L E Estorninos’s scientific contributions

The effects of different herbicide treatments and maturation stage on sugar content of sweet sorghum ‗Dale' were evaluated. Sweet sorghum (Sorghum bicolor (L.) Moench) is a C 4 plant with high biomass production potential and high sugar yield. It has a shorter growing season than sugarcane hence can be grown in many geographic areas, and contains about the same quantities of soluble (glucose and sucrose) and insoluble carbohydrates (cellulose and hemicellulose) as sugarcane. It is therefore recommended to plant sweet sorghum for biofuel production in hot and dry countries to help resolve the problems associated with nonrenewable energy usage. Weed control, however, is a problem in sweet sorghum. The cultivation window is limited, the seedlings are tiny, and the crop is sensitive to almost all the herbicides used in grain sorghum. Previous studies showed that metolachlor applied preemergence (PRE) was tolerated by both 'Dale' and 'Sugardrip' cultivars without yield reduction. This could help expand the label for metolachlor with mesotrione as a tank-mix partner. Experiments were carried out at the University of Arkansas, Fayetteville in 2007 and 2008. Four herbicide treatments and two harvest dates, 95 days after emergence (DAE) and 114 DAE, were tested. Treatments applied were metolachlor 0.48 lb ai/A PRE; metolachlor 1.43 lb ai/A PRE; metolachlor 1.43 lb ai/A PRE plus mesotrione 0.188 lb ai/A PRE; and, untreated check. Total solids were measured by Brix meter and sugar components analyzed by HPLC. Irrigation delayed the sugar accumulation in sweet sorghum, but there was no difference in total sugar content between irrigation regimes. In general, it is better to harvest sweet sorghum at the hard dough stage (109 mg/g FW), than at milk stage (88 mg/g FW), to ensure the highest sugar accumulation. Higher sugar content is mainly due to further sucrose accumulation in late harvested plants. Higher herbicide rate did not reduce sugar accumulation. Sugar content was lowest (134 mg/g FW) at the lowest rate of metolachlor (0.48 lb ai/A) without mesotrione; higher rates of metolachlor (1.43 lb ai/A) and mesotrione (0.188 lb ai/A) resulted in higher sugar content (144 mg/g FW), hence suggesting a beneficial effect of mesotrione as a tank-mix partner.

Cowpea has limited options for weed control. Hand weeding is expensive therefore herbicide options are needed to manage the weeds effectively and economically. The experiment was conducted in 2008 and 2009 at the Vegetable Research Station, Kibler, AR to evaluate the efficacy and crop safety of various herbicides when applied preplant (PP) or preemergence (PRE). Flumioxazin, fomesafen and sulfentrazone were applied alone at 0.188 and 0.375 lb ai/A. Halosulfuron was applied at 0.024 and 0.048 lb ai/A. The low rates of these herbicide were tank-mixed with s-metolachlor (0.75 lb ai/A) for herbicide combination treatments. Imazethapyr (0.063 lb ai/A) + s-metolachlor (0.75 lb ai/A) was used as the standard herbicide program. Cowpea stand was comparable between the two timings of application in both years. Stand was reduced by both rates of sulfentrazone in 2008 and 0.048 halosulfuron in 2009. Fomesafen and sulfentrazone at 0.188 and 0.375 lb ai/A in 2008 and 0.375 lb ai/A flumioxazin in 2009 stunted the growth of cowpea when applied PP. All herbicides, except halosulfuron (0.024 lb ai/A) alone or in combination with metolachlor and fomesafen (0.188 lb ai/A) in 2008 and both rates of fomesafen and halosulfuron in 2009, caused stunting when applied PRE. Both rates of halosulfuron in 2008 and the low rate of fomesafen in 2009 did not have sustained weed control until 4 wks after planting when applied PP. All herbicides had better weed control than the standard herbicide program in 2008 while both rates of flumioxazin had better weed control when applied PRE in 2009. Barnyardgrass was the predominant weed. PRE application of herbicides in 2008 and high rates of flumioxazin and sulfentrazone in 2009 delayed the flowering of cowpea. High soil moisture reduced cowpea yields in 2008 and caused harvest failure in 2009. Yields were greater when herbicides were applied PP than PRE. Overall, both rates of halosulfuron were safe to use in cowpea but did not control barnyardgrass. Flumioxazin controlled branyardgrass better but was injurious to cowpea.

