ISSUE 11   July 24, 2008

IMPACT OF DROUGHT STRESS ON CORN - 2008

More than half of the state is now rated abnormally dry or drier by the US Drought Monitor (http://www.drought.unl.edu/dm/DM_highplains.htm) and nearly a third of the state is under severe drought. Corn is one of the most water efficient crops grown in North Dakota. Nevertheless, it has a high water requirement because of its high yield potential and can be significantly impacted by drought. The impact of drought on corn growth and yield varies considerably depending on its timing and severity. Research has shown that there is little impact of drought on corn growth during early vegetative stages. During late vegetative development, however, short periods of drought stress (four days of sufficient stress to cause leaves to curl) during this growth stage can reduce yields by 5-10%. Currently most of the corn in North Dakota is in the 8 to 12 leaf stage. Kernels per cob are being set during this stage until just before silking, so drought stress now can impact the size of the cob. Drought stress during tassel emergence has the potential to reduce yields by 10 to 25%. The most sensitive period for drought stress in corn is during the period between silk emergence and the blister stage where yield losses between 40-50% can occur. Corn is most sensitive to drought during this stage because the male and female flowers are separated by a considerable distance and pollen and silks are sensitive to hot and dry conditions. When corn is severely stressed prior to flowering, silk growth is delayed and pollen shed will occur before the silks have emerged, resulting in barrenness. Silks can also dry before they are pollinated resulting in poor fertilization and missing kernels. Abortion of developing kernels is common, particularly towards the tip of the ears, with drought stress during early grain fill. Since the corn plant has the capacity to store considerable reserves in the stem, yield losses when drought stress is delayed until the dough stage usually are in the 20-30% range. These yield losses discussed above can be additive if stress occurs at more than one growth stage. With about half the growing season still ahead of us, the potential for yield losses due to drought appear to be quite high for a large part of the state unless we get some timely rains.

How is yield affected by late season drought stress?

During the first stage of stress, the upper leaves curl or roll towards the midrib during the hottest part of the day (see attached photo). If stress continues, premature leaf death begins at the bottom of the plant and proceeds upward. Leaf death is the first sign of permanent damage to the plant. With severe stress, the upper leaves roll so tightly that they appear like "onion leaves". With less leaf area capable of photosynthesis, grain filling is slowed even while maturing at an accelerated pace. Carbohydrates that had been stored in the stem earlier in the season are moved to the developing ear. Not surprisingly, drought stressed crops are more prone to lodging because of poor stalk health. There may be some kernel abortion in the tips of the ears, but for the most part, kernel numbers are not reduced significantly with late season drought. Yield losses will largely be due to reduced kernel size and reduction in test weight. The amount of reduction will be related to the amount of stress prior to harvest.

Damaged corn

Joel Ransom
Extension Agronomist - Cereal Crops
joel.ransom@ndsu.nodak.edu

 

HAIL DAMAGE

Each summer hail damages field crops leaving producers wondering if the crop will recover and how much yield loss will be incurred. Hail events are unpredictable; developing during some summer thunderstorms but not others. Thunderstorms typically occur during the late afternoon and early evening. The temperature contrast between the Earthís surface and the clouds can cause wind turbulence, creating up and down drafts within the storm cell. When water droplets are pushed upward into sub-freezing air layers the water freezes and frozen droplets eventually fall. The ice pieces may be pushed back up for several cycles increasing the size of the hail stones. Large hail stones, resulting from intense storm cells are more likely to cause severe crop damage compared to hail produced by weaker storm systems. In addition to hail damage, strong winds associated with summer storms may cause crops to lodge. The stage of crop growth and development at the time of a hail event is critical in the plantís ability to recover and still produce a decent yield. Damage to the leaf tissue may results in plant stress. However, if ample moisture and fertility are available, the crop should be able to recover quicker than crops experiencing drought stress. Hail damage can vary considerably between neighboring farms or from field to field on individual farms. The variation may be a result of the different stages of crop development at the time of the hail event or because the amount of hail produced tends to be inconsistent even within short distances. Researchers at NDSU have conducted many years of simulated hail research on various crops to produce hail adjustment tables to estimate yield reductions that are based on the stage of growth and percent defoliation.

During a simulated hail study conducted from 2002-2004, researchers investigated soybean yield reductions based on different levels of defoliation at the reproductive stages R1 (Beginning of bloom) and R4 (pods are ĺ inch long at one of the four uppermost nodes on the main stem with a fully developed leaf). Zero (control), one, two, or three leaflets were removed from each fully expanded trifoliate leaf per plant to study the effects on yield (Table 1).

Table 1. Soybean yield in % of the check at two growth stages and four defoliation levels. Research conducted at Prosper, ND, during the 2002-2004 growing seasons.

 

Defoliation in %

Growth Stage

0

33

66

100

Yield in % of the check

R1

100

99

93

92

R4

100

92

87

44

Source: Johnson and Petersen.

When the defoliation took place at the early reproductive stage (R1) the plants were able to compensate during the remaining season. Yield losses were 1, 7 and 8 percent at 33, 66 and 100 % defoliation respectively. Yield reduction as defoliation level increased was mainly a result of fewer pods per plant. Yields were lower when defoliation took place at the R4 growth stage compared with the R1 growth stage.

This research indicates that a plant has the ability to compensate for loss of leaves but it will depend on the growth stage of the plant and the remaining growing season. If defoliation occurs at an early growth stage, which allows more time to regenerate foliage, yield reduction will be less. This study was an attempt to simulate hail injury, however, in a real hail event the stems of the plant may also be damaged further reducing the plantís ability to recover.

Although field crops may appear to be heavily damaged after a storm, the plants will try to recuperate and produce seed. Contact your insurance agent for advice before you decide to destroy a damaged crop.

Hans Kandel
Extension Agronomist - Broadleaf Crops
hans.kandel@ndsu.edu


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