Calag Archive

A requisite for development of bacterial phloem canker in walnuts (caused by Erwinia rubrifaciens) was the presence of the highly susceptible Hartley cultivar; although, when interplanted with Hartley, the Franquette and Payne cultivars were sometimes also attacked by the disease. The recently developed cultivars Gustine and Howe developed active cankers when inoculated, but not as extensive as those in Hartley. The age of the plant part was important to the development of the disease. The only parts of the tree developing the complete disease syndrome were the trunks and primary (scaffold) branches. Extension of the cankers in the tree was most rapid during the summer when the temperature was high. This was correlated with the effect of temperature on multiplication and growth of the bacterium in culture. Another requisite to development of the disease in these tests was the presence of openings in the thick phelloderm of the trunks and branches through which the pathogen can enter the inner bark. Of the several types of breaks commonly occurring, those produced by mechanical harvesting equipment and by sap-sucking birds were found to be infection sites. The pathogen occurred in large numbers in a slimy substance which exudes through cracks and accumulates on the bark of infected trees. They survived for at least 123 days in the exudate and were disseminated laterally as far as 20 ft in windblown rain. In addition, the exudate with viable bacteria was picked up on the pads of mechanical harvesting equipment.

Meat-eating, ground-nesting yellowjackets have plagued man in summer and early fall throughout California and in many other states. Although yellow-jackets seldom become a problem in heavily urbanized areas, there are often large populations of these wasps in foothill and mountainous localities. Yellow-jacket nests are particularly common in parks, campgrounds, and foothill residential areas. Attendance at many public and private recreational facilities has been sharply reduced because of the menace and attack of yellowjackets. There are great variations in the severity of these pests from year to year, but yellow-jackets are responsible for many stings each year. Hypersensitive reactions to their venom are quite common and have resulted in death. Even the normal degree of reaction to multiple stings can be severe enough to require hospitalization.

High-rate, deep-placement applications of the soil fumigant, 1,3-D, have been successful over a 3-year test period in controlling both the nematode vector, Xiphinema index, and the fanleaf-yellow mosaic virus disease of grapevines. A 250-gal-per-acre application rate appears to be necessary, especially on heavy soils, until results of trials with lower rates have been evaluated. Recent commercial applications of methyl bromide under continuous polyethylene sheeting indicate a good potential for control of fanleaf virus-dagger nematode disease; however, preliminary tests show that shallow applications do not give satisfactory control in the deeper layers of soil. Further tests are underway to improve the effectiveness of this material.

These studies demonstrated the effectiveness of several herbicides (preplant incorporated in furrow-irrigated fields) for the selective control of weeds in sesame. Additional trials are needed to determine the effects on yield and oil quality…as well as the early retardation in growth of sesame caused by herbicides as compared with that caused by weed competition. The use of selective herbicides offers effective, economical weed control.