DISC HARROWING 85 



3. Fall plowing disturbs a number of insects that pass the 

 winter in the ground. The spring canker worm, in particular, 

 passes the winter in the soil in the pupa stage, and relatively 

 few of them will survive if the land is fall plowed. In any 

 case where a bad attack of canker worm is likely to occur it would 

 seem that fall plowing might be justified for this reason alone. 



4. It gets the old and diseased leaves under the ground where 

 they will not be a source of infection for the new leaves when 

 they come out in the spring. In apple scab, in particular, it has 

 been shown that the disease passes the winter on the old leaves 

 and if these can be disposed of it will aid materially in the fight 

 for clean fruit. Where the plowing is delayed until spring most 

 of the leaves will be blown off the land into the adjoining grass 

 or hedge-rows where they will produce an abundance of spores. 

 If the plowing is done in the autumn the bulk of them will be 

 still in the orchard and will be turned under, thereby securing 

 just so much extra humus as well as getting rid of a prolific 

 source of infection. 



The two principal arguments used against fall plowing are 

 that the soil is more likely to wash and that there is more danger 

 of injury to the roots of the trees by freezing. The first of 

 these is undoubtedly correct and is a sufficient reason for not 

 practising fall plowing in a great many cases on hillsides. 

 Still on many farms there are one or more blocks which do not 

 have slope enough to be damaged in this way and on most 

 farms " every little helps," especially in the spring. 



On the freezing argument there is need of more light. It 

 would be relatively easy, with soil thermometers, to determine 

 whether the ground will freeze more deeply in a plowed orchard 

 than in one under sod or a cover crop. If the land were har- 

 rowed down at all there is much doubt that the plowed land 

 would allow the frost to enter any more deeply. 



Disc Harrowing. Of course it is not always necessary that 

 the land should be plowed. On lightish lands in particular it is 

 often possible to fit them in the spring with some type of disc 

 harrow. One of these disc harrows, if set so as to reach its 

 greatest depth, will stir the soil enough. Where soils can be so 



