Do I need more than one dwarf apple to pollinate?
Most apple varieties need to cross-pollinate for good fruit set. There are a few cultivars that are self-fruitful. If the label or catalog description doesn't mention that the tree is self-fruitful or self-pollinating, plant another cultivar to be sure you have good fruit set. Some trees may be sold as "self-pollinating" or "self-fruitful." While they are able to pollinate themselves, they will produce more apples if they are cross-pollinated.
This article should help as well: https://www.gardeningknowhow.com/edible/fruits/fegen/dwarf-fruit-trees-a-planting-guide-for-fruit-trees-in-containers.htm
I have a 5-year-old semi dwarf Mcintosh apple tree and it has tons of yellow spots all over the leaves. On the underside of the leaves under the spots, it's kind of furry/fiberous (not sure how to explain it). It turns some of the leaves completely yellow.
It sounds like you may have wooly aphids. This article will help you with that:
http://www.nysipm.cornell.edu/factsheets/treefruit/pests/waa/waa.asp
I have just bought a dwarf apple tree online. It has arrived bare rooted. I had expected it to come with some info on how to plant it as I am a complete novice. Can anyone advise me?
This article will help you: https://www.gardeningknowhow.com/ornamental/trees/tgen/bareroot-planting.htm
Last year I planted semi-dwarf apple, peach and pear trees. The peach and pear trees are fine. Something is chewing up all the leaves of the apple tree. There is also a white fluffy substance on the branches. I would appreciate help with these problems.
It sounds like you have woolly aphids. This article will help with that: https://www.gardeningknowhow.com/plant-problems/pests/insects/woolly-aphid-control.htm As for the damaged leaves, what does the damage look like? It will help us narrow down which pests it could be and advise on getting rid of it.
I have two dwarf apple trees in 12-inch wide by 11-inch tall pots. They are about 4 ft tall and in flower. Can I repot them now and what size pot should I use?
Regards beverley
Assuming that you want to pot up, in other words put into a larger pot to promote growth, use a pot one size larger than the current one. From a 12" pot go to a 14" diameter. This article has general information: https://www.gardeningknowhow.com/edible/fruits/fegen/dwarf-fruit-trees-a-planting-guide-for-fruit-trees-in-containers.htm
The "when" to repot is a subject of debate. Some people say late winter - early spring, while the plant is still dormant; others say late spring - early summer, when the plant is heading into its period of greatest growth. The dormant period is recommended to avoid damaging roots, but I prefer the summer time, because bonsai growers have proven that cutting roots is not damaging to the plant, so that's not really a factor.
My dwarf pixie crunch last year looked great in the beginning but then it started to get the orange spots and leaves fell off, and all the apples fell. So this year I want to get a head start on whatever it is I can do. We do have an apple tree next door that needs to be cut down. It's horribly old but maybe we can treat that one too. It has the cedar apple rust too. So please, please tell me what to do. My tree is just starting to bud. These aren't the best pictures, but the first one of the branches show the buds just starting.
This article discusses cedar apple rust and prescribes a course of treatment:
https://www.gardeningknowhow.com/edible/fruits/apples/cedar-apple-rust-control.htm
My dwarf apple tree has brown/red spots on the leaves. The apples are not affected, also the leaves have been nibbled slightly at the edges. What could this be and how do I treat it if it needs treating?
This is caused by a fungus, likely apple rust. You can treat the tree with a fungicide and that should help. This article will help as well:
https://www.gardeningknowhow.com/edible/fruits/apples/apple-tree-diseases.htm