July 15th arrived with prediction for the state and the weekend for flash flooding in many areas for the entire weekend. That did not materialize and for that we are thankful. Instead we had a Saturday which was cool and cloudy for the first part of the day, followed by a high degree of sunlight be late afternoon. The Ft Dodge and Humboldt areas along with NW Iowa got pounded both Thursday and Friday with enough rain to keep farmers out of the fields for another five days or so. Rain at this time is not needed and most operators would welcome a few dry days. There have been waterholes that needed to dry up so they could possibly plant soybeans in them and keep the weed pressure down. Some of that was finally possible. The 2.5” that fell in the northwestern part of the state was not needed and it has kept a few of the rescue trips from being made.
Disease Issues
This Sunday morning just after sunup there was quite a bit of haze and lots of dew on the leaves of all plants. When this happens it creates the perfect environment for the many fungal diseases to continue their attack on major crops species. As mentioned last week, any plants deficient one or more of the major micro-nutrients will be prone to having a fungal spore gain entry into the plant and begin to spread systemically through the vascular system.
The major crops have certain times in their development stages when they are most prone to disease attack. For corn before, during, or right after pollination the plants tend to be the most susceptible to disease attack since energy supplies which were previously used to fuel the immune system have to be reallocated to forming pollen, silks and other plant other components involved in pollination. Fungal lesions or that were previously small and tough to identify can grow in number (incidence) and size (severity). If you are monitoring your fields a good pictorial field guide and 12-24X hand lens come in handy to use in making an ID. In many cases the guides will ask the scout to pay attention to whether the lower or upper leaves are being attacked. The ear leaf is usually the key leaf identified. In the past week the Anthracnose lesions tended to be greater in number, but were generally quite small. The GLS, which are currently small, rectangular with a dark colored margin are perhaps the second most noticeable disease. The heavy dews we are seeing most mornings are going to favor these leaf diseases. The fields with the greatest deficiencies in the major micros will be those likely needing a foliar fungicide application. Be aware of the brown slimy lesions in the lowest internode, or a leopard frog type pattern. Both are quite noticeable now.
Common and Southern Rust can be expected. NCLB prefers cooler temps. If cool and humid conditions rule in northern Iowa expect more Eyespot to occur. There will be many fields where fungicides or some means of control should be used, but with the collapse in grain prices, many could go untreated
The Soybean Disease Situation
As the plants have grown and began to close the rows on 15 and 20” rows Septoria brown spot has begun to appear as yellowing leaves near the soil. In time those leaves will abscise, reducing the plants’ ability to produce larger seed. A strobe or a mix like Trivapro will be needed to control that disease. Light infestations of Frogeye can be found. In recent years we have seen more of the lesions survive applications of any strobes. ISU researchers have verified that races of this fungus has developed resistance, just as beet growers in MN and ND have seen the same thing on the Cercospora in their beet fields.
The situation for white mold is ripe this year if soil temps are below 74F and lots of moisture is available. The fruiting bodies have been found by researchers in Wisconsin and Minnesota. The infection of the flowers takes place early in the pollination cycle at the low flowers.
Greensnap
About three weeks ago a series of rainstorm accompanied by strong winds moved thru an area east of Council Bluffs. Seasoned growers who had experience with green snapped corn were worried that this had happened again. Sure enough, it did not look good from the road and field inspections determined that up to 50% of the plants had been broken. Historically plants plumb with moisture in the two weeks before pollination are very prone to this phenomena based on genetics and silicon level. Plants varied as far as the point of breakage, from feet above the ground to above the ear node. In previous years the loss of all of those leaves reduce the plants’ ability to fill any ears.
I hope to find a few fields that were sprayed with the CaSiO4 product to see if it prevented snapping. The leaves in treated fields where one pint was sprayed have the thicker and soft leaves already. No paper cuts from walking thru them. Halleluiah. Now to see how the yields turn out.
Late N Applications
More corn fields are yellowing now. With the way the soils stayed saturated for five to six weeks, that is no surprise. Sidedressed N and the use of stabilizers helped many fields to combat any loss or two supplement fall of spring partial rates. A few weeks ago when the plants were shorter with high clearance rigs able to drive thru the fields there were more questions about the value of late applied N. By now most of the aerial applied 46% equipment has been switched out to nozzled booms. So a pertinent question for the yellowed fields is can late applied N help increase corn yields. A major university tested late applications at two weeks after pollination and saw yield benefits. In most cases the optimum product would be an anhydrous based foliar N.
The best of the nitrogen stabilizers did their job and gained fans this summer. Expect a new one next year that looked very good in the Purdue work by Huber and Tai back in the 80s.
Other Insects
As mid to late July arrives there are more insects to be aware of. Western Bean Cutworm catches are high in eastern Cornbelt states. They are perhaps the second toughest to scout for and most Bt traits do not control them. Aphids are appearing in S Dakota fields, so they like to more SE if the winds switch to the NW. The wrinkle in their activity is that pyrethroid resistant populations now exist. The result is that more expensive insecticides may need to be applied for their control. There are growers who are using nutrition to ward off insects, as in Mg and Moly. Japanese beetles numbers are quite high in many fields, especially if the field is partially lit by yard or city lights. The treatment thresholds are being reached with over half the leaf tissue being eaten.
Dicamba
The number of major lawsuits over the use of Dicamba and its drift continue to accumulate, with some of them being granted class action status. There are still several big suits in Missouri and now in cotton country from 2016. In Indiana the number of reported events is now about 25% over those in 2017. In a few of the earlier cases pre-release of the seed before the labeled product occurred, so attractive nuisance statues will apply. Being a custom applicator and having to observe all of a clean out requirements, set back barriers, and wind speed requirements were a nightmare.
There are also more questions about the right of any person to put at risk the survival of neighboring non-Dicamba beans, convention beans, trees, shrubs, fruit crops, alfalfa and other legume crops, pollinator species. The list goes on. More than one person has asked about the supply of Liberty seed beans for the 2019 season. The way this season has turned out, basing weed control on a planned post-emerge application is not always a sure bet. After a number of growers were forced by rain out of the fields for up to a month, the beans were already flowering and out of label restrictions before fields got dry enough to spray.
I mentioned last week a field in a very wet part of N Iowa that was sprayed with a new product after the untreated seed was planted in a wet field. About two week ago the grower reported the field as looking very tough as the stems were drooping, the plants had yellowed, and the roots were brown. It turned the field around in a few days and the beans recovered. The plants greened up, there are no more drooping stems, and the roots are no longer brown. We hope to inspect the field again and take pictures and well as pull soil samples for nematode counts.
Bob Streit is an independent crop consultant and columnist for Farm News. He can be reached at (515) 709-0143 or www.CentralIowaAg.com.