Donald R. Sumner

Biological Control of Yellow Nutsedge with the Indigenous Rust Fungus Puccinia canaliculata

Yellow nutsedge (Cyperus esculentus L.) is a serious weed problem in the United States and other countries. An indigenous rust fungus [Puccinia canaliculata (Schw.) Lagerh.], pathogenic on yellow nutsedge, was released in early spring as a potential biological control agent. The fungus inhibited nutsedge flowering and new tuber formation. The fungus also dehydrated and killed nutsedge plants. The successful control of yellow nutsedge by a rust epiphytotic under experimental conditions demonstrates the potential use of the rust in an integrated weed management system.

Methyl bromide alternatives in tobacco, tomato and pepper transplant production.

Abstract Metam-sodium, chloropicrin, 1,3-dichloropropene (1,3-D), 1,3-dichloropropene plus 17% chloropicrin (1,3-D+C-17) and 1,3-dichloropropene plus 35% chloropicrin (1,3-D+C-35) were evaluated alone and together under a polyethylene cover as alternatives for methyl bromide in tobacco, tomato and pepper transplant production over a two-year period. Eleven different weed species, 10 genera or species of fungi, two arthropods and four species of nematodes were evaluated in three different sites. All of the fumigant candidates were successful in controlling some of the pests. However, metam-sodium alone and in combination with 1,3-D+C-17, chloropicrin, and 1,3-D+C-35 were the most efficacious. Seventy-nine different parameters were measured over the two-year period including plant stands, vigour, plant heights and control of weeds, fungi, arthropods and nematodes. Metam-sodium and methyl bromide plus 2% chloropicrin (MeBrC) were not significantly different ( P =0.05) from each other in 76 of the 79 parameters evaluated; MeBrC was significantly better than metam-sodium for three of the 79 parameters. The combination of metam-sodium plus 1,3-D+C-17 was not significantly different from MeBrC for 74 of the 79 parameters tested. MeBrC was more efficacious than metam-sodium plus 1,3-D+C-17, for two of the 79 parameters, and metam-sodium plus 1,3-D+C-17 was significantly better than MeBrC for three of 79 parameters.

Methyl bromide alternatives in a bell pepper–squash rotation

Abstract Field studies were conducted to evaluate potential methyl bromide alternatives against multiple pests in a bell pepper (Capsicum annum L.) – squash (Cucurbita pepo L.) cropping sequence. Early in the growing season, the most effective treatments in suppressing purple nutsedge (Cyperus rotundus L.) emergence through the polyethylene mulch were methyl bromide, methyl iodide, and chisel-injected 1,3-dichloropropene plus chloropicrin [1,3-D+C35 (chisel)]. However by the end of the season in 1999, only methyl bromide treatment had less purple nutsedge emerging through the polyethylene than the nontreated control. Each soil-applied treatment resulted in nematode-susceptible pepper plants with lower root-gall indices [Meloidogyne spp. (root knot nematode)] than the nontreated control, while there were no differences among treatments with the nematode-resistant pepper cultivar. Total fungi isolated from soil was lower in all treated plots relative to the nontreated control, with the exception of methyl iodide. However, methyl bromide was the only treatment that was consistently effective against Pythium spp. and Fusarium spp. A treatment of metham prior to planting squash was beneficial in reducing root-gall indices in plots treated with 1,3-D+C35 (chisel) and methyl bromide prior to the pepper crop. Methyl bromide, methyl iodide, and 1,3-D+C35 (chisel) applied before pepper resulted in squash with lower root-gall indices than the nontreated control. Glyphosate applied between the first and second crop eliminated exposed weed foliage through the polyethylene mulch, possibly muting the effects of the second crop treatment on weed densities. Results of this study indicate that there are some potential methyl bromide alternatives available to growers for use in pest control, however there does not appear to be one broad-spectrum pesticide that will replace methyl bromide. Also, an effective control for nutsedge species within the pepper–squash cropping system is still elusive.

Alternative fumigants for methyl bromide in tobacco and pepper transplant production

Abstract Tobacco and pepper are high-value cash crops in the southeastern USA that require vigorous transplants free of pathogens and insects. Typically soil seedbeds are treated with methyl bromide prior to seeding. Soil fumigants metam-sodium, dichloropropene, chloropicrin and dazomet covered with polyethylene film were evaluated at several rates alone and in combination as alternatives for methyl bromide soil fumigation of tobacco and pepper seedbeds. The studies were conducted over a three-year period, with materials applied in the fall prior to seeding at the beginning of the following year. Nematode and insect pressures were low in each of three sites, but the tests extensively evaluated weeds and soilborne fungi management. Metam-sodium at 935 L ha−1 performed well in all three tests. The combination of metam-sodium (468 L ha−1) plus dichloropropene + 17% chloropicrin (126 L ha−1) provided good control of most of the pests and had high plant yield and vigor when covered with a polyethylene film immediately after treatment. A similar treatment not covered with polyethylene film but sealed with a mechanical soil cultipacker provided poor control of weeds. Stunting of tobacco and pepper was noted, especially in plots treated at the highest rates of metamsodium plus dichloropropene and chloropicrin. These treatments had a pungent odor associated with the treatment, which persisted for several weeks after polyethylene film removal. Many of the treatments, especially metam-sodium and metam-sodium in combination with dichloropropene and chloropicrin, compared well with methyl bromide fumigation for seedbed pest control.

