Powdery mildew biology

Sulfur Naturally occurring mineral used to control powdery mildew and rose black spot. It can harm predatory mites, so it should not be applied where biological controls are in use. 

Cucumber mosaic virus pictured on p.89) can, despite its name, affect all members of this family, and many other plant families, too. There Is no cure, but some cultivars show some resistance. Protect young plants from slugs. Powdery mildew may be a sign of dry soil late In the year It will not affect the crop. Under cover, biological controls can be used to control pests like red spider mite. Crop rotation, good... 

Wippich, C. and Wink, M. 1985. Biological properties of alkaloids. Influence of quinolizidine alkaloids and gramine on the germination and development of powdery mildew, Erysiphe graminis f. sp. hordei. Experientia 41,1477-1478... 

Herrington PJ, EC Hislop, NM Western, KG Jones, BK Cooke, SE Woodley and AC Chappie, 1981. Spray factors and fungicidal control of apple powdery mildew. In ESE Southcombe (ed.), Application and Biology. Proceedings of a Symposium held at the University of Reading, Berkshire 7th-9th January 1985. British Crop Protection Council, BCPC Monograph No. 28, Croydon, UK, 1985, 289-298. 

An example of the simultaneous anti-powdery mildew and acaricidal action is the biological effect of 6-methyl-2,3-quinoxalinedithiol cyclic carbonate (oxythio-quinox, 30) and of the related 2,3-quinoxalinediyl cyclic trithiocarbonate (thioquinox, 31), introduced originally as fungicides against powdery mildew and discussed already under the heading fungicides. These compounds were developed by research workers of the Bayer Co. in the course of their study of the acylated derivatives of 2,3-dimercaptoquinoxaline (Sasse et ai, 1958 19 Basse, 1960). 

Starting from the hypothesis that azo compounds with an ability to form active carbonium ions in vivo are biologically active, Biichel et al. (1972,1975) synthesised several derivatives of 1-trityl azoles. They established in extensive research work that the derivatives particularly active are those which contain only one substituent in one of the phenol rings, and in which the azole ring remains unsubstituted. This led to the very active antimycotic clotrimazole (see Section 5.7.1), which nowadays plays an important role in the local therapy of human mycoses, and to fluo-trimazole, of specific activity against powdery mildews. 

Of this biologically very effective group, the carbonic acid derivatives of 2,3-dithioquinoxaline have proved to be the most active (Sasse et al.. 1960). The active compounds first became known as excellent acaricides (Unterstenhdfer, 1960 Sasse, 1960) because they were also effective against acarus species resistant to phosphoric compounds. At the same time, they have the valuable property of being toxic to powdery mildew fungi. 

Later, during the development phase, H. K5hle and his colleagues discovered the physicochemical and biokinetic basis for its particular biological activity profile, namely its episystemic distribution properties (Section 13.2.3.3), which bring it into close contact with fungi like powdery mildews that grow on the leaf surface [8, 9, 34, 35]. 

Interestingly, the 8-chloro analogues of LY-186054 (18) showed diminished powdery mildew control yet were active against botrytis and other commercially interesting species of fungi. This shift in the biological profile is based on their different MO A 8-haloquinolines are known inhibitors of dihydroorotate dehydrogenase [65]. 

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