Chemical weed control in potatoes

Nine herbicide treatments were applied to potatoes grown at three locations in each of 3 years. The locations were characterized by widely different soil types—silty clay loam, sandy loam, and muck—and by differences in rainfall and temperatures during the growing season. None of the herbicide treatments applied pre-emergence gave adequate weed control at all locations and/or in all years. EPTC at 6 lb per acre (6.72 kg/ha) gave excellent weed control on both mineral soils but not on muck. Metabromuron at 4 lb per acre (4.48 kg/ha gave excellent weed control only on the low organic matter sandy loam. Propachlor at 6 lb. (6.72 kg/ha) and 2 lb amiben plus 3 lb propachlor (2.24 plus 3.36 kg/ha) gave variable control. Four herbicides: 1 lb paraquat (1.12 kg/ha), 2 lb linuron (2.24 kg/ha), 6 lb dinoseb (6.72 kg/ha) and 6 lb dinoseb plus 2.25 dalapon (6.72 plus 2.52 kg/ha) applied at potato plant emergence, when weeds were in the 2–6 leaf stage, also gave variable control but as a group generally gave better control than the pre-emergence herbicides, particularly on muck soil. The effectiveness of herbicides applied at potato plant emergence was less affected by soil type than those applied pre-emergence but was affected by the degree of weed emergence. On muck soil, weeds generally emerged well before “at emergence” herbicide treatments were applied. Tuber yields were not directly affected by the herbicides, but were reduced where weed control was inadequate. Tuber specific gravity and chip color were unaffected by the herbicides.     

Evaluation ofLaetisaria arvalis as a biological control agent ofRhizoctonia solani on white potato

Laetisaria arvalis, a soil-inhabiting basidiomycete, reducedRhizoctonia solani infection of white potato. A greenhouse study that monitored population levels of both fungi showed that soil infested withL. arvalis suppressed the growth ofR. solani after eight wks. Populations ofL. arvalis andR. solani increased after 11 wks. when both fungi were infested simultaneously and whenL. arvalis was introduced to soil previously infested withR. solani. Five years of field studies showed that variousL. arvalis seed treatments and soil amendments reducedR. solani infection of stems and stolons and sclerotial formation on tubers equal to the standard chemical treatment of pentachloronitrobenzene (PCNB) + thiabendazole. No relationship was shown between populations ofL. arvalis andR. solani in field plot soils, but native or wild strains ofL. arvalis were shown to be present at detectable levels in field soils.     

Combining residues of herb crops with soil heating for control of soilborne pathogens in a controlled laboratory system

Plant residues from herb crops were examined as organic amendments for the control of soilborne pathogens with and without soil heating for a short exposure of 2 weeks. Residues of herbaceous plants of oregano, sage, rosemary, tarragon, bay, wild rocket, spearmint and thyme were incubated for 14 days in a controlled laboratory system which emulates soil solarization. Green cabbage residues were included for comparison. The tested pathogens included Fusarium oxysporum f. sp. radicis-lycopersici, Macrophomina phaseolina, Rhizoctonia solani and Meloidogyne javanica. Heating soil amended with herb residues, particularly tarragon, spearmint and wild rocket, resulted in high mortality of the tested pathogens. Volatile compounds which were generated in heated soils amended with wild rocket or tarragon showed significant toxicity to M. phaseolina and R. solani. Only oregano, thyme, bay, wild rocket and tarragon amendments were effective in pathogen control without heating. Incorporation of leaf and stem residues of thyme, sage, tarragon, rosemary or wild rocket in soil and exposure to solarization under field conditions resulted in 95-100% mortality of the tested pathogen. This study demonstrates that the residues from herb crop production can serve as organic amendments for the control of soilborne pathogens, especially when combined with heating or solarization.     

Weed control research in Colorado potatoes—A review

Studies have been conducted for three years to determine the herbicides best adapted for the control of annual broadleaf and grass weeds in Colorado potato fields. The most effective registered herbicides are EPTC, EPTC + trifluralin, and metobromuron. Promising herbicides that are not registered are alachlor and 4-amino-6-t-butyl-3-(methylthio)-as-triazin-5-(4H)-one (BAY-94337). These experiments show the efficacy of several herbicides. The data indicate little need for the presently accepted pattern of extensive post planting cultivation when weeds are chemically conrolled.     

