Systemic Fungicides: Disease Control, Translocation, and Mode of Action

Abstract

The field of systemic fungicidal control has enjoyed several breakthroughs within the past 7 or 8 years, which undoubtedly will be landmarks in the history of fungicidal control. The discovery of the oxathiins (211), the pyri­ midines (61), and benzimidazoles (51, 201, 216) opened up practical possi­ bilities for the control of plant disease that have increased the intensity of work in the area of control, and subsequently on mode of action and translo­ cation. Systemic fungicides undoubtedly will cover susceptible foliage and flower parts more efficiently than protectant fungicides because of their ability to translocate through the cuticle and across leaves. For instance Ramsdell & Ogawa (166) reported that, after prebloom spray with benomyl, every sus­ ceptible flower part of stone fruit trees contained methyl-2-benzimidazolecar­ bam ate (MBC) and was protected against Sclerotinia laxa, the cause of brown rot. Also, Kaars Sijpesteijn (119) noted that the more specific modern systemic fungicides inhibited biosynthetic processes rather than cell respiration (en­ ergy producing processes). This quality should be advantageous in that con­ centrations of the fungicide too low to affect the relatively slower-growing plant might be active enough to suppress the faster-growing fungus. At least some of the systemics act at the DNA level (40). The world at this time is particularly concerned about chemical pollution, which might, at first thought, discourage work on systemic fungicides. How­ ever, if the total dosage and number of treatments needed for control can be reduced, excess chemical use could be avoided. Also systemics may replace certain dangerous chemicals. For instance Ogawa expects that benomyl may