Effect of fungicide application on activity of Neozygites fresenii (Entomophthorales: Neozygitacaea) and cotton aphid (Homoptera: Aphididae) suppression.

The development of resistance in aphid populations highlights the importance of biological control as a pest management tactic. Four treatments were evaluated to determine the effects of pesticides on the population dynamics of Aphis gossypii Glover and Neozygites fresenii (Nowakowski) Batko: (1) weekly applications of the insecticide imidacloprid (Provado 1.6 F); (2) weekly applications of the fungicide chlorothalonil (Bravo 720); (3) applications of imidacloprid (Provado 1.6 F) when aphid densities exceeded 30 aphids per leaf, and (4) untreated control. Differences in aphid density among the four treatments were shown only to be significant during the 1997 growing season; however, aphid densities were greater in the chlorothalonil treatment than in the other treatments during each growing season. Percentage of N. fresenii-killed aphids was most often highest in the chlorothalonil treatment as well. The fungal epizootic caused by N. fresenii was delayed approximately 1 wk in the chlorothalonil treatment when compared with the other treatments. This delay allowed the aphids to temporarily escape suppression by the fungus and to continue to increase in density until the density-dependent effects of the epizootic overwhelmed the aphid population. N. fresenii also appeared to persist in the system when imidacloprid was in use and does appear responsible for initial aphid reductions. Treatment did not appear to have a large influence on yield outcome. Yield was variable from year to year and from location to location.

Peanut-cotton-rye rotations and soil chemical treatment for managing nematodes and thrips.

In the southeastern United States, a cotton-peanut rotation is attractive because of the high value and extensive planting of both crops in the region. The objective of this experiment was to determine the effects of cotton-peanut rotations, rye, and soil chemical treatments on management of plant-parasitic nematodes, thrips, and soilborne fungal diseases and on crop yield. Peanut-cotton-rye rotations were conducted from 1988 to 1994 on Tifton loamy sand (Plinthic Kandiudult) infested primarily with Meloidogyne incognita race 3, Belonolaimus longicaudatus, Sclerotium rolfsii, Rhizoctonia solani, and Fusarium oxysporum. Continuous peanut, continuous cotton, cotton-peanut rotation, or peanut-cotton rotation were used as main plots; winter rye or fallow as sub-plots; and cotton with and without aldicarb (3.36 kg a.i./ha), or peanut with and without aldicarb (3.36 kg a.i./ha) plus flutolanil (1.12 kg a.i./ha), as sub-sub-plots. Population densities of M. incognita and B. longicaudatus declined rapidly after the first crop in continuous peanut and remained low thereafter. Neither rye nor soil chemical treatment affected M. incognita or B. longicaudatus population density on peanut or cotton. Cotton and peanut yields from the cotton-peanut rotation were 26% and 10% greater, respectively, than those from monoculmre over the 7-year study. Cotton and peanut yields were improved 9% and 4%, respectively, following rye vs. fallow. Soil chemical treatments increased yields of cotton 23% and peanut 32% over those of untreated plots. Our data demonstrate the sustainable benefits of using cotton-peanut rotations, winter rye, and soil chemical treatments to manage plant-parasitic nematodes and other pests and pathogens and improve yield of both cotton and peanut.

First Report of Cotton Lint Rot by Pantoea agglomerans in Georgia.

In September, 1996, cotton bolls of NuCotn 35B, DPL 90, Hart 404, NuCotn 33B, and DPL 5415 grown in three eastern Georgia counties were found to contain internal lint rot within single or multiple locules. No external boll damage was observed. Damage was always more severe on NuCotn 35B. Internal lint damage occurred in bolls tips that formed abnormal fissures or openings nearest the sutures. Such bolls often contained an additional locule. In one field of NuCotn 35B, over 30% of the bolls containing the abnormal tip morphology had locular lint rot. The abnormal boll morphology described previously as supernumerary carpel syndrome (SCS) has been associated with internal lint rot (2). Rotted lint within the locules was usually reddish brown mixed with yellow and olive to olive-brown. Gram-negative bacteria were isolated from infected bolls on nutrient agar and shown to be Pantoea agglomerans on the basis of rod shape, yellow pigmentation, and utilization of glucose both in an oxidative and fermentative manner without gas production. These characteristics are typical of bacterial strains belonging to the Enterobacteriaceae (facultative anaerobes). Even though bacterial taxonomists are uncertain about the species identification of certain genera within this family, strains 92-52D and 92-52E, isolated from NuCotn 35B, were identified within the complex P. agglomerans (Ewing and Fife) Gavini, Mergaert, Beji, Mielcarek, Izard, Kersters, and De Ley (=Enterobacter agglomerans;=Erwinia herbicola (1). Previously, P. agglomerans was reported to cause lint rot of cotton locules associated with SCS and stinkbug (Euschistus impictiventris) injury (2). In California, the lint rot bacterium was isolated from the stylar canal, especially when SCS was present. To confirm pathogenicity of the isolates, 30 bolls of NuCotn 35B were excised, brought into the laboratory, and surface disinfested with 70% ethanol. Bolls were inoculated by dipping sterile dissection needles in bacterial colonies from 24-h cultures on nutrient agar and immediately puncturing (3- to 7-mm depth) 10 bolls per strain. An additional 10 bolls were wounded with sterile needles for comparison. The bolls were placed in a moist chamber and incubated at 28°C for 72 h. Locule damage was rated on a 0 to 3 scale in which 0 = no damage, 1 = trace damage, 2 = moderate discoloration and deterioration, and 3 = total discoloration and deterioration of the fiber. Bolls inoculated with strains 96-52D and 96-52E had mean boll rot indices of 2.0 and 1.5, respectively, and Koch's postulates were completed for both strains. The noninoculated bolls had a discoloration indice of 0.6, but 7 out of 10 were rated as 0. The infections of the three bolls by P. agglomerans may have been caused by natural inoculum that survived the surface disinfestation. These findings are the first report of P. agglomerans causing lint rot of bolls with SCS in Georgia. References: (1) J. Mergaert et al. Curr. Microbiol. 8:327, 1985. (2) G. M. Watkins, ed. Compendium of Cotton Diseases. American Phytopathological Society, St. Paul, MN, 1981.

Toxic and antifeeding actions of melittin in the corn earworm, Heliothis zea (Boddie): comparisons to bee venom and the insecticides chlorpyriphos and cyromazine.

The acute and sublethal effects of melittin were compared to whole bee venom, chlorpyriphos and cyromazine injected into the corn earworm, Heliothis zea (Boddie). Melittin had twice the toxicity of crude venom, but only 3% that of chlorpyriphos. Melittin significantly reduced growth rate, diet consumption and food utilization efficiencies of fourth instar larvae. Bee venom and insecticides reduced these parameters to a lesser extent.

Effects of cuticular duvane diterpenes from green tobacco leaves on tobacco budworm (Lepidoptera: Noctuidae) oviposition.

Five cuticular chemical components isolated from the green leaves of tobacco introductions (TIs) and a commercial tobacco cultivar were tested for their effects on tobacco budworm,Heliothis virescens (F), oviposition in cage bioassays, and field experiments. These chemicals were sprayed onto budworm-resistant TI 1112 tobacco which produces low levels of most cuticular components. Individual duvane diterpenes (α- and ß-4,8,13-duvatrien-1-ols and α- and ß-4,8,13-duvatriene-1,3-diols) increased tobacco budworm egg laying on sprayed TI 1112 plants.cis-Abienol, docosanol, and docosanyl myristate were inactive.