Pest and diseases have always been a major factor in forestry production and can cause enormous damage. In the 1960's and 1970's, U. pumila cv. pyramidalis was introduced into the Korqin, mainly from Henan, in large quantities, causing serious pests, especially Ambrostoma guadriim pressum. This greatly affected growth and the area of plantations declined drastically. Since A. guadriim pressum is difficult to control, local people generally hold the view that pests and diseases are a serious obstacle to wider-scale use of elms.
Survey and study of the pests and diseases of the Elm open woodlands is a much-needed support to the use and development of the local elm resources and environmental improvement.
The following is a short description of the main pests on elm. It is by no means an exhaustive listing.
There exists a large variety of pests of the Elm open woodland in the Korqin Sandy Lands. Leaf-eating pests are pre-dominant, including the following:
Ambrostoma guadriim pressum
Pyrrhalta aenescens
Pyrrhalta maculicollis
Of the above, A. guadriim pressum is the most dangerous. The beetle can devour the totality of the leaves of an elm tree, and the tree will die.
P. aenescens also can cause death.
Some pests are not lethal to the trees, but will form pocket-like galls on the leaves, affecting the look of the tree.
It is recently reported that the larva of one type of pest hides inside the leaf, and starts eating the leaf flesh from the central part to the edge of the leaf, forming bubble-like swellings. The leaf then enlarges and turns yellow, and finally dies.
Pests harming the stems of elms include Cossus cossus orientalis, Anoplophora glabripennis, and Anoplophora chinensis.
Cossus cossus orientalis mainly bores the lower part of the trunk. It is difficult to detect and difficult to combat when finally detected. There are many studies on this borer and its sex hormone has been successfully synthesized.
Anoplophora glabripennis mainly affects poplar trees, but once the poplar trees are felled, it moves on to elms and can cause great damage.
Some underground pests, as Maladera orientalis and Polyphylla laticollis can cause harm in nurseries.
Diseases are seldom found on elm; only Cytospora sp. sometimes infects old trees.
The harm caused by pests to the different types of Elm open woodlands differs in extent. Species diversity also has an influence.
Open woodlands with mainly Hemiptelea davidii are almost immune to leaf pests, and insect galls are seldom observed. H. davidii has intact and clean leaves.
In open woodlands with mainly U. macrocarpa, leaves are usually not eaten, but the leaf surface is covered with insect galls in numbers up to 30 galls per leaf. The leaves turn yellow and growth and looks of the elm trees are affected.
The variety of pests in U. pumila open woodlands is relatively large. Sometimes, leaves are seriously affected, but the extent of the damage differs under different conditions.
The Elm open woodland in Wusitu Nature Reserve in Kezuozhong Banner has plant species such as U. pumila, Crataegus pinnatifida, Lespedeza bicolor, Rhamnus parvifolia and many herbaceous plants. Under these conditions, in spite of the many different pests on U. pumila, damage to U. pumila is not severe.
The situation is similar with the U. pumila in the U. pumila open woodland in Xiangshui District of Wengniute Banner (Chifeng City), there is a wide distribution of plants such as Caragana microphylla and Astragalus adsurgens among many others, reducing the severity of pest-attacks to U. pumila.
However, in the U. pumila open woodland in Baixingtu Village of Kezuohou Banner, there are practically no other plant species, making the elms particularly vulnerable, and pests are rampant. The density of adult insects and larva is high, as well as pest diversity.
Ambrostoma guadriim pressum is a major pest affecting the growth of Elm. It breeds one generation annually (both adults and larvae consume leaves). The pest starts to harm Elm in late April and early May, during flushing. By mid May, larvae appear, causing great damage to trees.
Previously, chemical control was the main measure adopted for its combat, but results have not been satisfactory, and it induced chemical resistance in the pests.
In certain areas, no measures are taken anymore against the pest. The genetic variety of Ulmus in the Korqin is rich. Different species, and different individuals have different resistance. By means of a thorough survey, it might be possible to select pest-resistant strains for propagation. This would be a more permanent solution to solving the pest problem then spraying chemicals.
