BLACK ROT OF CRUCIFKROUS PLANTS. 329 



family, whereas from the same field in the dry season of 1901 he harvested a reasonably 

 good crop.* Under drainage might, therefore, be advantageous in wet seasons. 



When the cabbage-plant is well along toward maturity before water-pore infection 

 takes place, to wit, in late summer or early autumn, the disease may sometimes be pre- 

 vented from entering the head by the removal of infected leaves or portions of leavesf 

 (experiments by the writer, and by Russell) , but of course it will not answer to rob the plant 

 of all or most of its leaves and expect a crop, nor is it likely that the experiment would 

 prove very successful when applied to a small part only of a very badly diseased field 

 (Geneva Sta. Bull. 232). 



Insects which distribute this disease may, of course, be reduced in number by insec- 

 ticidal treatments. 



Care should be taken that diseased plants do not find their way into the manure-heap, 

 barn-yard, or dump-pile and thence back on to the land. Several cases have come to the 

 writer's attention where wholesale infection of fields or parts of fields could be accounted 

 for only in this way. Potter also mentions one. Heavy manuring appears to favor greatly 

 the development of this disease, but on the other hand considerable manure is required for 

 the satisfactory growth of the plants. The most that can be done is to see that the manure 

 itself does not become infected. Diseased plants should be piled with dry brush and burned, 

 or effectually disposed of in some other way. 



Losses in winter in storehouses can be wholly or partially avoided by keeping the plants 

 in all parts of the house at a uniform low temperature, i. e., slightly above freezing. Of 

 course there should be a careful inspection of such heads or roots as they are stored, and 

 those showing decayed spots or blackened bundles should be rejected. Most of the winter 

 decay has been observed to take place in the warmest parts of the houses. Such houses 

 should be well ventilated and uniformly cool. 



By far the most common method of infection of healthy fields (so far as we yet know) 

 is through the seed-bed. This should be made with the greatest care, preferably on land 

 not previously used for cruciferous plants, and certainly on land which has never been sub- 

 ject to this disease, and with seeds which are not contaminated by the presence of this 

 organism, otherwise a very considerable proportion of the seedlings may carry the disease 

 with them from the seed-bed into the field, which thus becomes permanently infected. The 

 writer observed one case in Wisconsin where about 20 per cent of the seedlings were diseased. 

 The field set from this seed-bed became so badly diseased that it was abandoned by the 

 planter in midsummer. As early as the first week in September, 58 per cent of the plants 

 set from this seed-bed, (which was on land where the disease prevailed the year before) 

 were diseased, many of them badly. This was a field which had not been previously 

 planted to cabbage and consequently one which might otherwise have been expected to 

 yield a healthy crop. 



In 1 897 Stewart suggested that the disease is disseminated by seedsmen. This inference 

 was based on the fact that he found the disease in plants which had been reserved for seed 

 and were fruiting, although not, I believe, on the seeds themselves. It is not unlikely that 

 the disease may have been introduced into this country on seed from the old world or that 

 it is now being spread from place to place by cabbage-seed, etc., derived from plants grown 

 on land subject to the disease. This, however, is conjecture and must remain so until some 

 one has demonstrated the actual presence of the organism on cabbage-seed, etc., in spring 

 or at least has obtained diseased plants in healthy soil from the use of such suspected seed. 

 The writer has also seen the disease in cabbage-plants set out for seed and coming into 

 fruit. It is also a well-established fact that much of the cabbage-seed now grown in the 

 United States comes from regions much subject to this disease. The final proof must come 



*The crop on such a field well cared for should be worth : 

 fWhenever possible, portions only should be removed. 



