EFFECT OF AGRICULTURAL OPERATIONS AND PRECIPITATION ON VERTICAL-DISTRIBUTION OF A NUCLEAR POLYHEDROSIS-VIRUS IN SOIL

The Anticarsia gemmatalis nuclear polyhedrosis virus (AgNPV) was relea sed in two soybean plots in September, 1991; the soil in the plots was then sampled periodically through July, 1992, to determine the effect s of normal agricultural soil manipulations and precipitation on verti cal distribution of the polyhedral occlusion bodies (POBs). The amount of AgNPV increased at all depths down to 37.5-50 cm as long as there was virus-contaminated plant matter, even dead soybean refuse, above t he soil surface. Agricultural operations (dishing, harrowing, mowing, planting, cultivating) had no effect on the amount or vertical distrib ution of AgNPV in soil. After the crop refuse was dished into the soil in November, the amount of POBs began decreasing at all depths; these decreases continued over winter and at times appeared to be associate d with precipitation. The POBs were no longer detected below 37.5 cm b y April, 1992, or below 25 cm by July, 1992. However, in July there we re still 274 POBs/g in the top 2.5 cm of soil. Thus, agricultural oper ations should not hinder contamination of soybean leaves by AgNPV from its soil reservoir. (C) 1996 Academic press, Inc.