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- Author or Editor: Megh Singh x
Depletion of the weed seed bank by stimulating germination during winter months and subsequently exposing the seedlings to adverse air temperatures is a possible means of controlling weeds in small-scale horticultural operations. Johnsongrass [Sorghum halepense (L.) Pers.], hemp sesbania [Sesbania exaltata (Raf.) Rydb. ex A.W. Hill], and barnyardgrass [Echinochloa crus-galli (L.) Beauv.] were seeded in soil trays and maintained for 4 days at 4 or -12 °C, then heated to 32 °C for 4 days using electric heating pads. Germination percentages, after heating soils, were: 55% and 70% for hemp sesbania, 82% and 72% for barnyardgrass, and 45% and 55% for johnsongrass, respectively; for seeds kept at -12 and 4 °C, respectively. Subsequent exposure of seedlings to -12 °C for 7 days killed all seedlings, while exposure to 4 °C killed only 18% to 28%. The temperature regimes of -12 °C for 4 days, and 32 °C for 4 days followed by -12 °C killed 95%, 78%, and 68% of the johnsongrass, hemp sesbania, and barnyardgrass, respectively.
Under nonlimiting conditions for nutrients, water, and light, the growth of citrus rootstocks was generally less in the presence of lantana (Lantana camara L.) than when they were grown alone. Approximately 75% of the rough leaves plants died within 3 months. Cleopatra mandarin was the least-affected rootstock with about 20% reduction of the root and shoot dry weights. The growth of Milam, sour orange, and Swingle citrumelo was intermediate in the presence of lantana. Overall, the presence of lantana did not affect nitrogen content of roots, whereas nitrogen levels in shoots varied for the six rootstocks.
A field study was conducted to evaluate the effectiveness of Kinetic and Sylgard 309 organosilicone adjuvants to increase the efficacy of glyphosate for control of Florida pusley (Richardia scabr a L.), southern crabgrass [Digitaria ciliari s (Retz.) Koel], hairy beggarticks (Bidens pilos a L.), camphorweed [Heterotheca subaxillaris (Lam.) Britt. and Rusby], bahiagrass (Paspalum notatu m Fluegge), bermudagrass [Cynodon dactylo n (L.) Pers.], and torpedograss (Panicum repen s L.). Glyphosate, either at 0.5 or 1.0 kg a.i./ha, was applied alone or in combination with Kinetic, Sylgard 309, or X-77 using a tractor-mounted boom sprayer that delivered 187 liters·ha-1 at 207 kPa pressure. Glyphosate applied at 0.5 kg·ha-1 controlled > 94% of Florida pusley, southern crabgrass, hairy beggarticks, and camphorweed. Glyphosate efficacy improved on Florida pusley and southern crabgrass when applied with the adjuvants. Glyphosate, regardless of adjuvant, completely controlled hairy beggarticks and camphorweed. Control of bahiagrass, bermudagrass, and torpedograss with adjuvants was better than without adjuvants. However, glyphosate with Kinetic or Sylgard 309 was more effective in suppressing regrowth of these perennial grasses than glyphosate with X-77. Chemical names used: isopropylamine salt fo N -(phosphonomethyl)glycine with an in-can surfactant (glyphosate); proprietary blend of polyalkyleneoxide-modified polydimethylsiloxane and nonionic organosilicone adjuvant (Kinetic); silicone adjuvant mixture of 2-(3.hydroxypropyl)-heptamethyltrisiloxane, ethyloxylated, acetate EO glycol, -allyl, -acetate (Sylgard 309); mixture of alkylarylpolyoxyethylene glycols, free fatty acids, and isopropanol nonionic adjuvant (X-77).
These experiments were designed to evaluate the seasonal efficacy of several preemergence herbicides in the production of container-grown citrus trees. Sweet orange [Citrus sinensis (L.) Osb. cv. Hamlin] nursery trees on Carrizo citrange [C. sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf.] and on Milam (C. jambhiri Lush hybrid) rootstocks were potted in synthetic mix (1 sand : 1 peat: 1 wood shavings, by volume) and grove soil (Astatula fine sand) in 15-liter, black plastic containers. Treatments included high and low rates of the preemergent herbicides trifluralin, napropamide, oxyfluorfen, metolachlor, oryzalin, alachlor, and oxadiazon along with manually weeded and weedy checks. Initial herbicide treatments were applied in March 1981 and repeated 3 additional times at 90-day intervals. All herbicide treatments significantly reduced the total number and fresh weight of weeds. High rates were consistently more effective than low rates. No treatment resulted in any visual foliar phytotoxicity, although alachlor and metolachlor significantly reduced the root vigor of both Carrizo and Milam.
