Powdery mildew of Cereals

The N-cycloaliphatic derivatives of tetrahydro-l,4-oxazine (morpholine) or those with a long-chain alkyl groups are good specific fungicides against powdery mildew fungi (cereals, cucumbers, apples, roses, etc.) (Pommer and Kradel, 1967). 

Trichothecin is effective against several fungi, for example root rot of cereals (Helminthosporium sativum), loose smut of wheat (Ustilago tritici), diseases of sour cherry and cherry (Voros, 1955), fusarium wilt of Pinaceae (Belimova and Lopatin, 1963) and powdery mildew of tobacco (Manucharjan, 1964). Its most promising practical applications are the control Verticillium wilt of cotton and of the fusarium diseases of field crops (Askarova and Joffe, 1962 Bunina, 1960 1963). 

Besides the intrinsic properties of each resistance mechanism, the economic impact of Qol resistance on the Qol market is also governed by the availability of alternative fungicidal modes of action for disease control and resistance management in each crop. For example, the early and rapid development of resistance of cereal powdery mildew (Blumeria graminis) in European wheat and barley production from 1998 on had a remarkably low impact on Qol consumption. The broad disease spectrum controlled by Qols and the availability of several other modes of action for the control of powdery mildews in cereals such as DMIs, amines, cyprodinil, quinoxyfen, and metrafenone resulted in a nearly unchanged use frequency of Qols in European cereal production. 

The quinoline derivative quinoxyfen controls exclusively powdery mildews in cereals and broadleaved crops whereas phenylpyrroles such as fludioxonil are used as foliar, post harvest and seed treatment fungicides against a broad range of pathogens such as Botrytis cinerea and apple scab (Table 12.10). 

Quinoxyfen was introduced in 1996 [68] by Dow-Elanco and has been in commercial use since 1997 for the control of powdery mildews. Quinoxyfen is specifically active against powdery mildews on cereals and horticultural crops [69, 70-72]. 

As a result of this search for novel fungicides, a series of analogous phenoxyquinolines has been developed which controls sensitive and resistant strains of powdery mildew in cereals, cucurbits and grapes. The discovery and structure-activity relationships as well as the greenhouse and field efficacy of selected compounds are detailed in this report. 

Albaconazole (UR 9825) 1172 <1998JME1869> and fluquinconazole 1173 are used as antifungals, while proqui-nazid 1174 has high activity against powdery mildew diseases of cereals, grape and apple <2006H(68)561>. 

A8,7 Isomerase and A14 Reductase. Before the appearance of resistance to azole fungicides in cereal powdery mildew the A8,7 isomerase and A14 reductase inhibitors were of minor importance because of their limited spectrum. Only seven examples of this group have shown commercial potential fenpropimorph, fenpropidin, tridemorph, dode-morph, aldimorph, piperalin, the first member of the series, introduced by Eli Lilley (now Dow Agrosciences) in 1960, and spiroxamine, the latest addition (Figure 4.5). 

Quinoxyfen (DE-795). Quinoxyfen (DE-795), announced by Dow AgroScience in 1996 (Figure 4.35), is a specific powdery mildew fungicide with particular utility in cereals. The mode of action is unknown but the chemistry is close to LY214352, a known inhibitor of pyrimidine synthesis. Quinoxyfen and RNA-synthesis fungicides also inhibit appressorium formation. 

The almost exclusive use of triazoles for cereal powdery mildew control up to the mid-1980s has resulted in a shift in Erysiphe populations toward reduced sensitivity or resistance to this class of fungicides. However, use has continued because field performance of most triazoles has remained adequate (43). Decreased azole sensitivity in the Septoria population to azoles has also been noted. 

Triazole derivatives of the dichlobutrazole and paclobutrazole types are closely related chemically to the triazolyl-0,N-acetals previously mentioned. The oxygen atom of the acetal function was merely replaced by a methylene group. Dichlobutrazole (ICI) was developed for the control of powdery mildew, rust and scab in cereals. Paclobutrazole is under development as a growth regulator. 

In France and Germany, disease control measures on cereals are directed primarily against foot rot and leaf diseases, or leaf and ear diseases. In the United Kingdom, treatments are generally made for the control of leaf diseases, such as powdery mildew. It should be mentioned that these data do not include the use of the azole-compound triadimenol as a seed dressing for early season protection against powdery mildew and rust fungi on wheat and barley. 

The percent increase in yield is often related to weather conditions. In dry years (1976) a relatively small number of fungicide cereal trials showed an increase in yield, but during wet years (1978) 60% of the tests showed yield increases. In long-term trials (4) in the Western region of Germany, seed treatments and foliar applications of triazole fungicides reduced crop losses from powdery mildew up to 25% (Table VI). ... 

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