TY - JOUR
AU - Woglum, R. S.
AB - Abstract In recent years the red and black scales of citrus trees in California have, in certain districts, been developing increasing immunity to cyanide gas fumigation. One of the outgrowths has been the widespread use of sprays; those having an oil base have been the most successful. The California Fruit Growers Exchange, which handles three-fourths of the State's citrus crop, has been investigating this particular scale problem for several years. The observations of its Pest Control Department during the past season, which have covered the insect problems in all districts, might be summarized for oil sprays in part as follows: 1. The so-called quick breaking emulsions of white oil type, characterized by high viscosity and low volatility, and which leave an oil film on the tree for many weeks, has been the most effective type of spray against both armored and unarmored scales and the red spider where used in sufficient concentration. The concentration which assures dependable results appears to be not less than 1 1/2 per cent actual oil in the case of scale insects. 2. Heavy applications of the white oil type of spray at concentrations approximating 1 1/2 per cent actual oil appeared in many instances to produce certain undesirable effects on the plant itself, the extent of which was modified particularly by the environment of the plant, by the season of year, the variety of fruit and time of its maturity. Some of these effects were retarded coloration of fruit, reduced quality, lessened crop, drop of immature fruit and of tree ripe fruit, increase of aphis and possibly increased difficulty in controlling mealybug through the utilization of beneficial insects. At concentrations much lower than lY:l' per cent actual oil these troubles largely disappeared in most districts. Scale kill, however, at lower concentrations was irregular. 3. In the case of the California red scale these white oil types of sprays give decidedly better scale kill on cutinized surfaces such as fruit and new wood than on the old wood which more readily absorbs the oil. The residual oil prevents the settling of larval scale for a considerable period on fruit and new wood. 4. The application of certain oil sprays to red scale followed within one or two weeks by a furmigation has been the most effective method of controlling the most resistant type of scale. 5. Some brands of oil emulsions are safely used with sulphur compounds under normal weather conditions whereas others are non-compatible with sulphur. The mixture of lime sulphur with certain oil sprays in the presence of calcium caseinate results in a spray which leaves little or no oily coating on the foliage, does not retard frui coloration, nor affect the set. Such combination sprays are among the most effective against immature unarmored scale but are of little value against the armored scales of citrus trees. This content is only available as a PDF. © 1926 Entomological Society of America
TI - The Use of Oil Spray on Citrus Trees
JO - Journal of Economic Entomology
DO - 10.1093/jee/19.5.732a
DA - 1926-10-01
UR - https://www.deepdyve.com/lp/oxford-university-press/the-use-of-oil-spray-on-citrus-trees-HhGdoJs0NS
SP - 732
EP - 733
VL - 19
IS - 5
DP - DeepDyve
ER -