Yield Responses of Alfalfa to Simulated Alfalfa Weevil Injury and Development of Economic Injury Levels

Abstract

Although the alfalfa weevil Hypera postica (Gyllenhal)) is an important alfalfa (Medicago sativa L.) pest, relatively little is known about how defoliation at specific plant developmental stages affects yield. This study was conducted to characterize yield responses of alfalfa to simulated alfalfa weevil injury when injury was initiated at the early bud stage of the first growth cycle and to develop economic injury levels for the alfalfa weevil. The study was conducted on a silty clay loam (fine, montmorillonitic, mesic Typic Argiudoll) in a 3.6-ha alfalfa (cv. Haymaker) field near Walton, NE. Sixteen 1 by 1-m plots were arranged in a randomized complete block design with four treatments in each of four replicates. Treatments consisted of three levels of simulated alfalfa weevil defoliation and an undefoliated check. Leaflets were removed over 10 d. Dry matter yield and stem density responses were measured for both the first and second growth cycles. Simulated alfalfa weevil injury did not affect stem density before the first cutting or during the entire second growth cycle. When injury occurred during the early bud stage, the most significant effect was the loss of leaf tissue. Yield differences among treatments for the first growth were highly significant, and the relationship between percentage defoliation and percentage yield reduction was linear both years. Defoliation injury imposed during the early bud stage of the first growth cycle did not affect yields or stem densities of the second growth cycle. Dry matter yield responses of the first growth cycle were used to calculate economic injury levels for third and fourth instars feeding at the early bud stage of alfalfa development.

Economic injury levels for the scarabaeid Maladera matrida infesting peanut fields in Israel

“…This concurs with the studies of other soil dwelling insects, establishing the information that first instars feed on organic matter before they feed on plant roots (Forschler & Gardner, 1990). It should be noted that some monitoring programs, e.g., for the Colorado potato beetle, Leptinotarsa decemlineata (Say) and for the alfalfa weevil, Hypera postica (Gyllenhal), do not include first instars (Martel et al, 1986;Peterson et al, 1993).…”

“…Young grubs may cause negligible damage to yield, and intermediate developmental stages may cause substantial damage. By contrast, late developmental stages may not feed at all and may not cause any damage (Nyrop & Wright, 1985;Dent, 1991;Peterson et al, 1993). In our study, the effect of different years on the developmental stages of M. matrida was not significantly different, so that the data from our 3-year study could be pooled.…”

“…By contrast, late developmental stages may not feed at all and may not cause any damage (Nyrop & Wright, 1985;Dent, 1991;Peterson et al, 1993). Young grubs may cause negligible damage to yield, and intermediate developmental stages may cause substantial damage.…”

Leaf Area Assessment By Image Analysis

“…(Guo & Sun, 2001) A measurement of leaf area is apparently simple and fundamental. However, it is crucial for providing framework for future research in areas like agronomy, ecology, carbon cycle research, plant pathology; host plant resistant (Jansky et al 1999) , pesticide activity (Gonzalez et al 1992, Hoy and Hall 1993, Wheler and Isman 2001 and plant insect interaction (Peterson et al 1993, 7 Hammond et al 2000. Moreover, leaf area is an important parameter for phenotypic growth analysis of mutant screens.…”

The Probabilistic Economic Injury Level: Incorporating Uncertainty into Pest Management Decision-Making

“…Data for the I and D variables were obtained from Peterson et al (1993). Injury per pest equivalent, I, was expressed as the total consumption in leaf dry weight by both third and fourth instars (milligram/ larva).…”