Planting Dates and Hybrid Maturity Selection

As the calendar progresses through May and planting delays due to wet weather persist, many growers are faced with the tough decision of whether to switch into earlier season hybrids or not. Several factors are key in helping make that agonizing decision. Let’s address some of the more important ones.

The maturity of the hybrids you use is based on the normal amount of heat units received in a given area. Other factors which affect the maturity of corn that you can use is your soil type and the drainage of the ground you intend to plant corn on. If you have selected a corn hybrid using the assumption that early planting on this ground will allow for a full season hybrid to be used, then delayed planting of this hybrid becomes a factor sooner than a product chosen for ground that was not expected to be ready to plant at a very early date. In most areas, a range of corn hybrid maturities are chosen by farmers based on past experience and expected planting dates. If a hybrid is pushing the upper end of the accepted maturity in a given area, then those products will have to be changed first. When a full season hybrid is used, planting dates prior to May 15^th is critical to achieve full maturity when a normal growing season is received after that date. If a less than full season hybrid was chosen, then you may be able to use that hybrid selection into late May. For instance, if you live in an area where 95 to 105 day corn is produced, any 105 day corn that you have not planted by May 15^th needs to be considered for moving into an earlier product. The 95-day hybrids that you have selected could likely be used into late May.

It is one thing to be a little behind in planting, it is a completely different issue when that happens and we know that even with good weather, planting likely will not take place for several days. In most areas of the northern corn growing area, May 15^th is the date that tough decisions about hybrid maturities need to be made. If you decide that a full season product needs to be switched into a shorter season product, make a move up of at least 7 to 10 days. If a move of less than that is made, then you could have likely stayed with the original product chosen.

Estimates of yield loss associated with delayed planting vary. One university study suggests that for each day of delay after May 1^st, we lose about .5% yield per day. This would suggest that if planting were delayed up to May 20^th, on average, 10% of the total potential yield of a corn crop could be lost. This loss can occur in the form of immature corn at harvest time if moving to an earlier season corn is not considered, or from the lost yield potential from an earlier season corn when that option is used. The best option is naturally going to be based on the quality of growing season received after planting is completed, but the market generally has severe discounts for immature corn and harvest is severely hampered when full maturity is not reached by the end to the growing season. A shorter maturity hybrid with perhaps less total potential yield is often the best option with this in mind.

A study done by the University of Illinois in 1994 detailed on the next page shows the impact of delayed planting and reduced stand. This may give some insight into helping you make the decision of switching to an earlier season hybrid or not.

April 20	73	78	83	87	90	94	97	99
April 25	74	79	84	88	92	95	98	100
May 1	74	79	84	88	92	95	98	100
May 6	73	78	83	87	91	94	97	99
May 11	71	76	81	85	89	92	95	97
May 16	68	74	78	82	86	89	92	94
May 21	64	70	75	79	82	86	88	90
May 26	60	65	70	74	78	81	84	86
May 31	54	60	64	68	72	75	78	80
June 5	48	53	58	62	65	69	71	74
June 10	40	46	50	54	58	61	64	66

Table assumes a uniform stand				Chart: University of Illinois 1994