Corn pollination and stress conditions
By
John Grimes-
While weather was nearly perfect over the Fourth of July weekend, temperatures were certainly on the rise this past week. Several consecutive days of 90-plus degree temperatures made tasks such as baling hay and straw a bit more difficult. Believe it or not, I’ve already heard some people worrying about soil conditions getting a bit too dry. That sentiment didn’t seem possible as recently as a month ago.
Corn pollination
During the past week, tassels began appearing in corn fields that were planted in late April and early May. Corn planted in late May and early-mid June will probably not be tasseling until early to mid August. There is usually some variability in pollination within corn fields and the pollen shed period extends from one to two weeks. This year, we can expect even greater variability because saturated soil conditions and loss of nitrogen in poorly drained and compacted areas have inhibited corn growth. The pollination period, the flowering stage in corn, is the most critical period in the development of a corn plant from the standpoint of grain yield determination.
Stress conditions such as drought have the greatest impact on yield potential during the reproductive stage. Past research indicates that four days of stress (i.e. corn wilted for four consecutive days) at the 12th-14th leaf stage has the potential of reducing yields by 5 to 10 percent. The potential for yield losses to soil moisture deficits increases dramatically when plants begin to flower. During tassel emergence, four days of moisture stress has the potential to reduce yields 10 to 25%. Silk emergence is the most critical period in terms of moisture use by the plant. During this stage, leaves and tassels are fully emerged and the cobs and silks are growing rapidly. Four days of moisture stress during silk emergence has the potential to reduce yields 40 to 50%. However, the stress conditions we are alluding to over these “four-day periods” are severe and involve extensive leaf rolling (characterized by plants with “pineapple” like leaves) throughout much of the day. Also keep in mind that the corn plant is more vulnerable to hail injury during the period from tassel emergence (VT) to silking (R1) than during any other period because the tassel and all the leaves are completely exposed. Complete defoliation of the plant at VT usually results in 100% yield loss. The following are some key steps in the corn pollination process.
Pollen shed usually begins two to three days prior to silk emergence and continues for five to eight days with peak shed on the third day. Under very dry conditions, silk emergence may be delayed, and such asynchronization of pollen shed and silking may result in poor kernel set and reduced grain yields. However, in some years under favorable growing condition, silks may actually emerge before tassels fully emerge and pollen shed starts in certain hybrids. On a typical midsummer day, peak pollen shed occurs in the morning between 9 a.m. and 11 a.m. followed by a second round of pollen shed late in the afternoon. Pollen may be shed before the tassel fully emerges (“stretches out”). Pollen shed usually begins in the middle of the central spike of the tassel and spreads out later over the whole tassel with the lower branches last to shed pollen.
Pollen grains are borne in anthers, each of which contains a large number of pollen grains. The anthers open and the pollen grains pour out in early to mid morning after dew has dried off the tassels. Pollen is light and is often carried considerable distances by the wind. Pollen shed is not a continuous process. It stops when the tassel is too wet or too dry and begins again when temperature conditions are favorable. Pollen stands little chance of being washed off the silks during a rainstorm as little to none is shed when the tassel is wet.
Under favorable conditions, pollen grain remains viable for only 18 to 24 hours. However, the pollen grain starts growth of the pollen tube down the silk channel within minutes of coming in contact with a silk and the pollen tube grows the length of the silk and enters the female flower (ovule) in 12 to 28 hours.
A well-developed ear shoot should have 750 to 1,000 ovules (potential kernels) each producing a silk. The silks from near the base of the ear emerge first and those from the tip appear last. Under good conditions, all silks will emerge and be ready for pollination within 3 to 5 days and this usually provides adequate time for all silks to be pollinated before pollen shed ceases.
Pollen of a given plant rarely fertilizes all the silks of the same plant. Under field conditions 97% or more of the kernels produced by each plant may be pollinated by other plants in the field. The amount of pollen is rarely a cause of poor kernel set. Each tassel contains from 2 to 5 million pollen grains, which translates to 2,000 to 5,000 pollen grains produced for each silk of the ear shoot. Shortages of pollen are usually only a problem under conditions of extreme heat and drought.
Summer fires
Summer is a season of outdoor living. We tend to do as many activities outside as possible during this time. Two of the most popular summertime outdoor activities are grilling and fireworks. Both of these activities pose fire risks and therefore demand extra precautions to ensure the safety of people and property.
According to the National Fire Protection Association (NFPA), “in 2003-06, U.S. fire departments responded to an average of 7,900 home fires involving grills, hibachis or barbecues per year, including an average of 2,900 structure fires and 5,000 outside fires. These 7,900 fires caused annual average of 10 civilian deaths, 120 reported injuries and $80 million in direct property damage.” While grills are used throughout the year, June and July are the peak months for grill fires. NFPA cites the following safety tips for using grills:
* Propane and charcoal grills must be used outside.
