ABNORMAL DEVELOPMENT OF MAIZE EARS

During the 2014 season, various maize fields and cultivars were inspected to determine whether the abnormal ears could be ascribed to a particular cultivar. Several surveys were conducted and it was found that identical symptoms were present in various degrees in cultivars of all companies in the market. The duration of seasonal growth or the number of days up to physiological maturity played a role in the susceptibility of various hybrids. The abnormal development of a maize plant could occur during the V5 growth stage when ear initiation occurs and stress conditions could cause the abnormal development of the reproductive sections of the plant.

One or more of the following stress conditions may cause problems:

• Drought
• Extremely high and low temperatures. Hot, dry conditions can cause the earlier than normaldevelopment of maize plants. This can lead to the more rapid than usual succession of growth stages. It was also the reason why plants that were already knee-height had already passed the V8 stage. The plants weresprayed overhead with the result that many crops were sprayed too late because no accurate growth stage evaluation was done. 
• Disease or insect damage
• Nutrient deficiencies
• Incorrect application of pesticides

Most stress conditions cause specific symptoms and abnormalities in maize plants which could aid identification of the problem.

Weather conditions can be the cause of pollination problems in certain areas. As an example the weather data (2014/15) of the Hoopstad region will be considered here.

Figure 1. Minimum and maximum temperatures as well as rainfall and evaporation transpiration for the Hoopstad region

The graph on the left shows extremely high temperatures for January. It would also appear that mielies planted from around 15 to 25 November were more inclined to weaker pollination or abnormal ear development. Maize planted during December reached the sensitive R1 (pollination) stage after the rains at the end of January and do not show these symptoms.

Maize already in the V8 stage during 7-25 January had also repeatedly showed a certain degree of ear abnormality. These were planted between 15-30 November. From the V8 growth stage the plant had already lost some of its lower leaves and had to be cut open in order to accurately determine the growth stage.

The term `knee-high’ is generally used to determine the last stage of spraying and could be totally erroneous, particularly during a season where the internodes are shortened due to drought stress.

The farmer can therefore begin spraying at V8 but it may happen that some lands are sprayed too late and thus growth points may be damaged.

From the V8 stage the plant also shows rapid growth and every second to third day a new leaf appears in the growth stage.

From 7-25 January 2014 the evaporation transpiration of plants was around 114mm of water.During the same period rainfall was only 22mm. (See Fig. 2 below). This, together with an average maximum temperature of 33 degrees C caused severe stress which in turn led to  difficult pollination. From 25 January temperatures declined, welcome rain brought some relief and pollination improved. Pollen may die off in a combination of temperatures higher than 32 degrees C and low humidity.

1. “Ear Pinching” (Bierbottel sindroom) beer bottle syndrome

2. “Blunt ear syndrome” (Stomp kop, “Beercan”)

This characteristic has been generally observed in various cultivars and areas.

Characteristics

• Small, reduced ear;
• Few kernels per row;
• Ear may be of normal length.

Causes

• Associated with temperature stress conditions;
• Can also be caused by sudden abnormal cold conditions (cold shock) during V8-V12.
• Can also result from spraying before development of maize tassel during these periods.

More examples of “Beercan” abnormalities, left and right.

Figure 2. Evapotranspiration versus rainfall during 2014

As indicated by the graph above evaporation transpiration during January 2014 exceeded the rainfall. Crops were saved by the rain that fell at the end of January 2014. It indicates that drought stress was present during this period. The causes of malformation or abnormal ear development observed during this season are discussed below.

3. Incomplete kernel set

Characteristics

• Only a few kernels were pollinated and developed.
• Kernels occur on the ear sporadically and localized.

Causes

Several causes that influence pollination can also be the reason for this:

• Drought and high temperatures could influence the sinchronisation between the tassel and the appearance of maize beard.
• High temperatures could also render pollen sterile.

Characteristics

• Maize tassel often remains within the sheath and has not developed.
• Spikelets are closed and pollen did not shed to the outside.
• The tassel is compacted and did not open.
• The tassel is darker in colour that normal.

Causes

• Damage to the tassel occurred during initiation when the tassel was still within the calyx.
• Damage could be attributed to stress conditions caused by environmental conditions or chemical spraying.

It was also observed that ovules which generally occur on shoots developed more aggressively. (See photo on the right below). This occurs in places where the normal heads are also misshaped.

Symptoms that resembled silkballing were also present but are not normal symptoms and rather the results of ear deformity. The photograph below shows that ears were first deformed and formed silkballing afterwards.

Conclusions and recommendations

• The importance of correct identification of growth stages cannot be overemphasized.
• It could lead to significant crop loss when vegetative cones are damaged during late spraying on top of crops.
• The spraying of any substance on top of the crop during pollination could be fatal.
• From stage V8 must be sprayed with “valarms” to prevent damage.
• Practices that are effective in a normal year could have negative effects when plants are in conditions ofstress.
• Overhead spraying equipment allows for more leeway in spraying programmes but could result in spraying too late.
• The placement angle of nozzles must be adjusted so that they do not spray into the calyx or the growth pointsof the plants.

Acknowledgements

Anton Swanepoel, Technology Development Representative, Monsanto SA. Ohio State University, College of Food, Agriculture and Environmental Sciences.

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