Container-grown Chinese holly (Ilex cornuta Lindl. Paxt. cv. Burfordii) and Japanese holly (Ilex crenata Thunb. cv. Helleri) were treated with 6 preemergence herbicides: alachlor [2-chloro-2’,6’-diethyl-N-(methoxymethyl) acetanilide], napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide], oryzalin (3,5-dinitro-N 4,N 4-dipropylsulfanilamide), and oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one] at 2.2, 4.5, 9.0, and 17.9 kg/ha; oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene] at 1.1, 2.2, 4.5, and 9.0 kg/ha; and prodiamine [2,4-dinitro-N 3,N 3-dipropyl-6-(trifluoromethyl)-1,3-benzenediamine] at 4.5, 9.0, and 13.4 kg/ha. All herbicides at all rates significantly reduced the number and weight of weeds as compared to unweeded checks but higher rates were more effective. Lower rates of herbicides failed to control Pennsylvania bittercress, yellow wood sorrel, and purple nutsedge. Oryzalin at 9.0 and 17.9 kg/ha was phytotoxic to both hollies. Generally, Chinese holly was more tolerant to herbicides than Japanese holly. Oryzalin was most phytotoxic to Chinese holly and substantially reduced the growth and marketability of the plants. Oxyfluorfen at 9.0 kg/ha severely retarded the growth of Japanese holly.
Alachlor [2-chloro-2’,6’-diethyl-N-(methoxymethyl)acetanilide], napropamide [2-(α-naphthoxy-N,N-diethylpropionamide], oryzalin [3,5-dinitro-N 4, N4 -dipropylsulfanilamide], oxa-diazon [2-terr-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-∆2-l,3,4-oxadiazolin-5-one], each at 2.2, 4.5, 9.0 and 17.9 kg/ha, oxyfluorfen [2-chloro-l-(3-ethoxy-4-nitrophenoxy)-4-(trifluoro-methyl) benzene] at 1.1, 2.2, 4.5 and 9.0 kg/ha and prodiamine [2,4-dinitro-N 3, N3 -dipropyl-6-(trifluoromethyl)-l,3-benzenediamine] at 4.5, 9.0 and 13.4 kg/ha were evaluated for weed control and phytotoxicity in container-grown azaleas, Rhododendron indicum (L.) Sweet. ‘Formosa’ and Rhododendron obtusion (Lindl.) Planch. ‘Coral Bells’. All herbicides at all but the lowest rates effectively controlled grasses and broadleaved weeds. All herbicides at 9.0 kg/ha or higher rates were phytotoxic to these azaleas and restricted growth, root development and marketability. ‘Coral Bells’ was more susceptible to herbicide treatments than ‘Formosa’. Both azaleas were highly susceptible to oxyfluorfen.
Herbicides are usually applied multiple times by growers for season long weed control in Florida citrus (Citrus sp.). Rimsulfuron, a sulfonylurea herbicide has been recently registered for control of certain grasses and broadleaf weeds in citrus. To increase the weed control spectrum and reduce application cost, citrus growers often prefer to tank mix herbicides. Field experiments were conducted in 2010 and 2011 in citrus groves in central Florida to evaluate weed control efficacy and crop safety of rimsulfuron applied alone or in tank mixes with flumioxazin, pendimethalin, or oryzalin. Herbicides were applied sequentially in spring and fall in both years on the same experimental plot. Results suggested that rimsulfuron applied alone controlled >80% broadleaf and grass weeds up to 30 days after treatment (DAT) and was comparable to tank mixing rimsulfuron with pendimethalin or oryzalin; however, control was reduced beyond 30 DAT. Rimsulfuron tank mixed with flumioxazin was the most effective treatment at 30 and 60 DAT that provided, respectively, ≥88% and >75%, control of broadleaf weeds including brazil pusley (Richardia brasiliensis), dog fennel (Eupatorium capillifolium), common ragweed (Ambrosia artemisiifolia), cotton weed (Froelichia floridana), and virginia pepperweed (Virginia virginicum) compared with other treatments. Control of natalgrass (Melinis repens) was higher in all tank mix treatments compared with rimsulfuron applied alone with no difference among tank mix partners. Rimsulfuron tank mixed with pendimethalin or oryzalin had no advantage over rimsulfuron applied alone for control of broadleaf weeds. Among sequential applications, weed control was better after fall herbicide application (August) compared with spring (April) because of residual activity of fall applied herbicides. Rimsulfuron tank mixed with flumioxazin will provide citrus growers with an additional weed control option.
