While it is true that in many areas of the Cotton Belt early planting frequently results in an earlier, higher-yielding crop, growers should temper their enthusiasm with caution. In reduced tillage systems, soil temperatures are slow to warm. The flip side to this is that once adequate temperatures are achieved in no-till, soil temperatures are slower to cool than conventional till soils. Temperatures below 50 degrees can result in chilling injury or the death of seedlings if they occur while the seed is absorbing water.
Planting should be delayed until:
(1) Soil temperatures average 65 degrees or higher at a depth of four inches for three consecutive days.
(2) The five-day forecast calls for dry weather and a minimum of 25 DD-60s.
(3) Forecast lows will remain above 50 degrees for the two nights following planting.
DD-60, or degree days above 60, is a unit of measurement for the amount of heat received by the plant during the growing season. It is based on the concept that there is a minimum threshold temperature — 60 degrees — for cotton development. Degree days are determined by adding the daily high and daily low temperatures, dividing the result by two, and subtracting the temperature threshold of 60. For example, if the daily high is 90 degrees and the daily low is 70, 20 heat units will be accumulated for that day.
90 + 70 = 160/2 = 80 - 60 = 20 DD-60s.
Many experts believe DD-60s provide a more accurate measurement for plant development than the number of calendar days, which can vary with the weather.
Seedling vigor can be a key ingredient in cotton’s ability to survive the cool, wet conditions that may plague growers after planting. The more commonly used standard germination test, which is conducted in a temperature range of 68 to 86 degrees, can give growers an approximation of the field performance of seed lots. In cool germination tests, seed are tested for emergence and growth at 64.5 degrees F, a temperature that places enough stress on the seed so only those high in germination will germinate and produce normal seedlings. (Cool test results generally are not printed on the seed tag, but that information should be available from seed dealers.) When planting in less than favorable conditions, choose seed lots with higher cool test results to improve the potential to achieve uniform stands.
Protecting the Plant
Growers should plant seed that has been treated with two or more fungicides, since most of these materials have activity against only one species of seedling disease pathogens. They also have different control mechanisms. Protectants, such as captan or thiram, provide surface protection from disease organisms carried on the seed or in nearby soil. Systemics, such as carboxin or metalaxyl, are absorbed through the seed coat and are taken up by the seedling. Since practically all seed treatments are applied by a commercial seed processor, make sure recommended fungicides are being used that offer protection against more than one type of fungi.
Seed treatments can only provide so much protection (applying higher rates of fungicide might injure the seed). In fields with a history of seedling diseases or in areas which can experience cool, wet conditions at planting, some experts recommend the use of one or more in-furrow fungicides. (Note: Planting on raised beds can also improve soil warming and drainage, creating less favorable conditions for seedling disease.)
Experts feel that nematodes and insects can compound the severity of seedling disease by slowing root and plant growth. Plants suffering from leaf damage caused by thrips or root feeding by nematodes are not able to grow as rapidly. Or, it may be that seedling disease sets up the plant for more injury by nematodes and thrips and other insects. In numerous university research trials, combinations of in-furrow fungicides and insecticides/nematicides have produced significantly higher yields than treatments with any of the materials alone.
Some producers prefer to omit systemic insecticides because of the added expense, but such a decision can be fraught with peril. For openers, treatment threshold levels of thrips occur in almost all fields in the Mid-South each year. Adverse-weather conditions can prevent farmers from making timely applications of foliar sprays, adding to the time the terminal is subjected to feeding by thrips. Some in-furrow insecticides also provide control or suppression of plant bugs and aphids, possibly delaying or eliminating the need for insecticide applications for those pests. (Note: There is some evidence that thrips may contribute to increased square shed by providing a port of entry for secondary organisms that cause loss of small squares.)
Scout early and often
Whether or not systemic insecticides/nematicides are utilized at planting, cotton must be scouted in early season for signs of thrips or other insect damage. Lack of soil moisture or a damaged root system can limit the uptake of systemic insecticides. When thrips damage is occurring, try to select insecticides that are not phytotoxic to the cotton or harmful to beneficial insects. Cotton generally is no longer susceptible to injury by thrips after the plant has five true leaves and is growing vigorously.
Another note: Adverse weather conditions in early season can upset the best-laid weed control strategies. If pre-emergence herbicides are not activated due to lack of moisture or excessive rains cause delays in applying post-directed sprays, over-the-top applications of relatively harsh materials may be required. If possible, apply over-the-top sprays during warm periods when soil moisture is adequate and roots are actively growing.