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General view July 18, 2003Wow! Our field has finally started blooming.  Most of these plants have been blooming just a day or two. But there are still many plants that haven't bloomed yet.  We really have to watch our field now because this is the time when damaging insects attack. For the record, I counted some plants that had 28 leaves on them.  Also, for the record, the high temperature today was 105 F. 

R4 stage sunflowerThis plant is what most of the field looked like on Tuesday and Wednesday. This plant is in the late R4 stage. 


R5.1 stage sunflowerThis plant is at the R5.1 stage. The R5 stage means it has started blooming and the .1 means that 10 percent of the head is flowering or has completed flowering.  The ray flowers are the outermost flowers to which the yellow petals are attached. A flowering head, which botanically is called an inflorescence, is actually made up of many little flowers, as many as 1,000 to 2,000 per head. The flowers start blooming from the outside of the head and continue blooming toward the center of the head.  It takes an individual head about 5 to 7 days to complete blooming, but the field may be in bloom for 10 days or more. 


Water utilization chartAs you can see from this water use curve for sunflower, the bloom stage or R5 is the peak time for water use. Based on this graph, there's a 30-day period beginning with R1 and goes until R6 when the daily water use is above 0.3 inches of water per day.  Any drought stress during that period will cause yield losses. 


Different stages of maturityThis is the reason it takes the whole field longer to bloom than an individual plant. This is an example of heads being at different stages of maturity. You see three heads that really haven't started blooming yet and the next couple heads are well on their way. This could have been caused by delayed emergence. 


R5.4 stage sunflowerThe head has been blooming for a couple days already.  About 40 percent of the head has bloomed or is blooming, thus it's at the R5.4 stage. 


Closeup R5.4 stage sunflowerThis is the same R5.4 head from the previous photograph.  Moving inward are the disk flowers that have bloomed and next you see the pointy, dark structures called stigmas of more disk flowers which are blooming and are receptive to pollen.  The flowers in the center haven't bloomed yet. 


Bee pollinatorMany different species of insects aid in the pollination of sunflowers. Here's a bee that is laden with pollen. You can see yellow pollen on its legs.