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Title: Number of solaria needed to predict weed seedlings in two summer crops

item EYHERABIDE, JUAN - National University Of Mar Del Plata
item CENDOYA, MARIA - National University Of Mar Del Plata
item Forcella, Frank
item IRAZAZABAL, MARISOL - National University Of Mar Del Plata

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2010
Publication Date: 1/1/2011
Citation: Eyherabide, J., Cendoya, M., Forcella, F., Irazazabal, M. 2011. Number of solaria needed to predict weed seedlings in two summer crops. Weed Technology. 25:113-118.

Interpretive Summary: Solaria are simple clear plastic sheets, about 3’ x 3’, which are placed on the soil surface in very early spring. Like tiny greenhouses, sunlight passes through them, heats the underlying soil, and promotes precocious germination of annual weed seeds. These weeds emerge at least one month earlier than without solaria. Crop scouts or growers can monitor these early-emerging weeds under solaria and make decisions regarding weed control (such as herbicide selection and rate) before the crop is planted. What remained unknown, however, was the number of solaria required within a large field to reflect the expected densities of weed seedlings accurately in summer-growing crops like corn, soybean, and sunflower. Consequently, similar experiments were performed in the Pampas (Argentina) and Minnesota (USA) to determine the necessary densities of solaria for predicting populations of common weeds in forthcoming summer crops. To detect large crabgrass with 95% confidence, one solarium was needed for every 11 acres of crop field. The acreage that can be reliably covered by a single solarium for other species was as follows: common lambsquarters (5 acres), green foxtail (5 acres), prostrate knotweed (3 acres), and wild buckwheat (3 acres). The low cost and simplicity of assessment for technique makes it more appealing than other methods of forecasting weed populations (such as soil sampling for seed bank determinations). The use of solaria for confidently forecasting weed infestation levels may be especially valuable in small fields of high-value crops. By so doing, crop scouts and growers could make better and more informed decisions regarding the choice and rate of herbicides to be applied.

Technical Abstract: The utility of solaria to predict densities of a few weed species in summer crops had been demonstrated but needed confirmation. We tested the method with additional species and determined the minimum number of solaria required to predict the presence of weed seedlings in the forthcoming growing season. Three experiments were performed in Buenos Aires Province, Argentina, and one in Minnesota, USA. Solaria were set in fields with different previous crops and soil management: no-till (2 fields) and conventional till (2 fields). Preceding crops were corn (one field), wheat (one) and double cropped wheat/soybean (two). After weeds were enumerated, solaria were removed, sunflower (1 field) and soybean (3 fields) were planted, and weeds later assessed in each crop. Results indicate that with one solarium per 1.9 ha common lambsquarters can be detected with 95% of confidence. For other species, one solarium per 4.2, 1.2, 1.0, and 1.8 to 2.7 ha (depending upon field site) for large crabgrass, prostrate knotweed, wild buckwheat, and green foxtail, respectively. The low cost and simplicity of assessment make this technique more suitable than that of soil seed bank samples to predict forthcoming weed populations. The number of solaria required for confidently forecasting weed infestation levels are sufficiently low that their use may be justified, especially in small fields of high-value crops.