* Keep grills away from house, railing, eaves, and overhanging branches.
* Keep children and pets away from grills.
John Grimes is the Ohio State University Extension Educator for Agriculture and Natural Resources in Highland County.[[In-content Ad]]
Corn pollination
During the past week, tassels began appearing in corn fields that were planted in late April and early May. Corn planted in late May and early-mid June will probably not be tasseling until early to mid August. There is usually some variability in pollination within corn fields and the pollen shed period extends from one to two weeks. This year, we can expect even greater variability because saturated soil conditions and loss of nitrogen in poorly drained and compacted areas have inhibited corn growth. The pollination period, the flowering stage in corn, is the most critical period in the development of a corn plant from the standpoint of grain yield determination.
Stress conditions such as drought have the greatest impact on yield potential during the reproductive stage. Past research indicates that four days of stress (i.e. corn wilted for four consecutive days) at the 12th-14th leaf stage has the potential of reducing yields by 5 to 10 percent. The potential for yield losses to soil moisture deficits increases dramatically when plants begin to flower. During tassel emergence, four days of moisture stress has the potential to reduce yields 10 to 25%. Silk emergence is the most critical period in terms of moisture use by the plant. During this stage, leaves and tassels are fully emerged and the cobs and silks are growing rapidly. Four days of moisture stress during silk emergence has the potential to reduce yields 40 to 50%. However, the stress conditions we are alluding to over these “four-day periods” are severe and involve extensive leaf rolling (characterized by plants with “pineapple” like leaves) throughout much of the day. Also keep in mind that the corn plant is more vulnerable to hail injury during the period from tassel emergence (VT) to silking (R1) than during any other period because the tassel and all the leaves are completely exposed. Complete defoliation of the plant at VT usually results in 100% yield loss. The following are some key steps in the corn pollination process.
Pollen shed usually begins two to three days prior to silk emergence and continues for five to eight days with peak shed on the third day. Under very dry conditions, silk emergence may be delayed, and such asynchronization of pollen shed and silking may result in poor kernel set and reduced grain yields. However, in some years under favorable growing condition, silks may actually emerge before tassels fully emerge and pollen shed starts in certain hybrids. On a typical midsummer day, peak pollen shed occurs in the morning between 9 a.m. and 11 a.m. followed by a second round of pollen shed late in the afternoon. Pollen may be shed before the tassel fully emerges (“stretches out”). Pollen shed usually begins in the middle of the central spike of the tassel and spreads out later over the whole tassel with the lower branches last to shed pollen.
Pollen grains are borne in anthers, each of which contains a large number of pollen grains. The anthers open and the pollen grains pour out in early to mid morning after dew has dried off the tassels. Pollen is light and is often carried considerable distances by the wind. Pollen shed is not a continuous process. It stops when the tassel is too wet or too dry and begins again when temperature conditions are favorable. Pollen stands little chance of being washed off the silks during a rainstorm as little to none is shed when the tassel is wet.
Under favorable conditions, pollen grain remains viable for only 18 to 24 hours. However, the pollen grain starts growth of the pollen tube down the silk channel within minutes of coming in contact with a silk and the pollen tube grows the length of the silk and enters the female flower (ovule) in 12 to 28 hours.
A well-developed ear shoot should have 750 to 1,000 ovules (potential kernels) each producing a silk. The silks from near the base of the ear emerge first and those from the tip appear last. Under good conditions, all silks will emerge and be ready for pollination within 3 to 5 days and this usually provides adequate time for all silks to be pollinated before pollen shed ceases.
Pollen of a given plant rarely fertilizes all the silks of the same plant. Under field conditions 97% or more of the kernels produced by each plant may be pollinated by other plants in the field. The amount of pollen is rarely a cause of poor kernel set. Each tassel contains from 2 to 5 million pollen grains, which translates to 2,000 to 5,000 pollen grains produced for each silk of the ear shoot. Shortages of pollen are usually only a problem under conditions of extreme heat and drought.
Summer fires
Summer is a season of outdoor living. We tend to do as many activities outside as possible during this time. Two of the most popular summertime outdoor activities are grilling and fireworks. Both of these activities pose fire risks and therefore demand extra precautions to ensure the safety of people and property.
According to the National Fire Protection Association (NFPA), “in 2003-06, U.S. fire departments responded to an average of 7,900 home fires involving grills, hibachis or barbecues per year, including an average of 2,900 structure fires and 5,000 outside fires. These 7,900 fires caused annual average of 10 civilian deaths, 120 reported injuries and $80 million in direct property damage.” While grills are used throughout the year, June and July are the peak months for grill fires. NFPA cites the following safety tips for using grills:
* Propane and charcoal grills must be used outside.
* Keep grills away from house, railing, eaves, and overhanging branches.
* Keep children and pets away from grills.
John Grimes is the Ohio State University Extension Educator for Agriculture and Natural Resources in Highland County.[[In-content Ad]]