NURSERY PRACTICE FOR PRAIRIE-PLAIXS PLANTING 145 



west. Many deciduous tree seedlings are susceptible to the cotton 

 root-rot fungus; in fact, only a few are resistant to the disease. 

 Nurseries should be located only on root-rot-free land found by 

 previous survey to be well isolated from root-rot areas. The de- 

 termination of the presence or absence of cotton root rot can be 

 accomplished through the use of plant indicators as reported by 

 Peltier {29). 



By careful examination of the vegetation present on prospective 

 nursery sites, other root diseases may also be avoided such as that 

 caused by the shoestring fungus (Armillaria mellea (Vahl.) Fr.). 



Nematodes, commonly called "eelworms," also present a consider- 

 able problem especially on the southern plains. Soils severely in- 

 fested with nematodes should be excluded from nursery sites whenever 

 possible. Here again, careful inspection of the site prior to the selec- 

 tion of the nursery is advisable. In such inspections, the roots of 

 cultivated crops or native plants can be examined for indications as 

 to whether nematode galls are present to any extent. Since some 

 1,200 species of plants are susceptible to infestation by nematodes, 

 plant indicators are generally available that can be used to determine 

 the severity of the infestation. 



Damping -off 



Both preemergence and postemergence damping-off losses have 

 been frequent for certain deciduous species. The bulk of these losses 

 occur just prior to or within 3 to 4 weeks after emergence and are due 

 to soil-inhabiting fungi. In preemergence losses the seedlings fail to 

 appear. The fungi may attack the seed directly or infect the recently 

 germinated parts, preventing in either case the emergence of the 

 seedlings. In postemergence damping-off the seedlings may fall over 

 or remain erect and dry up. Sometimes there is a constriction of the 

 stem at the ground line where infection takes place. Examinations 

 of recently damped-off seedlings will show that a portion of the roots 

 and stems are decayed. Generally preemergence losses are greater, 

 but postemergence losses are more readily detected. Preemergence 

 losses frequently exceed 60 percent of the seed sown, while post- 

 emergence losses at times run higher than 50 percent of the emerged 

 seedlings. Later in the season these losses appear as gaps in the rows 

 and are commonly referred to by nurserymen as "failed spots." 

 Other factors besides damping-off can also cause these gaps, such as 

 excessive heat, drought, birds, poor seed viability, too deep sowing, 

 and caked soil. 



The broadleaf seedlings most severely infected with damping-off 

 fungi are American elm (llmus americana), Siberian elm (U. pit m Ha), 

 black locust (Robin ia psevdoacaeia), desertwillow (ChUopsis linearis), 

 and several other somewhat minor species, such as silver buffaloberry 

 (Shepherdia arge/ntea) and honeysuckle (Lonicera spp.). Isolations 

 from recently damped-off seedlings together with pathogenicity tests 

 have shown that the most common fungous parasites of deciduous 

 species in the prairie States are Cortidum solani and Pythium ulfi- 

 mvm 20 Other fungi, particularly Fusarium spp., have been isolated, 

 but their importance has not been determined. 



-'" Wright, Ernest, deciduous-seedling diseases in midwest nurseries. V . S. Bur. Plant Indus. 

 Plant Dis. Rptr. 21: 80-82. 1937. [Mimeographed.] 



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