84 FLORIDA STATE HORTICULTURAL SOCIETY, 1960 THE EFFECT OF COPPER ON RUST MITE CONTROL WITH FOUR RUST MITE MITICIDES Alfred, Florida during 1959. In both experi Roger B. Johnson ments brushing sprays were applied after Florida Citrus Experiment Station bloom and again in the summer using con ventional equipment and methods previously Lake Alfred described by Johnson (5). Treatments were evaluated for effective In 1957, Johnson, King and McBride (1) ness against citrus rust mite by frequent reported that zineb (zinc ethylene-bis-dithio- determinations of the density of mite popula carbamate) gave less control of citrus rust tions on fruit and by a harvest examination of mite, Phyllocoptruta oleivora (Ashm.) when fruit for mite damage in the manner also pre used with a fixed copper than when used viously described (5). Although the density alone. An explanation for this reduction in of mite populations was determined at fre control seemed to lie in the work of Winston, quent intervals in both experiments, these data Bowman and Yothers (2) who in 1923 showed are not presented in detail, but are summariz that citrus rust mite always became more ed in four tables. Tables 1 and 4 summarize abundant on trees sprayed with copper than the data obtained after application of post- on unsprayed trees. This fact was verified by bloom sprays. Tables 2 and 5 summarize the Griffiths and Fisher (3) who also reported an data obtained after application of both post- increase in the difficulty of citrus rust mite bloom and summer sprays rather than after control where zinc sulfate and lime had been just summer sprays, because the effectiveness sprayed. These findings indicate that reduc of summer sprays was modified by post-bloom tion in control with zineb through the con treatments. In general, in each case, the high current use of copper is merely due to the er the average percent of infested fruit, the ability of copper to increase the citrus rust shorter the interval of control and the higher mite problem, and therefore would occur with the population after the interval of control. other rust mite miticides. In 1958, however, The interval of control was arbitrarily set at McBride (4) reported that the addition of copper compounds to zineb sprays resulted in the approximate number of weeks between a chemical reaction in which copper ethylene- the date of application and the date when 15 bis-dithiocarbamate was formed, resulting in percent of the fruit was found to be reinfested. a corresponding reduction in the amount of In Experiment 1, host trees were the vari the zinc compound deposited by the spray. ety Pineapple. A split-plot design with three These findings with those of Winston, et al. replications was employed. Three main plots (2) and Griffiths and Fisher (3) suggest that of four trees were randomized in each replicate copper may reduce the effectiveness of any and each main plot was divided into four rust mite miticide through its ability to in sub-plots of one tree each. The main treat crease the citrus rust mite population; but will ments used on the main plots in both post- have a greater effect on zineb or any com bloom and summer sprays were: 1) no control pound with which it will react chemically, of citrus rust mite, 2) 0.5 lb. of 65% zineb per both because of its ability to increase the citrus 100 gallon, and 3) 1.0 lb. of 65% zineb. The rust mite population and because of the subtreatments used with each main treatment chemical effect of the copper on the miticide on the subplots were: 1) no copper, 2) 1.4 itself. The purpose of the study reported here lb. of 53% tribasic copper sulfate in the post- was not only to test this theoiy, but also to bloom spray, 3) 0.7 lb. of 53% copper in the determine the effect of various uses of copper summer spray, and 4) 1.4 lb. of 53% copper on citrus rust mite control. in the post-bloom spray followed by 0.7 lb. in the summer spray. Materials and Methods. — Two experiments In Experiment 2, host trees were the vari were conducted in citrus groves near Lake ety Valencia. A split-plot design with four rep Florida Agricultural Experiment Station Journal Series, lications was employed. Five main plots of No. 1152. JOHNSON: MITICIDES 85 four trees were randomized in each replicate Table 1. Effect of trlbaslc copper sulfate on post-bloom and each main plot was divided into four sub control of citrus rust mite with two amounts of plots of one tree each. The main treatments zineb applied April 13, 1959. used on the main plots in both post-bloom and summer sprays were: 1) no control of citrus Average Percent of Fruit Infes ted With Rust Mite Mltlclde In Citrus Rust Mltea»b rust mite, 2) 10.0 1b. of wettable sulfur per 100 Gallon No Copper Copper* 100 gallon, 3) 0.5 lb. of 65% zineb, 4) 0.5 Check 53.8 53.8 53.8 lb. of Chlorobenzilate 25W (25% ethyl 4, 65Z zineb. 