Evaluating the efficacy of pre- and post-emergence herbicides for controlling Amaranthus retroflexus L. and Chenopodium album L. in potato

Field studies were conducted from 2008 to 2010 to evaluate the control of Amaranthus retroflexus and Chenopodium album and tolerance of potato (Solanum tuberosum cv. Agria) to ethalfluralin, trifluralin, pendimethalin, rimsulfuron, EPTC and oxadiargyl applied pre-emergence (PRE) and post-emergence (POST) at seven rates. The experiments showed that trifluralin applied PRE, rimsulfuron applied PRE or POST and oxadiargyl applied POST provided the best control of A. retroflexus. Rimsulfuron and oxadiargyl applied POST and pendimethalin applied PRE were the best control options for C. album. Except for trifluralin and pendimethalin the susceptibility of the two weed species to the herbicides was similar. Trifluralin was more effective against A. retroflexus than C. album while the opposite was true for pendimethalin. Applied POST oxadiargyl was more effective than applied PRE. In contrast no differences were observed between PRE and POST applications for metribuzin, rimsulfuron and EPTC. Crop injury to rimsulfuron applied PRE or POST, trifluralin and pendimethalin was negligible while the other herbicides injured the potato crop. Metribuzin, oxadiargyl and ethalfluralin tended to cause more damage than EPTC. The results suggest that rimsulfuron and trifluralin would be the best options for weed control of A. retroflexus and C. album in Iranian potato fields.     

Differential susceptibility of potato cultivars to four herbicides

Greenhouse and field studies were conducted to evaluate the susceptibility of six potato (Solatium tuberosum L.) cultivars to injury by four herbicides. The White Rose cultivar was the most susceptible to injury, especially from metribuzin {4-amino-6-tert-butyl-3-(methylthio)-s-triazin-55 (4H) one}, and linuron {3-(3,4-dichlorophenyl)-l-methoxy-l-methyl-urea}. Injury was attenuated by decreasing the rate of herbicide in the range of 4.5 to 0.5 kg/ha (4 to 0.5 1b/A) and by increasing the seed piece size. Injury seemed to be associated with soil texture and was greater in a sandy loam than in a sandy clay loam soil. Greenhouse studies provided valuable leads on cultivar susceptibility to herbicides but reductions in foliar weight of 15 to 20% are required to justify any suspicion that field injury will occur.     

Synergistic interactions betweenRhizoctonia solani Kühn,Verticillium dahliae Kleb.,Meloidogyne spp. andPratylenchus neglectus (Rensch) Chitwood & Oteifa,in potato

Summary Samples of a sandy soil and a marine clay soil sterilized by steam were put in 55-1 containers insulated with polystyrene and placed outdoors on a brick pavement. Sandy soil was infested singly or in all possible combinations with root-knot nematodes (Meloidogyne spp.) and the fungiRhizoctonia solani andVerticillium dahliae, and the marine clay soil was infested with the root-lesion nematodePratylenchus neglectus and the same fungi to evaluate the effects of these organisms on the yield of potato. The experiments were carried out from 1983 to 1986. Tuber yield was reduced by single infestations of theMeloidogyne spp. andV. dahliae but not significantly byR. solani orP. neglectus. A three-factor interaction: nematode ×R. solani × V. dahliae was found in both experiments.R. solani andV. dahliae showed significant synergistic effects when soil was infested with theMeloidogyne spp. orP. neglectus.     

Timing of herbicide application and potato hilling

Weed management involving the time of hilling and various herbicide applications was compared. The best weed management program consisted of EPTC (S-ethyl dipropylcarbamothioate) at 3.3 kg ai ha^-1 preplant incorporated, followed by metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] at 0.6 kg ai ha^-1 applied delayed pree-mergence, or delayed preemergence applications of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide] plus linuron [N’-(3,4-dichlorophenyl)-N-methylurea] (2.2 + 1.1 kg ai ha^-1) or metolachlor plus metribuzin (2.2 + 0.6 kg ai ha^-1) regardless of the time of hilling. Alternatively, postemergence applications of sethoxydim [2-[1-(ethoxyimino) butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one] plus metribuzin plus crop oil concentrate at 0.2 plus 0.6 kg ai ha^-1 plus 1.2 L ha^-1 provided excellent season-long weed control regardless of the time of hilling. However, potato yield was reduced in 1 of 2 years by this treatment. Preemergence herbicides applied immediately after planting followed by an early hilling at ground cracking did not provide season-long weed control. The cultivar Atlantic was a better competitor with weeds than Russet Burbank in 1 of 2 years.     

