Of ultrafast maize and hail damage

In the light of the increased popularity of ultrafast-growing maize cultivars, Gideon Britz, an agriculturalist from Ficksburg and expert on hail damage, investigated the influence of defoliation at the same growth stage on the crop yield, by comparing a medium- to long- and ultrashort-season cultivar.
Issue Date 25 May 2007

- Advertisement -

In the light of the increased popularity of ultrafast-growing maize cultivars, Gideon Britz, an agriculturalist from Ficksburg and expert on hail damage, investigated the influence of defoliation at the same growth stage on the crop yield, by comparing a medium- to long- and ultrashort-season cultivar. He excluded all factors pertaining to cultivation, soil and the environment. The growth stages of maize in the vegetative phase were determined by the number of unfolded leaves.

By examining the leaf counts of commercial cultivars over three years, he determined that cultivars with a shorter growth period produced fewer leaves. The cultivar Phb 32A03, which develops 19 leaves, was used to represent the ultrashort-season (122 days to 127 days) cultivars. PAN 6839, which develops 23 leaves, represented the medium- to long-season (117 days to 165 days) cultivars. Two treatments, namely 50% and 100% defoliation with a control plot, were applied during the V7, V10, V13 (vegetative stages), and R2 and R8 (reproductive stages.) Gideon decided on 50% and 100% defoliation, which could be applied relatively easily in a uniform way. All leaves that were unfolded on the date of a specific growth stage were defoliated 50% or 100%, as shown in the photo. The cultivar with 19 leaves showed a much greater yield loss with the same treatment in the same growth stage when compared with the assessment table currently used by insurers to assess yield loss, as well as with the cultivar with 23 leaves.

The latter showed a yield loss very close to the current table, proving the credibility of this table as well as the trial’s results. This result is due to the fact that the ultrafast grower develops fewer leaves and reaches maturity sooner. The results of the experiment indicate the resemblance between the final leaf count of a maize cultivar and yield loss in the vegetative stage (V stage), while the final leaf count is not a factor in the reproductive stage (R stage). This can be explained logically by the fact that yield loss due to defoliation is connected to the vegetative stages as determined by the number of unfolded leaves on the date of hail, while the physiological development stage of the seed, and not the leaf count, is used to describe the reproductive growth stages. “The higher yield loss observed in the ultrafast grower can be rectified with a small modification to the current table,” said Britz.

- Advertisement -

He recommends further research to test the findings, and using the results of defoliation trials on cultivars with fewer than 22 leaves to further refine the table. In effect, modifying the table will make the current yield loss table for hail assessment relevant to all commercial maize cultivars with known leaf counts. “The modification table is the logical answer to reduce the cost and time required to test every cultivar, and ­correctly indicate the effect of defoliation on a grain crop,” Britz concluded. – Carien Britz • Contact Gideon Britz on (051) 933 3007, e-mail [email protected].