0.5 24.0 51.1 4'dichlorobenzilate), and 5) 0.5 lb. of Kepone 37.6 65X zineb, 1.0 8.4 50W (50% 1, 2 decachlorooctahydro-1, 3, 4- 28.4 18.4 metheno-2H-cyclobuta /cd/pentalen-2-one). Average 28.7 44.4 The sub-treatments used with each main treatment on the sub-plots were identical to those in Experiment 1. Average of mite counts made May 18, June 9 and July 1, 1959. Samples of 25 fruit per tree per count. FI6.I-EFFECTS OF COPPER ON RUST MITE °Poat-bloom dosage of 53X trlbaslc copper sulfate: 1.4 lb. per 100 ON LEAVES gallon. X NFESTED UNSPRAYED . _ POSTBLOOM COP. bloom spray than on unsprayed trees. Further 80 - / \ y•- *:\ SUMMER COPPER more, where copper was used in the summer spray, about 80 percent of the fruit remained 60 infested for 6 weeks and even more fruit was infested on trees that also received a post- 40 bloom application of copper (Fig. 1). 20 These effects of copper during July, August SUMMER SPRAY and September were only modified by the summer application of zineb. Although the 5/18 6/9 7/1 7/20 8/12 9/1 9/22 10/12 initial reduction was satisfactory with all zineb sprays except 0.5 lb. of zineb plus copper, Results — Experiment 1. — Citrus rust mite the length of control varied with the copper populations on trees that received no rust mite treatment and amount of zineb used. Control miticide increased at an equal rate during was excellent for more than 12 weeks on trees May and June whether copper was applied sprayed with 1.0 lb. of zineb whether zineb April 13 or the trees left unsprayed (Fig. 1). was used alone, combined with copper, or Where zineb was used, however, there were used on trees that received copper only in the striking differences, not only between amounts post-bloom spray. On the other hand, control of zineb, but especially between copper treat was excellent for only 8 weeks where copper ments. The initial reduction was inferior where was included in both post-bloom and summer copper was included with zineb and the in sprays. Results were entirely different with terval of control was shorter. Control with 0.5 0.5 lb. of zineb. Although the summer appli lb. of zineb was excellent for about 8 weeks, cations of 0.5 and 1.0 lb. of zineb were equally but for only 5 weeks where copper was in effective on trees that received no copper and cluded. Control was excellent for 11 weeks on trees that received copper in only the post- with 1.0 lb. of zineb, but for only 8 weeks bloom spray, control was completely unsatis in the presence of copper (Table 1). factory with 0.5 lb. of zineb where copper Summer sprays were applied on July 6 was included in the summer spray. when the citrus rust mite population on un Table 2 presents a summary of the citrus sprayed trees was at its highest level of about rust mite control obtained with each of the 90 percent infested fruit, but just before a 12 spray programs used in this experiment. sharp decline. Under these conditions the These data show that: 1) the seventy of the summer population trend was markedly citrus rust mite problem increased with each changed by all copper treatments. The pop increase in the use of copper, 2) control of ulation declined about two weeks later on citrus rust mite with zineb decreased with in trees that received copper in only the post- creased use of copper, but this decrease was FLORIDA STATE HORTICULTURAL SOCIETY, 1960 Table 2. Effect of post-bloom, summer and post-bloom plus summer applications of tri- basic copper sulfate on control of citrus rust mite with two amounts of zineb applied April 13 and July 6, 1959. Average Percent of Fruit Infested with Citrus Rust Mite » Main Treatments in No Post-bloom Summer Post-bloom and Pounds per 100 Gallon Copper Copper0 Copperd Summer Copper ' Average Check 36.7 40.3 53.9 51.8 45.7 657o zineb, 0.5 7.7** 23.4 33.9 37.9 27.5 65% zineb, 1.0 3.6** 11.7** 7.4** 18.5 10.3 Average 16.0 25.1 31.7 36.1 aAverage of mite counts made on May 18, June 9, July 1, 10 and 20, August 12, September 1 and 22, and October 12, 1959.