Control of damping-off of organic and conventional cucumber with extracts from a plant-associated bacterium rivals a seed treatment pesticide

Environmentally friendly control measures are needed for soilborne diseases of crops grown in organic and conventional production systems. We tested ethanol extracts from cultures of Serratia marcescens N4-5 and N2-4, Burkholderia cepacia BC-1 and BC-2, and Burkholderia ambifaria BC-F for control of damping-off of cucumber caused by the soilborne pathogens Pythium ultimum and Rhizoctonia solani; ethanol being an Organic Materials Review Institute (OMRI) -approved solvent for use in certain applications in organic crop production. Ethanol extracts from strains N4-5 and N2-4 inhibited mycelial growth and germination of sporangia of P. ultimum in vitro but those from strains BC-1, BC-2, BC-F, and the ethanol control did not. Ethanol extracts from strains BC-2 and BC-F inhibited mycelial growth of R. solani in vitro while ethanol extracts from strains BC-1, N2-4, N4-5, and the ethanol control did not. Thin-layer chromatography demonstrated that ethanol extracts from strain N4-5 contained prodigiosin while ethanol extracts from strains BC-2 and BC-F contained pyrrolnitrin; extracts from strains N2-4 and BC-1 did not contain either of these compounds. DNA sequencing confirmed the presence of a biosynthetic gene for prodigiosin in strain N4-5 and its absence in strain N2-4, while a biosynthetic gene for pyrrolnitrin was found in strains BC-2 and BC-F but not in strains N2-4, N4-5, and BC-1. Prodigiosin was previously implicated in inhibition of P. ultimum while pyrrolnitrin has been shown to inhibit R. solani. Certified-organic cucumber seed treated with an ethanol extract of strain N4-5 was the only extract treatment from any of these five microbial strains to effectively suppress damping-off caused by P. ultimum in growth chamber pot experiments. This ethanol extract provided suppression of P. ultimum on cucumber that was similar to that provided by a commercially available seed treatment pesticide and greater than that provided by a commercially available biocontrol agent for this pathogen. The inhibitory factor(s) in ethanol extracts of strain N4-5 was stable as a seed treatment for at least 14 weeks when incubated at 4 °C in the dark. No ethanol extracts applied as treatments of organic cucumber seed consistently suppressed damping-off caused by R. solani in growth chamber pot experiments. Experiments reported here suggest that certain natural products from microbial strains as seed treatments are promising alternatives for control of soilborne diseases in conventional or organic cucumber production systems.     

Effects of application of certain herbicides on soil nematodes and aquatic invertebrates in rice paddy fields in Japan

As representatives of herbicides which are used in rice fields in Japan, paraquat (Pa), chlormethoxynil (Ch), a mixture of thiobencarb and simetryne (BS), and oxadiazon (Ox) were chosen for investigation of their effects on invertebrates in soil and flood water of rice paddies. With regard to nematodes, plant-parasitic species from rice roots, mainly Hirschmaniella oryzae, were the most abundant in B plots. All herbicide plots yielded more plant-parasitic nematodes from the soil than did the hand-weeded control plots. Predaceous mononchids, which mostly live in the surface stratum (oxidation zone) were drastically decreased in B and Ch plots. The vertical distribution of the nematode population showed similar patterns between control plots and those to which Pa was applied 2 months before flooding, and also between Ch and B plots, both of which herbicides were applied after flooding. Measurement of the similarity values of the nematode community confirmed these results. Invertebrates in the flood water were not adversely affected in Pa plots, but other herbicides brought about a ripid decrease in arthropods. However, water fleas (excluding copepods) were restored to their usual population levels within a month. The similarity values of the insect community were high between the Ch and B plots (as found for nematodes). Pond snails increased in herbicide-treated plots, especially in Ox plots which had a dense growth of green algae.     

