The Department of Agriculture and Food has urged apple growers to check their trees for early signs of apple scab and powdery mildew.
DAF temperate fruit project manager Diana Fisher said recent wet weather had been conducive to the spread of the diseases.
She said apple scab had been found on a commercial property at Pickering Brook.
Apple scab appears as slightly raised black spots on the leaf surface and infected fruit will have cracks in the skin and flesh.
Infection of nearly mature fruit results in small spots.
Early signs of powdery mildew are distorted and stunted shoots and leaves will appear white from fungal growth.
Ms Fisher said growers could minimise the impact of the diseases by applying fungicides and following good orchard hygiene measures after harvesting.