17 Things to Look Out For in Your Crops • June 2015

Stunted Corn Crops

Stunted Corn Crops

Crop scouting #1. “Crappy looking corn,” is how Purdue’s Bob Nielsen characterizes your yellow, stunted corn, which results from a variety of issues. Among them: excessive rainfall and ponded fields; compacted soil from heavy equipment; light soil color which warms more slowly than dark soil resulting in fewer GDDs; damage from parasitic corn nematodes; seedling blights and fungal issues that erupt when seed treatments wear off, and the shortage of N uptake when wet soils stunt root development.

Japanese Beetles

Japanese Beetles

Crop scouting #2. Japanese beetles are hungry and awaiting your corn silks to emerge. They have emerged from the grub stage you noticed while looking for corn rootworms. IA St. entomologist Erin Hodgson says consider a foliar insecticide during tasseling and silking if: there are 3 or more beetles per ear, silks have been clipped to less than 1/2 inch, AND pollination is less than 50% complete. If they are in your beans, the treatment threshold is 30% defoliation before bloom and 20% defoliation after bloom.

European Corn Borer

European Corn Borer

Crop scouting #3. It has been a long time since you worried about European corn borer, but they have not become extinct. Your use of Bt corn for the past 8 years has diminished the ECB problem, however, as markets want non-GMO corn, corn borers are finding new fodder. If you have a non-GMO corn crop, ECB scouting should be a priority. Once inside they are protected.

Northern Corn Leaf Blight

Northern Corn Leaf Blight

Crop scouting #4. Northern corn leaf blight is beginning to appear, thanks to its widespread existence in 2014 and perfect weather this year for development of the fungus. Warm dry conditions will slow or halt disease development until favorable conditions return. IA St. plant pathologist Alison Robertson says it will be very important to scout fields that are planted to NCLB-susceptible hybrids. If the disease is present on 50% or more of the plants in the field, the hybrid is susceptible, and if cool, wet weather is forecast, a foliar fungicide application may be required. She said an R1 stage application is better than a V5-V6 to carry the corn through the dent stage.

Anthracnose Leaf Blight

Anthracnose Leaf Blight

Crop scouting #5. Anthracnose leaf blight is being found on lower leaves, and that is common for a wet spring. IA St. specialists say it does not need to be managed, and is different from anthracnose stalk rot. Corn will rapidly grow out of the disease, and the affected lower leaves, which do not contribute to yield, will die and fall off the plant within a couple of weeks.

Common Rust on Corn Crops

Common Rust on Corn Crops

Crop scouting #6. Producers with seed corn fields should be vigilant for common rust in corn. Most hybrids have resistance, but in-breds do not have resistance and seed production fields should be scouted and a fungicide applied if the disease is present. Common rust is only seen rarely in commercial corn fields, but may be found in seed fields.

Goss's Wilt Corn Crop

Goss’s Wilt Corn Crop

Crop scouting #7. Be on the lookout for Goss’s Wilt. It has been identified in both NE and MN, and could be present across the western Cornbelt. Elongated spots on leaves indicate tissue death and continue to enlarge. While the early stage may be similar to NCLB, Goss’s Wilt can be confirmed with decaying areas within the vascular tissue of the stalk.

Gray Leaf Spot

Gray Leaf Spot

Crop scouting #8. Gray leaf spot should be on your checklist during corn field scouting. The fungus that causes GLS infects corn during prolonged periods of warm weather of 75-80°F and at more than 90% relative humidity. Symptoms may not be noticeable for up to 2 weeks after infection. Consider fungicides if the hybrid is rated as susceptible or moderately susceptible and 50% of the plants have disease lesions on the third leaf below the ear or prior to tasseling. Fungicide will not increase yield on GLS resistant hybrids.

Excessive Rain and Flooding

Excessive Rain and Flooding

Crop scouting #9. Excessive rainfall and the resulting ponding, flooding, or saturated soils have likely caused some loss of applied and soil-derived nitrogen (N). Nitrate-N (NO3-N) is the form of N most likely to be lost from the crop root zone. Unfortunately, no matter what forms of N are added to the soil, all of them eventually convert to NO3-N. Soil testing to measuring the concentration of NO3-N and NH4-N remaining in the rootzone is an alternative to guesstimating how much N was lost, say Purdue agronomists.

