Injury to the leaves resulting from attacks by diseases and insects is one of the most common and important causes of poorly filled nuts. Every species and variety of tree nut suffers from at least one disease or insect pest that damages the leaves and hence limits or curtails the amount of elaborated food materials they can make. In most cases the fungi or bacteria causing foliage diseases infect the leaves in early spring at the time they are unfolding and growing in size, although the infection may not be noticeable until later. These infected areas, even though they are small and not numerous enough to cause the leaf to fall, seriously impair the functioning of the leaf out of all proportion to the area directly affected. Should the infection be so severe as to cause premature defoliation, the damage will be great even though only a small percentage of the leaves falls. The disease of eastern Mack walnut known as leaf spot, or anthracnose, is one of these defoliating diseases that causes untold damage from poorly filled nuts in the current crop year, and results in a small crop or none at all the following year. The development and spread of these diseases is gradual, and unsuspecting growers do not realize the damage they cause. On other hand, the injuries caused by such insects as the webworm, the walnut caterpillar, the pecan leaf case-bearer, the Japanese beetle, and others are somewhat spectacular in that the leaves may be partly or completely consumed on portions of the trees. The injury caused by the walnut aphis, the walnut lace bug, the pecan black aphis, and others, on the other hand, is less conspicuous; but the end result is far more serious than it usually is with the leaf eating insects, because the damage caused is more widespread, almost all of the leaves on a tree being affected. These sucking insects are small in size and may be overlooked until premature defoliation takes place. If nut trees are to bear satisfactory crops of well filled nuts, the diseases and insects that attack and cause injury to the leaves must be controlled. Under normal conditions the size of the crop produced, the regularity of bearing, and the quality of the nuts harvested is proportional to the leaf area of normal leaves carried by the tree from early spring until freezing-weather in the fall.