January 28, 1999 - GEORGIA COTTON NEWSLETTER
|Cotton Variety News 1|
Cutting Fertilizer Rates - How Low Can You Go? 2
Tobacco Budworm: Review of 1998 and Status of Pyrethroid Resistance 4
Observations from Ultra Narrow Row Cotton Plots 6
Cotton Variety News. (Brown) The UGA Cotton Recommended Variety list now includes NuCOTN 33B, NuCOTN 35B, and Stoneville BXN 47. Deletions from the current list include Paymaster 1215, 1220, and 1244 in part because of commercial (in)availability and also in response to the bronze wilt problem.
|1999 RECOMMENDED VARIETIES|
|Medium-Full Season||Medium||Short Season|
|AgriPro HS 44
AgriPro HS 46
NuCOTN 35 B
Paymaster H 1560
PSC GA King
Stoneville KC 311
Stoneville LA 887
NuCOTN 33 B
Conventional varieties from DP Seed (DP 90, DP 5690, and DP 5415) are in short supply as a result of a poor production year in Arizona and concentration on transgenic seed increases. Potential replacements from the Recommended list include Medium-Full Season varieties AgriPro HS 44 and HS 46; Medium Season varieties Stoneville 474 and Suregrow 501; and Short Season varieties Suregrow 125. PSC GaKing will be unavailable due to the untimely delivery of seed for planting purposes in 1998 [PSC is Phytogen Seed Company]. Keep in mind that the recommended list includes varieties that have been tested for 3 years and that have demonstrated yield and quality performance at least comparable to existing cultivars.
Several new varieties have been evaluated for a couple of years and show good potential. Among the promising mid-full season varieties are AgriPro 6101 and 4103; DP 90B, 5690RR, and 5415RR; FiberMax 989; and SureGrow 248, 821, and 180.
Two transgenic varieties--Stoneville 4740 BG and DP 688 B/RR-- have been dropped and will not be available in 1999. Stoneville Pedigreed Seed, apparently taking the "high road" in terms of product quality and performance, removed 4740 BG because of erratic yield performance and erratic corn earworm control. DP 688 B/RR has been discontinued because of the need for inventory reduction and its similarity to DP 655 B/RR. Expect some other transgenics to be phased out in this or the coming year.
Stoneville Pedigreed Seed Company is for sale. Previously, the company had been purchased by Monsanto in the overall acquisition of the biotech parent Calgene. To comply with antitrust concerns, Monsanto intends to sell Stoneville. Possible buyers are Aventis (the merged company of AgrEvo and Rhone Poulenc), Dow AgroSciences, Novartis, and DuPont.
Phytogen Seed Company is a newcomer in the cotton variety picture and will have some for sale in 1999. Given the AgrEvo/Rhone Poulenc merger, it is not yet clear what will happen to the FiberMax line of varieties.
Variety Selection. (Brown) With all the possible variety choices and with the inherent pest management options available in transgenic varieties, selection of varieties is an increasingly important issue. The following are a few ideas that should be factored into variety decisions.
Cutting Fertilizer Rates - How Low Can You Go? (Harris) The name of the game this year is cutting costs. One area growers are looking toward to save money is with fertilizer. There are some situations with fertilization and liming we can probably save some money, but there are others in where cutting back on inputs could prove costly. One county agent reported that he heard some farmers say, "I'm going to cut out my P and K fertilizer and just go with nitrogen and boron". Is this a good idea ? Probably not. But how do you know ?
The best guide is our good old friend the soil test. The UGA soil test recommendations are based on certain probabilities of yield response, the lower the soil nutrient level, the greater the likelihood for a yield increase due to fertilization. For example, for a MEDIUM soil test level in P or K, there is a 50% chance of a yield response to the recommended fertilizer application. It seems unwise not to fertilize in such a case, given the "flip-of-a-coin" chance of seeing less than optimum yields apart from added fertilizer.
What about the growers who are taking our recommendations and increasing them by 25 %, can they cut back ? In the short-term, and under financial pressure like most are, the answer is yes. The additional 25 % is likely just extra "maintenance". In other words, just follow the UGA recommendations very closely. If soil test levels drop significantly by fall (as indicated by a soil test) they can be corrected after we are hopefully in better financial shape.
What if I have high levels of both P and K and my recommendation really calls for no fertilizer ?
We don't have a whole lot of these high levels to begin with. Out of 2214 soil samples run for Coastal Plain cotton in the UGA lab last year, 33 % we're rated high in P and only 9 % were high in K. Phosphorous is probably less critical than K in this situation, but there are have been cases where crops have responded to P in starter fertilizer even when soil test P was high. With the problems we've had recently with potassium, especially on deep sands, short-season varieties and high-yield situations, be real cautious about cutting back K rates to zero. As another county agent says "I don't do zeroes".
