Runoff from crop land can enhance eutrophication of fresh water and hypoxia in sea water. We simulated rain at 25 mm hr‐1 for 2 hr, 8 d prior and 1, 14, 29, 49 and 108 d after fertilization and planting of corn (Zea mays L.). Experimental sites received 50 kg N, 45 kg P, and 125 kg K ha‐1 as granulated fertilizer broadcast and incorporated to a depth of 150 mm. An additional 118 kg N ha‐1 was surface‐banded as solution fertilizer at Day 28, which was 1 d prior to the Day 29 rain. The study was conducted for 2 yr on a Tifton loamy sand (fine‐loamy, siliceous, thermic Plinthic Kandiudults) with a slope of 4.5%, on micro‐ (5.57 m2) and meso‐scale (622 m2) plots. Runoff was equal for the two scales of plots. There were greater runoff losses of soluble‐P from meso‐ (1.4 kg ha‐1) than from micro‐plots (1.0 kg ha‐1). Nitrate‐N losses averaged 2.7 kg ha‐1 and bioavailable‐P losses were 2.3 kg ha‐1. Greatest NO3‐N and soluble‐P losses occurred the day after application of the soild fertilizer, whereas bioavailable‐P loss was greatest at Day 14 and 29. No increase in NO3‐N losses was found 1 d after the application of urea ammonium nitrate solution, possibly indicating that liquid fertilizers are not as susceptible to runoff losses as solid fertilizers. Results of this study should encourage the use of small plots, thereby saving research time and expense and provide data useful for estimating losses at similar sites.

There are few studies that relate the timing and amounts of pesticide washoff from plant foliage during rainfall to runoff losses at the edge of the field. We hypothesized that foliar deposits, if washed onto the soil slowly during rainfall, may then undergo less leaching during the period of infiltration that occurs prior to soil saturation and runoff, thus exhibiting larger runoff losses than pesticides on/in the soil at the beginning of rain. We measured the runoff of ethalfluralin, metolachlor, chlorothalonil, and rhodamine WT dye using simulated rainfall on 450 m2 mesoplots planted in peanut. Ethalfluralin was applied preplant incorporated, and metolachlor was applied preemergence on bare soil. Chlorothalonil and rhodamine WT were applied to the peanut canopy at maturity. Rainfall was simulated 24 h after each chemical application (in May and July, 1998, and May and August, 1999) using raindrop sprinklers, applying 5.5 +/- 0.5 cm over a 2 h period to create reasonable worst-case conditions; between 3 and 9 mm of runoff was generated. Volume-weighted average concentrations of chemicals in runoff were 7, 104, 163, and 179 ug L(-1) for ethalfluralin, metolachlor, chlorothalonil, and rhodamine WT, respectively. The total amounts of chemicals lost in the runoff events were 0.04 +/- 0.01, 0.2 +/- 0.1, 0.6 +/- 0.5, and 0.2 +/- 0.1, as percents of amounts applied, respectively. Rhodamine WT formed a vivid red solution on wetting and provided visual clues to the dynamics of chemical washoff/runoff. The washoff from rain-exposed peanut foliage appeared to be complete within a few minutes of the beginning of rainfall, and disappearance of dye from rain-exposed soil surface occurred within the first 10 min of rainfall. However, dye was present in runoff water at near-constant concentrations throughout the 2 h runoff event, indicating that near-constant amounts of chemical remained in the soil extraction zone. These results confirm earlier studies showing that soil incorporation at application significantly reduces runoff losses and that a majority of foliar residues can be washable if rainfall occurs within a few days after application. Runoff losses of foliar-applied pesticides were small relative to washoff amounts but were sensitive to runoff timing relative to washoff.

Nuclear polyhedrosis viruses such as the one isolated from the celery looper, Anagrapha falcifera (Kirby) (AfMNPV), have the potential to be successful bioinsecticides if improved formulations can prevent rapid loss of insecticidal activity from environmental conditions such as sunlight and rainfall. We tested 16 spray-dried formulations of AfMNPV to determine the effect of different ingredients (e.g., lignin, corn flour, and so on) on insecticidal activity after simulated rain and simulated sunlight (at Peoria, IL) and natural sunlight exposures (at Tifton, GA). The most effective formulation contained pregelatinized corn flour and potassium lignate, which retained more than half of its original activity after 5 cm of simulated rain, and almost full activity after 8 h of simulated sunlight. In Georgia, formulations made with and without lignin were compared for persistence of insecticidal activity when exposed to natural sunlight. In addition, the effect of fluorescent brighteners as formulation components and spray tank additives was tested. Results showed that the formulations with lignin had more insecticidal activity remaining after sunlight exposure than formulations without lignin. The inclusion of brighteners in the formulation did not improve initial activity or virus persistence. However, a 1% tank mix significantly enhanced activity and improved persistence. Scanning electron micrographs revealed discreet particles, and transmission electron micrographs showed virus embedded within microgranules. Results demonstrated that formulations made with natural ingredients could improve persistence of virus-based biopesticides.