Plant Diseases

Abstract

Field experiments conducted at Punjab Agricultural University, Ludhiana during 1972–73 and 1973–74 showed that post-emergence application of oxadiazon at 1 kg a.i./ha in transplanted onion gave remarkable weed control and maximum crop yield. Other treatments which performed well include pre-planting alachlor at 2.5 kg a.i./ha plus post-emergence propanil at 1.8 kg a.i./ha and also pre-planting nitrofen at 1.25 kg a.i./ha plus post-emergence nitrofen at 1.25 kg a.i./ha. Herbicides did not significantly influence the bulb quality, soil microflora or the emergence and yield of following crops of okra, bitter gourd and radish.     

Sodium 2,2,3,3-tetrafluoropropionate,a New Herbicide for Jute Field Weeds

Abstract

Sodium 2,2,3,3-tetrafluoropropionate (TFP) was tested as pre-planting and post-emergence applications on jute heavily infested with grasses and sedges. The herbicide was applied by two methods, at several rates and at different times before sowing. As a post-emergence application it was sprayed over a three week old crop. The best results were obtained when the herbicide was incorporated into the soil ten days before sowing at 3–4 kg a.i./ha. This practice controlled all grasses and sedges except nutsedge, which was only reduced by 30–40%, although higher rates gave better control. No phytotoxic effects on jute were observed with this rate and method of application.     

Chemical Control of Phalaris minor and Avena ludoviciana in Wheat

Abstract

In field experiments conducted at the Punjab Agricultural University, Ludhiana during 1973–74 and 1974–75, pre-emergence application (one day after sowing) of methabenzthiazuron (1.05 kg a.i./ha), metoxuron (1.6 kg a.i./ha) and chlortoluron (0.75 kg a.i./ha) gave effective control of Phalaris minor and Avena ludoviciana in wheat without any phytotoxic effect on the crop. Methabenzthiazuron, metoxuron and chlortoluron gave 1410, 1420 and 1090 kg/ha, respectively, more grain than the unweeded crop and 590, 600 and 270 kg/ha more than the crop hand-weeded twice. Nitrofen (1.25 kg a.i./ha) applied pre-emergence was effective against P. minor only and gave substantial increase in grain yield. Terbutryne, dichlormate and linuron, while effective against P. minor, also had a phytotoxic effect on the crop.     

Selective herbicides for establishing weed-free grass: The effect of mixtures and sequences of herbicides, including ethofumesate and methabenzthiazuron

Two field experiments compared various sequences of ethofumesate, methabenzthiazuron and mecoprop, and mixtures of metamitron, ethofumesate and methabenzthiazuron for their control of Poa annua L. and Stelluria media (L). Vill. during the establishment of autumn-sown perennial ryegrass (Lolium perenne L.). In experiment 1 pre-emergence treatments required a second, post-emergence spraying to give complete control of P. annua. Grass seedlings reappeared in early spring following ethofumesate treatment, but populations built up earlier where methabenzthiazuron had been used. The most successful treatment was ethofumesate at 1.4 kg a.i. ha^?1 followed by 0.7 kg a.i, ha^?1 in spring. Methabenzthiazuron at 0.8 kg a.i. ha^?1 followed by ethofumesate at 0.7 kg a.i. ha^?1 in December was also effective. Methabenzthiazuron at 1.6 kg a.i. ha^?1 damaged ryegrass but was effective as a secondary treatment at lower doses in spring. Most treatments controlled S. media satisfactorily, but this sometimes increased the yield of P. annua. Metamitron greatly reduced tiller numbers of P. annua in experiment 2, especially when sprayed with methabenzthiazuron. Only treatments which included ethofumesate controlled S. media adequately but there was no advantage in combining this herbicide with any other for controlling P. annua.     

Satisfactory Control of Echinochloa crus-galli in Rice Nurseries

Abstract

In field-scale trials at Hamoul in the north of the Nile delta in 1967 and 1968, certain herbicides applied to a soil heavily infested with barnyardgrass (Echinochloa crus-galli) gave very satisfactory results. Taking into account both grass control and increase in rice stand, molinate and propanil at 3-4 Ib/feddan* were shown to be most effective. Molinate used either as a liquid or granular formulation gave excellent results when applied pre-flood (liquid) or post-emergence (liquid and granules). Propanil used post-emergence gave good results provided that the field was drained 24 hours before treatment and flooded again 24 hours after.     