Sweet sorghum (Sorghum vulgare) is grown on very small acres in Arkansas for molasses, but is being considered as an alternative biofuel crop that can fit into existing cropping systems in the Delta. A study was conducted to evaluate the tolerance of sweet sorghum to metolachlor and mesotrione under non-irrigated condition. The experimental units were arranged in a randomized complete block design with four replications, with the treatments being combinations of metolachlor and mesotrione at different rates. Sweet sorghum cv. ‗Dale' was planted in plots with 4 rows, 20 ft long, 40 in apart. The experiment was conducted at the Main Agricultural Research and Experiment Station, Fayetteville, AR in 2007, 2008 and 2009. Mesotrione at 0, 0.094 and 0.375 lb ai/A and metolachlor at 0, 0.48, 0.96, 1.43 and 1.91 lb ai/A were applied preemergence, separately and as mixtures. A combination of metolachlor (1.91 lb/A) + mesotrione (0.375 lb/A) was included as a ‗standard treatment' for comparison of weed control efficacy and crop tolerance. In 2007, 13% injury was observed on sweet sorghum treated with metolachlor + mesotrione (1.43 lb ai/A + 0.094 lb ai/A), metolachlor + mesotrione (0.48 lb ai/A + 0.094 lb ai/A) and metolachlor alone (0.96 lb ai/A). Plots treated with metolachor alone (0.48 lb ai/A), metolachor + mesotrione (0.96 lb ai/A + 0.094 lb ai/A), mesotrione alone (0.375 lb ai/A) and metolachor + mesotrione (1.91 lb ai/A + 0.375 lb ai/A) had less crop stand than the non-treated plots. Average fresh biomass of 18.93 mt/acre as recorded where none of the herbicide caused any significant reduction in fresh biomass. In 2008, mesotrione (0.094 lb ai/A) caused 14% crop injury; metolachlor (0.48 lb ai/A), 23%; and metolachlor + mesotrione (0.48 + 0. 094 lb a.i./A), 29% at 21 d after application. Mesotrione alone (0.094 lb ai/A) had the highest stand count, followed by metolachor + mesotrione (1.91 lb ai/A + 0.094 lb ai/A), metolachor (0.48 lb ai/A) and metolachor + mesotrione (0.48 + 0. 094 lb a.i./A) treatments. Sweet sorghum sprayed with metolachor + mesotrione (1.91 lb a.i./A + 0.094 lb ai/A) had the highest biomass yield (28.935 mt/acre) comparable to other treatments. In 2009, of the 17 treatments, the combination of mesotrione and metolachor (0.094 + 0.48 lb ai/A), and metolachlor alone at 0.96 and 1.43 lb ai/A caused the least stand loss or early-season crop injury. Sweet sorghum in plots sprayed with metolachlor at 1.43 lb ai/A showed the highest biomass of 34.45 mt/acre. Therefore we conclude that a combination of mesotrione and metolachlor at (0.094 lb ai/A + 0.48 lb ai/A) is safe for sweet sorghum. Higher rates of metolachlor can be used alone without biomass yield loss.

