This leads to decreased levels of plastoquinone in plant tissue and reduced photosynthetic yield . Indirect inhibition of phytoene desaturase as a consequence of blocked plastoquinone biosynthesis subsequently leads to a decrease in carotenoids and consequently prevents stabilization of the photosynthetic apparatus so that chlorophyll molecules are destroyed by excessive light energy. Inhibition of HPPD also prevents biosynthesis of tocopherols that leads to reduced vitamin E synthesis, which means loss of protection against oxidative stress and against photo inactivation of the photosynthesis apparatus. The whole process will result in typical bleaching symptoms in the newly developing leaves during the first week after application. These bleaching symptoms progress toward necrosis and susceptible plants generally die within two to three weeks after treatment. Pyrasulfotale is the first significant compound with a new mode of action for broadleaf weed control in wheat, barley and triticale in more than 20 years. The prepacked mixture of pyrasulfotole & bromoxynil received US registration for use in wheat in 2008.
Bromoxynil belongs to the nitrile group and inhibits photosynthesis at photosystem II in susceptible plants. The premix also contains the safener mefenpyr-diethyl. The recommended dose of pyrasulfotole & bromoxynil is 207 to 282 g·ai·ha−1 and recommended stage of application in wheat is first leaf to flag leaf emergence. The herbicide label recommends tank mixing pyrasulfotole & bromoxynil with dicamba, MCPA, metsulfuron-methyl or 2,4-D for broad spectrum weed control. Currently not much information on use of pyrasulfotole & bromoxynil in winter wheat is available. The objectives of the study were 1) to evaluate premixed pyrasulfotole & bromoxynil with and without other herbicides for efficacy and safety in winter wheat and 2) to determine the optimum time for its application. In 2007-2008, at Hays, fall-POST application of all herbicides controlled henbit better than spring-POST treatments . Complete control of henbit was achieved with all fall-POST treatments. Among spring-POST treatments henbit control was lowest with tank mixture of pyrasulfotole & bromoxynil + metsulfuron-methyl and premixed triasulfuron & dicamba . Henbit control was essentially complete, vertical grow systems for sale regardless of herbicide or application timing at Hays in 2008-2009. At Manhattan, all pyrasulfotole & bromoxynil treatments applied fall-POST controlled henbit ≥ 98%, but control varied significantly among spring-POST treatments.
Lowest henbit control was observed with triasulfuron & dicamba applied either fall-POST or spring POST compared to pyrasulfotole & bromoxynil treatments, however fall-POST treatment was much better than spring-POST treatment . These results indicate that pyrasulfotole & bromoxynil with or without tank mixtures controlled henbit better than commercial standard triasulfuron & dicamba. However, fall applications of pyrasulfotole & bromoxynil were better than spring applications. This could be due to the fact that henbit was smaller in size in fall compared to spring . Contrary to our results, Martin et al. reported complete control of henbit with pyrasulfotole & bromoxynil alone or in combination with dicamba regardless of application timing . In our experiment it was also noticed that, in two instances, pyrasulfotole & bromoxynil + metsulfuron-methyl applied spring-POST controlled henbit less compared to pyrasulfotole & bromoxynil alone or in combination with MCPA. Generally, ALS-inhibiting herbicides control henbit better when applied in fall than spring. At Manhattan, wild buckwheat emerged late after fallPOST application and plants were small at the time of spring-POST application. Spring-applied pyrasulfotole & bromoxynil alone or in combination with MCPA provided poor wild buckwheat control However, when pyrasulfotole & bromoxynil was tank mixed with dicamba or metsulfuronmethyl control of wild buckwheat was 84% or more.
Even though wild buckwheat had not emerged at the time of fall-POST application, pyrasulfotole & bromoxynil + metsulfuron-methyl and triasulfuron & dicamba applied in fall controlled wild buckwheat 73% and 87%, respectively. This might be due to residual activity of metsulfuron and triasulfuron in the soil. Metsulfuron-methyl and triasulfuron can persist in the soil up 4 and 12 weeks, respectively . These results indicated that pyrasulfotole & bromoxynil premix alone applied in spring has very little effect on wild buckwheat. Dicamba and 2,4-D are herbicides that have been used throughout the United States for more than half a century to control broadleaf weeds in grass crops Dicamba and 2,4-D are synthetic growth regulating herbicides that control susceptible broadleaf weeds by mimicking naturally occurring auxins found in plants .