Chemical weed control in irrigated direct-seeded rice in the Sudan Gezira

Unrestricted weed growth resulted in serious yield losses (60–75%) in rice (Oryza saliva L.). Hand-weeding once at 2 weeks after crop emergence was ineffective, but weeding at 2 and 2 weeks after crop emergence brought yield losses down to 20%. Pre-emergence application of bifenox and oxadiazon (12 l) and post-emergence application of molinate + propanil gave crop yields comparable to that of the clean weeded control (91–129%). Grain yields obtained with pre-emergence application of oxadiazon (25 EC) and post-emergence applications of propanil, bentazone + propanil, and bifenox alone or as a tank mix with propanil or bentazone were considerably less than those obtained from the clean weeded plots. Bifenox, oxadiazon (12 l) and propanil + molinate gave adequate and persistent weed control (72–97%), and did not damage rice. Oxadiazon (25 EC) gave good weed control but resulted in a serious stand reduction. Post-emergence application of propanil, propanil + bentazone bifenox alone or as a tank mix with propanil or bentazone had no adverse effect on crop stand, but gave poor control of grasses (0–40%).     

Possible Methods for Controlling Ischaemum afrum (J. F. Gamel) Dandy,in Fallow

Abstract

Different mechanical cultivations and herbicide treatments were compared for controlling Ischaemum afrum in a heavily infested fallow area. Of the mechanical cultivations, disc ploughing to a depth of more than 15 cm, following removal of tufts and watering, was found very effective (83% reduction). Incorporated pre-emergence triluralin (1.90 kg a.i./ha) alone or in tank mixtures with oxadiazon (0.95 + 0.95 kg a.i./ha) was also found promising (79 and 76% reduction respectively). Three applications of dalapon (8.09 kg a.i./ha), as post-emergence, at two weekly intervals or two applications followed by another application at 4.05 kg a.i./ha gave almost complete eradication of Ischaemum afrum seedlings for about 12 weeks (99% reduction).     

Correspondence

Abstract

Twenty-seven different herbicides were tested at the AUB Agricultural Research and Education Center in the Beqa'a, Lebanon, to determine their effects on weeds in wheat, barley, maize, onion and sugar beet. Each herbicide was tested at three different rates as pre-emergence and post-emergence applications. Unweeded and hand-weeded check plots were included. Data on yield, quality and other agronomic characteristics of the crops tested were recorded.

Concentrations of 1,000 and 10,000 ppm of 2, 4–D caused a significant decrease in the height and grain yield of wheat and barley when sprayed at the 3-leaf stage. At the 5-leaf stage, injury to wheat and barley occurred only when sprayed at 10,000 ppm, whereas an increase in the grain yield was obtained at 1,000 ppm of 2, 4–D acid equivalent (1 kg a.i./ha).

Pre-emergence treatments of atrazine and simazine at 2.5 kg a.i./ha caused a significant increase in the forage and grain yields of maize as compared to unweeded check plots. Wheat, oats, vetch and sugar beet were injured when planted after triazine-treated maize, whereas onions and soyabeans were tolerant. Other promising herbicides tested on maize were C 3095 (N–3–trifluoromethylphenyl–N'–methyl–N'–methoxyurea) and BV– 201 (1–(3′, 4′–dichlorophenyl)–3–methylpyrrolidin–2–one) applied as a pre-emergence spray at 1 and 2 kg/ha respectively.

Pre-planting treatment of EPTC and pre-emergence treatment of pebulate at 2 kg/ha gave a slight increase in the yield of roots of sugar beet. BV–201 and BV–207 (1–(3–chloro–4–methylphenyl)–3–methylpyrrolidin–2–one) were phytotoxic to beet.

In onions, nitrofen, BV–201 and BV–207 at 1–2 kg/ha were promising as pre-emergence and post-emergence sprays. DNOC and dinoseb at 1.5 kg/ha and ioxynil at 0.5 kg/ha sprayed post-emergence increased the yield of onions significantly over the check. No significant effects of these herbicides were observed on the bulb index, moisture content and total soluble solids of onions.     

Use of substituted urea herbicides for weed control in Euphorbia lathyris L., a potential fuel-producing crop

Some substituted urea herbicides (chlortoluron, diuron and methabenzthiazuron) were tested for possible use in the cultivation of Euphorbia lathyris L. Diuron showed high phytotoxicity for this species, which was tolerant to chlortoluron and methabenzthiazuron. In preliminary experiments two triazine herbicide (atrazine and simazine) were also used, but both were so toxic to E. lathyris that their use was not continued beyond this stage. In glasshouse experiments, chlortoluron showed slight phytotoxicity to E. lathyris but this did not appear in field experiments. Both chlortoluron and methabenzthiazuron were very efficient against weeds which were present and significantly increased yield of E. lathyris in comparison with unweeded plots. The poor competitive ability of E. lathyris against weeds was confirmed.     

