Effects of Preblossom Miticides and Subsequent Insecticide Applications on Mite Populations on Apple in Wisconsin1

Abstract

The effect of Genite 923® (2,4-dichlorophenyl benzenesulfonate), chlorbenside, and tetradifon as preblossom miticides and lead arsenate, ryania and carbaryl as insecticides on European red mite, Panonychus ulmi (Koch), two-spotted spider mite, Tetranychus telarius (L.), and phytoseiid mite populations on Red Delicious apple was studied in Door County, Wise., during 1959 and 1960. Single applications of the miticides at the open cluster stage in 1959 kept the European red mite population below 10 per leaf throughout the growing season. The population responded by increasing to higher numbers late in the season, and by laying more overwintering eggs in the miticide plots than in the fungicide (captan) check. The population in the insecticide check plot was delayed in building up, and reached a lower peak than that which occurred in the fungicide check. Suppression of the European red mite by preblossom miticides in 1959 was followed by higher populations on the same trees in 1960 in the absence of miticides. The number of eggs hatching was larger; the spring generation laid more eggs; the first summer generation was higher; and the peak population was higher than on the fungicide check trees. The number of eggs hatching on the insecticide check trees in 1960 was double that on the fungicide check. Tetradifon was the only miticide which adversely affected the two-spotted spider mite population in 1959. Populations in the miticide plots and the insecticide check plot were higher than in the fungicide check with the highest population occurring in the Genite 923 and chlorbenside plots. In 1960 the two-spotted spider mite population increased earlier and at a higher rate, and then remained higher on the former miticide trees and on the insecticide check trees than on the fungicide check. The highest phytoseiid mite population occurred in the fungicide check during 1959. The population was generally lower and peaked later in the miticide plots and insecticide check plot than in the fungicide check. In 1960 the phytoseiid population on the fungicide check trees was only about one-half that of 1959. Phytoseiids on the former miticide trees and on the insecticide check were almost eradicated by carbaryl. Six species were present during 1960 with Amblyseius fallacis (Garman) and Typhlodromus caudiglans (Oudemans) the most numerous, in that order. The European red and two-spotted spider mites had 4 generations each year. The former species reached a peak population around August 1 and then abruptly declined, being replaced by the latter species. Overwintering two-spotted spider mite females were first observed between September 1 and 7. Temperature and rainfall averaged 65°F and 19 in. from May through September of 1959, and 63°F and 22 in. during 1960. Excessive rainfall and low temperatures during May and June adversely affected mite populations in 1960. Captan had almost no effect on mite populations, lead arsenate and ryania had some, whereas carbaryl had a very definite effect, increasing phytophagous mites and decreasing predaceous mites.