Oak wilt: Is plowing enough?
The ground shakes and there is a thunderous noise in the forest. All eyes and ears are riveted on the huge yellow machine crawling through the oak trees that is causing this incredible phenomenon. Moreover, a six foot steel blade is slicing through the soil, as if it were butter.
Is Steven Spielberg shooting a film here? Not really, the shaking is caused by the vibratory action of the steel blade as it slices through the soil and all the tree roots. And the noise is coming from the diesel engine as it powers both the blade and the tractor.
The purpose of this endeavor is to sever root grafts between healthy and oak wilt infected trees to control the spread of oak wilt. This seems like a radical and expensive treatment for a tree disease. But it isn't! Oak wilt can be controlled in a backyard, neighborhood, woodlot or township and installing vibratory plow line is the first step.
From the tip of Houston County up to Stearns and Chisago Counties, many people are laboring to rid their landscape of oak wilt. Normally, two plow lines are established around the perimeter of an oak wilt infection center. Oak trees to the inside of the lines are infected or are potentially infected; beyond the lines, they are free of infection. At this point, oak wilt is contained, it can't spread via root grafts to any oaks outside the plowline because all root grafts have been cut by the plow.
But is plowing enough? If you are dealing with white or bur oaks, the answer is yes. If you are dealing with red, pin, or black oaks, the answer is definitely, NO. The oak wilt fungus is still able to escape the plowed perimeter. It doesn't get out below ground, instead this wiley fungus grows up the stem in recently killed trees and produces spores under the bark. Then insects (especially picnic beetles) carry the spores to nearby, freshly wounded oaks. This is called overland spread and it usually occurs in April, May and June the year after the oak died.
So, the second step in controlling the spread of oak wilt deals with preventing overland spread. More noise. Red, pin and black oaks that died due to oak wilt this year need to be cut down before the next growing season. In addition to that, the wood needs to be treated so that the fungus is killed ( chipping, cut and split, tarped, burned, buried, etc.) before April. Trees that have been dead longer than one year do not have to be cut down for oak wilt control purposes.
The easiest and most reliable way to control oak wilt is to contain the fungus with one or more plow lines and then cut all the live and freshly wilted oak trees down within the lines. Wood from freshly wilted trees must be treated to kill the oak wilt fungus.
Many oaks and several other trees and shrubs in central Minnesota have developed tan to brown or yellow leaves from damage caused by lace bugs in August. These insects insert their piercing-sucking mouthparts into the green tissues between the upper and lower leaf epidermises. The adults can be recognized by their beautifully sculptured wings that resemble lacy networks. Their immature stages (black nymphs), black egg masses, and excrement can also be found on leaf undersides. Twenty seven species of lace bugs in the genus Corythucha feed on deciduous trees and shrubs in the United States. Control is usually not warranted on oaks and other trees and shrubs because leaf damage does not become severe until August. By this time the leaf buds for l999 are well formed and there is minimal impact on tree vigor.