Environmental factors affecting the herbicidal activity of DPX-A7881

DPX-A7881, methyl 2-[(4-ethoxy-6-methyl-amino-1, 3, 5-triazin-2-yl)carbamoylsulphanoyl] benzoate, is a sulfonylurea herbicide being developed in Canada and Europe for post-emergence broadleaf weed control in spring and winter rapeseed. Growth room studies were conducted to determine the environmental factors affecting the herbicidal activity of DPX-A7881 applied post-emergence on winter rapeseed (Brassica napusu L. ‘Tandem’) and on a closely related weed species, Sinapis arvensis L. (wild mustard). Laboratory tests were carried out at tempera tures ranging from 2–26°C, at relative humidities from near 40% to >95%, with rain-free periods from 0.25–8 h after herbicide application, at soil moisture contents from 50–200% of field capacity, and with irradiances from 23–450 μEm^?2s^?1 Significant control of S. arvensis was demonstrated for all treatments except under poor growing conditions at the lowest temperatures and irradiances tested. After two weeks' exposure to each of the tem perature treatments, the herbicide maintained control of S. arvensis during a subsequent week of favourable growing conditions. Relative humidity, soil moisture or simulated rainfall did not significantly alter the herbicidal activity of DPX-A7881 on S. arvensis. DPX-A7881 showed a high degree of crop safety on B. napus. The herbicide did not significantly reduce the dry weights of B. napus grown under any of the environmental conditions tested.     

The selectivity of methabenzthiazuron between barley, perennial ryegrass and Poa trivialis

In field experiments methabenzthiazuron at 1.1 kg ai/ha applied pre-emergence gave good control of Poa trivialis L. in perennial ryegrass S23 which was undersown in spring barley (Zephyr); no significant damage to barley or perennial ryegrass resulted from 2.2 kg ai/ha. However this dose applied when barley had three to four leaves decreased the subsequent barley yield. In pot experiments in the glasshouse methabenzthiazuron was active mainly due to uptake through the soil. Much greater damage to barley and perennial ryegrass resulted when herbicide-treated soil was placed below seed level than above the seed. The difference was less marked with P. trivialis. The latter started to develop secondary roots near the soil surface earlier than either perennial ryegrass or spring barley.     

Effects of the herbicide methabenzthiazuron on the physiology of wheat plants

Spring wheat (Triticum aestivum L. “Caribo”) was grown in vermiculite containing methabenzthiazuron (N-(benzothiazol-2yl)-NN′-dimethylurea) presowing. Effects of the herbicide on plant development and plant composition were analysed up to an age of 4 weeks. Inhibition of photosynthetic oxygen evolution represented the primary effect induced by the herbicidal treatment and led to a decreased concentration of soluble reducing sugars. Photosynthetic activity however recovered after 3 weeks and even increased above control values. Secondary effects following methabenzthiazuron treatment included a delayed chlorophyll breakdown, a decreased chlorophyll a/b ratio, enlarged chloroplasts, an increased concentration of soluble amino acids and of soluble protein, and an increased in vitro nitrate reductase activity. These responses are taken to indicate an increased photosynthetic and metabolic capacity in methabenzthiazuron treated wheat plants. Comparable results can be obtained with plants grown at low light intensities. It is concluded that the “physiological effects” observed in wheat plants after treatment with methabenzthiazuron are similar to a natural adaptation reaction to low light intensities. It is assumed that this adaptation reaction is caused by a low concentration of soluble reducing sugars. Experiments with plants growing at different light intensities indicated that effects due to herbicidal action were more pronounced at high light intensities. Measurements on daily fluctuations revealed a peak around noon for the sugar content and the nitrate reductase activities measured in vivo as well as in vitro. In vivo nitrate reductase activity in plants treated with 5 parts/million methabenzthiazuron was very low, presumably because of lack of sugars for the production of NADH. The protein concentration was increasing and the amino acids were decreasing during the day in herbicide treated plants, possibly indicating increased protein synthesis in the light in plants treated with methabenzthiazuron.     

