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What are you afraid of? Some have phobias of small six-legged organisms that crawl within their houses, swarm around their food, and even bite them in some instances. Many of these creatures can be found in the Order Insecta. Insects are commonly thought of as pests. Annoying creatures that only disrupt the way of life for ordinary people. Some of these insects can actually be very beneficial. They are known as key pollinators for major food crops all over the world and help aid in the maintenance of beautiful flower gardens.
Along with pollinating, some insects can act as predators to be utilized as a biological control of other infestations. However, there are some within this order that can have detrimental effects on crops, buildings, and environmental habitats. One of the greatest insect problems that foresters are combatting today is the Emerald Ash Borer.
The Emerald Ash Borer is very harmful to Ash trees that are grown in the United States and Canada.
Knowing all the information about this problem, it is reasonable to contemplate what other pests could have the potential to have negative effects on other tress that are grown specifically for their products. Black Walnut trees have been grown for many uses including some health benefits and herbal remedies, but it is mainly grown for its highly prized hardwood. When Black Walnuts are fully grown, they can be worth significant amounts of money. There are costs when growing Walnut trees and there is always the potential for something to have a negative effect on the plant, either insect, viral, or fungal related.
All of which have the capability to reduce the plants ability to photosynthesize, move metabolic materials, and reproduce successfully. Carefully analyzing both species of trees and their associated pests could lead to a better correlation between two problems. This includes looking at the Emerald Ash Borer and its ecology, establishing similarities and differences between Black Walnut trees and Ash trees, and determining if the Walnut Twig Beetle has the potential to be as harmful to trees as the Emerald Ash Borer.
The disheartening pest called the Emerald Ash Borer is scientifically known as Agrilus planipennis. This species of beetle can be classified in the family Buprestidae otherwise known as the wood boring beetle family. Like many within this family, the Emerald Ash Borer has a flat head and are similar to a bullet-like shape. This allows them to easily move within the trunks of the trees when they are boring into the wood. After mating female Emerald Ash Borers “deposit their eggs individually on ash trees, between layers of outer bark and in cracks and crevices of the trunk and major branches” (Biology and Life Cycle of Emerald Ash Borer). Once the immatures hatch, they begin feeding on the tree. They make their way towards the phloem, where they do most of their feeding. The phloem contains the photosynthetic materials that are utilized by the borer. During their movement through the tree bark, they create small tunnels. If there is a major infestation, some tunnels can overlap within the wood of the tree.
While feeding on the phloem, materials that are needed for growth and development of the tree are intercepted by the Emerald Ash Borer larvae. This leads to wilting of the tree and some limb dieback, eventually killing the tree. Once they molt into adults, the destruction only continues. They emerge from the Ash tree trunk and continue to feed on the foliage of Ash tree species. Woodpecker damage on large limbs of Ash trees are good indicators of an Emerald Ash Borer infestation. Larvae are prey items for woodpecker, but the woodpeckers damage the tree while searching for the larvae. This type of damage is displayed visually “resulting in light-colored (orange-pink) patches of bark along the usual grey” color of Ash tree bark (Biology and Life Cycle of Emerald Ash Borer). They can be widely dispersed, flying many kilometers before finding an acceptable location to mate and lay their eggs. This type of dispersal has enabled them to become a major problem in a relatively short amount of time.
Ash trees are grown and harvested for their hardwood properties. Ash wood is most famously used in the production of baseball bats. However, Ash has many different uses including flooring, furniture construction, and tool handles. It is also sought after for its beautiful finishing capabilities and its ability to mimic Oak wood materials. Ash trees are grown all over the United States and in parts of Canada and Europe. They are even grown in parts of Asia, where the Emerald Ash Borer originated. Unfortunately, “all true ashes such as green ash (F. pennsylvanica), white ash (F. americana), and black ash (F. nigra) are susceptible to the Emerald Ash Borer” (Emerald Ash Borer and Your Woodland). Since these pests can infect almost every species of Ash within North America, eradication efforts have been inadequate. The pest is thought to have been brought over in infected wood that was used in pallets during international shipping of products.
While being used in a variety of different consumer products, Ash was sought out within the lumber industry. There was not a shortage of demand at any point when logging for Ash trees of any species, there was a steady flow of products. Once the Emerald Ash Borer was labeled as an invasive species in 2007, there was a major change within the lumber market. The classification of invasive worried loggers and growers. Some estimated that the Emerald Ash Borer would eventually cause most Ash species to become extinct in North America. There was a rush to harvest all eligible Ash trees before the devasting effects of the insect took place. “The short-term effect of this blight on the Ash population served to sharply increase the inventory of Ash logs available to mills” (Ash Timber Prices Improve). This led to a great supply of Ash wood that the market did not have the demand for, flooding the entire market and ultimately led to the decrease in lumber prices for Ash species. Even though Ash is used in a multitude of products, the industry did not have the capacity to withstand a drastic harvest event. With the Ash trees still growing in North America, it is assumed that the supply of Ash lumber will soon decrease rapidly. This caused by the harvest progression of most of the Ashes growing and the continuation of the Emerald Ash Borer spread. Eventually, the demand will increase the price of a wood that will soon be very scarce to find in healthy, harvestable conditions.
