161 
III. To control natural enemies — 
'a) Weeds. 
^b) Insects. 
'c) Plant diseases. 
This paper relates primarily to the last item, the r61e ol plant diseases in crop rota- 
tion, though it manifestly will be necessary to include some consideration of the 
other related factors. 
The problems of crop rotation vary in different parts of our country, and most of 
what has been written on the subject relates to our northern condition-, where plant 
diseases have an influence quite subordinate to the fertility factors. The principal 
plant diseases that modify rotations in the North are potato scab, cabbage club foot, 
onion smut, etc., which are familiar examples to us. This paper deals with southern 
problems, the section treated being bounded on the north by Virginia and on the 
wot by the Mississippi River. Here in this eastern cotton belt rotation of crops is 
needed more and practiced less than anywhere else in the country. 
P2JESENT PRACTICES. 
The methods that have contributed so Largely to the decline of agriculture in the 
South have changed but little as yet. All practices still center around the great 
staple crop — cotton — which consequently will be the principal topic of this paper. 
There is, first, the all-cotton system on immense numbers of acres, where no rotation 
is practiced and only commercial fertilizers are used to maintain the productiveness 
of the land; that cotton is not an exhaustive crop is amply proved by the fact that 
much land remains productive to-day after forty years of continuous cropping. Sec- 
ond, cotton with corn; the most common rotation now practiced in the South is 
cotton alternating with corn, which may or may not have cowpeas {'hinted between 
the rows. Third, fallowing or resting is practiced where land is exhausted. This is 
not done as much as it was before the era of commercial fertilizers; but old farmers 
still lay stress upon the mysterious influence of '" broom-sedge" in renovating land, 
and on the sea islands of South Carolina fallowing is the accepted practice, and all 
good fanners allow half their land to lie out and grow up in weeds while the other 
half is planted in cotton. This is their regular rotation, except that some plant half 
the fallow in cowpeas, making a four-course rotation — cotton, rest, fallow, cowpeas. 
The fallowing system is a wasteful one. We see no reason why a useful forage 
crop might not be grown instead of the weeds, and a legume put in to gather more 
nitrogen. The rotation with corn shares with the all-cotton plan the great defect 
that it gives continuous clean culture, a feature especially bad in the South, where 
the intense heat of the summer sun and the torrential winter rains burn up or wash 
away more plant food than is taken up by the crops. The soil is deprived of its 
humus, and its physical condition is lowered. This reacts directly on the cotton 
plant, producing the pathological conditions commonly referred to as "shedding of 
bolls" and '"rust." It is not merely that the size of the plant is reduced from the 
lack of nutrition, but it has become more sensitive to changes in environment and is 
easily thrown out of balance, so that it sheds its bolls more readily when subjected 
to sudden drought or any other unfavorable circumstance. 
Rust in cotton, probably the most destructive of its diseases, causes an annual loss 
mounting into the millions of dollars, all due primarily to lack of rotation. It 
occurs on land where the supply of vegetable matter has been depleted, and espe- 
cially when there is also a lack of potash or poor drainage. If one visits a farm 
where a good system of rotation is practiced no complaint of rust will be heard, for 
the disease is easily overcome in this way. 
Other common diseases of cotton, such as anthracnose, angular leaf spot, cerco- 
spora, etc., which are due to fungus or bacterial parasites and spread through the air 
rather than in the soil, may not be so directly controlled by rotation, but they would 
undoubtedly be diminished, both by the superior vigor and hardiness of the cotton 
plants and by the diminution of the opportunities for infection. 
PRESENT NEEDS. 
The great need of the South to-day is the general adoption of a better system of 
rotation, for this would imply more diversification of crops. To control the diseases 
we have mentioned it will be necessary to restore and maintain the supply of veg- 
etable matter in the soil, and to do this two things are essential — (1) that some 
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