Welcome to UC Cotton Research & Information
Optimum Planting Temperatures
Germination of cottonseed requires a minimum soil temperature of 58°F at planting depth and favorable weather during the subsequent five-day period. While the temperature for optimum growth rate of the emerging radical and hypocotyl is between 91°F and 96°F, planting usually occurs when temperatures are much cooler. Cottonseed requires 50 degree-days to emerge from optimum planting depth. An accumulation of 20 degree-days in the 5-day period following planting is ideal. To aid in the 5-day weather decision, a link has been made between the National Weather Service Forecast and growth models through the UC IPM web site. This information can be obtained at ipm.ucanr.edu/WEATHER/cottonforecast.html
Planting in less than optimal conditions has some long lasting impacts. Germinating seeds are most sensitive to chilling at two different stages, during imbibition and 1 to 3 days after germination. Temperatures below 53°F inhibit cottonseed germination and seedling growth. Chilling during imbibition results in radical tip abortion. Soil temperatures below 41°F cause seed death. Chilling 1 to 3 days after germination causes root cortex damage prompting lateral roots to prematurely initiate. In addition, germinating seeds once exposed to temperatures less than 58°F do not immediately resume growth when temperatures increase. The length of chilling time has an accumulative effect on plant growth. Two day chilling (50°F) reduced plant height by 2 inches and delayed first flower by 3 days. Six day chilling reduced plant height by 14 inches and delayed first flower by 10 days. Crop productivity is thus negatively affected.
To get off to a good start plant when soil temperatures are above 58°F and the 5-day weather forecast calls for an accumulation of 20 degree-days.
What is FOV Race 4?
Fusarium oxysporum f. sp. vasinfectum (or “FOV”) is a soil-inhabiting fungus that causes a vascular wilt disease in susceptible cotton varieties. It has been widely recognized in the San Joaquin Valley since the 1950’s. Historically, Fusarium wilt in cotton produced visible symptoms and caused economic damage only in susceptible varieties in combination with significant populations of the root knot nematode (Meloidogyne incognita). Fusarium wilts usually seen in these prior recognized cases were caused by race 1 or race 2 of FOV. In recent years, however, several localized occurrences of FOV infections with moderate to severe plant damage have been confirmed in the absence of nematode populations.
In these cases, the disease was caused by race 4 FOV. Evaluations in 2003 indicated that all widely-grown commercial Pima varieties tested were more seriously damaged than tested Acala or non-Acala Upland varieties. Field trials also indicated good levels of resistance to race 4 FOV in some experimental Pima varieties. It is significant, however, that many Upland/Acala varieties field-tested under high race 4 inoculum loads in 2003 were also infected, albeit with fewer symptoms and less damage than in most Pima varieties.
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