Bentazon—a New Herbicide for Chemical Weed Control in Soyabeans

Abstract

Basagran is the trade name of a post-emergence herbicide belonging to the thiadiazines. The active ingredient is bentazon. It was developed by BASF for the control of broadleaved weeds in soyabeans. Bentazon is a contact herbicide with low mammalian and fish toxicity. As it is absorbed by the green parts of the plants, full coverage is essential for complete success. It is selective in soyabeans at all stages of crop growth, and has a broad herbicidal spectrum. Annual weeds in soyabeans, including cocklebur. (Xanthium pensylvanicum) which is a serious problem in the soya-growing areas of the USA, are effectively controlled by 0.75–1.0 kg a.i. bentazon/ha. The most suitable time of application was found to be between the development of the first and third trifoliate leaves of the crop.     

Interaction between timings and doses of quindorac in rice

Quinclorac (3,7-dichloro-8-quinolinecarboxylic acid) is a new herbicide in United States rice production. Field studies were conducted in 1990 and 1991 in Mississippi to determine the influence of application timings and rates on weed control efficacy and rice yield. Control of Echinochloa crus-galli (L.) Beauv. (barnyard-grass), Sesbania exaltata (Raf.) Rydb. ex A. W. Hill (hemp sesbania) and Ipomoea wrightii Gray (palmleaf morning glory) were greatest with early post-emergence application. Efficacy of pre-emergence application depends strongly on soil moisture, with significantly reduced weed control resulting when applied to dry soil. Weed control with pre-emergence application to moist soil was comparable with early post-emergence application at higher rates of quinclorac. Pre-plant and incorporated quinclorac controlled weeds effectively. Control of E. crus-galli, S. exaltata and I. wrightii ranged from 73 to 99%, 75 to 99%, and 92 to 99% at 28 days after treatment, respectively. Rice yield generally reflected weed control. No rice injury was observed for any treatment. Results indicate that early post-emergence application of quinclorac is the best time for using reduced rates and field conditions at application should be considered with these rates pre-emergence.     

Anwendung von Isoproturon, allein und in Kombination mit anderen Wirkstoffen, im Nachauflauf-Winter (NA-W) und Nachauflauf-Frühjahr (NA-F) zu Winterweizen und Wintergerste

Use of isoproturon, alone and in combination with other compounds, post-emergence in winter and spring on winter wheat and winter barley Isoproturon, alone and combined with dinoseb acetate and bifenox, was applied post-emergence in winter and spring to winter barley and winter wheat. The experiment was on two sites (sandy and clay soils) and lasted for two years. Although after winter application the initial herbicide level in the soil was higher than after spring treatment, there were no differences at the end of the growing season. The DT₅₀ (time to 50% disappearance) value for isoproturon was between 12 and 33 days in both years for both soils and the DT₉₀ value varied from 34 to 68 days. Soil residues of isoproturon were not affected by the presence of the other compounds. Winter application gave better weed control and higher crop yields.     

Use of mesotrione and tembotrione herbicides for post-emergence weed control in alkaloid poppy (Papaver somniferum)

Two field experiments were carried out a year apart on the alkaloid poppy (Papaver somniferum) in 2012 and 2013 in north-west Hungary, to assess the efficacy of mesotrione and tembotrione herbicides for post-emergence weed control. Our experiments tested (1) a single application of mesotrione at 144 g active ingredient (a.i.) ha^–1, (2) two separate applications of mesotrione at 144 g a.i. ha^–1, (3) a single application of tembotrione at 88 g a.i. ha^–1, (4) two separate applications of mesotrione at 88 g a.i. ha^–1, and (5) the combination of a single application of mesotrione at 144 g a.i. ha^–1 followed by a single application of tembotrione at 88 g a.i. ha^–1. Both non-treated and hand-weeded plots were used as controls. Among the most important weeds, Chenopodium album was most successfully controlled in the majority of the test treatments, but Fallopia convolvulus and Polygonum aviculare tolerated each herbicide application in 2012, likely due to the dry weather conditions. Because of the botanical similarity to the crop, none of the treatments proved to be significant against Papaver rhoeas. One dosage of tembotrione alone never reduced the dry weights of the target weed species or weed numbers significantly. The cuticular wax layer of the opium poppy can provide a natural defence against these herbicides, but some temporary phytotoxic yellowish discoloration occurred after tembotrione treatments. Our results show that mesotrione in combination with tembotrione is the most effective treatment and should be employed in poppy cultivation.     