a pressurized CO 2 backpack sprayer with a four-nozzle boom delivering a spray volume of 10 gallons per acre. A natural population of diclofop-resistant Italian ryegrass was treated at boot stage (24 inches tall) with several herbicides labeled for spring burn-down. Weed control was evaluated 12, 26, and 48 days after application. Italian ryegrass control of 90% or greater 48 days after application was achieved with Roundup PowerMAX at 88oz/A, Roundup PowerMAX at 22oz/A + Select MAX 16oz/A, Roundup PowerMAX at 44oz/A + Select MAX 8oz/A, and Roundup PowerMAX at 44oz/A + Select MAX at 16oz/A. Select MAX alone at 8 and 16oz/A controlled Italian ryegrass 74% and 81%, respectively 48 days after treatment. Ignite at 40 oz/A controlled Italian ryegrass only 20% at 48 days after treatment. Tank mixes of Ignite and Select MAX did not improve ryegrass control over Select MAX applied alone. Both the resistance survey and efficacy studies in this project are ongoing. In addition to the spring burn-down trial, fall burn-down and residual treatments will also be evaluated. A few more ryegrass samples from counties that did not participate in the initial survey may be added next spring. Loss of seed dormancy during after-ripening of weedy rice (Oryza sativa), collected from Arkansas, was investigated. Freshly harvested, mature seeds, from rice fields in Cross, Desha, Drew, Lawrence, Lee, Lincoln, Lonoke, Monroe, Prairie and Randolph counties were used. Seeds were after-ripened at average room temperature of 28 C. Dormancy was tested at intervals of 0, 4, 8, and 12 weeks after harvest by germinating seeds at 30 °C in the dark. The experiment was conducted in Split-plot design with three replications. Twenty five seeds from each plant sample were placed in Petri dishes lined with filter paper, and moistened with 5 ml of deionized water. At daily evaluations, seeds were considered germinated when radicle emergence was noted. Germination was recorded over a 15 day period. Variations in dormancy were observed among accessions at different after-ripening periods. All accessions showed high dormancy immediately after harvest, but dormancy was released in the majority of accessions after longer durations of after-ripening. Weedy (red) rice produces seeds that persist under unfavorable conditions. This experiment suggests different abilities of red rice populations to persist due to different seed dormancy traits. The distribution of these high-dormancy populations are shown on the map. For such populations, longer rotations out of rice culture are required to deplete the soil seed bank. On the other hand, seeds which are otherwise non-dormant can go into secondary dormancy if unfavorable conditions occur such as, deep seed burial during land preparation or low temperature in the winter. Such deeply buried seeds or those that transitioned into deep secondary dormancy may persist long in the soil seed bank.

Outcrossing between rice and red rice has been a concern because of their morphological similarities and oftentimes synchronous flowering. In 2000, pairs of rice and red rice with near synchronous flowering were planted in isolated field plots. In 2002, at least 2300 seeds produced from two of the pairs were planted in a greenhouse, and DNA was extracted from leaves of the 14-day-old seedlings. Outcrossing between 'Kaybonnet' rice and AR1994-8 black-hulled red rice was estimated at 0.10% with AR1994-8 as the pollen donor, but was not detectable with Kaybonnet as the pollen donor. Outcrossing between 'Starbonnet' rice and AR1994-11D red rice was estimated at 0.23% with AR1994-11D as the pollen donor and 0.14% with Starbonnet as the pollen donor. Although preliminary, these results suggest that gene flow from red rice to rice may be higher than from rice to red rice, and that greater panicle height differences between rice and red rice may reduce outcrossing.

Red rice is a troublesome weed problem in Arkansas rice fields and numerous biotypes are present. Outcrossing between rice and red rice occurs at low rates, resulting in unusual plant types, and can complicate weed management efforts. STRUCTURE (STR) analysis of DNA SSR marker data is useful to infer population structure, to as- sign individuals to different populations, and to identify hybrids. Thus, this procedure was used to evaluate the genetic backgrounds of numerous red rice types that, based on visual traits, apparently had developed from natural outcrossing with rice. STR analysis of suspected red rice crosses obtained from a multi-county, multi-state area yielded little evidence that genetic markers initially associated with rice were retained in red rice populations at high levels over time. Additional studies involving a larger number of markers or markers specifically associated with rice cultivars (e.g. semidwarfism or herbicide resistance) may be necessary to confirm these preliminary findings. In contrast to the aforementioned results, STR analysis clearly showed that a group of red rice plants obtained from Mississippi Co., Ark., partially shared a genetic background with both long-grain commercial rice and red rice. They probably resulted from a recent cross between the two plant types. These studies demonstrate that STR analysis can be used to identify and characterize red rice crosses in some cases, and that it could be useful as a diagnostic tool.