Research was conducted to evaluate the residual effect of burning and mechanical removal of sugarcane crop residue on weed control and sugarcane growth and yield. In one study, crop residue was removed in December or January within 3 wk after sugarcane harvest. Mechanical removal of residue from the row top and placement in the row middle using a Sunco Trash Tiger® was compared with burning and a no removal control. Superimposed on each residue removal treatment was tillage of row sides and middles in March and in May and a no-tillage program. Tillage efficiency in March when sugarcane was emerging from the winter dormant period was not negatively affected when residue was removed mechanically. Crop residue on the soil surface did not completely suppress winter weed emergence and growth. Based on sugarcane and sugar yield averaged across locations and tillage programs, mechanical removal of residue was as effective as burning. Sugar yield was reduced 7.9% when residue was not removed from the row top compared with burning or mechanical removal. In another study, crop residue of sugarcane harvested in early December was burned or removed mechanically from the row top 4 d after harvest and also mechanically in January, February, or March. Crop residue ground cover of 79% in March on the row top where residue was not removed provided some suppression of winter weeds. Sugarcane shoot population in April was reduced 16.1% when residue removal was delayed until March compared with December. Averaged across tillage and no-tillage treatments in March, sugarcane yield did not differ when residue was removed by burning in December compared with mechanical removal in December or January. Delaying mechanical removal of residue until February or March compared with residue removal in December decreased sugar yield an average of 13.1%.

BACKGROUND: Weedy sunflower (Helianthus annuus L.) is a troublesome weed in row-crop production fields in South Texas. Populations with suspected resistance to glyphosate were evaluated with 1X and 4X rates (X = 868 g ae ha −1) of the herbicide, followed by a dose-response assay of the most resistant population. Molecular studies were conducted to determine if targetsite mechanisms were responsible for resistance in these populations. Additionally, field experiments were conducted at two locations (Somerville and Granger, TX) to evaluate the effectiveness of different tank-mix combinations in controlling naturally infesting glyphosate-resistant (GR) weedy sunflower populations in GR corn. RESULTS: In a study conducted in the growth chamber, seven of the 11 tested populations survived up to the 4X rate of glyphosate. The most-resistant population (TX15-11) was 29-fold more resistant to glyphosate, compared to the susceptible standard. In resistant populations, 5-21 more copies of the EPSPS gene were observed compared to the susceptible standard. In the field studies, tank-mix applications of glyphosate + halosulfuron-methyl, glyphosate + prosulfuron, glyphosate + a premix of halosulfuron-methyl and dicamba or glyphosate + a premix of diflufenzopyr and dicamba effectively controlled GR weedy sunflower populations. CONCLUSION: Glyphosate-resistance was observed in 81% of the putative resistant weedy sunflower populations tested in this study. Resistance in these populations was conferred primarily by amplification of the EPSPS gene. Effective control of GR weedy sunflower can be achieved by tank-mixes tested in the current study, which provides acceptable levels of crop safety.

Tillage is used in sugarcane to control weeds, eliminate ruts caused by harvest, destroy residue from the previous crop, and incorporate fertilizer. The effect of weed control and tillage programs on sugarcane growth and yield and on economics was evaluated over two growing seasons. In the first study, weeds were effectively controlled with a March application of hexazinone at 0.59 kg ai/ha plus diuron at 2.10 kg ai/ha either banded or broadcast. When tillage of row shoulders and middles in March was eliminated, soil temperature in the sugarcane drill early in the season was equal to that where March tillage was performed. Sugarcane early and late season stalk population and sugarcane and sugar yield were each equivalent for the full season tillage (tillage of row shoulders and middles in March and in May) and the no-till programs. Elimination of a single tillage operation reduced cost $16.28/ha, and herbicide applied as a band rather than broadcast reduced cost $30.49/ ha. For the no-till program, with herbicide banded in March, net return was increased $32.56/ha. In a subsequent study conducted at five locations, weed control was excellent when either pendimethalin at 2.77 kg ai/ha plus metribuzin at 1.26 kg ai/ha or hexazinone plus diuron at 0.59 kg/ha and 2.10 kg/ha was used. When the March tillage was eliminated, sugar yield was increased 8.6% (620 kg/ ha), and net return was increased $152.68/ha compared with March tillage. When the May tillage was eliminated sugar yield was increased 8% (580 kg/ha), and net return was increased $143.88/ha compared with May tillage. A reduction in tillage cost accounted for only $16.28 of the increase in net return per hectare, with the remainder due to increased yield with the elimination of the tillage operation.

No abstract

During the summer fallow period of the sugarcane production cycle, glyphosate in conjunction with frequent tillage is used to destroy sugarcane regrowth and reduce perennial weed infestations. For tillage to be reduced or eliminated in fallowed fields, weed control must be maintained and sugarcane must be completely destroyed so as not to interfere with the subsequent planting operation. Field studies were conducted to evaluate glyphosate rates and formulations for control of sugarcane, bermudagrass, and johnsongrass. Glyphosate (isopropylamine salt) applied in April at 1.68, 2.24, and 2.80 kg ai/ha controlled 15-cm sugarcane at least 95% 42 d after treatment (DAT). Control of 25- and 40-cm sugarcane was maximized at 1.68 kg/ha (91 and 86% control, respectively). In another study, 25-cm sugarcane was controlled equally with isopropyl amine and potassium salt glyphosate formulations. Bermudagrass control 40 d after glyphosate was applied at 1.12 kg/ha was 86% and increased to 98% when the same rate was applied sequentially. In fallowed sugarcane fields, conventional-tillage, reduced-tillage, and no-tillage programs were implemented from mid-April through mid-August to evaluate weed control and economics. When a glyphosate application was substituted for a tillage operation, bermudagrass and johnsongrass control was increased compared with the conventional tillage alone program, but differences in sugarcane and sugar yield among the various programs the following year were not observed. Based on 2006 costs, elimination of a single tillage operation reduced cost $18.49/ha and addition of glyphosate (2.8 kg/ha plus application cost) increased cost $43.47/ha. Total cost for the conventional tillage–alone fallow program was $110.94/ha; where herbicide was used in the reduced-tillage and no-tillage programs, total cost was $19.47 to $77.38/ha more.