Another type of tree that consumers have adopted to planting and growing themselves is the Black Walnut, Juglans nigra. Black Walnuts can grow in most of the United States and in parts of Canada. They produce large, rounded nuts that are then dispersed by squirrels and other animals. Black Walnuts are known to have a vigorous life style, allowing them to thrive in multiple locations throughout North America, its native habitat, (Beineke). Black walnut trees can grow up to 125 feet tall. The majority that are grown and harvested average a height of 80 feet tall. Varying between locations, “Black Walnut normally begins flowering about mid-April” (Index of Species Information: Black Walnut). Most interesting about Black Walnut trees is the relationship it has with other plants. The roots of Black Walnut’s produce a chemical compound known as juglone. This substance is toxic to some coniferous species and vegetable varieties (Index of Species Information: Black Walnut).
Recently, there has been an increase in the purchase of saplings and seeds of Black Walnut trees. Landowners are designating plots of land to establish a growth of these trees for the production of lumber. Black Walnuts can be planted on 8-12 foot centers, creating a grid pattern where the trees are essentially grown in rows. Some of these producers even collect the walnuts that fall from the trees each year and sell them as well. Black Walnut trees are considered one of the most durable hardwoods grown in North America. It is used in furniture, cabinetry, and gun stocks. Like Ash, this wood has a smooth finish that can be stained to enhance its appearance. According to multiple sources, it is hard to accurately estimate the value of Black Walnut trees in the future. There has to continue to be a high demand for walnut lumber and there will be inflation associated with market values of products. “According to Bruce Thompson, author of “Black Walnut for Profit”, a mature, well-established stand of Black Walnut trees could potentially be worth around $100,000 per acre in timber value” (Wallin). Some plots can be worth much more, depending on the age of the stand, stand density, and size of the trees. Individual tree values vary on the quality of wood within the tree and the amount of board feet the tree can produce. Some of the highest quality trees sell for thousands of dollars each. Since this would be considered a perennial crop, it takes years to see returns on investments and foresight to dedicate the necessary amount of land needed to grow these trees. To ensure the desired yield quality, proper care and maintenance must be practiced.
Both Ash and Black Walnut trees are considered to be hardwoods. Their wood is even used in most of the same products because each characteristically have smooth, stainable, straight grains. Surprisingly, there are even more similarities between Black Walnut trees and Multiple Ash species. Hardiness zones for both range from 2-9 on the U.S. Hardiness Zone Map. Most trees grow between 50 and 85 feet tall, growing at a moderate rate per year, with only Green Ash growing at a fast-yearly rate. When comparing types of trees, both are shade intolerant, wanting at least six hours of sunlight a day. Variable soils are no problem for either tree to grow in with both able to flourish in acidic, alkaline, loamy, moist, sandy, well-drained, wet and clay soils (Black Walnut: Juglans Nigra). All of which also rely on some sort of animal dispersal to transport seeds to new locations. When comparing Black Walnut and Ash trees, there are many qualities the two have in common with each other. Environment, hardiness, and growth rate can all factor into productivity within an area and the tree’s ability to survive when under stress. What sort of stresses could hinder the productivity of Black Walnuts? Since Ash trees have been devastated under the stresses of the Emerald Ash Borer, what is preventing a similar scenario to occur in a principal associate of the Ash trees, the Black Walnut?
While there are some native species of wood borer insects targeting Black Walnut trees, there is a pest that has recently been considered to be problematic to these trees, Pityophthorus juglandis otherwise known as the Walnut Twig Beetle. It belongs to the insect family Curculionidae, or the weevil family. Most can be recognized by elbowed antennae and large snout. The Walnut Twig Beetle has a large pronotum that covers its head. They are also reddish-brown to brown in color and on average are only 1.5-2mm long. They originate from Mexico, Arizona, and New Mexico. Like Emerald Ash Borers, the Walnut Twig Beetle creates tunnels or galleries beneath the bark of the tree and feed on the phloem of the tree, often aggressively. This behavior alone usually only has little harm on most trees. However, there is a relationship between the Walnut Twig Beetle and the fungus Geosmithia morbida.
This association between this disease-causing fungus and the beetle enables the beetle to be a vector. A vector is defined as an animal with the ability to transmit a pathogen. Insects can begin the development of disease by visiting infected plants, causing wounds on the plant leaving a site for pathogens to enter the plant, weaken the plant through feeding on them, and by moving diseases to multiple healthy plants that exponentially increases the spread of the pathogens (Agrios). From what is known, Geosmithia morbida comes into contact with the Walnut Twig beetle once the beetle begins its feeding on an infected plant. The fungus is ingested by the beetle and is then distributed into the healthy plant and the inoculation of the disease begins. Because of the insect vector, fungi is able to be transported further than it could.
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