42 
Colorado Experiment Station 
such fertilizer is free from this objection, its use should be regarded 
as a doubtful practice. 
SUMMARY 
1. The bacterial stemi blight of field and garden peas occurs 
generally over the San Luis Valley and Northern Colorado, and to 
a limited extent in Nebraska, South Dakota and Utah. 
2. It is characterized by the watery, olive-green to olive-brown 
color of the stems, and by the yellowish, bruised and watery- 
appearing stipules and leaflets. 
3. A severe outbreak when the plants are young may reduce 
the stand one-third. 
4. The blight is caused by Pseudomonas pisi, n. sp., which 
enters the tissue thru the stomata and thru wounds produced by 
mechanical injury. 
5. Resistant varieties offer the only satisfactory remedy for 
the trouble, altho later planting may reduce the amount of the 
injury somewhat. 
A C K N o W L ED G M E N T 
I am very greatly indebted to Professor B. O. Longyear for 
the preparation of the colored plate which appears in this bulletin, 
and to Mr. E. H. Thomas, of Alamosa, Colorado, for the many 
courtesies extended to me while studying the disease in the San 
Luis Valley, and for much of the field data presented herewith. 
EXPLANATION OF PLATES. 
PLATE % JZ 
Fig. I.— Pea leaf sprayed with a suspension of Ps. pisi, show¬ 
ing stomatal infection six days after inoculation. 
Fig. 2.—Gelatin stab culture oif Ps. pisi, kept at 20° C. and 
photographed after three days. Broad funnel-shaped liquefaction at 
surface, and slight growth along the line of the stab. 
Fig. 3.—Gelatin stab culture of Ps. pisi, kept at 20° C. and 
photographed after eight days. Stratiform liquefaction at the sur¬ 
face, and slight growth along the line of the stab. 
PLATE IT. 
Fig. I. —Photomicrograph of Ps. pisi stained with carbol 
fuchsin, 24-hour agar culture. Xiooo. 
