When you want to know what the Elm Pests are, two main agents can be highlighted: on the one hand, the beetles that nest and consume the organic material of the tree and, in turn, the fungi, which are parasites that use these insects as carriers of their disease-contaminated spores. If you want to know more, we invite you to continue reading this interesting article.
Beetles a Pest of the Elm Tree
Elm bark beetles, barely half a centimeter long, are identified as the most harmful to this plant, as they cause very severe, even fatal, damage to these shrubs in a short period of time. These pests are mainly characterized by opening holes in the trees to lay their eggs under the outer layer of the stems and when they hatch, the thick white larvae begin to feed on all the nutrients rapidly as they move through the invasion , creating numerous tunnels in the trunk.
However, the greatest deterioration occurs when this species becomes the vector of the fungi that cause Dutch elm disease, also called graphiosis, because to the extent that they become infected when they feed on these woody plants and then disperse it to the moving from one tree to another, a multiplier effect of such damage is produced. On the other hand, reference is made to the so-called elm leaf beetles, from which they take their nutrients from their larval stage as well as in adulthood, causing total defoliation and weakening of the trees, especially if they are exposed to invasion. of rhytidome insects.
This unwanted being that damages this tree is olive green, which can measure up to a centimeter in length, has two dark colored bands on the extension of the external wings and a thin band that runs through the middle of it. At the same time, it is worth knowing that the existence of this species in the trees mentioned can be confirmed by observing that they have their eggs placed in the form of rows on the lower surface of the leaves of the plant, which later in the larva phase will have the appearance of a black worm.
Elm tree infected by bark beetle
Some of the characteristics that indicate the presence of this plague, is the amount of remains in the holes or the base of the elm trees, if this occurs, it is a clear sign that under the outer layer of the trunk there are mature beetles with their stems. feeding under it. If, in addition, the foliage of the plant is observed to be yellowing and withered, accompanied by extensive defoliation through the canopy of the tree, Dutch elm disease could be starting and therefore the beetles will move to another tree.
Elm tree infected by the leaf beetle
On the other hand, regarding the damage they cause, it can be pointed out that some specialists highlight certain similarities with the Dutch elm disease, but indicate that this pest in adulthood, when it bites the foliage, leaves marks that gradually disappear the structure. and functionality of the leaves, which makes it very noticeable the holes they make when feeding on this part of the bush, causing it to fall prematurely.
Fungi that affect the Elm
Another of the pests that affect these trees are the types of fungi, which are Ophiostoma ulmi and Ophiostoma novo-ulmi, which are integrated into the Ascomycota group and have a favorable morphology to adhere to the body of different arthropods. The life cycle of the fungus has two stages of reproduction, asexual or imperfect and sexual, starting with the spores carried by the beetles, the asexual phase begins, where the mycelium is generated, which in turn is formed by hyphae.
This mycelium gives rise to colorless conidia. These conidia rise to the top of the tree through the sap. At this stage, synemas are also formed that contain synemiospores (this is the name of the spores that are produced in the synema), which will give rise to sexual hyphae during their germination, which, when meeting with other hyphae, take place in the sexual phase. The ophiostome stage generates perithecia that give rise to eight ascospores.
It is believed that after settling on the tree, the fungus spreads through the xylem, which is more effective when the tree forms the spring vessels, since these are made up of larger cells, the fungus moves faster. The pathogen releases toxins that eventually disrupt the xylem channels, causing the upper branches of the tree to starve for water and, as a result, wilt. The fungus then feeds on the phloem of the dead tree, producing spores that stick to the body of the beetles, since when they emerge they can be transported again.
Depending on the season in which the tree is found, if it is infected in spring by the elm plague, the specimen will die that summer or the following year, but if it is infected in the middle of the year it will show greater resistance, thanks to its wood that has narrow channels that make it difficult for the fungus to spread. In turn, they can react to the pathogen by generating parenchymal barriers to isolate the fungus, preventing the Ophiostoma from reaching the vascular exchange.
On the other hand, it can be noted that, thanks to the research of experts in the field of elm pests, they point out that the tree can also block the channels where its nutrients flow using some species of gels and linden (thickeners), preventing vertical propagation of the illness. The accumulation in the xylem of mansonones, which are fungicidal substances, has also been described in affected specimens.
Diseases caused by Elm Pests
Among the most common diseases that the elm presents, is fundamentally the so-called Dutch disease, produced by the graphium ulmi Schwarz, which causes an evident decay of the tree and notable symptoms that show the seriousness of the situation and that usually trigger the death of the trees. infected trees. As well as the so-called agaric rot, generated by Armilaria mellea fvalh, ex Fr. Kummer; white spongy caries caused by Ungulina ulmaria (Sow) Pat, as well as trunk rot caused by Pholiota aegerita Quél.
Methods to combat Elm Pests
Chemical controls have traditionally been used to eradicate pests and diseases of all plants. However, these are expensive, harmful to nature, and often not as effective given the severity of some fungi. Therefore, research and applications of genetic improvement have been carried out under optimal ecological conditions to make them more resistant to strains of parasitic organisms, especially those related to elm disease, in order to extend the reproduction of the strongest trees to plant.
Notwithstanding the above, if the vegetation is already affected by these elm pests, it is better to apply an effective treatment to eliminate them, applying insecticides or fungicides at the base of the plant, to control all exposed beetles and those that are not visible. and thus prevent the appearance of new pests. In this sense, it is desirable that this type of tree, due to its great vulnerability to the attacks of these organisms, is vital to keep them under a good irrigation system, biological controls and ensure the rest of the conditions that favor a healthy elm.
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