Maize ear and floret response to dinitroaniline herbicides

My practice of isolating pet strains of maize in soybean fields has been complicated in recent years by a switch to preplant soil-incorporated herbicides. Some maize plots invariably end up at least partially on soil treated with dinitroaniline herbicides ("Treflan" or "Tolban") applied at the double rate recommended to suppress rhizome Johnsongrass in soybeans. The usual outcome of this herbicide incompatibility is no more than a slight reduction in maize plant vigor and seed yield.

However, three strain specific dinitroaniline herbicide responses in maize ear or floret structure have thus been brought to my attention. These are:

1) a marked increase in proportion of "two-squared" ears (see W. Galinat, MNL 52:60) among ears of an eight-rowed strain (see Figure),

2) a marked reduction in ear and tassel branching in an ra strain, and

3) a marked inhibition of fertile pistil production in a Pt-like, Bf strain.

All have been confirmed as herbicide dependent by split plantings of single ear populations on herbicide treated vs. untreated soil.

Responses similar to (1) and (2) can be generated by unfavorable growing conditions including drought, leaf pruning, or growth in pots. On the other hand, these same conditions tend to reduce the severity of Pt action rather than accentuate it as per (3) (see A. Williams, MNL 54:123). Specific roles for dinitroanilines in eliciting these responses will therefore be difficult to demonstrate. I plan to see what effects more delayed and direct application of "Treflan" have on these strains of maize.

Figure.

Absalom F. Williams


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