Abstract:
Plants and trees are effectively treated with erythorbic acid or salts thereof to reduce ozone damage to their crops.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to the treatment of plants and trees with an antioxidant to reduce ozone damage to crops. 
     Ozone is a common air pollutant, particularly near urban areas, and the detrimental effect of ozone to plants and trees is well-known. One method of reducing ozone damage to plants is disclosed in U.S. Pat. No. 4,055,412 suggesting treatment of the plants with certain ureas. This patent reference includes data showing reduced damage to foliage of annual plants. However, the influence on crop yield is not discussed. Vitamin C has been suggested for increase of plant growth and productivity in H. T. Freebairn, Journal of th Air Pollution Control Association, Vol. 10, No. 4, 314 (1960). The high and frequent spraying levels used, however, make the disclosed method commercially unacceptable and economically impractical. 
     SUMMARY OF THE INVENTION 
     The invention relates to a process for the protection of plants or trees which comprises applying to a plant or tree an effective amount of erythorbic acid or a salt thereof. 
     Particularly, the invention relates to the treatment of crop plants, fruit trees and nut trees to reduce ozone damage to the crop yields of these plants and trees. More particularly, the crop plants are perennial crop plants, such as grape vines. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Erythorbic acid and sodium erythorbate are used by the food and beverage industries as antioxidants and are thus readily available products. For purposes of the invention, those salts of erythorbic acid may be employed which are agriculturally acceptable such that they are not toxic under the treatment conditions. Thus, the salt of use does not have a detrimental effect on the plants or trees being treated during treatment or thereafter. Preferably, the salt is water soluble for ease of application in aqueous solution. The preferred salt is sodium erythorbate. When reference is made below to erythorbic acid, this includes sodium erythorbate and other agriculturally acceptable salts of erythorbic acid. 
     It was found according to the invention that the treatment with erythorbic acid at the levels and frequencies set out below does not have a beneficial effect on the yield of the first crop harvested after treatment has begun. Continued treatment, however, increases the yield of the second and subsequent crops. The invention, therefore, is particularly of use in the treatment of crop plants which are not annual plants. Advantageously, the plants are perennial plants such as grape vines. The invention is further of use in the treatment of trees, particularly those trees which bear fruits or nuts. Again, continued treatment is required to attain increased crop yields in the second and succeeding years after the first crop is harvested. Trees that can be successfully treated include orange trees and almond trees. 
     Erythorbic acid is applied in an effective amount such that on continued annual treatment an increase in crop yield is obtained after the first crop is harvested. In general, erythorbic acid is applied at a range of about 1.5 to about 3.5 pounds per acre although higher rates can be used. The proper rate of application depends on the particular circumstances such as the plant or tree being treated, the ozone content in the atmosphere, the amount of rain, the amount of other oxidants in the atmosphere, etc. 
     Erythorbic acid can be applied in the form of compositions containing adjuvants such as carriers or diluents which are inert under the conditions of treatment. Such carriers and diluents are known in agriculture for the treatment of pests, and can be in the form of dusts, water-dispersible powders, high-strength concentrates, and aqueous or organic liquid dispersions. The compositions may contain usual adjuvants such as surfactants to provide essential coverage and wetting properties, and buffering agents to enhance overall solution stability. 
     Erythorbic acid is conveniently applied by spraying, e.g. by ground sprays or aerial spraying. For most effective treatment, complete coverage of the plant or tree, particularly its leaves, is essential. Per month, the level of erythorbic acid applied is at least about 500 ppm, and more likely at least about 1000 ppm or 2000 ppm. Erythorbic acid sprays or dusts are applied at levels of at least about 50 gallons, and usually at least about 150 gallons, per acre. 
    
    
     EXAMPLE 
     Three formulations of sodium erythorbate were prepared containing the following in percentage by weight and having the following pH: 
     
         ______________________________________Formulation      A         B      C______________________________________Sodium erythorbate            51.6      78.8   75.4Sodium citrate, arhydrous            13.8      20.8   --Citric acid, anhydrous            34.8       0.4   --Sodium tripolyphosphate            --        --     24.6pH                5.0       7.0    8.2______________________________________ The three formulations were dissolved in water and about 1% of the nonionic surfactant Pluronic® F68 (polyethylene oxide with condensate of propylene oxide with propylene glycol) in concentrations of 2000 and 4000 ppm erythorbic acid resulting in six different aqueous solutions. These solutions were sprayed on twelve separate plots, six plots being sprayed weekly and six other plots biweekly. One test plot was not sprayed and another was sprayed with 0.01% aqueous solution of Pluronic® F68. The fourteen treatments were as follows: 
    
     
         ______________________________________Treatment             Concentration                             ApplicationNumber  Treatments    (ppm)       Frequency______________________________________1       Control (dry) --          --2       Control (surfactant)                 --          Weekly3       Formulation &#34;A&#34;                 2000        Weekly4                     2000        Biweekly5                     4000        Weekly6                     4000        Biweekly7       Formulation &#34;B&#34;                 2000        Weekly8                     2000        Biweekly9                     4000        Weekly10                    4000        Biweekly11      Formulation &#34;C&#34;                 2000        Weekly12                    2000        Biweekly13                    4000        Weekly14                    4000        Biweekly______________________________________ 
    