CLASSIFICATION OF SWEET ONIONS BASED ON INTERNAL DEFECTS USING IMAGE PROCESSING AND NEURAL NETWORK TECHNIQUES

Maintaining product quality is the key to success in the fresh fruit and vegetable market. Quality assessment with computer vision techniques is possible; however, two basic issues need to be addressed before an automatic sorting system can be developed: (1) which image features best correlate with the product quality, and (2) which classifier should be used for optimal classification. To address these issues, sweet onions were line–scanned for internal defects using x–ray imaging. Spatial and transform features were evaluated for their contributions to product classification based on internal defects. The Bayesian method was used for selecting the salient features. Spatial edge features combined with selected discrete cosine transform (DCT) coefficients proved to be good indicators of internal defects. A neural classifier performed better than the Bayesian classifier for sorting onions into two classes (good or defective) by achieving an overall accuracy of 90%. Losses and false positives were limited to 6% and 10%, respectively. The accuracy, losses, and false positives for the Bayesian classifier were 80%, 16%, and 17%, respectively.

Root diseases, populations of soil fungi, and yield decline in continuous double-crop corn.

Grain yield in the spring crop of continuous double-cropped irrigated corn declined from 11.3 to 7.2 t/ha during 1978-1983. Soil fumigation with DD-MENCS in February reduced root disease, eliminated symptoms of decline, increased yield and reduced populations of basidiomycetes, Phoma spp., Fusarium spp. and total fungi in soil. Fertility and tillage practices, a winter crop of rye, and soil treatments with fenamiphos and metalaxyl did not prevent decline(.)

Application and crop safety parameters for soil fumigants

Abstract Metam sodium alone and in combination with 1,3-dichloropropene plus 17% chloropicrin (1,3-D+C-17) were evaluated under polyethylene mulch film as alternatives for methyl bromide in tobacco and tomato transplant production for both efficacy against pests and crop safety. Eight different weed species, 10 genera or species of fungi and several agronomic criteria were evaluated at three different sites. In general both the metam sodium alone and in combination with 1,3-D+C-17 were highly efficacious when compared to methyl bromide. Short polyethylene film retention times and short aeration times resulted in poor stands and poor crop vigor while relatively long polyethylene film retention times and long aeration periods at the same rates typically resulted in high stand counts and vigor. Combination treatments were more phytotoxic to germinating seed of tobacco and tomato. Vigor and stand counts of the seedlings were higher as aeration time increased, suggesting phytotoxic residues dissipate with time. Method of application of metam sodium, either injected with chisels or sprayed onto the soil surface and incorporated with a tractor-powered tiller alone or co- applied with 1,3-D+C-17 chisel injected, did not affect the efficacy of the treatments. Caution regarding phytotoxicity must be exercised when seeding into soil fumigated with metam sodium alone or combined with 1,3-D+C-17. Additional work will be required to establish safety periods required prior to transplanting crops into fumigated soil.

Sclerotia Formation by Rhizoctonia Species and their Survival

Rhizoctonia has a “loose type” of sclerotium that is not organized into a rind, cortex, and medulla, and only Rhizoctonia spp. have sclerotia of this type (Townsend and Willetts, 1954). Isolates of AG 1-IA that have “sasaldi type” sclerotia are exceptional and have dark outer cells and have been referred to as a “primitive rind type” (Tu and Kimbrough, 1975). Sclerotia are formed primarily from compact masses of monilioid cells, but they may be formed from undifferentiated hyphae. The barrel-shaped cells average 20–22μm wide, and 30–35μm long, and are thicker than the ordinary hyphae. The central area of the sclerotium may have a pseudo-parenchymatous appearance. The sclerotia enlarge by repeated branching and formation of new cells (Townsend and Willetts, 1954). Sclerotial cells have the same number of nuclei as undifferentiated hyphae (Tu and Kimbrough, 1975).

Soilborne pathogens in a vegetable double-crop with conservation tillage following winter cover crops

Abstract A cucumber-cucumber double-crop followed by a cucumber-snap bean double-crop was grown in a system using conservation tillage in relay-cropping following winter cover crops. Twenty different winter covers were legumes, grasses, legume-grass mixtures, crucifers, or fallow (no cover, resident vegetation). Population densities of Pythium spp. (primarily P. irregulare ) and Rhizoctonia solani anastomosis group (AG-4) were greater following legumes than following grasses or fallow; legume-grass mixtures and crucifers were intermediate. Cucumber fruit rot (induced primarily by R. solani AG-4) was more severe following legumes and crucifers than following grasses; legume-grass mixtures were intermediate. In the snap bean crop following cucumber, root and hypocotyl diseases were more severe following winter covers of legumes or fallow than following grass or legume-grass mixtures; crucifers were intermediate. Root-knot nematodes ( Meloidogyne incognita ) caused injury to the second vegetable crop each year in all winter cover rotations.

Bacterial Streak and Bulb Rot of Sweet Onion: II. Epiphytic Survival of Pseudomonas viridiflava in Association with Multiple Weed Hosts

A semiselective agar medium (T-5) was used to sample environment and plant material as a habitat for Pseudomonas viridiflava. Soil, irrigation water, soybean foliage, and foliage from various weeds in an onion-growing area were assayed over a 5-year period. P. viridiflava was recovered only as an epiphytic resident from weed species that included cutleaf evening primrose, dandelion, common fumitory, purple cudweed, spiny sowthistle, Virginia pepperweed, and wild radish. The bacterium apparently overseasons in association with these weeds, because its presence was detected prior to, as well as during, the onion-growing season. Preliminary tests indicated that weed control may suppress bacterial streak and bulb rot levels.