Citrus (Citrus spp.) is one of the most important crops in Florida agriculture. Weed control is a major component in citrus production practices. If not controlled, weeds may compete with citrus trees for nutrients, water, and light and may also increase pest problems. Herbicides are an important component of integrated weed management program in citrus. Saflufenacil, a new herbicide registered for broadleaf weed control in citrus, can be applied alone or in a tank mix with other herbicides to improve weed control efficacy. A total of six field experiments were conducted in 2008 and 2009 to evaluate the efficacy of saflufenacil applied alone or in a tank mix with glyphosate and pendimethalin for weed control. In addition, experiments were also conducted to evaluate phytotoxicity of saflufenacil applied at different rates and time intervals in citrus. The results suggested that saflufenacil applied alone was usually effective for early season broadleaf weed control; however, weed control efficacy reduced beyond 30 days after treatment (DAT) compared with a tank mix of saflufenacil, glyphosate, and pendimethalin. For example, control of weeds was ≤70% when saflufenacil or glyphosate applied alone compared with tank mix treatments at 60 and 90 DAT. Addition of pendimethalin as a tank mix partner usually resulted in better residual weed control compared with a tank mix of saflufenacil and glyphosate, and this herbicide mixture was comparable with grower's adopted standard treatment of a tank mix of glyphosate, norflurazon, and diuron and several other tank mix treatments. Saflufenacil applied once in a season at different rates or even in sequential applications did not injure citrus trees when applied according to label directions. It is concluded that with its novel mode of action, saflufenacil tank mixed with glyphosate and pendimethalin would provide citrus growers with another chemical tool to control broadleaf and grass weeds.
Glyphosate is the most widely used herbicide for postemergence weed control in Florida citrus (Citrus spp.). Variation in susceptibility of certain weed species to glyphosate has been observed in last few years. Therefore, understanding the mechanism underlying such phenomenon is required. Experiments were conducted to evaluate differences in tolerance of four weed species to glyphosate by quantifying glyphosate efficacy, the amount of epicuticular wax, absorption, and translocation of carbon-14-labeled glyphosate (14C glyphosate). The results of glyphosate efficacy study suggested that application of glyphosate at 3 oz/acre resulted in 99%, 90%, and 84% control of florida beggarweed (Desmodium tortuosum), spanishneedles (Bidens bipinnata), and johnsongrass (Sorghum halepense), respectively. Increasing application rate and addition of nonionic surfactant (NIS) usually did not improve glyphosate efficacy. Ivyleaf morningglory (Ipomoea hederacea) was the most tolerant and resulted in 0% and 25% control when glyphosate applied at 3 and 24 oz/acre, respectively. Biomass reduction in all weed species reflected a similar trend to percent control in response to all glyphosate treatments. Glyphosate absorption and translocation in the weed species were differed with the quantity of wax extracted. Ivyleaf morningglory had the lowest leaf wax content (10.8 μg·cm−2) and showed less absorption (62% to 79%) and translocation (15% to 39%) of 14C-glyphosate compared with other weed species. The absorption of 14C-glyphosate was in the range of 87%, 71% to 83%, and 72% to 83%; and translocation was 34% to 50%, 32% to 52%, and 53% to 58% in florida beggarweed, spanishneedles, and johnsongrass, respectively. Increasing glyphosate application rate from 6 to 12 oz/acre and addition of NIS usually increased 14C-glyphosate translocation.