Calag Archive

Recent studies provide very strong evidence that quick decline disease of pears is caused by a virus transmitted by the pear psylla rather than by an insect toxin alone.

Graft transmission studies provide further evidence that quick decline pears is caused by a virus and that, under experimental conditions, it cause the disease in the absence of pear psylla.

Big vein of lettuce is a disease well known to lettuce growers in California and Arizona. The disease is characterized by coarse chlorotic bands along the leaf veins, as shown in photo, and by a delay in maturity and a reduction in head size. The disease does not kill lettuce plants and marketable crops are produced in spite of big vein infections. During the winter and spring when lettuce is shipped from the Imperial and Salinas valleys and big vein is severe, salad bowls across the country commonly contain lettuce leaves with big vein symptoms.

A constant search is carried on by scientists of the Department of Vegetable Crops at Davis and Riverside for plant breeding materials—among both wild species and cultivated varieties —that will contribute resistance to specific plant diseases of concern to the vegetable industry. After crosses are made between the resistant types and commonly cultivated varieties, a prolonged process of backcrossing and selection has to be followed. The progenies have to be checked and rechecked to be sure that the resistance is not lost. Ultimately the breeding lines are brought back to horticulturally desirable types. Then they have to be tested for their adaptability to the various climatic areas of the state— usually with the help of county farm advisors. The processing and shipping ability of the crop has to be determined, as well as edible quality. Only after all of these evaluations is the decision made to release a new variety to the seed industry for seed increase and distribution to growers. This report reviews some of the varieties developed in the past few years that have found a place in the state's production, as well as some new varieties just released.

The problem of spider mite resistance to acaricides has stimulated interest in the use of petroleum oils as a means of mite control. In 1963, plots were established in a Red Delicious apple orchard to evaluate one new acaricide and several oils of varying viscosity and unsulfonated residue against the European red mite. Among several acaricides that had been studied in 1962, the most promising material was Morestan, a new cyclic carbonate insecticide.

Increasing interest in wildlands and the pressures exerted on existing range indicate that greater utilization of these areas is possible by introduction of better and more highly productive plants. The University's agronomy department maintains nurseries for evaluating plant species for use on range and wildlands at the Davis campus, Riverside campus, South Coast Field Station, West Side Field Station, and the Hopland Field Station. The Davis nursery is the largest, and promising species are planted at the field stations to determine degrees of adaptation, production, growth characteristics, and disease resistance. A shrub nursery at Davis also allows study of the behavior and adaptability of woody range plants.

Enveloping perforated bituminized fiber and plastic subsurface tile drain in a safflower straw sandwich gave excellent performance in maintaining field drainage in Sacramento-San Joaquin Delta tests. A 1-inch glass fiber mat also gave good performance, but tile drains tested without a protecting filter envelope were not successful. The drain failure resulted from sealing by the muck soil, which reduced water movement into the tile—probably a major reason for disappointing experiences with tile in the Delta.