146 MISC. PUBLICATION 4 3 4, U. S. DEPARTMENT OF AGRICULTURE 



There is little apparent correlation between soil acidity and damp- 

 ing-off losses. A soil which is neutral or only slightly acid is generally 

 favorable for growing most broadleaf seedlings. There are indica- 

 tions, however, that the types of previous crop cover is correlated to 

 some degree with the incidence of damping-off. Rotation of seedling 

 crops from year to year is advisable. None of the susceptible species 

 named should follow the next year on land previously occupied by 

 any of these species. Cereals in general are more favorable rotation 

 crops than legumes. Rye, however, is undesirable. 



A practice occasionally followed by some nurserymen has been to 

 mark the rows where the deciduous seed is sown by mixing it with 

 faster germinating truck crop seed. Lettuce, radish, and turnip seed 

 have been used for this purpose. While this method is readily applica- 

 ble to nursery procedure and does aid in locating the rows for cultiva- 

 tion and weeding prior to the emergence of the tree seedlings, the use 

 of truck crops is questionable. Unfortunately, most truck crops are 

 susceptible to the same damping-ofT fungi that commonly attack 

 deciduous tree seedlings, and they may, therefore, increase the losses 

 in the latter by building up the parasitic fungous population in the 

 seed drills. If it is desirable to mark the rows in this way, both field 

 and greenhouse tests indicate that wheat seed could be more safely 

 used. 



It is imperative to avoid injury to the cotyledons of the seedlings 

 during cultivation or in crust-breaking operations just prior to emer- 

 gence of the seedlings. Preliminary trials under controlled conditions 

 indicate that injury to the cotyledons of emerging deciduous seedlings 

 stunts the growth of the plants. Severe injury to the cotyledons 

 frequently kills the seedlings. Any reduction in the vigor of the 

 seedlings is always undesirable. 



In general, too dense or overdeep sowing increases both preemer- 

 gence and postemergence damping-off losses. Dense sowings may also 

 aid in the rapid spread of fungi through the tops of the seedlings during 

 wet weather. 



So far it has not been necessary to artificially fertilize the soil in 

 broadleaf nurseries, but no doubt this will be required in the near 

 future. It has been reported that nitrates and ammonium salts 

 increase the damping-off hazard of conifers (Jj.2, 14)- A similar 

 correlation may exist for broadleaf species. Fertilizers should there- 

 fore not be applied indiscriminately in broadleaf nurseries until it is 

 determined what the effect will be on increasing damping-off and root 

 rots. Preliminary tests, however, indicate that if the application of 

 ammonium sulfate or ammonium nitrate is reduced to 100 pounds 

 per acre, or if the application is delayed until the seedlings develop 

 woody stems, the addition of fertilizing material does not increase 

 damping-off losses. 



Methods for controlling damping-off of deciduous tree seedlings 

 necessarily must differ from those applied in coniferous nurseries, 

 since broadleaf seedlings are usually grown in rows in open fields over 

 extensive areas and are not confined to seedbeds. Many methods 

 applicable to coniferous seedbeds therefore cannot be applied econom- 

 ically to deciduous seedling nurseries. 



Prompt emergence is of importance in reducing preemergence 

 losses. Presoaking the seed in water sometimes accelerates germi- 



