Although many "How to Grow Apple" manuals cite dozens of diseases and pests, most are either rare or regional. There are actually only about a half-dozen problems and pests that you need to actively combat!
Pests: The "worm" in your wormy apple
is most probably one of three types of insect larva.
Found in the Eastern US, this little bugger is tough to get rid of with either sprays or traps. Your best bet is to scare it to death! Curculios like to roll over and play dead when they are startled. An effective method of ridding your orchard of them is to lay sheets on the ground in the mornings during blossom time. Shake your tree. The curculios will fall into your sheets. Empty the sheets into waste bags and be rid of them!
An alternative method to combat curculios is with a repellant spray that contains two tablespoons of garlic extract, two tablespoons liquid seaweed, one-tablespoon neem oil, and one-tablespoon fish oil per gallon of water. Use of this spray is where having a flowering crab at hand comes in handy! Since this is a repellant spray and not a pesticide, the beetles will migrate from your fruiting trees to your flowering crab.
The codling moth is probably one of the most prevalent pests known to apples. After petal fall, moth larvae enter young fruits through the blossom end. moths lay eggs on leaves and twigs about the time petal fall begins. Within days, larvae find their way to fruits and tunnel inside them, often beginning with the tiny openings left by the flower, feasting on the fruits of your labors.
Codling moth traps lure male adult moths with female pheromones and trap them. If your moth problem is small, you can effectively protect your orchard with these. However, for larger codling moth problems you need to spray your trees with Bt (Bacillus thuringiensis). Fish oil added to the spray mix both helps stick the bacterium to leaves and slows its breakdown. Beginning 15 days after petal fall, you'll need to spray three times at five-day intervals.
Also known as the railroad worm because of the tracks it leaves in your apples, the Apple Maggot causes pitting and dimpling in your fruit. Trap adult flies on red sticky balls by hanging them in your tree after petal fall. Another way to reduce apple maggots is to promptly remove any fallen fruit.
Named because it looks like a healed-over scab, it is the most widespread and damaging of apple diseases. Control scab by spraying your trees with sulphur near the time when your buds begin to turn pink.
Powdery Mildew is a fungus that attacks many flowers, fruits, and foliage plants. Characterized by white to gray, talcum-powdery growth, it thrives in warm, dry climates but needs high humidity to germinate its spores. The best way to control powdery mildew is by pruning to let air circulate freely through your tree. Sulphur spray also controls outbreaks of powdery mildew.
This fungus looks like quarter-inch rust colored blisters. It also can be controlled with sulphur spray.