What if I'm starting with low levels of P and K ? You don't have much choice here but to go with the full recommended rate. There is a 90 % chance of a yield response to following our recommendations when soil test levels are low. And according to those samples run last year, 29 % low in P and 36 % were low in K. This illustrates why the best strategy is to build P and K levels to medium (or a "low high") and fertilize with moderate rates of fertilizer. This is better than building soil test levels real high and not fertilizing (i.e. rely on soil to provide all the nutrients) or running soil test levels real low and having to fertilize heavy (i.e. not take advantage of what the soil can provide).
Along these lines, a ballpark figure for fertilizer and lime cost for cotton is $50 to $60 per acre. This obviously depends on each filed situation but is a good "jumping-off" point for discussion. If you are spending a lot more than $50-60 per acre and it's because you have low levels of pH, P or K and a high yield goal, that may be OK. But if you are spending a lot more than this and you have high levels of pH, nutrients and a low yield goal, you may be able to save some money on fertilizer and lime. On the other hand, if you are spending a lot less than $50-60 per acre and you have high levels of pH, P, K or a low yield goal, this may be OK. However, if you are spending a lot less than this and have low levels pH, P or K and a high yield goal, you could be hurting yourself by "under" fertilizing and liming.
Can I save money on lime ? Lime seems to be one of the first inputs to be cut out when money gets tight. This can really hurt if you need lime and don't apply it. The reason is because it is so important to reduce aluminum toxicity and keep essential soil nutrients available. Precision ag sampling has shown pretty clearly that soil pH's can vary quite widely across fields in South Georgia. High soil pH's (above 6.5) are also undesirable from an economic standpoint and once above 7.0 can start "going the other way" and make essential plant nutrients unavailable.
Should I cut out my boron ? No. Foliar boron should only cost about $1.00 - 1.50 per acre. Since it is mobile in sandy soils and critical to pollination and fruiting, again stick with the standard recommendation which is 0.5 lb B/a. Boron can also be applied with preplant, starter and sidedress fertilizers.
Should I cut back my sidedress N rate on dryland ? This is an area where we may be able to save some money. Much like being more aggressive with Pix under irrigation vs. dryland, we can be more aggressive with N under irrigation vs. dryland. A good strategy on dryland cotton would be to apply preplant N, then cut back on sidedress by 20 -30 lb/a and finish the crop off with foliar N if weather conditions and yield potential are good. For example, apply 20 lb N/a preplant, then 40 lb/a sidedress (instead of 60), then apply 20 lb/a foliar if conditions are good. Notice the total N rate is the same.
Finally, another area where we can cut back is on "yield-enhancers"or "miracle products" (Snake Oils !). This is obviously not the year to go with new products that have not been proven. We need to go with what we know works and what we can afford. This includes in-furrow and foliar nutrient/hormone products. The desperate situation does not call for desperate grasping at straws in this case. Some are looking for that "silver bullet", but don't expect to find it in a 5 gallon bucket. Also, remember if it costs twice as much, it better be twice as good. If not, what did you gain ?
Tobacco Budworm: Review of 1998 and Status of Pyrethroid Resistance: (Roberts) In response to unseasonably warm temperatures during early 1998, insect pests such as tobacco budworm (TBW), corn earworm (CEW), and fall armyworm (FAW) infested cotton one to two weeks earlier than normal. During June, tobacco budworm pressure in south Georgia was typical with light to moderate infestations occurring. However, first generation TBW problems were higher than normal in east Georgia and parts of central Georgia. Multiple applications of insecticide were needed in June in some areas of east Georgia to control TBW.
Much of the state experienced severe drought during June and part of July and dryland fields were much less attractive as egg laying sites compared with irrigated acres. As a result, much of the TBW activity in July was occurring on irrigated fields, of which a large percentage were Bt cotton. Bt cotton provided excellent control of TBW. To date, we have not observed a TBW larva survive on Bt cotton in the field. However, supplemental treatment of CEW and FAW was needed on Bt cotton in some parts of the state. On non-Bt cotton, there were scattered reports of TBW control problems with pyrethroids. Although several factors can influence insecticide efficacy (timing, rates, application, etc.), pyrethroid resistance was suspected in some cases, especially since resistance problems had been documented during 1997. Field collections were made from problem fields and were tested for pyrethroid susceptibility by Dr. Gary Herzog, research entomologist. Results of studies during 1998 did not indicate the presence of pyrethroid resistance. However, control problems were observed in various locations scattered across the state which cannot be fully explained. Because of these problems, coupled with the fact that pyrethroid resistant TBW were documented during 1997, and that we failed to see wide spread pressure from TBW during 1998 due to drought, we believe the potential for problems controlling TBW with pyrethroids during 1999 is possible in all parts of the state. Unfortunately, we cannot predict when, where, or even if pyrethroid resistant tobacco budworm will be encountered in 1999.
