68 



Yearbook^ of Agriculture 1949 



feet on the best sites. Its life expect- 

 ancy is 75 years or more. It has a short 

 trunk and a broad, massive top that 

 gives moderately dense shade. The 

 slender flower catkins and the leaves 

 appear in midspring. The bur oak does 

 well on many soils but prefers rich 

 bottom lands. Drought-resistant and 

 frost-hardy, it should be planted more 

 extensively despite its slow growth. 



Twig galls are common, but few 

 insects attack the tree. Leaf rollers are 

 observed frequently and red spider 

 occurs in dry years. Foliage diseases 

 usually are not serious. Powdery mil- 

 dew and leaf scorch sometimes do 

 damage. Gronartium rust is common 

 on oak leaves in some localities. Rab- 

 bit damage is severe to the young seed- 

 lings in the western part of the area. 

 Bur oak is susceptible to the cotton 

 root rot fungus. 



Other species more limited in use 

 are pin oak, black oak, and the chin- 

 quapin oak. In the uplands of Nebras- 

 ka, the trunks of pin oaks often have 

 vertical cracks that are the result of 

 freezing injury. 



Several broadleaf species have a 

 more restricted use. 



AILANTHUS, or tree-of-Heaven, can 

 be planted in the eastern part of the 

 central and southern Plains. It grows 

 rapidly, gives moderate shade, and 

 lives 30 to 50 years. It develops best 

 in light, moist soil but tolerates fairly 

 heavy soils. It stands smoke and dust 

 better than most trees and it is, there- 

 fore, adapted to street planting in fac- 

 tory districts. Only the female plants 

 should be used, because the flowers of 

 the male trees have a disagreeable odor 

 and the pollen is said to cause ca- 

 tarrhal troubles. The brown seeds hang 

 on the trees until late winter. Some 

 persons may consider them unsightly. 

 Ailanthus suckers so readily that it is 

 objectionable in some locations. Web- 

 worms frequently defoliate the young 

 trees. Ailanthus is moderately resist- 

 ant to cotton root rot. Moderately 

 drought-hardy, it does not stand flood- 

 ing, and it is subject to wind damage. 



EUROPEAN WHITE BIRCH, which has 

 drooping branches, can be used in the 

 easternmost part of the northern 

 Plains. This widely used ornamental 

 has several horticultural varieties. It 

 gives moderate shade, prefers moist 

 soil, and is not frost-hardy on dry soil 

 sites. On favorable sites its life ex- 

 pectancy is 25 to 35 years. It is not 

 drought-resistant. Bronze birch borer 

 causes serious injury and is perhaps 

 the main factor that limits survival. 

 The young trees sunscald readily. 



Yellow birch is better suited to dry 

 sites. The best use for the birch species 

 is as ornamentals. 



THE BOXELDER^ a native, is mainly 

 a yard tree in the northern and cen- 

 tral Plains. It develops best on deep, 

 rich, moist soil but survives surpris- 

 ingly well on the dry and droughty sites. 

 It gives moderate shade. It is short- 

 lived, 20 to 40 years, depending on site 

 quality. All in all, it deserves wider 

 use in this zone. 



One reason why it is in disfavor for 

 planting near dwellings is that the 

 boxelder bug, which breeds on the 

 female trees, enters houses or cellars in 

 search of hibernating places. Because 

 the insect lays its eggs on the fruit, only 

 male trees should be planted as a yard 

 tree in the northern and central Plains. 



NORTHERN CATALPA can be planted 

 in the eastern part of the central and 

 southern Plains. It commonly lives 35 

 to 40 years and is not especially 

 drought-hardy. The large leaves are 

 frequently affected by a Phyllosticta 

 leaf spot disease, which, however, is not 

 ordinarily serious. An insect known as a 

 midge causes a leaf scorch. Decay fungi 

 commonly invade the wood through 

 wounds; the rot often advances rap- 

 idly and shortens the life of the tree. 

 The species is not resistant to cotton 

 root rot but it is moderately frost- 

 hardy. The leaves sometimes turn yel- 

 low because of iron deficiency. Catalpa 

 is not particularly popular because its 

 blooms and seed pods can be a nui- 

 sance. Rabbits damage it. 



