Bowsnbucks, the main thing for deer apples imo is to keep them healthy enough to get a good start. Keep underneath the trees clean of competition and keep the entire orchard mowed as much as possible. Make sure they get as much sun as possible and good airflow. Also stake and keep window screen on the bases of trees to keep both mice/vols and borers away. And above all cage them from deer using individual cages or block fence for at least 4-5 years.
Now, a main fungus which is a problem is scab, which will infect both leaves and apples. In early years on these younger trees it will slow growth if leaves are moderately to highly infected. So for deer apples that will slow things up for you. Another fungal problem is ceder apple rust, which again can slow growth. If you don't have red ceder anywhere near you (up to 1-3 miles depending on orientation) this won't be a problem.
A good all around fungicide for scab is Captan 80 or 50wp It should be applied at a rate of 2 tablespoons per gallon of water. A fine mist so that the leaves are covered, but if it is dripping off, you sprayed to much. Timing is critical, spray at tight cluster, petal fall and at 7-14 day intervals thru June. If you get over 2" of rain it should be applied again reguardless of how long it's been since the last spray. Scab spores are released on a rain so the main idea is to make sure the trees are covered before the rain.
Captan is not very effective on CAR, but it's better than nothing. The spray schedule for scab will cover CAR. There are better fungicides for CAR but I believe in most states they are restricted use. With both these fugus's though, they can be eliminated with the planting of disease resistant varieties. That's why I and others have been suggesting varieties such as Liberty, Enterprise, Galarina and so forth. They eliminate at least the problem of scab and several are disease resistant to CAR too. Most crabs are very easy to grow and will do good without spraying. All the talk on this site and the other one about the 5000 different varieties being grown is unnecessary imo, at least for deer. Which is what you asked about.
As for insects tent caterpillars and sometimes aphids on young trees can be a problem and slow growth. They can be spot sprayed w/ Malathion or a regular spray of Imidan will normally keep them at bay. It can be sprayed with captan and at the same schedule. as Captan. However it is important to note that it should only be sprayed at first light or last light so you do not kill any bees that may be flying around during the day. Use at the same rate at 2 tbls. Also the use of dormant oil spray in springtime can be effective against mite and aphid numbers and can be picked up at most garden centers. Use as directed on label.
There is a lot more to spraying apples, but this a decent starter schedule for deer apples and will get them a better head start than if you did no spraying. If you have any wild apples in the area you can be assured the will effect your trees of these maladies and maybe more. Can you grow them without spraying yes and sometimes no depending where you live in the country and how bad the fungal diseases and pest saturation is in your area.