Effect of atrazine and methabenzthiazuron on oxygen evolution and cell growth of Chlorella pyrenoidosa

Cultures of Chlorella pyrenoidosa Pringsheim were grown photoautotrophically in the presence of two concentrations (0·25 and 0·50 μm ) of atrazine and methabenzthiazuron. The cell density and chlorophyll content were greatly reduced in presence of both herbicides. These herbicides affected net photsynthesis equally without affecting oxygen uptake. However, cell division was more inhibited by atrazine than by methabenzthiazuron, but chlorophyll content per cell was more inhibited by methabenzthiazuron than by atrazine.     

Assessment of Chemical and Manual Weed Control Approaches for Effective Weed Suppression and Maize Productivity Enhancement Under Maize-Wheat Cropping System

Effective weed management in maize-wheat (M-W) cropping systems are accountable for higher yield and plant biomass. The objective of this study was to evaluate the effectiveness of manual weeding and chemicals (pre- and post-emergence herbicide) for actual weed control to enhance maize yield and M?W system productivity. Herbicides were treated as pre-emergence (sole), post-emergence (sole) and its combined application (pre- and post-emergence) for weed eradication and suppression. Sole pre-emergence herbicide (acetyclour?+?atrazine) and sole post-emergence herbicides (nicosulfuron), and its mixed application were used in the experiments. The experiment was comprised on 6 treatments with one weedy check or control plot: W1?=?weedy check, W2?=?acetyclour?+?atrazine, W3?=?atrazine, W4?=?nicosulfuron, W5?=?nicosulfuron?+?atrazine, W6?=?acetyclour?+?atrazine?+?nicosulfuron and W7?=?manual weeding. Main weeds were Cyperus rotundus, Tribulus terrestris, Dactyloctenium aegyptium and Cynodon dactylon. Experiential findings revealed that manual weeding was found most effective in terms of controlling weed and suppression. Among the herbicides application, promising results in terms of weed destruction and suppression were shown by combined application of acetyclour?+?atrazine?+?nicosulfuron which effectively controlled weeds as compared to other treatments. It was concluded that manual weeding drastically reduced weeds frequency and biomass while among the herbicides application acetyclour?+?atrazine and nicosulfuron could be promising for weeds suppression and clamp downing as compared to all other treatments under M?W cropping system.

     

Effect of low volume copper sprays with polyisobutene sticker on mango blossom blight (Glomerella cingulata) in Dominica

Abstract

Two spraying strategies to control mango blossom blight caused by Glomerella cingulata were tested in Dominica In one trial, a single dose of 4% copper oxychloride (18 g per tree) was applied to foliage before flowering had started, while the other trial compared fortnightly applications of concentrations up to 2%, starting after flowering. The early single dose gave a significant increase in fruit set, whereas the repeated doses gave no significant effects. Early application, followed by a low volume spraying of protectant fungicides, may reduce the cost of disease control. The addition of 0.5% polyisobutene sticker, tested in the single dose trial, gave a consistently improved fruit set compared to the non‐sticker treatment, significant at one recording date; the overall evidence was encouraging. In vitro tests showed that the fungus was less sensitive to copper than to chlorothalonil and some systemic fungicides.     

Performance of pyrazosulfuron-ethyl in non-puddled transplanted rainy season rice and its residual effect on growth of the succeeding crop in rice-wheat cropping pattern

Abstract

A study was carried out in sandy clay loam textured soil of Mymensingh, Bangladesh to evaluate weed control efficiency of pre-emergence herbicide pyrazosulfuron-ethyl either alone or in sequential application with post-emergence herbicide in transplanted rainy season rice under non-puddled strip-tilled (NPST) field condition and also to examine the residual effect of those herbicides on germination and growth of the subsequently grown wheat crop. Five treatment combinations of pyrazosulfuron-ethyl were tested against one weedy check and one weed-free check. The study revealed that NPST rice field was mostly infested by grass and sedge weeds and herbicide treatments offered a wide range of control (above 50% to 95%) on all types of weeds. Application of pyrazosulfuron-ethyl followed by (fb) orthosulfamuron fb butachlor plus propanil provided the most effective and economic weed control over two years of the study. Moreover, micro-plot bioassay study claimed germination and growth of subsequently grown wheat were not adversely affected by herbicides that were applied in rice. Therefore, application of pyrazosulfuron-ethyl followed by post-emergence herbicide could be effective and economic to control weeds in NPST rice under rice-wheat system, but proper rate and time of application should strictly be followed.