Ash Plant Bug.
This common sap feeder on ash tree foliage causes discrete white speckles on the upper surface of the leaves. The leaf undersurface is marked with shiny black specks of excrement called varnish spots.
The feeding stipples are often clustered and in some severe cases, enough speckles accumulate to cause shriveling or browning of the leaves. Premature leaf drop is possible later in the season when the second generation has further stippled the same leaves. Control is seldom warranted except on stressed or newly transplanted trees.
Brown blotch mines within elm leaves are now quite obvious. Of course, this damage occurred earlier in the season and most of the larvae have already left the leaf after they ate the green tissue from between the lateral veins. A few small leafminer larvae may still be visible within the leaves but mostly what you will find within the mines are black fecal pellets. There is only one generation of elm leafminer each year. Damage can not be "cured" at this time. Damaged leaves remain on the tree and appear unsightly for the rest of the summer or until covered by new, normal growth. Trees may be stunted by severe damage but healthy tress, especially the vigorous, weed-like Siberian and slippery elms, appear to suffer no ill effects (unfortunately).
Elm Leaf Beetle.
Eggs and small larvae of this common elm leaf- feeding pest are present now. Make your observations now to determine if any small, newly-transplanted or stressed elms warrant an insecticide application. Few do.
Spraying elm leaf beetles of the second generation in July will be more useful to those people who have had problems with overwintering elm leaf beetle adults residing as accidental invaders in the house.
Shade Tree Galls.
Many galls are now apparent and creating concern. Galls can not be cured after they have formed, and they do not significantly affect the vigor of established, healthy trees. See the gall pamphlet, IC-417 for more information.
Galls that are easily noticed now include maple bladder gall on silver maple, succulent oak gall on pin oak, ash flower gall on ash, and elm pouch gall on slippery elm. The latter gall is a one inch by 3/16th inch pouch extending from the upper leaf surface and is caused by an aphid.
This article originally appeared in the June 3, 1992 issue, p. 92.