Calag Archive

Russian thistle (Salsolu iberica Sennen and Pau), a plant native to Eurasia, has become a widespread weed in California and other western states. In these areas it serves as a favored alternate host plant for the beet leafhopper, Circlulifer tenellus (Baker), vector of the destructive “curly top” virus of such crops as sugar beets, tomatoes, and melons. The plant also harbors a variety of other insect pests such as lygus and stink bugs. These large, bushy “tumbleweeds” are common sights on neglected or abandoned croplands, vacant residential and industrial lands, and highway and railroad right of ways. The plants fracture at the base at maturity and scatter seeds as they are blown about by the wind. Tumbleweeds fill irrigation and drainage canals, pile up against fence and buildings, fill backyards and swimming pools, and startle motorists who encounter them while driving. Unsightly accumulations of the dead, dry plants are not only difficult to remove, but also create fire hazards and traps for other windblown debris.

Investments in the U.S. food and fiber system from production through final sales are so large that few of the individuals and firms comprising it can afford to leave their destiny to chance or individual whims. Large-scale retailers and food service firms require consistent supplies at predictably uniform prices, as do the food manufacturing firms that supply them. Moreover, individual farmers with large capital investments cannot gamble on future market outlets.

Lesion nematodes (Pratylenchus sp.) are recognized as pathogens of apples in the eastern part of the United States, and various preplant control measures have been demonstrated beneficial in re-establishing orchards. During the early ′60s two small-scale preplant fumigation trials were conducted in replanted orchards in the Oak Glen area of San Bernardino County, California. Many tree replants or interplants in established orchards in this area were dying or demonstrating lack of vigor at that time. Soil and root analysis showed that high populations of Pratylenchus sp. were present in the orchards and were believed to be a major contributing factor to tree failure in these orchards. The results of these two early trials showed that preplant measures for nematode control were beneficial.

Cantaloupe is grown on a wide variety of irrigated soils in southern California. Of the root-knot nematodes, Meloidogyne incognita, is the most common species which attacks this crop. This nematode, as well as other species of the genus, is generally a problem on coarsertextured soils in the southern valleys. When M. incognita is present at planting time it stunts the young plants soon after emergence and causes severe galling of the roots (photo). Plants infected in the very early stages of growth remain stunted and unproductive and seldom bear marketable melons (photo). Localized infestations in a field range in size from a few square yards up to several acres. Sometimes entire fields are uniformly infested with the nematode and, if proper preplant control measures are not taken, the entire field may be unproductive.

Because scions and rootstocks are sensitive to heat, they sunburn readily following grafting. When walnut rootstock is grafted, either the year planted or the following year, ordinary whitewash or a 50% solution of interior latex paint and water have commonly been applied for sunburn protection. In orchards where these sunburn treatments have been applied, erratic growth and poor grafting frequently occur, suggesting the whitewash treatment might be responsible. The experiment reported here was conducted to determine the influence of a sunburn protection treatment on growth of newly grafted trees.