ISSUE 8   June 22, 2006

Sunflower growth and development responds to heat units similar to corn and several other crops. The base temperature of 44 F is used to determine Growing Degree Days (GDD). GDD formula = [(daily maximum temperature + daily minimum temperature)/2] - 44 F.

In the table below research data was collected at the Carrington Research and Extension Center over a number of years on sunflower stage development and heat units.

Growing Degree Days were averaged over 5 hybrids each year and 5 plants per hybrid per plot were observed. Sunflower was planted on May 25 and May 23 in 1994 and 1995 respectively.

GDD units/data for 2006 can be found on NDSU’s Extension site under Ag weather (NDAWN). http://ndawn.ndsu.nodak.edu/applications.html Just click on the applications section and then to "Degree Days".

The appearance of flowers on soybean plants is controlled by a complicated interaction between photoperiod (length of light period) and temperature, with temperature being more important in the northern soybean belt and photoperiod being more important in the southern soybean belt. Nearly all soybean varieties are stimulated to flower by decreasing photoperiod length (short-day plants). In nature, decreasing photoperiods occur after June 21. Because of the sensitivity of soybean to photoperiod and temperature, soybean varieties are grouped into maturity group bands. These bands are about 100- to 150-miles wide and are somewhat parallel (but not exactly) to Earth's latitudes. In general, soybean varieties planted south of their adapted maturity group will flower more quickly, and plants will be shorter than normal. This often decreases yield potential.

The first flower on soybean plants with an indeterminate growth habit (type in ND and MN) is initiated at R1 on the third to the sixth main stem node and proceeds upward and downward. The coteledonary node, the unifoliolate leaf nodes and the first two trifoliolate nodes are initiated in the seed, so their buds are vegetative. Flowering proceeds toward the top of the plant and continues as vegetative growth proceeds. The flowering period is usually 20 to 30 days. Nodes higher and lower than this quickly produce flowers, so within a few days all nodes possess flowers. By the R5 stage the plant has completed most of its flowering but a few newly opened flowers may be present on branches and in the upper stem nodes. Almost all soybean flowers pollinate before opening. Therefore little if any pollen drift does or will occur. High temperatures and droughty growing conditions can have an influence on flower abortion and less pod and seed set. Also application of certain herbicides at this flowering stage can cause pods to abort. One must always check the label to insure that it’s safe to apply a herbicide if the soybeans are flowering.

Three to four days following flower opening, the flower petals will dry and the pod begins to elongate. Two and a half weeks after the flower opens the full length pod will have been formed. Pod growth is most rapid between the R4 to R5 growth stages.

Duane R. Berglund
NDSU Extension Agronomist
duane.berglund@ndsu.edu

There have been numerous reports of tillering in corn this past week. In my own plots I have noted the development of tillers on nearly every plant on some hybrids. The following are some basic facts about tillering in corn.

• Tiller production in corn is much less common than in small grains. Nevertheless, corn tillers result from normal physiological development processes similar to those in small grains. All basal nodes of the corn plant have buds that have the capacity to develop into tillers or ears. These buds are stimulated to develop tillers in favorable environments (i.e. adequate moisture, good fertility, reduced plant populations, border rows, etc.) or after early season injury. The unusually high number of corn plants with tillers this year is probably associated with the very favorable conditions for corn growth of these past few weeks.
• Hybrids vary in their propensity to develop tillers. However, it is not uncommon for a hybrid that has a high proportion of tillering this year to produce few tillers next year. Environment tends to be more important than hybrid when it comes to tillering in a given year. If you are growing a hybrid that yields well, don’t abandon it just because it has tillers this year.
• Tillering generally does not have a detrimental effect on corn yield, nor it is beneficial to yield. Tillers rarely form ears so do not contribute directly to yield, but the photosynthates produced in the tillers can readily move to the main stem if no ear forms on the tiller.
• Tillers very commonly produce tassel-ears, tassels that develop kernels and appear like an ear. Tassel-ears generally will not contribute to yield significantly and can be problematic in environments that are prone to the development of aflotoxins.

Tiller in corn

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