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Tobacco crop area and yield forecasts are important in stabilizing tobacco prices at the auction floors. Tobacco yield estimation in Zimbabwe is currently based on statistical surveys and ground-based field reports. These methods are costly, time consuming, and are prone to large errors. Remote sensing can provide timely information on crop spectral characteristics which can be used to estimate crop yields. Remote sensing application on agriculture in Zimbabwe is still very limited. Research should focus on identifying suitable reflectance indices that are related to tobacco growth and yield. Varietal yield response to fertiliser and planting dates as well as suitable temporal windows for spectral data collection should be identified. The challenges of the different tobacco land sizes have to be overcome by identifying suitable satellite platform, with sufficient spectral resolution to separate the tobacco crop from the adjacent competing crops and noncrop vegetative surfaces. The identified suitable index should be strongly correlated with tobacco in season dry mass and yield. The suitable vegetative indices can be employed in establishing tobacco cropped area and then apply the long-term area yield relationship from government and nongovernmental statistical departments to estimate yield from remote sensing derived cropped area. BackgroundZimbabwe is the largest producer of tobacco in Africa and the world's fourth-largest producer of flue-cured tobacco (Nicotiana tabacum), after China, Brazil, and the United States of America. Tobacco production has been the leading driver behind the 34% growth in Zimbabwe's agriculture and one of the major sources of foreign currency [1]. Tobacco crop plays an important role in the economy of Zimbabwe and in the 2012/2013 marketing season, 144 million kg of tobacco was sold, earning the country $525 million [2].Crop area and yield forecasts play an important role in stabilizing tobacco prices at the auction floors. Crop forecasting is the art of predicting crop yields and production before the harvest actually takes place, typically a couple of months in advance [2]. Zimbabwe mostly relies on crop statistical forecasting/estimation, crop reports/field visits from extension officers, and statistical crop forecasts for crop yield forecasts [3]. However, data from crop estimates, which are obtained through surveys conducted after harvests, are in most countries available quite late for early warning purposes.Crop yield estimation in many countries is based on conventional techniques of data collection and ground-based field reports [4]. A variety of mathematical models relating to crop yield have also been proposed in recent years for many crops [4,5]. In Zimbabwe crop surveys are mostly used in estimating crop yield [3]. The method is costly, time consuming, and prone to large errors due to incomplete ground observations, leading to poor crop yield assessment and crop area estimations [4]. Remote Sensing Applications in Crop Area AssessmentRemote sensing is defined as acquirin...

Pythium species have a wide host range and are important pathogens of many agricultural crops. In Zimbabwe, 15 isolates of Pythium have been obtained from symptomatic tobacco (Nicotiana tabacum) in the new float seedling production system. This production system now accounts for 25 to 30% of the tobacco industry's annual requirement of 975 million seedlings. Disease symptoms are observed usually 5 to 6 weeks after sowing as wilting and yellowing of leaves followed by rotting of the roots, and in severe cases, seedling death. Up to 70% seedling loss has been reported in commercial seedbeds. In a study to fulfill Koch's postulates and to determine the susceptibility of 16 commercially grown tobacco cultivars, seedlings were produced in float trays and inoculated individually with 1 ml of Pythium (Isolate Py 19) spores (1 × 104 CFU/ml) and mycelium pipetted around the base of the stem of each seedling 9 weeks after sowing. First symptoms appeared 7 to 10 days after inoculation as yellowing and wilting of leaves. When seedlings were pulled, the lower portion of the stem and roots were brown and rotted. Seedling mortality averaged 29% and disease incidence was 96 to 100% among cultivars. All 16 tobacco cultivars were susceptible to Pythium root and stem rot and there were no significant (P > 0.05) differences in their susceptibility to the disease. The pathogen was reisolated from the inoculated seedlings. The representative isolate (Py 19) sent to Centraalbureau voor Schimmelcultures, the Netherlands was identified as Pythium myriotylum Drechsler (CBS Accession No. 125021) (2). P. aphanidermatum, causing black stem rot, and P. debaryanum and P. ultimum, responsible for damping-off (3), have been reported in the predominant conventional soil-based tobacco seedling production system, but do not cause economic losses. However, stem and root rot caused by P. myriotylum threaten the float seedling production system in Zimbabwe, although a chemical curative control of the disease has been recommended and is now widely practiced. P. myriotylum has previously been reported in the tobacco float seedling production system in South Carolina (1). To our knowledge, this constitutes the first published report of P. myriotylum on tobacco in Zimbabwe. References: (1) M. G. Anderson et al. Plant Dis. 81:227, 1997. (2) Centraalbureau voor Schimmelcultures. Retrieved from http://www.cbs.knaw.nl , 2010. (3) A. J. Masuka et al. List of Plant Diseases in Zimbabwe. Department of Research and Extension and Tobacco Research Board. Harare, Zimbabwe, 2003.

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Results of a test on the effects of Antiblue and Biocide at various concentrations and times of immersion on the growth sapstain and mould fungi are presented. Antiblue (active ingredient, sodium pentachlorophenate) was the better chemical providing com ete control at the lowest concentration of 1.5 %. Biocide, a chlorinated derivative and local suestitute for Antiblue, provided 55 control at 4 and 8 % concentrations and 74 % control at the highest concentration of 12 Yo. The time of immersion did not have a significant effect on the incidence of stain and mould.