No abstract

resulted in the highest yields in these fields. Nitrogen applications at GS-25 can stimulate tiller development As no-till acreage increases, N management guidelines need rein southeastern wheat production because winter wheat examination due to the potential effects of surface residue on N transformations and crop development. Our objectives were to deter-does not enter a dormant state in these southern latmine: (i) if N applied at Zadok's Growth Stage (GS) 25 improves itudes. grain yield of no-till winter wheat (Triticum aestivum L.), (ii) if any Applying N at GS-25 to increase tiller density and yield increase was the result of increased spring tillering, and (iii) if yield (Scharf and Alley, 1993) may be even more importhere is a critical tiller density above which N application at GS-25 tant in no-till wheat because tiller development is often in no-till wheat was not required. Research was conducted at three slower compared with conventional tillage (Weisz and sites in North Carolina with seven site-years between fall 1996 and Bowman, 1999). Tiller densities are often very low in spring 1999. A continuum of GS-25 tiller densities was generated no-till fields in the Southeast. Where wheat is planted (161-1774 tillers m Ϫ2 ) by planting at different seeding rates and dates late after soybean [Glycine max (L.) Merr.] or cotton in a randomized complete block design. Five N treatments were ap-(Gossypium hirsutum L.), GS-25 tiller densities can be plied at GS-25, and three were applied at GS-30. Tillering response to early spring N, yield, and yield components were measured. increasing as low as 350 tillers m Ϫ2 . With the rapid adoption of noearly spring N rates resulted in higher tiller densities at GS-30, and till, we believe it is important to develop N management GS-25 tiller density was a significant covariate. With GS-25 tiller systems that optimize tillering and yield. This is espedensities Ͼ550 tillers m Ϫ2 , yields were higher when all N was applied cially true in sandy Coastal Plain soils, which are comat GS-30. In years without spring freezes, wheat with Ͻ550 tillers mon to the wheat-growing regions of the Southeast. m Ϫ2 achieved optimum yields when spring N was applied at GS-25. Thus, our primary objectives were to determine: (i) if Manipulating the timing of spring N application can optimize early N applied at Zadok's GS-25 improves grain yield of nospring tillering and yield component formation. till winter wheat, (ii) if any yield increase was the result of increased spring tillering, and (iii) if there is a critical tiller density above which N application at GS-25 in no-R. Weisz, Dep. Of Crop Sci., North Carolina State Univ., Box 7620, emergence, strips were divided into 12.2-m-long plots by spray-Raleigh, NC 27695-7620; C.R. Crozier, Dep.

developed a N management strategy using these two critical periods for wheat. TheyThere is increasing evidence that scouting of winter wheat (Tritifirst determined the whole-field tiller density at GS 25. cum aestivum L.) fields to determine tiller density at Growth Stage (GS) 25 is useful in deciding if N should be applied. However, to If the tiller density was low (Ͻ1000 tillers m Ϫ2 ), applying obtain an accurate average of field tiller density, frequent and intensive

Site-specific agriculture uses maps to optimize within-field placement of agricultural practices. This technology introduces the potential to optimize pest management by varying pesticide or other inputs to better match within-field variation in pest density. Current sampling plans are designed to estimate mean density and may not be suitable for mapping, although useful sampling plans could be developed for map generation for integrated pest management. Using Colorado potato beetle, Leptinotarsa decemlineata (Say), adults, larvae, and egg masses as model systems, the influence of the sample unit on map validity was explored. Adapting currently used sampling plans for potato integrated pest management by spatially referencing each sampled stem failed to resolve spatial dependence and resulted in maps with poor reliability. Increasing the sample unit improved resolution of spatial dependence and map reliability for each life stage. A distance-walk sample unit for adult and late instar Colorado potato beetles which has high potential for map generation is introduced. Using this sample unit, generalizations about Colorado potato beetle spatial dependence are made to discuss issues of developing sampling programs for map generation. An iterative process of sampling, spatial analysis, and error analysis is suggested for evaluating sample units for mapping pest density in high value crops.

Measuring and understanding spatial variation of pests is a fundamental component of population dynamics. The resulting maps can drive spatially variable pest management, which we define as precision integrated pest management (IPM). Precision IPM has the potential to reduce insecticide use and slow the rate of resistance development because of the creation of temporally dynamic refuges. This approach to IPM requires sampling in which the objective is to measure spatial variation and map pest density or pressure. Interpolation of spatially referenced data is reviewed, and the influence of sampling design is suggested to be critical to the mapped visualization. Spatial sampling created problems with poor precision and small sample sizes that were partially alleviated with choosing sampling units based on their geostatistical properties, adopting global positioning system technology, and mapping local means. Mapping the probability of exceeding a threshold with indicator kriging is discussed as a decision-making tool for precision IPM. The different types of sampling patterns to deploy are discussed relative to the pest mapping objective.