Chemical control of weeds in transplanted tomatoes in Saudi Arabia

The herbicides metobromuron, diphenamid and dinitramine were tested either singly or in combination with dalapon for the control of weed species in transplanted tomato crops in Saudi Arabia, during 1979 and 1980. All herbicides were effective in controlling Chenopodium murale L., the primary broad-leaved weed in the area. However, they were less effective against other broad-leaved weed species and, even in combination with dalapon, failed to reduce populations of grass weeds. Tomato seedlings showed various degrees of injury: dinitramine was the most phytotoxic herbicide, followed by metobromuron and diphenamid. No toxicity was observed for dalapon. Diphenamid was the most promising herbicide for controlling weeds and producing significantly higher yields of tomatoes.     

Flame soil disinfestation: A novel,promising, non-chemical method to control soilborne nematodes,fungal and bacterial pathogens in China

Flame soil disinfestation (FSD) is a novel, promising non-chemical method to control soilborne nematodes, fungal and bacterial pathogens in China. The efficacy of FSD on soilborne nematodes, fungal and bacterial pathogens was evaluated during two field trials. The field trials revealed that the treatment with FSD once (FSD1) and treatment with FSD twice (FSD2) sharply reduced the total number of soilborne nematodes (>95%) and completely controlled Meloidogyne incognita in the soil. Both FSD1 and FSD2 also provided promising efficacy against soilborne Fusarium oxysporum (>44%), Phytophthora spp. (>47%) and Ralstonia solanacearum (>67%) on media. However, there was no significant difference between FSD1 and FSD2 in controlling soilborne nematodes, fungal and bacterial pathogens (P = 0.05). Currently, there are two challenges to distribute the technology in China: its high cost and relatively low efficiency because of the low speed of application compared with soil chemical fumigation. Despite the drawbacks, FSD is still promising in organic agriculture for controlling soilborne nematodes, fungal and bacterial pathogens.     

Efficacy of reduced rate fumigant alternatives and methyl bromide against soilborne pathogens and weeds in western forest nurseries

Preplant soil fumigation is commonly used to control soilborne pathogens and weeds in forest seedling nurseries of Oregon and Washington. However, lower chemical inputs are desired to meet state and federal application regulations, to minimize buffer zone size requirements, and to help protect the environment. Therefore, the objectives of this research were to evaluate the efficacy of three reduced rate soil fumigants under totally impermeable film (TIF) in managing soilborne diseases and weeds, and to determine if combined applications of up to four biocontrol agents improved soilborne disease control. Reduced rates of methyl bromide, metam sodium, and 1,3-dichloropropene, all applied in combination with chloropicrin, were effective in decreasing soil populations of Pythium and Fusarium as well as the presence of Pythium in root debris from the previous crop. The roots of Douglas-fir (Pseudotsuga menziesii) seedlings transplanted into each fumigant treatment were also colonized less by Pythium and Fusarium than those transplanted into nonfumigated control plots. However, biocontrol treatments were not effective against either pathogen. Weed biomass and weeding times were also significantly reduced by fumigation. Application costs were similar for all three fumigant treatments, but seedling size was largest from the methyl bromide and metam sodium treatments followed by the 1,3-dichloropropene treatment. Based on the results of this study, reduced rates of methyl bromide, metam sodium, and 1,3-dichloropropene show promise in managing soilborne diseases and weeds in forest nurseries.     

