Extreme weather events have begun again in 2016 with renewed force. Frost damage in May impacted early planted corn in parts of the state, with exposed leaf tissue showing extreme necrosis. Alternating periods of wet and dry conditions has also led to some variability in crop stage in some fields. Corn ear development occurs throughout the growing season, and extreme temperature or moisture stress at different growth stages will decrease different aspects of grain yield. Below is a quick summary of the yield component most affected by environmental stress at different growth stages:
- Before V5: The growing point is typically protected from extreme temperature fluctuations below the soil surface, and should be able to overcome early-season leaf damage. Soil crusting may impact ease of emergence, which could result in some stand variability. Uneven or late emergence can impact the yield potential by limiting the light quality received and causing competition with plants that emerged earlier.
- V5-7: Number of kernel rows. Corn plants are determining the number of kernel rows as early as V5 in some corn hybrids. By V7, the number of kernel rows in the primary ear has been determined for most hybrids.
- V9-VT: Number of potential kernels per row (row length). Each potential kernel comes from one floret on the ear (female flower), and as conditions are more favorable for development the plant will initiate more florets. The number of potential kernels on the ear can be set through late vegetative stages (through V16). Stress during this phase can reduce the yield potential of each plant, and can limit overall yield potential of a field. Flex-ear hybrids may initiate more kernels as compared to a fixed-ear hybrid during this stage.
- VT/R1: Number of potential kernels that are fertilized. Pollination is a critical stage in producing yield. If the florets are not pollinated, a harvestable kernel will not develop. High temperatures and moisture stress can cause pollen release to occur before silk emergence resulting in poor pollination, and can decrease pollen grain viability. Ear elongation is occurring during R1, and if stress occurs total ear length could be decreased. Yield losses have been estimated up to 13% per day of stress.
- R2-R3: Kernel number to be filled. Stress at the blister (R2) and milk (R3) stage can cause fertilized kernels to be aborted due to poor carbohydrate availability. Carbohydrate production will decrease as temperature and moisture stress increase because photosynthesis is reduced. The limited production of sugars will cause the plant to abort kernels, typically those that were the last to be pollinated (at the tip).
- R4-R5: Kernel size. At the dough (R4) and dent (R5) stages, carbohydrate accumulation within the kernels will be reduced due to environmental stress. At the start of R5, only 45% of the dry matter in each kernel has been accumulated, leaving half of the starch to be added during R5. However, the kernel contains 90% of its dry matter halfway through the R5 growth stage (milkline halfway down the kernel). Early season frosts during this stage can reduce final grain yields by preventing starch accumulation before maturity (R6).
Abendroth, L.J., R.W. Elmore, M.J. Boyer, and S.K. Marlay. 2011. Corn growth and development. Iowa State Univ. Ext. PMR 1009.
Shaw, R.H. and J.E. Newman. 1991. Weather stress in the corn crop. Purdue Univ. Coop. Ext. Serv. NCH-18.