Crop conditions declined again this past week, a trend that's likely to continue with extremely hot weather forecast for the rest of this week—and no rain in sight. Hot temperatures and dry soils can hurt yields of both corn and soybeans at this point in the growing season. Much of the state's corn crop is now in the grain filling period and the soybean crop needs to fill pods.
"We have a late planted crop and it's running behind in development," notes Roger Elmore, Iowa State University Extension corn agronomist. "We've had cool weather in July and the first half of August, and that helped the crop get by on very little rain in a large area of the state this summer. Now, during the last two weeks of August, the weather has turned hot and it has stayed dry in much of the state. Weather at the end of the growing season could have more of an impact on the final results for this year's crop than the weather before."
The big worry is a possible earlier than normal frost, which would reduce yield potential in addition to causing grain quality problems--if crops are killed by frost before reaching maturity. Being in a La Nina weather pattern there is a slightly higher than normal probability of a killing frost occurring earlier than normal, says ISU Extension climatologist Elwynn Taylor.
Hot temperatures and dry soils can hurt yields of both corn and soybeans at this point in the growing season
The weekly Iowa Crops & Weather report issued August 26 shows topsoil moisture is 72% short and subsoil moisture is running 66% short-to-very short statewide. The USDA survey also shows the development of this year's late-planted crop is running well behind normal. For example, only 46% of the Iowa corn crop had reached dough stage on August 25, compared to a normal of 77% for this time of year.
Hot weather is forecast for the next seven days. That will give the Iowa crop an additional 75 growing degree days above normal, which will help late-planted corn and soybeans advance in crop development. However, on the negative side, this week of hot weather is likely to hurt yield potential somewhat. Stress that comes at the R2 to R3 stage of corn development may cause some kernel abortion, or "tipping back" on the ends of the ears at bit.~~~PAGE_BREAK_HERE~~~
"Cooler weather during the reproduction stages of the corn plant extends the grain fill period and maximizes yield potential," says Elmore. "But with hot weather and with no rain and plants running short on soil moisture, that situation reduces yield potential."
Iowa's subsoil moisture supply is now rated 66% short to very short; only 33% of the state has adequate subsoil moisture for thirsty crops to draw on
CROP REPORT: While most of southern Iowa was dry, northern portions of the state received some much-needed rain during the week ending August 25, 2013, according to USDA's National Agricultural Statistics Service, which conducts the weekly survey. Higher than average temperatures coupled with the lack of significant precipitation heightened concerns regarding soil moisture and crop conditions across most of Iowa. Statewide there was an average of 6.3 days suitable for fieldwork.
A total of 28% of topsoil and 34% of subsoil is in the adequate and surplus moisture categories, both declining 7 percentage points from the previous week. Also of August 25, topsoil moisture rated 35% very short, 37% short, 28% adequate and zero percent surplus. Subsoil moisture levels rated 26% very short, 40% short, 33% adequate and 1% surplus. With 95% of its topsoil in the very short and short categories, the Southeast Iowa crop reporting district was the driest region in the state.
Only 9% of Iowa corn crop has reached dent stage, more than two weeks behind normal
With nearly all of the state's 2013 corn crop silked as of August 25, they survey shows 80% of the crop has reached milk stage, trailing the normal of 95%. Forty-six percent of the crop has reached dough stage, well behind the normal 77%. Nine percent of the corn crop has reached the dent stage, more than two weeks behind normal. Corn condition declined from the previous week, and was rated at 6% very poor, 15% poor, 35% fair, 37% good and 7% excellent.
With almost all the soybean crop blooming, pods were being set on 83% of the soybean crop, behind last year's 98% and the normal 95%. Soybean condition declined slightly from the previous week and was rated 6% very poor, 14% poor, 35% fair, 37% good and 8% excellent as of August 25.~~~PAGE_BREAK_HERE~~~
The warm and mostly dry conditions allowed harvest of third cutting alfalfa hay to reach 61% complete, matching the normal pace, but still well behind last year's 95% at this time. Both hay and pasture conditions continued to deteriorate, and the amount rated in the good and excellent categories fell 5 and 6 percentage points, respectively. Hay condition was rated at 8% very poor, 17% poor, 34% fair, 36% good and 5% excellent. Pasture condition statewide on August 25 rated 15% very poor, 26% poor, 37% fair, 20% good and 2% excellent.
Unseasonably cool weather of recent weeks came to an end, as hot weather took over this past week and the dryness continues
IOWA PRELIMINARY WEATHER SUMMARY—for week ending August 25, 2013
By Harry Hillaker, State Climatologist, Iowa Department of Agriculture & Land Stewardship
Most of Iowa endured another dry week last week, while the mild weather of recent weeks rapidly came to an end. The primary precipitation event of the week came Wednesday (August 21) evening into Thursday (August 22) morning with thunderstorms occurring over much of the northern one-third of the state. Rains of an inch or more fell in a narrow band from Plymouth County eastward to Clayton and Allamakee counties. Le Mars reported the most rain from this event with 2.75 inches. The only other rain of consequence came Saturday (August 24) morning over the northwest one-quarter of Iowa with Hawarden reporting the most rain with 1.61 inches.
Southern Iowa remains quite dry with no rain there this past week
Unfortunately no rain fell over much of southern Iowa during the past week. The last measurable rain (0.01 inch or more) at Burlington, Mount Pleasant and Keokuk came on July 30. The statewide average precipitation for the past reporting week was 0.34 inches while normal is 0.98 inches. The week began with unseasonably mild temperatures as Chariton and Battle Creek reported Sunday (August 18) morning lows of 46 degrees. However, temperatures quickly pushed well above normal over western Iowa by Monday (August 19) afternoon and statewide on Tuesday (August 20). Highest temperatures were 94 degree readings on Wednesday (August 21) at Ankeny and Osceola and a 95 degree maximum at Des Moines on Saturday (August 24). Temperatures for the week as a whole averaged 3.0 degrees above normal for the statewide average.