I planted some pear seedlings this winter. They're now in leaf and some of the leaves are not looking so good. Does anyone know what this is and how to fight it?
This will not be easy but with your help we might get close. I shall begin with Fireblight. This is caused by a bacterium, not virus. Fungus and bacteria diseases are rampant with Pear, not so much virus.
Do you remember the variety of your trees? Were there any labels saying your trees are resistant to such and such? Have you fertilized at all? You did well if you planted 'flush' to the ground talking about your root ball...good word to describe; keeping the top of the root ball flush to the surface so no soil touches the bark of the trunk.
Your plum trees are also susceptible to this disease but pear is highly susceptible...I am only 50/50 about this diagnosis, but because fireblight is so common I thought I'd start with this one. Notice the symptom of OOZING blisters. Your trees are young and might not be showing any blisters.
Don't touch your trees too much. That will spread disease as well. When we get to the pruning part you will have to always clean your tools with alcohol before working on another plant/tree.
Have you ever fertilized? What is the variety of pear?
Keeping your trees healthy is the best preventative measure. That would mean a balanced fertilizer. Not too much but a balanced fertilizer would give your plants a chance to fight off the infection by themselves or even resist infections. Pulling these trees might be the only answer, depending on what we discover. Ugh. This is just the first answer and there will be others. We have some Orchard specialists that should be piping up, let us wait until they have given their answers, okay? I chose this disease because it is very common with Pear and I am able to see healthy leaves and growth in one of your pictures. Fireblight looks like parts of a plant were torched...at first.