Home-growers of lemon trees lament the amount of fruit that drops soon after the blossoms fade. Although fruit drop is normal for citrus plants, disease, insects and the environment can cause drop as well.
The Alabama Cooperative Extension System says that lemon fruit drop, known as abscission, is a normal thinning process typical of citrus trees. A lemon tree produces more flowers than it can supply with nutrients, so the tree loses the immature fruit.
According to the NSW Government of Australia, lemon scab, a fungus that can attack the lemon flower petals as the blossoming ends, causes the newly forming fruit to drop.
The University of Florida IFAS Extension says that another problem is post-bloom fruit drop; heavy rains or irrigation keep the blossoms wet long enough to develop a fungus.
According to the University of Florida IFAS Extension, a common pest is the immature scale. These insects feed on plant juices, causing moderate to severe defoliation and fruit drop. In addition, chewing insects, including grasshoppers, crickets, katydids and caterpillars cause fruit drop, when the leaves become damaged.
Environmental factors that cause fruit drop include too much dry heat and water stress. According to the Texas A&M System AgriLife Extension, the soil must have the correct balance of 13 nutrients to prevent unnatural fruit drop.