572 INSECTS AFFECTING VEGETATION 



the disease in the bins remains to be ascertained. (Journal of My- 

 cology, Vol. VII, No. 1.) 



Stem Rot Wilt. The plants gradually die and wither away 

 in the field, the stem and roots being affected by this dry rot fungus. 

 Use seed from an uninfested locality and plant on fresh land as far 

 as possible. Gather and burn all affected vines. 



Soft Rot. A soft decay of the potatoes in storage, caused by a 

 black mold which appears on the surface. Handle the potatoes care- 

 fully while green and let them cure or dry thoroughly before stor- 

 ing. Pack in dry sand for long keeping. (Cal. E. S. B. 218.) 



MALNUTRITION DISEASES OF TRUCK CROPS. 



While the diseased condition does not manifest itself in precisely 

 similar symptoms in all crops, there are a number of points of gen- 

 eral resemblance. 



1. The plants stop growing when they should be making their 

 most rapid development. In many cases they slowly weaken and 

 die, while in others growth is resumed later in the season after rains 

 have occurred. 



2. There is a change of leaf color to a lighter green, especially 

 in the spaces between the veins, which turn yellowish-green or even 

 brown. In cabbage the margins of the leaves are frequently of a 

 uniform yellow color. 



3. The roots of the affected plants are poorly developed. Many 

 of the lateral feeders are killed back repeatedly, until the root sys- 

 tem becomes stubby. 



4. No fungi or bacteria can be connected with the disease. In 

 most cases none are present. 



Causes of Malnutrition. The most prominent conditions dis- 

 covered in land subject to this trouble were their acidity, deficiency 

 in humus, and the absence of desirable nitrifying bacteria. Each of 

 these factors doubtless contributes towards the diseased condition 

 of the crop. 



Acid soils are less favorable for the production of most truck 

 crops than neutral soils. A slight amount of acidity is not ordi- 

 narily injurious, but examinations made at our request by the Bureau 

 of Soils of samples from fields where cabbage suffered from malnutri- 

 tion, showed these soils to be abnormally acid, so much so that 3,500 

 to 6,300 pounds of lime would be required to neutralize an acre to a 

 depth of one foot. This condition is apparently the result of many 

 years of intensive trucking, involving the use of repeated heavy ap- 

 plications of commercial fertilizer made up in large part of chemi- 

 cals which leave the soil more acid. 



Only a portion of the fertilizer applied is actually taken up by 

 the plants, the remainder being left in a different form which will 

 have an influence on the soil reaction. For example, sulfate of 

 ammonia, muriate and sulfate of potash, and acid phosphate tend to 

 leave the soil more acid, while nitrate of soda, carbonate of potash 

 and Thomas phosphate tend to make the soil alkaline. In the brands 

 of fertilizers most used in this section, the acid forming ingredients 

 largely predominate. 



