C.O.R.N. Newsletter 2010-11

Dates Covered: 
May 4, 2010 - May 11, 2010
Editor: 
Glen Arnold
Wheat Scab Risk Assessment Tool Now AvailableHeadscab website

Wheat Scab Risk Assessment Tool Now Available

In Ohio, wheat typically starts heading and flowering during the third week of May. As the crop approaches these growth stages, it is time to prepare for Fusarium head bight (scab) and vomitoxin management. Wheat is most susceptible to scab during the flowering and early grain-fill stages. Weather conditions, such as high humidity and rainfall, prior to and during flowering contribute to inoculum (spore) production and spread, and infection of the wheat spike. However, cool, dry conditions may slow spore production, fungal growth, and scab development. The wheat scab risk assessment tool helps predict the risk of scab based on weather conditions leading up to flowering. The 2010 risk tool is now available online: www.wheatscab.psu.edu 

To use the risk tool, you will need to identify the flowering date(s) for your winter wheat. Flowering is dependent on variety and planting date, so flowering date may vary across your farm. Check the risk tool frequently during heading stages, as weather the week before flowering contributes most to spore production and scab severity. If you anticipate flowering will occur soon, you may use forecasted weather for 1, 2, or 3 days prior to the flowering date. Since tillers will mature at slightly different times, estimate when 50% of heads show anthers as the “flowering date” for a given field. 

Once you’ve selected flowering date on the tool’s calendar, choose a wheat class model. For Ohio growers, select the winter wheat model. You may select Ohio from the country-wide map and click on a weather station close to your farm for details. The tool will provide a current risk level: low, medium or high, for the selected location/flowering date. You will also be able to see the risk probability, temperatures and precipitation from the previous 7 days. Low risk probability means wheat flowering on the selected day will likely have less than 10% scab severity, according to the model. If the risk probability is in the medium or high categories, you may want to consider a fungicide application, since most winter wheat varieties are susceptible and even the most resistant varieties my become infection and contaminated with vomitoxin if weather conditions are highly favorable. In addition to favorable weather and variety susceptibility, local spore load also affects the risk of scab development. The spore levels in fields with corn residue may be quite high due to severe outbreaks of Gibberella ear rot in some areas of Ohio in 2009. Gibberella ear rot of corn and wheat scab are caused by the same fungus. 

Local commentary on scab risk in Ohio will be provided by OARDC wheat pathologist and extension specialist Pierce Paul throughout the season. Check for these updates at the bottom of the risk map tool (click “View Commentary”), in C.O.R.N. newsletters or on the US Wheat and Barley Scab Initiative blog (http://scabusa.org/modules/wordpress/). 

Most importantly, the risk tool should be used as part of a larger integrated management plan. This tool helps predict scab-potential based on weather, scab development on your farm will also depend on your cropping system and resistance level of your varieties. The most effective management of scab is achieved by planting resistant varieties after soybean and applying a fungicide during anthesis if the weather becomes favorable. 

Injury to Corn from Ponding and Saturated Soils

The extent to which ponding injures corn is determined by several factors including: (1) plant stage of development when ponding occurs, (2) duration of ponding and (3) air/soil temperatures. Prior to the 6-leaf collar stage (as measured by visible leaf collars) or when the growing point is at or below the soil surface, corn can usually survive only 2 to 4 days of flooded conditions. Since most of the corn that’s been planted so far is not beyond the VE stage, it’s especially vulnerable to damage from ponding and saturated soil conditions. The oxygen supply in the soil is depleted after about 48 hours in a flooded soil. Without oxygen, the plant cannot perform critical life sustaining functions; e.g. nutrient and water uptake is impaired, root growth is inhibited, etc. If temperatures are warm during ponding (greater than 77 degrees F) plants may not survive 24-hours. Cooler temperatures prolong survival. Once the growing point is above the water level the likelihood for survival improves greatly.

Even if ponding doesn't kill plants outright, it may have a long term negative impact on crop performance. Excess moisture during the early vegetative stages retards corn root development. As a result, plants may be subject to greater injury during a dry summer because root systems are not sufficiently developed to access available subsoil water. Ponding can also result in losses of nitrogen through denitrification and leaching. Even if water drains quickly, there is the possibility of surface crusts forming as the soil dries that can impact the emergence of recently planted crops. Growers should be prepared to rotary hoe to break up the crust to promote emergence.

For corn that’s emerged check the color of the growing point to assess plant survival after ponding. It should be white to cream colored, while a darkening and/or softening usually precedes plant death. For corn not yet emerged, evaluate the appearance and integrity of seeds or seedlings that have yet to emerge (likely rotting if discolored and softening). Look for new leaf growth 3 to 5 days after water drains from the field.

Disease problems that become greater risks due to ponding and cool temperatures include pythium, corn smut, and crazy top. Fungicide seed treatments will help reduce stand loss, but the duration of protection is limited to about 10-14 days. The fungus that causes crazy top depends on saturated soil conditions to infect corn seedlings. There is limited hybrid resistance to these diseases and predicting damage from corn smut and crazy top is difficult until later in the growing season.

For more information on ponding and flooding damage to corn, check out the following article written by Dr. Bob Nielsen at Purdue University -

Nielsen, R.L. 2010. Effects of Flooding or Ponding on Young Corn. Corny News Network, Purdue Univ. [On-Line]. Available at: http://www.kingcorn.org/news/timeless/PondingYoungCorn.html [verified 5/3/10].

Slug Activity Starting Gray garden slug from Entomology Factsheet

Slug Activity Starting

 

Flooding and ponding effects on soybeans

Soybean prefers adequate soil oxygen for maximum productivity. Oxygen content of water is much lower than air therefore saturated soils and flooding reduces the amount of oxygen available to the plant. Research has shown that oxygen concentration can be close to zero after 24 hours in flooded soil, depending on water movement. Without oxygen, the plant cannot perform important functions like respiration, an important function of plant growth. Soybeans can generally survive for 48 to 96 hours when completely submersed. The actual time frame is dependent upon air temperature, cloud cover, soil moisture conditions prior to flooding, and rate of soil drainage.

Temperatures influence the speed of respiration so high temperatures will be more detrimental to soybean recovery since the faster the respiration is “running” the faster the oxygen is depleted and the plants then start rotting. Cool, cloudy days and cool, clear nights increase the survival of a flooded soybean crop.

Research from Minnesota shows that flooding for 6 days or more may result in a significant yield loss or loss of the entire crop. With temperatures in the 80s, soybean plants may only survive a few days. Ohio researchers found that plants in flooded fields are injured from a buildup of toxins and carbon dioxide, which is up to 50 times higher in flooded soils than in non-flooded soils. They concluded that plants are more injured from the buildup of carbon dioxide than from lack of oxygen. During emergence, soybean fields subjected to flooding and saturated soil conditions are at major risk from Phytophthora and Pythium damping-off.

(adapted from Palle Pedersen, ISU) Reference
Pedersen, P. 2008. Effect of flooding on emerged soybeans, Department of Agronomy

 

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About the C.O.R.N. Newsletter

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.