The effect of certain added materials on bordeaux mixture in the control of peach blight and leaf curl

Abstract

Experiment Station. S Italic numbers in parentheses refer to "Literature Cited" at the end of this paper. 'T"he literature is not unanimous regarding designation of the qualities that determine the efficacy of insecticides and fungicides. Thus the amount of spray per unit of surface remaining after application, is called "initial spray deposit" (16), "deposition" (8), "initial adhesiveness" (9), and "retention" (fB); the distribution of the material over the surface is "coverage" (3) ; and the resistance to weathering is "adherence" (10) or "tenacity" (2). Horsfall, Heuberger, Sharvelle, and Hamilton (8) designate as "fungicidal value" that ability of the material to prevent spore germination; but the present writer prefers "toxicity" or "toxicological value." [491 ] 492 Hilgardia [VOL.14, No.9 EFFECT OF PETROLEUM OIL, COTTONSEED OIL, AND BENTONITE ON TENACITY OF BORDEAUX Each spray treatment was given in the autumn to four randomized plots, each containing four Paloro peach trees of fairly uniform size. The treatments were bordeaux mixture (10-10-100) to which had been added different amounts of petroleum-oil emulsion, tank-mix petroleum oil, cottonseed oil, or bentonite. Emulsion A was a flowable-type emulsion containing 80 per cent, by weight, of a petroleum oil of 102 seconds Saybolt viscosity and 70 per cent unsulfonated residue. Tank-mix oil was a. petroleum oil similar to that in emulsion A emulsified with blood albumin just before it was added to the spray tank. Emulsion B was a paste-type emulsion containing 82 per cent, by weight, of a petroleum oil of 96 seconds viscosity and 94 per cent unsulfonated residue. The cottonseed oil was a commercial grade. The bentonite was a natural product containing some magnesium oxide. As soon as the spray dried, 200-to 250-gram samples of twigs produced during the past summer were collected and weighed. The twigs were then cut into convenient lengths, placed in glass jars, and shaken for 10 minutes with 500 co of nitric acid water (20 cc nitric acid, of 1.42 sp. gr., per liter). The wash water was filtered and tested for copper by the sodium diethyl dithiocarbamate method" that Callan and Henderson (1) described. Other collections were made after several inches of rain had fallen (December or January) and a.gain just before the buds swelled in the spring (February). The amounts of copper on these samples were the basis for determining the weather resistance or tenacity of the bordeaux. Experiments of 1936-37.-Sprays were applied November 20,1936, well before the first major wave of twig infection by Coryneum which was initiated during rains falling between December 20 and 28. The season was marked by recurrent attacks of the disease during January, February, and March-particularly severe being a wave initiated in early March. According to the November 20 analyses (table 1), considerable variability existed in the initial amount of copper deposited by the various treatments. These data, together with those secured in other years, will be discussed later.

Depositional and weather-resisting qualities of some copper fungicides affecting the control of peach blight

“…After the sprays had dried, samples of twigs produced in the previous. growing season were collected; the copper deposits were determined by the iodo-metric method as described in another paper (Wilson, 1942). In late February, other samples were taken and the residues remaining after weathering were determined.…”

“…For a study of this point, the sprays had to be applied under conditions less variable than those in the orchard. A laboratory atomizing applicator, described earlier (Wilson, 1942), was employed. The surface to be sprayed was a thin film of cellulose nitrate deposited on glass slides.…”