you will be fine.
Can I remove excess foliage from my 5 yr old black, red and white currant bushes? There is so much foliage I cannot get between bushes easily. I have pruned and fed and watered them as directed by RHS.
Here is a link to help you clear and clean up your Currants.
A few of the branches of my red currant bush have little orange blobs. Although the bush is probably more than 12 years old, it is not something that I have noticed in previous years. Is this a disease that I need to worry about and, if so, what is the best way to get rid of this problem? I have thought about removing this bush to replace it with a black currant bush, so would this be a good time to remove the bush? If it is, how would I ensure that the problem does not get passed onto a new bush? Thank you in advance for your help, Stephen Hartley
This is a fungus called Coral Spot.
Treatment is removal of the diseased plant material.
This link has more information for you.
I get lots of flowers and fruit in the beginning, but I lose 90% of the fruit as it ripens. It falls off the plant, leaving very little fruit to enjoy. What can I do to save the fruit and keep it on the plant?
This is known as "fruit drop" or "running off", and it's a common problem with currants. The explanation seems to be that self-pollinated flowers produce fruits that drop off so that the plant can focus on growing cross-pollinated fruits. Providing a second plant to cross-pollinate the first and/or taking measures to attract more pollinators will likely help with the problem.
Fruit drop may also be influenced by temperature, as discussed in the following article (scroll all the way to the bottom):
Hi, My redcurrants have gotten some bumps and a red colouring on their leaves. Are they missing a certain nutrient, or what is the problem? Please Help! Thanks,
This is an infestation of what is called Currant Blister Aphids. This article will help you deal with aphids: https://www.gardeningknowhow.com/plant-problems/pests/insects/homemade-aphid-control.htm