Tobacco Budworm Management for 1999: (Roberts) We have two basic systems to manage tobacco budworm (TBW). First, transgenic Bt cotton, which has provided excellent control of TBW to date, could be utilized. Alternatively, non-Bt varieties may be used and foliar insecticides may be applied on an as-needed basis. Use of non-Bt varieties will place a premium on good management skills. Some growers will choose this option due to variety availability and/or their thoughts that they may be able to produce cotton more economically by avoiding technology fees when TBW problems may not occur. In areas of the state where difficulty controlling TBW has occurred, Bt cotton is a good investment. In others, it maybe more of an insurance policy. During the past season, the number of insecticide sprays applied to non-Bt cotton averaged about 3.8 per acre. However, there was a large range in the number of sprays, from less than two to greater than eight. If we could predict the future, the decision on which system to use would be much easier.
Bt cottons were planted on approximately half the acres in Georgia this past year. Heavy concentrations of Bt cotton were planted in parts of the state. Bt cotton is a valuable technology and our efforts in preserving efficacy (delaying resistance development) should be a primary objective. When Bt cotton is planted, growers are obligated to follow resistance management guidelines. It is in our best interest that these guidelines are followed as they are our best defense in delaying this potential problem.
Management of TBW on non-Bt cotton will demand good management skills to be successful. It is imperative that good decisions are made concerning insecticide selection and timing of applications. Typically the first of three generations of TBW will infest cotton in late May or early June. These time frames will vary from year to year and generally occur earlier in the more southern production areas. In many situations, these early infestations do not reach economic levels. But the potential is there and thus scouting is a necessity. Problems with June TBW are much more likely if beneficial populations are low (i.e., if a plant bug spray has been made). Therefore, one should be hesitant to treat plant bugs unless absolutely necessary. It has also been observed that these early infestations of TBW occur on the older or earliest planted cotton. Many growers have successfully raised treatment thresholds during June from 7-8 small larvae per 100 plants to 10-15 small larvae. The degree of threshold adjustment should be based on experience as there are some inherent risks with this strategy. Often when growers are trying to "ride out" these early infestations, field visits will be more frequent and particular attention is given to the age or size of larvae. If threshold populations of larvae are sizing or developing (i.e., large worms), treatment will be needed immediately. Pyrethroids should be avoided during this window. If used, pyrethroid sprays will select for resistant individuals which could create problems in July by increasing the frequency of resistant individuals. Alternative chemistries which are selective or "soft" on beneficials would be preferred. We should make every effort to keep beneficials in the field until July.
Tobacco budworm populations generally are most severe in early July. Plants have set many squares and some bolls by this time. It is generally best to take a more conservative approach concerning thresholds at this time. Treatments should be initiated at 7-8 small larvae per 100 plants prior to the first insecticide spray or when five larvae are found after the first spray. If you are in an area where pyrethroid resistance is suspected, use a non-pyrethroid insecticide. If pyrethroids are used, an ovicide should be added. We believe the potential for pyrethroid resistance is statewide. Most would agree that TBW control with pyrethroids is not as good as five years ago. Timing of applications will be critical. Resistant populations become more tolerant to pyrethroid sprays as they age much quicker than susceptible populations. If we get behind TBW, efforts to gain control of established populations can be futile. Stay informed. If problems are occurring in your area be sure to make appropriate decisions concerning insecticide selection. Tracer has performed well on TBW during this July window. As we enter mid-July, we will also begin to see an increase in corn earworm (CEW) populations. Often we will have a mixed population. When this occurs, it is generally best to treat them as TBW. If the predominant species is CEW, pyrethroids would be the treatment of choice.
During August we often have a mixed population of TBW and CEW. Pyrethroids and/or pyrethroid tank-mixes have generally been used at this time of year. Decisions concerning insecticide selection during this time should be based on experiences in your area during July.
Observations from ultra narrow row cotton plots: (Bader) Narrow row cotton (UNRC), cotton planted in 10 inch rows or less, has received cyclical interest and attention over the past 40 years. Theoretically, close row, high population cotton requires only a few bolls per plant for acceptable yields and can be produced in a short period of time with limited resources. In the last few years, the concept of UNRC has been re-introduced with the development of broad spectrum over-the-top weed control technology and herbicide-tolerant varieties. Other developments that support ultra narrow row cotton are the use of plant growth regulator and the availability of precision drills and close-row planters.
Another driving force is the interest in reducing production costs. Until recently, the majority of cotton produced in Georgia has been harvested with spindle pickers. The renewed interest in UNRC production has created many unanswered questions in Georgia. UNRC field demonstrations and experiment station plots were conducted at several locations across the state. The following are some observations from these plots.
Yield data from experiment station and grower fields have shown that UNR cotton has comparable and sometimes higher yields than wide row cotton.
Getting a stand is important. The uniformity of a stand is probably more critical than the number of plants. The more evenly a stand is spaced the better. We are not certain of the minimum number of plants per acre required. Above 100,000 plants is better but we may be able to be satisfied with a lower number of plants.
UGA Cotton Web Address: www.griffin.peachnet.edu/caes/cotton
Steve M. Brown, Extension Agronomist-Cotton
Mike Bader, Extension Engineer-Cotton
Glen Harris, Extension Agronomist-Soils & Fertilizer
Phillip Roberts, Extension Entomologist-Cotton