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Tomato spotted wilt virus (TSWV) continues to be a major production constraint in flue-cured tobacco in Georgia. Pretransplant applications of acibenzolar-S-methyl (Actigard) and imidacloprid (Admire and Provado) were evaluated in field trials, singly and in combination, in four locations in 1999. Acibenzolar-S-methyl was also evaluated for its effect on growth and yield, potential phytotoxicity, and activity against tobacco blackshank incited by Phytophthora parasitica var. nicotianae. Acibenzolar-S-methyl alone and with imidacloprid significantly reduced TSWV incidence in all four locations, but the disease incidence in the imidacloprid-treated plots was lower in only one of the four sites. Applications of acibenzolar-S-methyl starting at 4 weeks posttransplant had no effect on TSWV incidence, size, or yield of tobacco compared with nontreated plots. Acibenzolar-S-methyl did not reduce blackshank in a field trial. In the greenhouse, rates of acibenzolar-S-methyl ranging from 0.25 to 8 g a.i. per 7,000 plants showed reductions in growth that did not seem to be related to rate. Pretransplant applications of acibenzolar-S-methyl were critical to the suppression of TSWV, while initial applications made posttransplant had no effect, suggesting that plants must be protected prior to introduction into the field.

The peanut root‐knot nematode [Meloidogyne arenaria (Neal) Chitwood race 1] causes significant economic losses in many peanut (Arachis hypogaea L.) production areas of the world. The objectives of this study were (i) to examine the peanut core collection to identify sources of resistance, (ii) to estimate the level of resistance that occurs in the U.S. germplasm collection, and (iii) to examine the geographical distribution for resistance in peanut germplasm. Seven hundred forty‐one accessions from the core collection were tested in greenhouse trials. The egg‐mass rating for cultivar Florunner, the susceptible check, was 4.0 on a 1.0 to 5.0 scale with a nematode reproduction rate of 15 496 eggs per gram of fresh root weight. Fifty‐six accessions exhibited an egg‐mass rating of ≤2.5. Thirty‐six core accessions showed a reduction in root galling, egg‐mass rating, egg count per root system, and egg count per gram of root in comparison to Florunner. Twenty‐one accessions showed a 70% reduction in egg count per root system and per gram of root, and two accessions showed a 90% reduction of these variables in comparison with Florunner. The 56 resistant indicators from screening the core collection identified 39 clusters in the entire germplasm collection that should be examined more thoroughly. China and Japan appear to be valuable geographical sources for resistance to this nematode.

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