Fungal pathogens andPratylenchus penetrans associated with preceding crops of clovers,winter wheat,and annual ryegrass and their influence on succeeding potato crops on Prince Edward Island

The incidence of soilborne fungal pathogens of potatoes and root lesion nematodes were determined in preceding crops of clovers, annual ryegrass, and winter wheat, in the succeeding potato crops and soils and severity of associated potato diseases recorded in two, 2-yr field trials. Differences were not evident in yearly recovery ofRhizoctonia solani, Verticil-Hum dahliae, V. alboatrum, andColletotrichum coccodes from previous crops and soils. However, overall trends were present with a higher recovery ofV. dahliae from wheat and a greater recovery ofR. solani from clover than either wheat or ryegrass. A previous crop of ryegrass resulted in lower levels ofR. solani in succeeding potato soils in both trials and after clover in one trial at the pre-harvest sampling time. In trial 1 greater numbers ofPratylenchus penetrans were recovered from clover soils than from soils of ryegrass or wheat. One instance of lower nematode recovery in potato soils following ryegrass occurred but no differences in their recovery from potato roots were observed. Potato wilt incidence was lowest after clovers. Stem rot severity was positively correlated with recovery ofR. solani andV. dahliae from potato stems and roots and negatively correlated withV. alboatrum from potato stems only. Nematode populations were not related to potato disease symptom severity ratings. Results reported herein indicate that only a portion of soilborne diseases of potatoes on Prince Edward Island may be related to previous crops produced in the 3-yr rotation selected for this study.     

Two-year investigations on the integrated control of weeds and root parasites in Virginia bright tobacco (Nicotiana tabacum L.) in central Italy

The current revision of pesticides in the EU, including those for soil disinfection, will necessitate the introduction of alternative integrated methods for the control of weeds and parasites in tobacco production in Italy. The present study compared the effect of some soil fumigants, biocontrol agents, cover crops and mulching for the control of tobacco weeds and root parasites. The results show that the different soil fumigants had an important role in increasing tobacco yield, due to their ability to control weeds and the nematodes Meloidogyne incognita and Meloidogyne javanica. In particular, a typical nematicide like 1,3-dichloropropene did not control only nematodes but also Portulaca oleracea, a common weed in Italian tobacco fields. Fenamiphos, although showed a certain efficacy in controlling root-knot nematodes, did not generally have a satisfactory activity at the dose of 40 g m⁻¹; cover crops like Trifolium squarrosum and Eruca sativa and a commercial formulation composed by the endomycorrhizal fungi Glomus spp., the antagonistic fungi Trichoderma spp. and bacteria including Pseudomonas, Bacillus and Streptomyces (Micosat F, CCS Aosta, Italy), were not able to control root tobacco diseases. The investigations confirmed that a prolonged monoculture causes a reduction of black root rot. Soil fumigation and the use of Good Agricultural Practices (GAP), influencing the inoculum density of Chalara populations, can contribute to the maintenance or to the establishment of particularly unfavourable conditions for the saprophytic growth of the pathogen, leading to a lower development of the disease.     

Chitin-based bioformulation of Beauveria bassiana and Pseudomonas fluorescens for improved control of leafminer and collar rot in groundnut

The talc-based formulation of Beauveria bassiana (B2 and B4) and Pseudomonas fluorescens (TDK1 and Pf1) strains and its mixture amended with and without chitin were developed and tested for their efficacy against the leafminer insect pest (Aproaerema modicella) and collar rot (or) seedling blight pathogen (Sclerotium rolfsii) in groundnut under glasshouse and field conditions. Application of talc-based formulation of B2 + TDK1 + Pf1 strains mixture (amended with or without chitin) through seed, soil and foliar spray effectively reduced the incidence of leafminer and collar rot in groundnut compared to individual bioformulation and control treatments both under glasshouse and field conditions. Groundnut leaves when treated with this bioformulation mixture, altered the feeding behavior of leafminer larvae and increased larval mortality under in vitro. Further, a significant increase in growth parameters and yield were observed in groundnut plants treated with B2 + TDK1 + Pf1 compared to individual bioformulation and untreated control. Increased accumulation of chitinase enzyme was observed in groundnut plants treated with mixture of B2 + TDK1 + Pf1 against A. modicella and S. rolfsii when compared to other treatments.     

