136 Diseases of Truck Crops 



erroneously confused by Harter with the true mal- 

 nutrition which is also found there (but rather rarely) . 

 The blight has been shown by McClintock and Smith 

 to be a true mosaic, communicated by aphids. ' 



WEEDS 



" Disease is not confined to cultivated crops only, 

 but it also attacks weeds. In attempting to control 

 the diseases of cultivated crops, we cannot lose sight 

 of the various weed pests of the truck garden, inas- 

 much as they are liable to several important diseases 

 in common with the cultivated crops. Clean culture 

 tends to destroy those weeds which act as carriers of 

 some of these diseases. The more important weeds 

 in this family are lamb's-quarters (Chenopodium 

 album), the wormseed (Chenopodium anthelminticum) , 

 orache (Ar triplex patula), and Russian thistle (Salsola 

 tragus, Salsola kali, and Salsola pestifer). As far as 

 we know, none of the diseases which attack beets are 

 known to prey on these weeds. However, the downy 

 mildew of spinach, Peronospom effusa, attacks also 

 the lamb's-quarters, the worm seed, and the orache. 

 From this fact may be seen the importance of clean 

 culture in the control of downy mildew. In trucking, 

 as in every system of intensive culture, weeds are sel- 

 dom tolerated. But they are often overlooked on the 

 roadside and around old fences, where they cause 

 clean culture to be of no avail. Weeds should 

 never be tolerated anywhere within the reach of the 

 trucker or gardener. 



