In field studies trifluralin and pendimethalin at 1.7 kg ai ha-1 applied PPI controlled itchgrass 87 and 78%, respectively, in late season when averaged over a 2-yr period. Clomazone at 1.1 kg ai ha-1 applied PRE to the soil surface in one year controlled 80% of itchgrass compared with 51% when applied PPI. POST application of 0.15 kg ai ha-1 fluazifop-P, 0.21 kg ai ha-1 haloxyfop, 0.10 kg ai ha-1 quizalofop, and 1.1 kg ai ha-1 diclofop controlled at least 90%. Itchgrass control was less effective with 0.43 kg ai ha-1 sethoxydim and 0.07 kg ai ha-1 clethodim POST and poor with 0.15 kg ai ha-1 imazaquin and 0.07 kg ai ha-1 imazethapyr.

Field studies were conducted to document the response of itchgrass [Rottboellia exaltata (L.) L.f. ♯3 ROOEX] in soybean [Glycine max (L.) Merr. ‘Forrest’] to selected herbicides and postplanting cultivation. Early cultivation stimulated emergence of itchgrass seedlings; however, when plots were cultivated two or three times, itchgrass was effectively removed from the tilled area. Cultivation had no effect on the density, height, standing biomass, or seed production of itchgrass plants in the soybean row but did increase soybean yield. In response to a density reduction of 90%, the average weight, number of tillers and branches, and seed production of single itchgrass plants increased by a factor of 2.9, 3.1, 2.3 and 2.6, respectively, in trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine)-treated plots. Individual plants did not increase growth following density reduction by a postemergence application of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}. Itchgrass plants competing for the entire season in plots treated with trifluralin reduced soybean yield approximately 21 g per weed, while itchgrass recovering from diclofop treatment and competing the remainder of the season reduced yield approximately 5 g per weed.

Greenhouse studies were conducted to determine host status of weed species for Rhizoctonia solani AG-1, which causes Rhizoctonia foliar blight of soybean. Weed species were barnyardgrass, broadleaf signalgrass, common cocklebur, entireleaf morningglory, hemp sesbania, itchgrass, johnsongrass, large crabgrass, northern jointvetch, prickly sida, purple nutsedge, redweed, sicklepod, and smooth pigweed. Seedling weeds were inoculated with suspensions containing intraspecific group IA and IB isolates of the fungus. In the first study, sclerotia of IA were recovered from tissue of all weeds except smooth pigweed, and mycelia of IA were recovered from all except smooth pigweed and redweed. In that study, neither microsclerotia nor mycelia of IB were recovered from sicklepod, barnyardgrass, or large crabgrass, and only microsclerotia were recovered from itchgrass and purple nutsedge. In the second study, sclerotia of IA, microsclerotia of IB, and mycelia of each isolate were recovered from all weed species. In other studies, R. solani spread from at least six of seven weed species to a noninfected soybean plant growing in close proximity. These studies emphasize the importance of weed control, not only for reducing plant competition and increasing yield, but also for the potential impact on development of RFB.

Field studies were conducted in the northern and southern cane belt areas of Louisiana to determine the effect of itchgrass on sugarcane growth and yield. Itchgrass was allowed to interfere with sugarcane season-long, early-season from emergence in the spring until layby (last cultivation) in mid-June, and late-season from layby until harvest. Itchgrass germination occurred throughout the growing season. Populations of millable sugarcane stalks and yields of cane and sugar were similar for no interference, early-, and late-season interference. Season-long itchgrass interference reduced sugarcane stalk populations and cane and sugar yields an average of 34, 42, and 43%, respectively, compared with no interference.

Preemergence control of itchgrass in sugarcane with nonincorporated pendimethalin and prodiamine increased as rate for each herbicide increased from 2.2 to 3.4 kg ai ha-1. Itchgrass control at 3.4 kg ha-1 was similar for both herbicides, ranging from 78 to 94% (86% mean) for pendimethalin in six field experiments and 83 to 91% (86% mean) for prodiamine in three experiments. Incorporated trifluralin at 2.2 kg ha-1, the standard, gave 99% mean control of itchgrass. None of the nonincorporated treatments with pendimethalin or prodiamine consistently prevented a decrease in the sugarcane stalk population at harvest. Asulam applied postemergence at 3.7 kg ae ha-1 controlled itchgrass that survived the preemergence herbicides, and sugarcane stalk populations were maintained. Preemergence control of johnsongrass with nonincorporated treatments of pendimethalin or prodiamine at 2.8 kg ha-1, in a mixture with atrazine at 2.2 kg ai ha-1, ranged from 86 to 95% (89% mean) for pendimethalin and 80 to 95% (88% mean) for prodiamine. Metribuzin at 2.2 kg ha-1, the standard, gave 97% mean control of johnsongrass. Mixtures of pendimethalin with metribuzin or terbacil generally gave more effective control of johnsongrass than mixtures with atrazine. When used in conjunction with other herbicides, nonincorporated pendimethalin and prodiamine were effective alternatives to soil-incorporated treatments for weed control in sugarcane.

In field and greenhouse studies, tank mixing 0.3 and 0.4 kg ai/ha of the butyl ester of fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid} with 0.4 kg ai/ha of acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} reduced control of large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] and itchgrass (Rottboellia exaltata L.f. # ROOEX) compared to fluazifop applied alone in soybeans [Glycine max (L.) Merr.]. Less antagonism between the two herbicides was observed in a year when conditions were optimum for large crabgrass control with fluazifop. Application of acifluorfen 1 to 3 days before application of fluazifop decreased large crabgrass control. Antagonism between fluazifop and acifluorfen was avoided when fluazifop was applied 3 to 5 days before acifluorfen. No antagonism was observed when fluazifop at 0.3 or 0.4 kg/ha was tank mixed with acifluorfen at 0.4 kg/ha for control of itchgrass. Itchgrass was more susceptible to fluazifop than large crabgrass.

