Potential Impacts of Dry Conditions on Corn
The impact of dry weather on potential corn yield hinges on two factors: 1) the severity of the moisture stress (dry conditions) in the corn plant, and 2) the developmental stage which the crop reaches before stress is relieved with rainfall. Dry weather early in the season (May to mid-June) can often be beneficial to the corn crop in Ontario as it allows for early planting and root development that is not restricted by elevated water tables.
Consider a crop to be under severe stress if leaves are rolled throughout the entire daytime period. Seven days of this type of stress which terminates prior to tassel emergence will result in yield losses of five to 15 per cent.
If the crop remains under stress through the phase where the tassel emerges and the ear shoot growth expands in preparation for silk emergence, yield reductions may reach the 20 to 45 per cent range. The most critical stage for moisture stress is the next phase, where the silks emerge from the ear and pollen is shed from the tassel. Failure to relieve moisture stress during this window can cause yield reductions of up to 75 per cent or more.
Plants that continue to have soil moisture reserves and are wilting only for portions of the day may experience much less severe yield reductions.
The synchronization between pollen shed and receptive silks may be disrupted by dry weather and is the basis for at least part of the yield reduction. Silks that continue to grow from the ear shoot and appear abnormally long may be an indication that pollination has not occurred successfully.
Detecting successful pollination without waiting for blisters to appear on the ear can be done by carefully removing the husks, turning the ear upside down and shaking it. Silks will only remain attached to those parts of the ear which have not been pollinated.
Relief of severe moisture stress after the crop has passed through the pollination phase cannot increase the number of kernels that have formed on the ear, but may increase the size and density of kernels and aid in improving yields.
Stress from dry conditions after pollination and fertilization can result in aborted kernels or poor kernel fill, causing low test weight and reduced yield. It may also predispose the plants to development of stalk rots.
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