Japanese Knotweed

Outdoors

By:  Eddie Ayers, County Extension Agent

Driving around the area, I have been seeing a plant that has become a problem in both Gilmer and Fannin Counties.  The weed I’m talking about is Japanese knotweed, commonly known as crimson beauty, Mexican bamboo, or Japanese fleece flower.  It was probably introduced to the U.S. as an ornamental and a plant that has flowers that bees love. It’s fairly easy to spot as it has been growing in large patches all over the area.  The leaves are alternate, 6 in. (15.2 cm) long, 3-4 in. (7.6-10 cm) wide, and are broadly-ovate or heart shaped. Flowering occurs in late summer when small, greenish-white flowers develop in long panicles in the axils of the leaves.

This native of Japan was initially useful for erosion control, as an ornamental, and for landscape screening.  It spreads quickly to form dense thickets that can alter natural ecosystems or interfere with landscaping. It is a semi-woody, bushy perennial and a member of the Polygonaceae (Knotweed) family.  Another fact about the plant is that the stem is hollow. Knotweed spreads rapidly from stout long rhizomes. Seeds are distributed by water in floodplains, transported with fill dirt, and to a lesser extent are wind-blown. Populations escaped from neglected gardens, and discarded cuttings are common methods of distribution. Once established, populations are quite persistent and can out-compete existing vegetation.

Japanese knotweed can tolerate a variety of adverse conditions including full shade, high temperatures, high salinity, and drought. It is found near water sources, in low-lying areas, waste places, utility rights of way, and around old home sites. It can quickly become an invasive pest in natural areas after escaping from cultivated gardens. It poses a significant threat to riparian areas, where it can survive severe floods. It is rapidly colonizing scoured shores and islands.

Controlling this invasive fast growing plant is very difficult.  One method that is used is grubbing. This method is appropriate for small initial populations or environmentally sensitive areas where herbicides cannot be used. Using a digging tool, remove the entire plant including all roots and runners. Juvenile plants can be hand-pulled.  Any portions of the root system not removed will potentially resprout. All plant parts, including mature fruit, should be bagged and disposed of in a trash dumpster to prevent re-establishment.

There are several herbicides that can be used, but it takes some work for them to be effective.  One treatment method is the cut stump treatment. Use this method in areas where plants are established within or around non-target plants. Cut the stem 2 inches above ground level.  Immediately apply a 20% solution of glyphosate or a 10% solution of Arsenal AC, Polaris AC or Imazapyr 4SL and water to the cross-section of the stem. A subsequent foliar application may be required to control new seedlings and resprouts.

The other spray method is foliar spraying the plants.  Use this method to control large populations. It may be necessary to precede foliar applications with stump treatments to reduce the risk of damaging non-target species.  Apply a 1% solution of glyphosate or 20%Garlon4 and water to thoroughly wet all foliage. Do not apply so heavily that herbicides will drip off leaves. The ideal time to spray is after surrounding vegetation has become dormant (October-November) to avoid affecting non-target species.  A 0.5% non-ionic surfactant is recommended in order to penetrate the leaf cuticle.

For more information, contact me in the Gilmer County UGA Extension office.

Eastern Tent Caterpillar

Outdoors

By:  Eddie Ayers, County Extension Agent

As I ride through the county I’ve noticed some webs are back in the wild cherry trees but before you start having nightmares about the webbing we had last fall, you can rest assured that this insect is different.  This culprit is the Eastern Tent Caterpillar. The webs serve as a home to the newly emerged larvae or as we like to call them, caterpillars. The eggs are timed to hatch when the cherry buds unfurl as they need to eat to grow and complete their life cycle.

Older larvae are generally black, with long brown hair and a white stripe down the middle of their backs. Along the midline is a row of blue spots with brown and yellow lines. At maturity, the caterpillars may reach a length of 2½ inches. The adults are reddish-brown moths which have two white oblique stripes on each forewing.  These are harder to notice, but they are the final step in the life cycle.

The adult moths emerge in May and early June and lay egg masses that resemble chocolate-colored collars that encircle the smaller limbs of their host. Each egg mass is about 1 inch long. Eggs overwinter and hatch in mid-March of the following year to start the cycle again. From each egg mass, several hundred tiny feeding machines emerge, and for four to six weeks they hungrily strip the trees of their leaves. The larvae are gregarious and upon hatching they gather in the forks of the limbs and develop the web that can be seen in the trees.  This serves as their home for the larvae. From this mass of silk, the developing larvae move outward to feed on developing leaves, but they return at night and during rainy weather. The nest gradually becomes larger and larger as silk accumulates. Although the nests are most commonly seen in the forks of wild cherries, this pest can be found in other ornamental, shade and fruit trees, especially apples. While not a serious pest in the natural forest, the unsightly web insect can reduce the beauty and esthetic value of shade trees and other hardwoods in the landscape.

About four to six weeks after hatching, full-grown larvae will crawl away from their nests and accumulate on the sides of homes, on driveways and sidewalks and on various woody ornamentals in search of sites to complete the next phase of life, the pupae phase.  This phase is a shell or cocoon in which the caterpillar matures into a moth. There is concern that they may be attacking other plants, but when they do leave their web, the larvae are finished with their feeding and will do no damage to plants on which they are found. The caterpillars are primarily a nuisance and do not usually pose a danger to the overall health of a larger, well-established tree as the tree can produce another flush of foliage.  However, young fruit and ornamental trees may be damaged, so it is a good idea to remove the web from these trees.

Usually, no chemical controls are necessary or very effective.  One reason is that the web is water proof and insecticides that are applied usually do not reach the larvae but you can break open the web and apply an insecticide such as carbaryl (Sevin), BT or a pyrethroid if you would like. If you decide to use an insecticide, please read the label and follow the instructions.  In addition, the egg masses can be clipped from the limbs in late June to prevent nests from developing the following spring.

For more information about the webs in trees right now, contact me in the Gilmer County UGA Extension office.

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