602 INSECTS AFFECTING VEGETATION 



necessary since there are crops that can be grown on land containing 

 the root-knot organism without receiving any injury. Wheat, oats 

 and rye are examples of such crops. Clean cultivation which would 

 rid the soil of infected weeds and diseased crops would be of great 

 value in retarding the spread. The best means of control rest in a 

 proper system of rotation, using crops that are not susceptible, and 

 in this way starving out the nematodes. 



Texas Root-Rot. The first indication is a sudden wilting fol- 

 lowed by the death of the plant in most cases. The disease usually 

 appears about the latter part of June or the first of July though it 

 can be found at an earlier date and even when the plant is more 

 mature. On pulling up the plant and examining the roots closely 

 a further indication of disease can be noted. The diseased roots 

 are covered with dirty yellowish filaments of the fungus which 

 causes the trouble. Sometimes numerous scars are visible on the 

 roots. The smaller roots are dead and dried up. 



This disease is attributed to the work of a parasitic fungus 

 which lives in the ground and rapidly spreads throughout the soil. 

 It can enter the roots through wounds, but is perfectly able to pene- 

 trate healthy roots. Its strands or mycelia plug up the water con- 

 ducting vessels and cut off the water and food supply. This fungus 

 remains in the root and unlike the wilt fungus does not extend into 

 the stem. 



Deep plowing, together with a proper system of rotation seems 

 at present to be the only adequate means of checking this disease. 

 Mr. Shear, of the Department of Agriculture, advises fall plowing at a 

 depth of 7 to 9 inches. In addition to this he advises a two or three 

 year rotation with grasses or grains. The deep plowing aerates the 

 soil to quite a depth and offers unfavorable conditions for the devel- 

 opment of the fungus which thrives better in a compact soil that 

 lacks air. That this work may be properly done, the cotton mule 

 and ordinary plow will have to be replaced by heavy animals and 12 

 to 14 inch plows. 



Cotton Leaf Blight. This disease is very common on cotton. 

 It is found on the less vigorous or old leaves. It is likely to attack 

 all the leaves of weak plants if the soil is wet and the climatic con- 

 ditions favorable for the development of the fungus. This trouble 

 affects the leaves by producing spots upon them. These spots are 

 red at first, grow larger centrifugally and later turn brown. Some- 

 times the centers of these spots are white. This is the case when the 

 spores are abundant. In the last stages of disease the leaves are 

 ragged and full of holes. The fungus Ceerospora Gossypina is the 

 direct cause of this leaf blight. The strand or filaments are found 

 within the plant while the fruiting bodies or spores are produced on 

 the surface. 



Cotton Rust. Black rust, yellow leaf blight and mosaic dis- 

 ease are classed under the general term of rust. They are merely 

 different names for the same malady. 



This disease affects the leaves. The first indication of trouble 

 is shown in the yellow mottled appearance of the leaf. The yellow 



