Primary symptoms

High temperature: Senescence along the edges of lower leaves. Upper leaves show yellowing and bleaching due to photo-oxidation.
Low temperature: Early growth slow and leaves may turn purple. Symptoms disappear as the plant grows.
Frost damage: Uppermost exposed leaves dried off. Leaves Inside the canopy are protected from low temperatures and remain green.
Low radiation: Look for thin stems and tall, thin (etiolated) plants.

Confirm your findings below.

Summary

The maize crop can tolerate a wide range of temperatures (from 5 to 45°C), but very low or very high temperatures can have a negative effect on yield. Usually a farmer cannot do much to change the effect of temperature other than shift the planting date slightly or plant a better adapted or earlier maturing variety. Maize varieties do differ significantly in their temperature responses.

The crop is usually not damaged by high sunlight unless it is also under temperature or drought stress. The crop is often affected by low sunlight when extended periods of cloudy weather occur, especially if they coincide with flowering. Again, the farmer often cannot do much to change the amount of sunlight available to the crop, but it is important that you are able to recognize the symptoms associated with these problems so that you do not confuse them with other factors.

Is sun or temperature a problem?
Evidence: low temperatures.

1. Look over the field between emergence and the V3 stage. Are the plants growing slowly, and do they have a purplish color? This symptom can indicate P deficiency, but it can also result from low temperatures even if P supply in the soil is adequate.

2. Look for symptoms of frost damage.

Evidence: high temperatures.

1. Is germination poor? If the soil temperature in the top 5 cm was above 40°C, seed sown at 5 cm or less may have been damaged. The seed is swollen with water, but will not germinate. Deeper planting may avoid this problem.

2. Look for symptoms of photo-oxidation (yellowing or bleaching of the leaves), especially on those areas of the leaves which are at right angles to the sun's rays at midday.

3. Look for sterile tassels, poor seed set, and/or firing of upper leaves. The leaves may be a pale green color due to the effects of high temperatures on chlorophyll formation.

Evidence: low radiation (sunlight).

NOTE: These symptoms can result from many other causes as well. You should check records on the hours of bright sunlight, look at rainfall records, and talk to farmers about the growing conditions during the season before concluding that low radiation was the cause of these symptoms.

1. Look for thin stems and tall, thin (etiolated) plants.

2. Look for a low number of ears/plant (below 0.9) and extensive lodging. This could result from low sunlight at flowering.

Evidence: high radiation (sunlight).

1. Look for symptoms of photo-oxidation. Again, you would expect a problem only if photosynthesis was impaired by drought, micronutrient deficiencies, salinity, low night temperatures, or some other factor.