Sclerotinia minor (Jagger) Kohn is serious and increasingly prevalent pathogen of peanut (Arachis hypogaea L.). Peanut stem tissues were reported to differ in their resistance to S. minor, but field performance is not always correlated with laboratory evaluations of resistance to Sclerotinia diseases in other crops. Differences in genotype performance in field and laboratory results may reflect differences in mechanisms of resistance. The objective of this study was to characterize mechanisms of resistance to S. minor in selected peanut genotypes by using agar culture tests, wounded and nonwounded stem inoculations, and field trials. For the culture test, sap was expressed from five genotypes with different levels of field‐resistance toS. minor. Each extract was incorporated into an agar medium, which was overlaid with a dialysis membrane. The fungus produced distinctive infection hyphae on the media. Genotype extracts differentially affected size of terminal and secondary hyphae and the number of hyphae per organized cluster. Nine genotypes were evaluated for resistance to S. minor in two stem inoculation tests. Inoculation sites were wounded in the first method, and were not wounded in the second method. Significant differences in lesion size were found with both methods, but more differences were found among genotypes in the nonwounded inoculation. Genotype performance in culture and stem inoculation tests was not correlated with performance in the field. These studies demonstrated that although some genotypes had resistance to stem colonization by S. minor, other mechanisms account for most of the resistance expressed in the field.
Five field studies, during 3 yr (1990–1993) and at two locations, were conducted in eastern Virginia to determine the effect of naturally occurring barley yellow dwarf virus (BYDV) infection on yield components of susceptible ‘Barsoy’ winter barley (Hordeum vulgare L.) and susceptible ‘Wakefield’ winter wheat (Triticum aestivum L.) At each study site, yield components were compared for grain harvested from 25 disease loci and 25 adjacent asymptomatic areas. Rhopalosiphum padi L. and Sitobion avenue Fabr. aphid populations were monitored weekly by visual inspection of plant leaves and stems. Aphid numbers were low in all studies, with only one site exceeding the economic threshold of 15 aphids/row ft at any time during the season. The BYDV, PAV strain, was present in all five studies; the MAV strain was present at only one location in 1990–1991. Fall infection was predominant and occurred in all studies, with plants showing typical disease symptoms. Symptoms consistent with spring infection were observed in only one study. With few exceptions, fall infection significantly reduced tiller height, head number, seed number, number of seed per head, 1000 seed weight, and yield. Yield components were not equally affected. Seed number, number of seed per head and yield were reduced the most, by 28%, 22%, and 34%, respectively, compared with only about a 5 to 13% reduction in the other components. Spring infection significantly reduced number of seed per head and 1000 seed weight, but not the other yield components. Research Questions Barley yellow dwarf virus (BYDV) is a recurring plant disease problem in many winter small grain fields in Virginia. What are the yield losses associated with BYDV infection? Economic thresholds for aphids in Virginia small grains are currently set at 15 to 25/row ft in the fall, and 100 to 300/row ft in the spring. Are these thresholds too high, allowing economic loss to occur from BYDV infection transmitted by viruliferous (virus carrying) aphids? Literature Summary Grain aphids are recurring pests of small grains throughout much of the central and eastern USA. The greatest threat to yield reductions associated with aphids (in the eastern states) is the ability of these pests to transmit BYDV, a sporadic but important problem in Virginia winter small grains. Documented yield losses have ranged from 3% to almost 15% in some commercial fields. Crop loss depends on many factors such as the number of aphids, whether the aphids are viruliferous, and when the virus is transmitted in relation to crop growth stage. Low aphid populations in the fall can cause significant crop losses due to fall BYDV infection, while spring BYDV infection has less impact. Because of this, aphid economic thresholds are set at 15 to 25/row ft in the fall, and 100 to 300/row ft in the spring. However, these thresholds may be too high and allowing yield reductions by BYDV infection. New aphid management insecticides are now available to small grain farmers. But they can be expensive and should only be used where BYDV is...
Efficacy of selected insecticides, with and without adjuvants, was evaluated against CEW in soybean. Double-crop ‘Holladay’ soybean was planted in 15-inch rows on 29 Jun. Treatments were applied on 31 Aug with water using a CO2 pressurized backpack sprayer calibrated to deliver 12.0 gpa at 18 psi through 8002VS fiat fan nozzles spaced 18 inches apart on the spray boom. A randomized complete block design was used with 4 replicates; plots were 10 ft by 30 ft. Treatments were evaluated 1 h before and 2 and 6 DAT by comparing numbers of larvae using a rigid beat cloth sampling technique. Percent pod damage was determined 9 DAT by randomly selecting 3 plants from the center rows of each plot and recording the number of damaged pods. Yield was determined by combining the 3 center rows of each plot (97.5 row ft) using an Almaco small-plot combine. Data were analyzed using ANOVA and LSD statistical procedures.
The objective of this paper was to identify the factors that generated economic growth during the 1950-1960 decade for the counties making up the Tennessee Valley region.Principal component analysis was applied to one set of data in order to derive an index of economic growth. Factor analysis was employed as a method for identifying and summarizing the structural re lationships between the many variables thought to affect regional economic growth so as to combine highly related variables into clusters called fac tors.The derived factors were then utilized as independent variables in a multiple regression analysis of the variations in the index of economic growth derived from the principal component analysis.The results of this study indicated the importance of the interrelation ships between social, political, and economic factors in explaining economic growth.
, 1998: Effects of at-planting (seed and field broadcast) and fall foliar broadcast insecticide treatments were evaluated on grain aphid populations (EGA and BCOA, combined), BYDV symptoms and wheat yield. Two experiments were conducted, one using conventional and one using no-till practices, in a producer's field in Henrico County, VA. In each experiment, Southern States FFR 555 was planted 20 Oct using a 7-inch row spacing. Gaucho 480 was applied to seed before planting. Di-Syston 8E and Karate 1EC were broadcast with water using a Melroe Ingersoll-Rand SprayCoupe Model 220 sprayer calibrated to deliver 20.0 gpa at 30 psi through 8004VS flat fan nozzles spaced 20 inches apart on the spray boom. Di-Syston was applied at-planting and Karate was applied in late Nov. A RCB design was used with four replicates on plots were 25 ft x 300 ft each. Plots were sampled for aphid populations on
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