There are several products available. All contain naphthaleneacetic acid (NAA) or ethephon. These chemicals will cause flowers to abort at blossom time. NAA and ethephon should be applied as a spray at mid-bloom and again at full bloom. The entire tree should be sprayed. If there are other fruit trees nearby which are in bloom, make sure that no NAA or ethephon gets on them as it will cause flower abortion on any fruit tree. NAA and ethephon may be used to abort the fruit on apples, crabapples, carobs, cottonwood, elm, flowering pear, horse chestnut, oaks, pine, liquidamber, and sycamore. On each species the product must be applied while the tree is in bloom. As mentioned above, mid-bloom and full bloom sprays give the best results. One spray will usually be only partially effective, but it will help in reducing the number of fruit that develop.