There may be stands of glyphosate-tolerant volunteer corn sometimes in fallow fields of wheat-corn-fallow cropping systems. A common question is how these volunteer corn stands affect subsequent winter wheat yields and at what point they should be controlled.
Research on this has been conducted by K-State agronomists across 9 site years in western Kansas. In 8 of 9 site-years available soil water at wheat planting was reduced when uncontrolled volunteer corn was present. Overall, wheat tillers were reduced by 1/square foot for every 170 volunteer corn plants per acre and wheat grain yields were reduced 1 bu/acre for every 500 volunteer corn plants/acre. Producers can estimate volunteer density using the following table:
|
Plant population / acre |
Plants in a 30-ft x 30-ft area |
|
250 |
5 |
|
500 |
10 |
|
1,000 |
21 |
|
1,500 |
31 |
|
2,000 |
41 |
|
4,000 |
82 |
|
6,000 |
124 |
The economic threshold of control is likely between 1,000 and 1,500 plants/acre depending upon the price of wheat and the producer’s cost of herbicide and application. In years of extremes – either very high wheat yields (i.e. greater than 70 bu/acre when water is largely non-limiting), or years of very low yield potential (<35 bu/acre) -- the effect of volunteer corn will be much less. But for the majority of years yield reductions in wheat should be expected when volunteer corn density is greater than 500 plants/acre and not controlled.
Quantifying the density of volunteer corn stands within a field and determining priority among fallow fields is a potential use for UAV imagery. Imagery collected in northwest Kansas clearly shows volunteer corn plants in a chem-fallow field (Figure 1). Volunteer corn densities could be evaluated manually or with software tools.
Figure 1
Figure 2
A variety of herbicide options are available for attaining control. Clethodim products (e.g. Select Max) provide control to volunteer up to 36 inches in height. Volunteer corn should be controlled as soon as possible however to minimize water use and increase the probability of achieving full control.
Achieving good coverage, the use of adequate spray solution volume, and proper use of crop oil and AMS are key to attaining good control. For example, the SelectMax label specifies a minimum of 10 gallons/acre spray solution, NIS at 0.25% v/v or COC/MSO at 1 qt/acre or 1% v/v, and the use of ammonium sulfate (AMS) at 2.5 to 4 lb/acre. In drought-stressed conditions or when treating large plants, using the full rate of AMS will improve efficacy. Producers should be aware that some products have a restriction period before planting wheat. Always read and follow label directions.
In addition to chemical control, crop management that minimizes lodging in corn, proper adjustment of combine settings at corn harvest to minimize grain losses, and the use of no-till can reduce volunteer corn populations. Previous research found 80% germination of volunteer corn kernels within a tillage system, and only 10% germination within a no-till system.
For more information see K-State Research and Extension publication SRL141, Keeping Up With Research: Volunteer Corn in Fallow at:
http://www.ksre.ksu.edu/bookstore/pubs/SRL141.pdf
Lucas Haag, Northwest Area Crops and Soils Specialist
lhaag@ksu.edu
John Holman, Cropping Systems Agronomist, Southwest Research-Extension Center
jholman@ksu.edu
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