Last week was comparatively benign for the nation’s corn crop: In the week ended July 31, USDA’s 18-state corn condition again held steady at 76 percent good/excellent, but the poor/very poor end of the scale crept up one point.
Iowa’s crop improved one point on the upper end of the ratings, while Nebraska and South Dakota lost two points. Like the 18-state number, Nebraska’s poor end of the range increased one point.
Silking has reached 91 percent of corn acres in the 18 states USDA includes in its weekly report. It is ahead of average in the FCSAmerica states, with Iowa 10 points ahead of average; Nebraska, four points and South Dakota, seven points. Corn has reached dough states on 30 percent of acres, also exceeding its 25 percent average for this time of season.
|
State
|
Percent Silking
|
Good/Excellent
|
Poor/Very Poor
|
|
|
July 31
|
July 31
|
July 24
|
July 31
|
July 24
|
|
18 States
|
91
|
76
|
76
|
6
|
5
|
|
Iowa
|
95
|
83
|
82
|
4
|
4
|
|
Nebraska
|
95
|
77
|
79
|
5
|
4
|
|
South Dakota
|
81
|
58
|
60
|
11
|
11
|
Soybeans
The soybean crop development also is ahead of normal: USDA now reports 85 percent of soybeans blooming and 54 percent pod setting, both ahead of average (79 and 44 percent respectively).
The biggest change in rating in the FCSAmerica states was a two-point improvement in the good end of the range in Iowa; other ratings listed in the table didn’t change more than one point.
|
State
|
Percent Pod Setting
|
Good/Excellent
|
Poor/Very Poor
|
|
|
July 31
|
July 31
|
July 24
|
July 31
|
July 24
|
|
18 States
|
35
|
72
|
71
|
7
|
7
|
|
Iowa
|
44
|
83
|
81
|
3
|
4
|
|
Nebraska
|
19
|
76
|
77
|
4
|
4
|
|
South Dakota
|
42
|
60
|
61
|
7
|
7
|
Little Weather Effect?
Heat has returned and promises to stick around through Thursday in the upper Plains and Western Corn Belt before shifting east toward the weekend. It does not appear this week’s temperatures will have big impacts on overall corn yield, however. As always is the case, some locations will be dry but odds favor some rain over much of the FCSAmerica region.
Roger Elmore, University of Nebraska agronomist, noted while at Iowa State University that a rule of thumb is that when corn dries enough for leaves to roll, yield is reduced by 1 percent for every 12 hours of leaf rolling. This increases to 1 percent for each four hours of leaf rolling during silking.
When there is enough soil moisture, the crop does not have a measurable yield response to one day of temperatures between 93° F and 98° F. If the maximum temperature is 93° F or higher for four days, a 1 percent yield loss may occur in addition to what is indicated by leaf rolling; the fifth day brings an additional 2 percent loss; and the sixth day, an additional 4 percent loss. During silking, a six-day heat wave generally ensures yield will not to exceed trend (Iowa trend yield is near 174 bu./acre) and warmer-than-normal nights that continue for a six-week period lead to below-trend yields.
Soybeans, being less heat-tolerant than corn, suffer stress and yields may be affected when the temperature is over 85°F. During flowering, pollen may be sterile and fewer seeds will set, while pod count also may drop. Heat stress’s impact on yield is greatest during the beginning of seed development, according to the Iowa.
