Phomopsis longicolla is a major seed pathogen of soybean (Glycine max) in hot, humid environments. The objective of this study was to monitor the infection and development of P. longicolla on vegetative and reproductive tissues of six cultivars and to determine the relationship between this infection and subsequent seed infection and seed germination. Cultivars were grown for 3 years (2002 to 2004) without irrigation or with irrigation applied at pre- plus postflowering or at postflowering growth stages. P. longicolla was isolated most frequently from leaf, stem, pod, root, and seed. Diaporthe phaseolorum and three unidentified Phomopsis sp. were also isolated. Diaporthe aspalathi, which previously has not been reported on soybean, was also recovered from leaf samples. These isolates, however, were recovered very infrequently. Recovery of P. longicolla from roots was much lower than from leaves, stems, and pods in all years and irrigation environments. The recovery of P. longicolla from seed was affected by irrigation environments. Seed from irrigated plots had more P. longicolla than that from nonirrigated plots. Isolation of P. longicolla from seed was negatively correlated with percentage of seed germination in irrigated environments but not in the nonirrigated environment. Pod infection was correlated with seed infection in all three irrigation environments. Even though infection of leaves and stems increased with increasing moisture availability, such infection did not consistently correlate with seed infection. Seed germination and seed infection were negatively correlated with percent hard seed. This study provided the first demonstration of the seasonal progression of P. longicolla on soybean cultivars grown under three irrigation environments.
Ten commercial soybean [Glycine max (L.) Merr.] cultivars were evaluated for reaction to over-the-top applications of two rates of 3′,4′-dichloropropionanilide (propanil) at the growth stage when three nodes on the main stem had completely unrolled leaves. Propanil, a herbicide commonly applied to rice [Oryza sativa L.] for control of grass weeds, was applied at 0.56 and 3.36 kg/ha; the higher rate is commonly used for control of weeds in rice. ‘Davis’, ‘Hood’, and ‘York’ soybean cultivars were damaged more by propanil than ‘Hill’, ‘Lee’, ‘Lee 68’, ‘Pickett’, ‘Semmes’, ‘Bragg’, or ‘Dare’ when damage was measured by reductions in seed yield and stand and by leaf injury.
At intervals of 3 to 56 days, propanil (3′,4′-dichloropropionanilide) at 4.5 kg/ha was applied after treatments of carbofuran (2,3-dihydro-2,2- dimethyl-7-benzofuranylmethyl carbamate) at 0.7 kg/ha. Their interaction injured rice (Oryza sativaL., ‘Starbonnet’) vegetatively, but did not reduce grain yields, milling quality, or seed viability. Leaf chlorosis and necrosis developed within 7 days after propanil treatment and lasted for 2 to 4 weeks. As the time interval between carbofuran and propanil treatments increased, leaf injury decreased. Older rice recovered more quickly than younger rice. Interaction of carbofuran and propanil did not cause chlorosis or necrosis of rice leaves when the insecticide was applied 5 days after the herbicide. Propanil alone, applied once at 4.5 kg/ha, or applied sequentially at 4.5 kg/ha each time, caused only slight chlorosis of rice leaves.
Postemergence herbicide treatments that controlled tighthead sprangletop [Leptochloa panicoides(Presl) Hitchc.] and redstem (Ammannia auriculataWilld.), did not injure water-seeded rice (Oryza sativaL.), and substantially improved grain yields included: (a) a single application of propanil (3′,4′-dichloropropionanilide) at 4.5 kg/ha applied to weeds 8- to 10-cm tall; (b) two sequential treatments of propanil each at 3.4 kg/ha, with the first treatment applied to weeds 2- to 5-cm tall, and a second treatment applied 4 to 8 days later; (c) a tank mixture of propanil at 3.4 kg/ha and 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] at 0.6 kg/ha, applied to weeds 8- to 10-cm tall; and (d) a tank mixture of propanil and molinate (S-ethyl hexahydro-1H-azepine-1-carbothioate), each at 2.2 kg/ha, applied to weeds 8- to 10-cm tall. Treatments that controlled tighthead sprangletop or redstem unsatisfactorily or inconsistently and did not improve grain yields as much as more effective treatments included: preplant or postemergence treatments of molinate, or preplant treatments of nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether), fluorodifen (p-nitrophenylα,α,α-trifluoro-2-nitro-p-tolyl ether), CNP (2,4,6-trichlorophenyl-p-nitrophenyl ether), or He-314 (p-nitrophenyl-m-tolyl ether).
A nonphytotoxic paraffinic oil at 2.5, 5, and 10% (v/v) or a blended alkylaryl sulfonate surfactant at 0.5, 1, and 2% (v/v) did not enhance the activity of propanil (3′,4′-dichloropropionanilide) at 1.7, 3.4, and 6.7 kg/ha applied as a foliage spray in aqueous systems on barnyardgrass [Echinochloa crus-galli(L.) Beauv.] or rice (Oryza sativaL. ‘Starbonnet’). Time and rate of applying propanil affected control of barnyardgrass. Barnyardgrass control and rice yield were best with treatments of 3.4 or 6.7 kg/ha of propanil to four-leaf grass plants. Propanil at 6.7 kg/ha controlled tillering and jointing barnyardgrass well enough to increase grain yields over those of untreated rice.
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