复合生防菌群对连作土壤大豆根际可培养微生物区系的影响

土壤微生物区系的变化是引起大豆连作障碍的主要因素之一。本实验采用盆栽试验,研究了复合生防菌群对大豆根际土壤可培养微生物区系的调节作用。结果表明,复合生防菌群可以明显改变大豆根际微生物区系组成。在大豆不同时期,复合生防菌群处理的大豆根际细菌、真菌和放线在数量发生较大改变。在大豆真叶期和复叶期,复合生防菌群接种处理大豆根际细菌较对照增幅分别达到71.8%和114.3%,而根际真菌较对照减少12.9%和22.3%.。在大豆真叶期,复合生防菌群接种处理大豆根际放线菌数量较对照减少9.9%,而在复叶期,根际放线数量较对照增加27.4%。此外,研究结显示,施用复合生防菌可有效降低土传病原菌镰孢菌属（Fusarium）和丝核菌属（Rhizoctonia）的比例,并且提高根瘤菌（Rhizobium）、固氮菌（Azotobacter）、木霉属（Trichoderma）、假单胞菌属（Pseudomonas）和芽孢杆菌属(Bacillus)等有益菌的比例。总之,该复合生防菌群对改善连作土壤大豆根际微生物区系方面有良好的效果。     

Evaluation of thiabendazole and pentachloronitrobenzene for control of the Rhizoctonia disease complex on white potato (Solanum tuberosum L.)

Thiabendazole (TBZ) and pentachloronitrobenzene (PCNB) alone and in combination were laboratory, greenhouse, and field tested during a five-year period (1977-1982) for their effectiveness in reducing incidence and severity of damage caused byRhizoctonia solani to white potato (Solarium tuberosum). Growth ofR. solani on amended potato dextrose agar was prevented at 7 ppm TBZ and 80,000 ppm PCNB. Tuber-borne sclerotial germination and hyphal growth were prevented following seed treatment with 6,000 ppm TBZ, and severely inhibited by combination treatments of 12,500 or 50,000 ppm PCNB and 1,500 ppm TBZ. Seed treatments which provided the most effective field control ofR. solani were combinations of PCNB (50,000, 25,000 ppm) and TBZ (1,500 ppm), followed by TBZ alone (6,000 ppm) and PCNB alone at rates of 50,000 ppm or above.     

The use of additives,temperature, and plant position to increase efficacy of dinoseb for potato (Solanum tuberosum) vine desiccation

Chemical vine desiccation is an important management practice for late season potatoes (Solanum tuberosum L.) in Michigan. A number of desiccants are registered; however, most Michigan growers apply dinoseb (2-sec- butyl-4,6-dinitrophenol). Greenhouse experiments were initiated to evaluate the potential of ammonium salts and ethephon (2-chloroethyl)phosphonic acid) to increase the efficacy of the chemical harvest aids dinoseb and endothall (7-oxabicyclo[2,2,1]heptane-2,3-dicarboxylic acid) on potato vines. Temperature and potato vine position were evaluated to determine their influence on vine desiccation. All treatments with endothall applied at 0.6 kg/ha resulted in unsatisfactory potato vine desiccation. Ethephon and ammonium sulfate increased efficacy of dinoseb. High temperature both before and after treatment contributed to greater dinoseb efficacy. The horizontal placing of potato vines resulted in the desired desiccation rating of 9.0 or greater using the combination of dinoseb at 2.8 kg/ha, plus ammonium sulfate at 9 kg/ha plus 2.4 L/ha X-77 surfactant.³     

Evaluating novel microbe amended composts as biocontrol agents in tomato

An investigation was conducted to evaluate the potential of antagonistic cyanobacteria/bacterial cultures amended compost and compost tea preparations for suppressing diseases caused by plant pathogenic fungi Fusarium oxysporum, Pythium debaryanum, Pythium aphanidermatum and Rhizoctonia solani in tomato. Two types of microbe-fortified composts and the compost tea preparations, along with the recommended biological control (Trichoderma formulation) and chemical control (Thiram-Carbendazim), were used for inoculating the potting mixture. Comparative performance of the treatments revealed the superiority of both the composts/compost tea preparations in enhancing seed germination, seedling length and biomass in the fungi challenged treatments. The most effective control of the diseases was obtained by the composts amended with Anabaena oscillarioides C12 and Bacillus subtillis B5 and the compost tea preparations. Both treatments provided significantly better control than the other treatments in terms of reduction in disease severity, reduction of fungal load and enhancement of plant parameters. Our study reveals the efficacy of microbe-fortified composts for use in control of the studied root diseases caused by phytopathogenic fungi.