Itchgrass biotypes from 34 countries or territories were evaluated under controlled and natural day length at Houma, LA. They could be placed in five broad groups based primarily on the effect of day length on flowering but also on general morphology and pattern of growth. The Group 1 biotypes (Argentina, Bolivia, Costa Rica, Cuba-1, Ecuador-1, Florida, Guadeloupe, Honduras-1, Louisiana-1, North Carolina, Papua New Guinea-1, Panama, Peru, Philippines-1, and Venezuela) were not affected by day lengths of 12 and 14 h (day length neutral) and flowered 35 to 57 d after germination. The Group 2 biotypes (Australia, Kenya-1, Reunion, South Africa, and Zimbabwe) also were not greatly affected by photoperiod and flowered 54 to 67 d after germination, and were taller with fewer and larger diameter culms than the Group 1 biotypes. The Group 3 biotypes (Brazil, Colombia, Jamaica, and Philippines-2) were moderately sensitive to photoperiod. They took longer to flower at 14 h than at 12 h and flowered in 63 to 95 d. The Group 4 biotypes (Cuba-2, Dominican Republic, Ecuador-2, Honduras-2, India, Louisiana-2, Malaysia, Papua New Guinea-2, Puerto Rico, Taiwan, and Thailand) were short-day plants that did not flower in the screenhouse until August or September (130 to 163 d), after the natural photoperiod had decreased to 13 h. The Group 5 biotypes (Indonesia, Kenya-2, Nigeria, Sudan, Tanzania, and Trinidad) were strict short-day plants that flowered only in September to November (167 to 226 d), after the day length had decreased to about 12 h. Most biotypes were diploids with 2n = 20 chromosomes, but some were polyploids (2n = 40 or 2n = 60). The shape of the glume tip on the pedicellate spikelet was found to be acuminate, acute, or obtuse for the biotypes with 2n = 20, 40, and 60 chromosomes, respectively, and was a reliable marker to distinguish diploids from polyploids.

Patterns of weed emergence in upland and lowland soils were observed for several months after tillage by counting all emerged species. Forty to 50% of weed emergence occurred within 6 weeks of tillage on both sites. Significant emergence occurred within 3 weeks on both sites, but very little emergence occurred within 1 week in lowland soil. The data confirm the strong influence of soil tillage on weed emergence. They also suggest an influence of radiant energy on weed emergence. Peaks of weed emergence 6 or more weeks after tillage often occurred coincident with or soon after peaks of radiant energy.

Polyacrylamide electrophoresis and spectroscopic methods were used to characterize biotypes A and B itchgrass [Rottboellia exaltata L.f. # ROOEX] and their F2 progeny. Electrophoretic analyses of F2 progeny showed that differences between these two biotypes are multiallelic. Spectrophotometric data indicated differences between the photosynthetic apparatus of the two biotypes. These differences may reflect different abilities to adapt to varying light conditions and infer that these biotypes promote survival of the species by increasing the number of environmental nitches that R. exaltata can occupy.

Autumn-planted sugarcane was seeded with itchgrass in early March to give 1 plant per 30.5 cm of row length (1.8 plants m−2). In three of four experiments, itchgrass was allowed to reseed and develop naturally in the second or third-yr ratoon crops. In the first-yr crop, itchgrass stands developed by May 15 and itchgrass was removed after 30, 60, or 180 d of interference. After 30 d interference, on about June 15, itchgrass biomass ranged from 200 to 2700 kg ha−1 in four experiments and reduction in sugar yield averaged 7%. After 60 d interference, on July 15, the biomass ranged from 1400 to 2900 kg ha−1 in two experiments and reduction in sugar yield averaged 17%. Itchgrass removed at harvest in November, after 180 d interference, reduced sugar yield by 19% in four experiments. Itchgrass infestations removed in the second-yr crop on May 1, June 1, and November 15 harvest reduced sugar yield in one experiment by 3, 11, and 72%, respectively, compared to a 2-yr weed-free control. Itchgrass interference reduced sugar yield primarily by reducing stalk population even though full-season interference increased sugar concentration of juice by 2 to 10%. These studies indicate that itchgrass must be removed from sugarcane well before June 15 (30 d of interference) under Louisiana growing conditions to prevent a rapid increase in itchgrass biomass and loss in sugar yield. However, sugarcane stands and yield recovered almost completely when maintained weed free in the second-yr crop following full-season itchgrass interference in the first-yr crop.

In field experiments, nicosulfuron at 35 g ai/ha controlled itchgrass in corn 28 d after treatment better than primisulfuron at 39 g ai/ha (80 vs. 44%). Control with both herbicides was greater when applied to six-leaf itchgrass than to 10-leaf and with the addition of nonionic surfactant than with an organosilicone surfactant and methylated seed oil blend. Weed control for nicosulfuron plus nonionic surfactant resulted in corn yield approximately 1.5 times that of primisulfuron plus nonionic surfactant and 1.6 times that of nicosulfuron plus an organosilicone surfactant and methylated seed oil blend. When primisulfuron was applied with organosilicone surfactant and methylated seed oil rather than nonionic surfactant, corn yield was reduced by 25%. For nicosulfuron with nonionic surfactant, corn yield averaged approximately twice that of the nontreated check. In other field experiments, itchgrass control 28 d after treatment with nicosulfuron was enhanced with addition of an organosilicone and nonionic surfactant blend or methylated seed oil (83 and 78%, respectively) compared with nonionic surfactant (69%). Nicosulfuron was less effective when applied with crop oil concentrate or organosilicone surfactants compared with nonionic surfactant.