     The plots were located in a fifty year old Thompson Seedless vineyard near Reedley, California in the San Joaquin Valley. This area is exposed to atmospheric ozone levels ob 10-12 pphm during mid-May or early June through mid-September, which is the growing and harvesting season for Thompson Seedless grapes. The vineyard was divided in half, both north-south and east-west to provide four quadrants. In each quadrant, there were 28 plots, i.e., two sets of the 14 plots described above. Each plot had five vines. The above fourteen treatments were thus done 8 times. 
     The plots were established in May 1984 and treatments were begun in the first week of June 1984. In accordance with standard cultural practice in the area, the vineyard was sprayed three times per year with the fungicide Bayleton®, 1-(4-chlorophenoxy)-2,3-dimethyl-1-(1H-1,2,4-triazol-1-yl)-2-butanone, for mildew control, twice with the insecticide Kryocide, sodium aluminum fluorite, for control of chewing insects and worms, and twice with dimethoate, 0,0-dimethyl S-(N-methylcarbamoylmethyl)phonsphorodithioate for control of leaf hoppers. About 36 acre-inches irrigation water per year was applied to the vicinity of each vine. 
     The mean yield of grapes per vine over the previous six years from 1977 to 1983 had ranged from about 13 to 20 kilos per vine. The mean production of these six years was about 16.5 kilos per vine, or about 10.25 tons per acre. 
     The following tables 1-3 show the fruit yields for 1984, 1985, 1986 and 1987, and the fruit quality for 1984 and 1985 determined from fruit samples taken from the five vines in each plot and subjected to standardized tests for mean berry weight, total sugars, pH and titratable acid. 
     Tables 1 and 2 show that the erythorbate sprayings provided no yield response in the first season, and an average of 12.4% more fruit during the second, third, and fourth years. 
     Table 3 shows no differences in sugar content, pH or titratable acidity due to the treatments. Mean berry size, i.e. the mean weight of 100 berries, was essentially the same for treated and non-treated vines. The higher yields without reduction in berry size or sugar content indicate that the vines were not overcropped. 
     
                       TABLE 1______________________________________Weight of fruit (kg/vine) produced by treated anduntreated grapevines.*                                      % of                              3 year Av.                                      Con-Treatment  1984   1985   1986 1987 1985-1987                                      trol______________________________________ 1 Control 18.18  15.28  16.58                         13.29                              15.05   100 2 Surfactant      17.75  14.47  17.38                         12.50                              14.78    98  only 3 &#34;A&#34; weekly      16.45  16.10  20.97                         13.92                              17.00   113 4 &#34;A&#34; biweekly      18.66  16.58  19.42                         14.31                              16.79   112 5 &#34;A&#34; weekly      18.00  17.24  18.80                         14.68                              16.91   112 6 &#34;A&#34; biweekly      19.40  17.28  19.04                         16.02                              17.45   116 7 &#34;B&#34; weekly      18.54  17.04  18.44                         13.83                              16.44   109 8 &#34;B&#34; biweekly      17.74  16.77  17.34                         15.12                              16.41   109 9 &#34;B&#34; weekly      16.75  16.04  17.80                         14.07                              15.97   10610 &#34;B&#34; biweekly      17.64  15.41  18.49                         14.50                              16.13   10711 &#34;C&#34; weekly      18.45  18.04  19.43                         15.57                              17.68   11712 &#34;C&#34; biweekly      18.10  16.87  18.06                         14.74                              16.56   11013 &#34;C&#34; weekly      17.14  16.34  18.48                         15.07                              16.63   11014 &#34;C&#34; biweekly      18.16  16.86  20.00                         15.59                              17.48   116______________________________________ *All values represent the average of eight plots (five vines each). 
    
     
                       TABLE 2______________________________________Fruit production (kg/vine) by Thompson Seedless grapes asinfluenced by various factors.                                  3 year Av.Factor         1984   1985   1986 1987 1985-1987______________________________________Treated vs. UntreatedNon-treated    17.96  14.87  16.98                             12.90                                  14.92All Treated    17.92  16.71  18.86                             14.78                                  16.78FormulationAcid           18.12  16.80  19.56                             14.74                                  17.03Neutral        17.67  16.32  18.02                             14.38                                  16.24Basic          17.96  17.02  18.99                             15.24                                  17.08Concentration2000 ppm (low) 17.99  16.90  18.95                             15.83                                  17.234000 ppm (high)          17.84  16.53  18.77                             14.58                                  16.62Frequency of ApplicationWeekly         17.55  16.80  18.99                             14.52                                  16.77Biweekly       18.28  16.63  18.73                             15.04                                  16.80______________________________________ 
    
     
                       TABLE 3______________________________________Fruit quality of Thompson Seedless grapes from treated andnon-treated vines.                1985    1984                    Non-Quality Criteria      Treated  Non-treated                          Treated treated______________________________________Mean berry wt. (g)      1.66     1.60       1.56    1.60Brix (% sugar)      20.2     20.3       20.0    20.1pH         3.76     3.75       3.58    3.61Titratable acidity      .443     .453       .490    .490______________________________________