Cooler Temperatures and the Possibility of Purple Corn

BY Dairyland Seed Agronomy Team

2024 Corn

Cooler temperatures are predicted for much of the Dairyland Seed footprint this week with nighttime temperatures dipping into the 40s for some areas. Most of the corn is at the 6-leaf stage or less and several areas are in the process of making post emergence herbicide applications. Anytime corn plants are at about V6 or less and experience cooler nighttime temperatures, there is a strong possibility we will see purple corn.

Purple Corn: When nighttime temperatures are below 50°F and daytime temperatures are above 60°F, conditions are right to trigger purpling in corn (Figure 1). The purple color is a result of the accumulation of anthocyanin pigment. Corn leaves produce sugars through photosynthesis which get metabolized for energy. When cooler temperatures cause plant growth to slow down, these sugars accumulate and cause the anthocyanin pigment formation. Some hybrids are more prone to anthocyanin production under cool spring conditions, but this does not affect plant growth or yield. Corn will usually outgrow the purpling by the time it is 12 inches tall. If warm weather returns and crop growth speeds up this process will be quicker.

Figure 1. Purple corn due to cooler weather which causes the accumulation of anthocyanin pigment.

Herbicides: Cold weather can greatly reduce the effectiveness of herbicides. Weed control is best achieved when herbicides are applied to actively growing weeds. Systemic herbicides like glyphosate and 2,4-D need to be taken up by the plant (absorption) and move through the plant (translocation) to work properly. When temperatures drop below 60°F, absorption and translocation are reduced which causes herbicides to act slowly. As a rule of thumb herbicide application should be avoided if nighttime temperatures drop below 40°F.

If nighttime temperatures are below 40°F, it is best to wait for warmer weather to make the application. If herbicides must be applied before ideal conditions return, then make sure you are using the full rate and appropriate spray adjuvants. This is especially important if the water you are using as a carrier is coming out of the well and/or is very cold. Colder water temperatures can have a dramatic negative impact on herbicide performance.