Corn Crops Under Water Late June 2015

Corn Crops Under Water Late June

Crop scouting #10. IL researchers say the amount of N is not disappearing as fast as expected, even in heavy precipitation areas. That provides confidence that loss of N availability to corn has not been very high. They say as soils dry and roots regain their ability for nutrient uptake, soil N should drop, and canopy color will be a better gauge of N availability to the plant than will amounts of N measured in the soil. Beware of N levels slipping below those needed to maintain crop growth before uptake starts to slow.

Use Drones to Inspect Crops

Use Drones to Inspect Crops

Crop scouting #11. Where do you apply a rescue treatment for N-deficient corn? Former IL fertility specialist Fabian Fernandez suggests, “a full-rate application is likely not the best alternative, because the plant won’t be able to use all that nitrogen to make yield. Some studies have shown that when corn is severely limited by nitrogen availability, the crop has great capacity to use rescue nitrogen and produce an increase in yield until silking.” Use your drone camera to find trouble spots.

Broadleaf Weeds

Broadleaf Weeds


Crop scouting #12. Do you have more broadleaf weeds that you used to? Are you using less atrazine? Are you using more glyphosate? If you answered “yes” to each, the reason comes from WI researchers, who investigated that long term trend. “The weed community composition consisted of more broadleaf weeds in fields where atrazine has not been used in the recent decade coupled with greater glyphosate use. These results provide evidence of negative long-term implications for glyphosate resistance where growers increased reliance on glyphosate in place of atrazine.”

Palmer Amaranth

Palmer Amaranth

Crop scouting #13. The magic bullet to controlling Palmer amaranth may be the air temperature at which you spray it. KS St. researchers have achieved improved control on 8-12” Palmer with mesotrione (Callisto or Tenacity) when sprayed at lower temperatures, such as less than 80° with nighttime lows under 60°. At higher temperatures the plant more easily metabolizes the herbicide and resists the HPPD enzyme inhibitor. That was not the case at lower temperatures. You have to get up early in the morning to beat Palmer amaranth.

Photo: University of Illinois

Photo: University of Illinois

Crop scouting #14. If you have Palmer amaranth, address that issue immediately, says Clemson weed specialist Mike Marshall. “It all boils down to timing. If you wait a week to ten days to spray emerged weeds, your expected control can drop off significantly, especially with Palmer amaranth. It can take control of a field in a matter of days because of its ability to produce up to 1 mil. seeds per plant. Waiting to address a Palmer amaranth problem, even for a few days, could mean the difference between a clean field and one overrun with weeds.”

Palmer Amaranth

Palmer Amaranth

Crop scouting #15. If Palmer amaranth is becoming an issue for you, get ahead of it before it takes over your fields completely. Control all growing Palmer with tillage or a grammoxone burndown. Consider planting LibertyLink beans until it is controlled. Use a soil applied pre-emergent herbicide such as Valor or Fierce prior to or immediately after soybean planting. Post emergent herbicides such as Liberty must be applied before Palmer is 3” tall. Tank mix that with a residual such as Dual II, Magnum, Warrant, Outlook or Zidua. Follow with additional post-emergent applications.

2014 Plot Trials Show Clean Fields Using GF-3471 from Dow AgroSciences

2014 Plot Trials Show Clean Fields Using GF-3471 from Dow AgroSciences

Crop scouting #16. Watch for a new Dow corn herbicide that does not contain glyphosate or atrazine, but has 3 other herbicides, never before blended, that offer 3 modes of action against troublesome weeds. If you attend a university field day, look for the product as GF-3471. Regulatory approval is pending, but is being demonstrated in test plots. It is expected to offer flexible application timing from pre-plant to early post-emergence.

Flood Tolerant Soy Bean

Flood Tolerant Soy Bean

Crop scouting #17. What you need this year is a flood tolerant soybean. It is coming, and will be ready for the next flood, should you know when that will happen. Actually it is a soybean that does better than others on flat land, with heavy soil that drains slowly. MO researchers have worked with genes on 19,000 specimens to get some with flood tolerance.

Posted in Cornbelt Ag.