40 MISC. PUBLICATION 4 4 0, U. S. DEPARTMENT OF AGRICULTURE 



brown and cause a frayed and tattered appearance of the foliage. 

 Narrow brown to black streaks are produced on the stem, petioles, 

 and other parts of the vine. The fruit pedicel lesions often extend 

 over into the calyces and pod tissues. Most of the pod infections 

 appear to begin under or near the calyces. 



The organism causing this disease has a minimum temperature for 

 development of about 37° F. The optimum temperature is around 

 70° and the maximum between 88° and 93°. The fungus is appar- 

 ently carried from year to year in plant rubbish and in the soil and 

 may also be carried in the seed. All varieties tested so far have 

 proved susceptible but show varying degrees of infection. 



No satisfactory control measures are vet known. 



(See m.) 



SEED SPOT 



A spotting of green pea seeds, apparently due to a nonparasitic 

 cause, has been found on the markets in shipments from several im- 

 portant pea-growing sections. This disease is most common in the 

 Surprise variety and closely related types, and in crosses between 

 Surprise and other varieties. On the market there is no way of 

 detecting this trouble except by opening the pods and examining 

 the seeds. The spots appear as small circular, water-soaked areas on 

 the seed coat next to the pod wall (pi. 11, A). Sometimes these areas 

 are greenish yellow and resemble the lesions caused by the bacterial 

 blight organism. So far, however, no bacteria or fungi have been 

 found associated with this trouble and usually not all seeds in a pod 

 show spotting. The seeds usually are normal in size and appearance 

 except for the slight discoloration of the seed coat next to the pod 

 wall. Affected seeds germinate well, and may or may not produce 

 spotted seeds in the following crop, development of the blemishes 

 apparently depending on environmental factors or soil conditions 

 that are not yet understood. 



(See 159.) 



SPOTTED WILT 



The spotted wilt virus is becoming more and more prevalent on a 

 wide variety of vegetable crops in the field and on the market. Many 

 of the symptoms manifested are very similar to those of mosaic and 

 related virus troubles. See Mosaic, page 37. 



Spotted wilt of peas is characterized by brown streaks on the 

 stems and leaf veins and by brown spots on the leaves and pods. 

 Irregular brown patterns with concentric markings may also appear 

 on the pods, or the pods may be stunted, distorted, and collapsed. 

 Sometimes the seeds also show brown spots. 



The infective principle (virus) that causes this disease is carried 

 from plant to plant by thrips. 



(See 120, US.) 



THRIPS INJURY 



(Thrips fabaci Lind.) 



The feeding punctures made by thrips on pea pods sometimes 

 cause blemishes (hat tend to reduce the market value of severely 



