My Gala apple tree has been looking pretty rough lately - started noticing yellow leaves about three weeks ago, mostly on the lower branches. I've been watering it regularly and it gets good sun. Is this a nutrient deficiency or something else I should worry about?
Yellow leaves on the lower branches in summer usually points to nitrogen deficiency rather than a disease or pest issue. Since those older, lower leaves are the first to show it when the tree's running low on nitrogen, that's a pretty classic sign. The fact that it's getting good sun and regular water means those aren't your problems - it's more likely the soil just doesn't have enough available nitrogen for the tree to pull from right now.
You can fix this pretty straightforwardly with a balanced fertilizer or something higher in nitrogen - something like a 10-10-10 or even a 20-10-10 would work well for apple trees. Apply it now rather than waiting, since the tree needs it during the growing season. Just follow the package directions based on your tree's size and don't overdo it, because too much nitrogen can actually delay fruiting and make the tree more prone to pests. Water it in well after applying.
Keep an eye on whether new growth at the top stays green while you're addressing this. If the yellowing keeps spreading upward even after you fertilize, or if you notice any spotting or unusual patterns on the leaves, then you might be looking at something fungal or a different nutrient issue. But honestly, nitrogen deficiency is the most common culprit in this scenario, and a good feeding should turn things around within a few weeks.
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