168 
though it has heeu known to be attacked. Beggar weed subserves a different pur- 
pose, an<l its growth should be encouraged for the fine hay it makes and on account 
of its entire freedom from root knot. The peanut has been free from root knot in 
all the cases examined, but requires further study. Its BpeciaJ merits are its value 
as a forage for \\< gs, its adaptability to southern conditions, and its service in improv- 
ing land. Farther north and in the upper sections of the South, alfalfa, clover, and 
other legumes are available and are efficient in rotations for improvement, l>ut their 
susceptibility to root knot is unknown to the speaker. Corn is not attacked and can 
be used at will. Oats are particularly good, as is wheat or rye, but the latter two 
are not so well adapted to the far South. ( »ats may be followed by a natural growth 
of crab grass if care is taken to exclude Aniarantiis and other- weeds that harbor 
root knot. Bermuda grass allowed to remain for hay and pasture would effectively 
dispose of the root-knot problem. I can not speak of sorghum, hut sugar cane is. 
attacked by root knot to a considerable extent. The injury is not so apparent to the 
cane as it is to cotton following it the next year. The small amount of cane grown 
in the Southeast makes this of small importance, but land free from root knot should 
be chosen for it. 
Two points are important in connection with these rotations. One is that the 
preparation of the land should be thorough, and the seeding of oats, beggar weed, 
or other crop heavy, in order to secure a perfect stand and prevent the growth of 
weeds that harbor the root knot. The benefit expected from a rotation may be 
Largely lost if weeds are allowed to propagate the nematodes. 
The second point is that many southern soils are so weak and deficient in avail- 
able plant food and vegetable matter that the removal of a forage crop like hay. sor- 
ghum, or even grain, causes marked injury unless it is balanced by the culture of a 
legume. On such soils the rotation should introduce a legume at more frequent 
intervals. 
We have experiments under way to show the practicability of controlling root 
knot by rotation of crops, and we shall use the wilt-resistant cotton to avoid wilt. 
WATERMELOX WILT. 
Another instance where a plant disease compels rotation is the watermelon wilt, 
caused by a soil fungus (Neocosmospora vasinfecta var. nivea), closely related to the 
cotton-wilt fungus. This is one of the most active parasites known and is found 
almost everywhere that watermelons are grown comjnercially, especially North 
Carolina, South Carolina. < Teorgia, Florida, Illinois, and California. It is in most 
cases impossible to grow more than one crop on any land, and even where no sign of 
wilt is discovered in the first crop a second planting in the same field is almost cer- 
tain to result in failure. For that matter, it is equally impossible to succeed on land 
that has received the drainage water from a watermelon field, since the fungus spores 
are carried in this way, as many a grower can testify from his personal failures. The 
rotation here must be a lon^r one; seven to ten or twelve years are the periods allowed 
by some growers, while others never plant land a second time in watermelons. The 
period the fungus will live in the absence of a melon crop varies according to the 
nature of the soil. There is a lack of well-authenticated experiences bearing on this 
point. 
Another instance of compulsory rotation is the Fusarium wilt of tomatoes, a dis- 
ease of general distribution in Florida, where it has an important bearing on the 
trucking industry. In this case, also, only one crop can be grown with <_ r ood success, 
and a period of three to five or more years must elapse before tomatoes can be planted 
again on that land. No regular system of rotation has yet come to be practiced with 
watermelons and tomatoes. Melon growing is a transient industry, following the 
new railways and becoming unprofitable as soon as all the land near the railway 
has been planted once. The tomato wilt affects a crop that is worth $3,000,000 
annually to Florida alone. It hinders the permanent development of the promising 
trucking sections of that State and will do so until other crops come in to make a 
regular system of rotation profitable. 
The wilt diseases in general require more than rotation. They are difficult to 
control by this means, since the period of soil infection is so long, and as a practical 
means of relief it is necessary to obtain wilt-resistant varieties, if the areas to be cul- 
tivate" I are too huge to allow of using fresh land each year. The cabbage wilt, for 
instance, is a garden disease and can be dealt with by moving the garden. The 
cowpea wilt usually disappears after two or three years' rotation. The occurrence of 
this co wpea wilt, Neocosmospora vasinfecta var. track* iphila, is an indication of the need 
for crop rotation. In the northern States and in European countries clover sickness 
prevents the continual use of clover. The cowpea in the South in like manner 
finally succumbs to "pea sickness," and we find the cause to be this wilt fungus or 
