ISSUE 11 July 19, 2007
ROOT LODGING AND GREEN SNAP IN CORN
Following the near 60 mph winds of last week there have been reports of root lodging and green snap in corn. Even though the high winds swept through virtually the entire state, the incidence of lodging and green snap fortunately was localized.
Causes of root lodging
Root lodging occurs when roots are not able to anchor the plant against the force of the wind. Plant growth stage, rooting depth, root feeding by rootworms, wind velocity, soil moisture content at the time of heavy winds, and corn hybrid are factors that influence root lodging. Root lodging is most common during the mid-vegetative stage of development before brace roots have formed. Brace roots provide a valuable function in anchoring and supporting the plant and do not fully develop until after silking. Furthermore, excessive moisture during vegetative growth may have limited early root growth this year, further limiting the depth and strength of the roots.
Moist soil at the time of high winds increases the likelihood of root lodging as roots on the windward side of the plant are more easily pulled from moist soil than those in dry or compacted soil. Differences in soil moisture may have been one reason that lodging was localized this year. Rootworm feeding can dramatically reduce root mass and increase the potential for lodging. Check fields with lodging for rootworm damage. Corn rootworm is currently not a widespread pest of corn in North Dakota, but it can be a localized problem and may be a causal factor in lodging in some fields. Hybrids can vary significantly in their resistance to lodging. If lodging appears to be hybrid-specific, select hybrids with better resistance to lodging in future years.
Yield losses caused by lodging
Estimates in yield losses caused by lodging vary from a low of 3% to a high of 40%. The plant stage at the time of lodging and the environment after lodging are important factors in the yield loss equation. Plants that have lodged usually erect themselves within a few days. Often stems from lodged plants will goose neck as they erect themselves, making harvest more difficult. A reduction in the number of ears per plant is the yield component most affected by lodging in the mid- to late-vegetative stage.
Green snap in corn
The heavy winds that caused root lodging also caused "green snap" in corn. Green snap is the term used to describe the breaking of rapidly growing stalks of corn. Corn is most susceptible to green snap during the 5 to 8 leaf and the 12-leaf to tasseling stages. During these stages, if conditions are conducive to rapid growth (i.e. water and nutrients are not limiting and temperatures are high), cell division and elongation occurs so rapidly that there is no time for the cell wall to fully harden. Factors such as the timing and velocity of the wind, the rate of growth of the corn plant and the hybrid that is grown are factors associated with the incidence of green snap. High levels of nitrogen during vegetative development can increase the likelihood of this problem as can the use of growth regulator type herbicides such as 2, 4-D, dicamba, and clopyralid.
Reports on how much yield loss is caused by green snap vary considerably. Green snap at or near the soil surface can cause complete yield loss. If green snap occurs above where the dominant ear would normally develop, however, losses will be moderate and will depend on how widespread the damage is in the field. Given the difficulty of managing the environment and the likelihood of high winds during critical stages of corn development in North Dakota, the most effective way of managing green snap is by growing a hybrid with known resistance.
NDSU Plant Science
COVER AFTER HARVESTING THE MAIN CROP
Producers have maintained high crop production levels with farming practices that use intensive tillage, monocolture or 2-year rotations, and high fertilizer and pesticide inputs. However, such farming practices may result in soil erosion, reduced soil organic matter, deteriorating soil structure, reduced water infiltration, increased compaction, weed infestations, and severe plant pathogen problems. Having a healthy soil and adequate organic matter are important in long term farming.
Many of the spring seeded early crops are developing quickly and some of the winter wheat will be harvested in the next few weeks. Barley, oats and spring wheat will follow shortly after that. The relatively early harvest this year provides some opportunities to seed a cover crop to capture sunlight during the remaining growing season, anticipating that there will be rain during the rest of the summer months and into the fall. Producers can use different plant species after the summer harvest of grain, as green manure, as winter cover, or as a trap crop. "Green manuring" is the incorporation into the soil of any field or forage crop while green or soon after flowering, for the purpose of soil improvement. A "cover" crop is any crop grown to provide soil cover and may be incorporated into the soil at some point. Cover crops are grown primarily to prevent soil erosion by wind and water. Cover crops and green manures can be annual, biennial, or perennial herbaceous plants grown in a pure or mixed stand during all or part of the year. In addition to providing ground cover and, in the case of a legume, fixing nitrogen, they also help suppress weeds and reduce insect pests and diseases. When cover crops are planted to reduce nutrient leaching following a main crop, they are often termed "catch" crops. The benefit of selecting legumes is that they will fix nitrogen from the atmosphere. The amount of nitrogen fixed depends on the legume and the management system. Selection of annual legume cultivars for rapid emergence after planting, rapid leaf area expansion, high productivity and maturation before the end of the growing season would favor highest nitrogen fixation.
One fast growing green manure or cover crop species is buckwheat. It will germinate rapidly during the warmer soil conditions and provide cover and biomass accumulation during the remaining of the summer. Buckwheat is very sensitive to cold temperatures and plants will die with a frost. It is important to terminate the growth when the plant is starting to produce seed in order to avoid volunteer buckwheat in the next crop.
The extension publication Crop Rotations for Profit in North Dakota (http://www.ag.ndsu.edu/pubs/plantsci/crops/a1059w.htm#manure) has a section with more information about green manure crops.
NDSU Extension Agronomist