Compared with the number of insects which infest fruit trees, very few attack nut trees.  One of those which does is the walnut-leaf caterpillar.  These appear as a closely congregated group of small worms which feed on the leaves of black walnut and hickory trees during the latter half of the summer season.  Very often they are all to be found on a single leaf, which should be picked from the tree and crushed underfoot.  A simple spray of lead arsenate of the strength recommended by companies selling spray material, will effectively rid trees of these pests.  Another insect often found in a nut orchard is the oak tree girdler, which also is active in the latter part of the summer.  It often causes limbs as large as an inch in diameter to be cut through and to fall to the ground.  By removing such freshly girdled branches and cutting into the hollow made by the larva, it is possible to find the live worm and destroy it.  A good way to combat this pest is to keep each tree pruned of all dead branches and to burn all broken and dead wood each fall.  While some nut trees are subject to other insects, the two described here are the most frequently found.  Fortunately, they are easily controlled if a watch is kept for them.

Chapter 14

WINTER PROTECTION OF GRAFTS AND SEEDLINGS

It is not enough to make a successful graft and to watch it carefully during the growing season, picking all sprouts off the stock, spraying it so that insects will not chew the tender leaves and bark, bracing it against windstorms and perching birds.  Each graft must also be protected from winter injury.  For many years I have studied and experimented to find a successful way of achieving such protection.  To enumerate my many experiments, from simple to far-fetched, would be to write another book quite as long as this one.  My conclusion, now, is that there is little one can do to assist nature in the process of acclimatizing grafted plants and seedlings.

I have repeatedly noticed that the place where most damage is done by the cold is at the union between stock and graft.  For example, I observed this on the European walnuts, imported from Poland, grafted to Minnesota black walnut stocks.  Although both the buds and the wood of the top remained fresh and green, the unions suffered severe, and sometimes total winter injury.  In grafts where the latter occurred, the dead cells soon caused the wood to ferment and sour.  Occasionally, a small group of healthy cells succeeded in re-establishing circulation with the unharmed, grafted top and the graft, continuing its growth, would eventually overcome the injury it had suffered.  I have seen this occur with grafts of English walnut, apricot and pecan.