UGA Cotton Newsletter
February 25, 2000
Recommended Variety List for 2000 Season 1&4
Variety Selection 1
Eradication of Other pests 3
New Cotton Breeder 3
Recommended Variety List for 2000 Season. (Brown) Attached is the current Recommended Variety list. Varieties are added to the list as a result of three years data in the Official Variety Trial (OVT), with indications that lint yield and fiber quality are equal or superior to currently recommended varieties.
We are among the few states that continue to have a recommended list. Many take the position that the rapid introduction and acceptance of new varieties have rendered such lists obsolete. Over the past several years, variety commercialization has coincided with availability of seed for testing by universities. In part, this has come because of farmer demands for transgenic varieties. Perhaps it is time that we return to a more sane approach, that we have considerably more information and experience with a variety before we commit significant acreage to it.
Variety Selection. (Brown) Obviously, the Recommended List is a good starting point for variety selection. Growers should diversify across technology, genetics, planting date, maturity class, and company. There are numerous suggestions for variety selection and diversification, but the keys are not only to plant several different varieties (Adon=t put all your eggs in one basket@) but also to plant varieties of known performance.
For dryland production, mid-full season varieties have broad appeal for most of Georgia, especially for nonirrigated production. As compared to early maturing varieties, mid-full season varieties are more indeterminate and thus have greater Acomeback potential@ in the midst of occasional drought. Early varieties are bred for rapid fruit set; in other words, they are selected to make and mature a crop in as short a time as possible. Early varieties fit best under irrigation, for planting dates beyond May 20 to 25, and if drought occurs in August.
Keep in mind that some varieties developed for the South were bred in the Delta where earliness influences almost every management decision. Earliness refers to rapid fruit set, boll maturation, and harvest in order to minimize insect control costs and harvest losses. For the lower half of Georgia, ENDURANCE is far more important than earliness. Endurance is the ability to withstand drought and stress and resume fruiting with subsequent rainfall and favorable temperatures. With our long growing season, we have a wide window for bloom, from June 20 to the first week in September, almost 11 weeks. Normally, the effective bloom period of any cotton crop is only 4 to 6 weeks, but this wide window gives greater opportunity to set and make a crop...at least at some point. Again, the mid-full season varieties tend to take greater advantage of this broad fruiting window and have greater capacity to withstand mild stress and recover.
Certain varieties, particularly Delta and Pine Land RR and B/RR types, may be in short supply. Limited data exist for B/RR or Astacked gene@ varieties. DP 458 B/RR and DP 655 B/RR were among the most widely planted varieties in 1999, and of the two, performance of DP 458 B/RR was generally better. Other B/RR varieties that looked good last year but on very limited acreage included Sure-Grow 125 B/RR and Sure-Grow 501 B/RR. Again, there is no substitute for data across years and locations to gain confidence in performance of a variety. Presently, such data and experience are not available for stacked varieties.
Apparently, quantities of DP 458 B/RR are far less than expected, reportedly because of seed dormancy issues. Dormant seed are viable and appear normal but do not readily germinate. There are several possible causes for dormancy, many are not understood. Dormancy is sometimes reflected in low cool test, which is thought to be the case in DP 458 B/RR. Several factors or treatments may Abreak@ dormancy, even simply time in cool storage.
Purpose: measure optimum germination
Method: constant temperature of 86oF or alternating temperature of 86/68o F, count normal seedlings at 4, 8, 12 days
Comment: law requires 80% germination for commercial sale
Purpose: evaluate seed/seedling vigor
Method: constant temperature of 64.5oF, count emerged radicles 1.5 inches or longer at 7 days
Comment: results hard to accurately reproduce across laboratories, time
It is possible that some lots of DP 458 B/RR may be offered with less than 60 percent cool test. Should a grower purchase/plant such seed? First, a farmer should acquire available data on a particular lot of seed, especially information from warm germination and cool test evaluations. If warm germination numbers appear strong and cool test numbers are 50 percent or better, such lots might be suitable for planting under good conditions--warm temperatures and favorable soil moisture. Remember, DP 458 B/RR and related cultivars are not noted for strong vigor and should not be planted when marginal temperatures are expected.
Supplies of DP 451 B/RR are plentiful and are being offered as an alternative to DP 458 B/RR. Is this a good idea? On a wholesale basis, no. While DP 451 B/RR performed well in several early maturing tests in 1999, it has been evaluated in considerably fewer trials and fields than DP 458 B/RR. DP 451 B/RR is derived from Deltapine 51, the latter is of course an early maturing variety not noted for superior yields or fiber properties in much of the state. Favorable results in a single year and the desire for stacked gene technology should not lead us to a variety for which limited local information is available.
Eradication of Other Pests? (Roberts) At a recent cotton production meeting the question was asked, AWhy don=t we eradicate tobacco budworm and corn earworm?@ The question stems from the success cotton producers have enjoyed since elimination of the boll weevil. In addition to eradication of the boll weevil, another example of successful pest eradication is the screwworm. In both cases, there are unique features in the insect=s biology which make eradication feasible.
The boll weevil only reproduces on one plant species in Georgia, and that is cotton. Thus, if we are able to achieve 100 percent control of boll weevils in all cotton fields, we can eradicate the species. A means of detecting very low numbers of boll weevils in a field is also needed and is available in the form of pheromone traps. In addition to cultural practices such as stalk destruction, the use of traps and intensive insecticide applications have been instrumental in eliminating this pest from Georgia.
Many are less familiar with the screwworm eradication program. The screwworm is a pest of animals. It infests wounds and feeds on exposed flesh. Extensive studies demonstrated that a female screwworm mates only once in her lifetime. This, together with the relatively small natural population size, made this devastating pest a candidate for eradication using sterile male releases. Male screwworms were mass reared, sterilized by radiation, and released. Sterile males competed with wild males for mating opportunities and when a sterile male mated with a wild female, the resulting eggs were also sterile. In due time, eradication was achieved by preventing reproduction.
Extensive studies of the biology of other pests such as tobacco budworm and corn earworm do not reveal a Auniqueness@ which allow eradication. However, these studies are the building blocks of Integrated Pest Management (IPM) programs in that we target the most susceptible link in their biology with control measures.
New Cotton Breeder Joins UGA Tifton Faculty. (Brown) On February 1, 2000, Dr. Lloyd May joined the University of Georgia Crop and Soil Sciences faculty as our new Cotton Breeder. Lloyd served as a USDA Cotton Breeder at Florence, SC, for 9 years before coming to Tifton. His efforts will focus on the development of traits related to yield improvement, yield stability, nematode resistance, improved fiber quality, and genetic diversity. Lloyd follows Shelby Baker, who retired in December 1998 after a distinguished career and who continues to contribute to the Georgia cotton industry on a part-time basis.
See 'Breaking News' for Recommended Cotton Varieties or
Steve M. Brown, Extension Agronomist-Cotton
Phillip Roberts, Extension Entomologist-Cotton
Last updated by D. Bridges 2.26.2000