The seasonal occurrence of cotton bollworm, Helicoverpa armigera, mortality factors and egg and larval distribution on cotton were determined. The peak of occurrence of the pest was recorded at 57, 78, and 106 days after emergence (DAE) on cotton planted within the season, in Guimba, Nueva Ecija, Pozorubio, Pangasinan and Polomolok, South Cotabato, Philippines, respectively. The pest occurred earlier in late-planted cotton than in the early-planted ones, with peaks of occurrence at 54 and 75 DAE, respectively. Rainfall, relative humidity, air temperature and sunshine duration did not significantly influence the population trend of the pest. The mortality factors on the various insect stages were: physiological defects, diseases, natural enemies and dispersion. The eggs were predominantly laid on top of young leaves and growing terminals of the upper third-portion of the cotton plant. The larvae were confined on the upper third-portion from 43 to 64 DAE, at the middle-third portion from 78 to 85 DAE and at the upper third from 92 to 106 DAE. The availability and type of fruiting forms were the primary cues for the pattern in the egg and larval distribution within the cotton plant

"Most Paraguayan cotton is produced in small family plots, with much lower productivity than in other countries. Based on a series of surveys of farmers and traders, this study reviews several aspects of cotton growing including agricultural practices, profitability levels, peasant institutions, technical assistance, credit availability, and trading"--Handbook of Latin American Studies, v. 57.

This thesis presents an analysis of maize yield levels and yield gaps between predicted and observed yield types in the coffee-tea, main coffee and cotton agro-ecological zones on the eastern slope of Mount Kenya, in Embu district. Maize yield data were obtained from experiments performed by the Fenilizer Use Recommendation Project for the 1986-91 period, plus the results of maize trials executed during this study for seasons I (mid-March to September) and II (October to mid-March) of 1992-93. Investigations on the influence of fertilizer application, weeding and insect control on maize yields were included in the latter trials at Embu study site. Maize yields from selected farm fields within the three agro­ecological zones were determined from crop cuttings. .. Soil and climatic data related to three specific study sites (Kavutiri, Embu and Gachoka, representing the coffee-tea, main coffee and cotton agro-ecological zones, respectively) were used in the WOFOST crop growth simulation model to determine calculated potential and calculated water-limited yields. The calculated water-limited yields were used in ALES to determine estimated yields. The yield gaps were analysed within and between the three study areas. Natural factors causing yield gaps include the inherent soil fertility and the climate, particularly the rainfall amount and distribution. Low soil fertility could be ameliorated by application of fenilizers and manures, but it is not feasible to entirely rectify soil moisture constraints under rainfed conditions. The human causal factors include the non-application or inadequate application of essential inputs and losses due to weeds, pests, diseases, birds and wild animals. It is not possible for farmers to eliminate most of these limitations because of lack of funds for purchasing inputs, lack of adequate agricultural knowledge and lack of technological capability. Since weeds were found to be a very important yield-controlling factor, efficient weeding by family labour could contribute substantially towards improving maize yields. Under the present traditional farming practices, the coffee-tea zone is marginally suitable for maize production in seasons I and II, while the cotton zone is marginally or severely limited for maize production in seasons I and II. The main coffee zone has high and marginal suitabilities for maize production in seasons I and II.LThe current farmers' maize yield levels can be increased and sustained by improving the efficiency all along the maize production line, beginning with better land preparation, more timely planting of the most suitable maize varieties, proper fertilization, and improved control of weeds, pests and diseases. More research is needed to determine the right types and quantities of inputs for maize production in the different agro-ecological zones. Appropriate arrangements should be made to promote efficient agricultural extension services, provide adequate credit facilities and put in place proper maize pricing policies.

This thesis presents an analysis of maize yield levels and yield gaps between predicted and observed yield types in the coffee-tea, main coffee and cotton agro-ecological zones on the eastern slope of Mount Kenya, in Embu district. Maize yield data were obtained from experiments performed by the Fertilizer Use Recommendation Project for the 1986-91 period, plus the results of maize trials executed during this study for seasons I (mid-March to September) and II (October to mid-March) of 1992-93. Investigations on the influence of fertilizer application, weeding and insect control on maize yields were included in the latter trials at Embu study site. Maize yields from selected farm fields within the three agro­ecological zones were determined from crop cuttings. Soil and climatic data related to three specific study sites (Kavutiri, Embu and Gachoka, representing the coffee-tea, main coffee and cotton agro-ecological zones, respectively) were used in the WOFOST crop growth simulation model to determine calculated potential and calculated water-limited yields. The calculated water-limited yields were used in ALES to determine estimated yields. The yield gaps were analysed within and between the three study areas. Natural factors causing yield gaps include the inherent soil fertility and the climate, particularly the rainfall amount and distribution. Low soil fertility could be ameliorated by application of fertilizers and manures, but it is not feasible to entirely rectify soil moisture constraints under rainfed conditions. The human causal factors include the non-application or inadequate application of essential inputs and losses due to weeds, pests, diseases, birds and wild animals. It is not possible for farmers to eliminate most of these limitations because of lack of funds for purchasing inputs, lack of adequate agricultural knowledge and lack of technological capability. Since weeds were found to be a very important yield-controlling factor, efficient weeding by family labour could contribute substantially towards improving maize yields. Under the present traditional farming practices, the coffee-tea zone is marginally suitable for maize production in seasons I and II, while the cotton zone is marginally or severely limited for maize production in seasons I and II. The main coffee zone has high and marginal suitabilities for maize production in seasons I and II. The current farmers' maize yield levels can be increased and sustained by improving the efficiency all along the maize production line, beginning with better land preparation, more timely planting of the most suitable maize varieties, proper fertilization, and improved control of weeds, pests and diseases. More research is needed to determine the right types and quantities of inputs for maize production in the different agro-ecological zones. Appropriate arrangements should be made to promote efficient agricultural extension services, provide adequate credit facilities and put in place proper maize pricing policies.

The international distribution of vegetative plant parts is restricted by the risks of introducing diseases and pests to non-infected areas. Methods used at IITA to produce and distribute virus-free yams to requesting national programs and collaborators are described. The selected yam clones are cleaned from virus disease infection through thermotherapy and meristem culture. The regenerated plants are virus indexed. The negatively indexed plants are then multiplied in vitro for international distribution. Plantlets of about 4–6 cm height grown in sterile culture media are packed for distribution by hand carriage. Node cuttings of the in vitro plantlets are also sub-cultured in a medium containing sucrose (5%) for micro-tuber production. Micro-tubers are harvested from 4–5 months old cultures and packed in sterile petri plates with sterile moist cotton wool for dispatch to national programs. Some virus-free yam plantlets are also transplanted to sterile soil in a screenhouse where they grow to maturity. Harvested tubers are used for distribution. The advantages and disadvantages of each method are discussed.