ISSUE 3   May 24, 2007

REPLANTING SMALL GRAINS AND CORN

Poor stands of wheat and corn due to excessive moisture and/or crusting prior to emergence are common this year in southeastern North Dakota. Stands of early-planted spring wheat were especially affected due to water logging with most of the damage occurring in low-lying parts of the fields. Though corn stands in general look good, especially when compared to adjacent wheat fields, there have been several reports of low corn populations due to crusting. What to do with fields with poor plant populations is an urgent question now that all of the plants that are going to emerge have emerged.

For wheat fields with few or no plants in low-lying parts of the field, replanting only the affected areas is probably the best solutions. Any advantage of using a different variety that might be better adapted for later planting (i.e. varieties from South Dakota tend to be earlier maturing and may escape some of the deleterious effects of the heat of the summer) is probably offset by other logistical considerations, so using the same variety that was planted earlier seems to make sense. Decisions on when and how to apply herbicides and fungicides to fields with two distinct planting dates should be based on label restrictions as well as product efficacy and logistical factors.

For wheat fields that have low populations throughout, replanting is recommended when the plant density falls below 8 plants/ft2. Replanting should be done as soon as possible, as yield losses can exceed 1.5% per day for every day delay after May 15th. When planting spring wheat after May 20th, use a higher seeding rate to compensate for the reduced tillering of the later planted crop. After June 1, consider growing the earliest varieties that are available in addition to using the higher seeding rate.

For corn fields with poor stands but few large gaps and no significant areas without any plants, use the publication "Estimating Yield and Dollar Returns From Corn Replanting" by R.L. Nielsen and published by the Purdue Extension Service (http://www.agry.purdue.edu/ext/pubs/AY-264-W.pdf) to assist you in your decision about replanting. This guide considers biological factors and economics to help the user determine if replanting will be profitable. Relative to small grains, corn is thought to be very responsive to plant population. Nevertheless, corn does have the capacity to compensate when stands are sub-optimal. Data from the central corn belt, for example, indicate that a half stand (14,000 plants per acre) planted in early May will yield about the same as a full stand planted at the end of May (see the article by Nielsen referred to above for more details).

In most circumstances, the original stand of corn should be destroyed before you replant. Late planted plants that grow next to an early-planted plant will be at a competitive disadvantage and will very likely not produce an ear. Data suggest that destroying the original stand before replanting will improve the yield of the replanted crop by 10%. If there are few plants in the original stand, however, there will be limited benefit from destroying these plants as the chance for plant-to-plant competition will be minimal. Replanting should occur as soon as possible in order to minimize yield losses and limit the amount of moisture in the grain at harvest. Consider switching to a hybrid five relative maturity units earlier, now that we are approaching the 1st of June.

Joel Ransom
Extension Agronomist for Cereal Crops
Joel.Ransom@ndsu.edu

 

ALFALFA HARVEST IS UPON US!

Even though this is May 22, alfalfa harvest is upon us! Alfalfa at Fargo measured 25 inches in height and is in the mid to late bud growth stage. In addition, some fields are starting to lodge with the rainstorms that occurred the last couple of days. Alfalfa harvest at Dickinson will be later since it measured 12 to 18 inches.

Plant height is the primary factor to consider when determining when to harvest alfalfa assuming weather (rainfall) is not limiting harvest. The primary objective when harvesting alfalfa hay is to obtain prime hay in the bale or hay with a relative feed value (RFV) of >151. The RFV changes markedly with plant height at the same maturity stage (Table 1). Note that the RFV drops from 191 for 20 inch tall hay to 130 for 40 inch tall hay at the late bud growth stage. Alfalfa at Fargo was 25 inches in height at the mid to late bud growth stage. According to the table, the hay standing in the field should run about 180 to 170 RFV. This is the exact range when the hay should be harvested since about 25 to 30 units of RFV will be loss with the harvesting operation (leaf loss).

Table 1. Forage quality with plant height and maturity.

Height of tallest stem

Maturity of stem

LV1

LB

LF

inches

----relative feed value----

20
25
30
35
40

213
191
173
156
142

191
172
156
142
130

171
155
141
129
118

1LV = Late vegetative; LB = Late bud; LF = Late flower

Alfalfa this year is very early, presumably due to the above-average temperatures in late April and most of May. Normally alfalfa at Fargo at 25 inches would still be in the vegetative growth stage and would not make the late bud stage until nearly 32 inches in height. This illustrates why you can not use maturity stage as the only criteria to determine when to harvest alfalfa.

Lodging has occurred on some fields with the heavy rainstorms and strong winds. If lodging has occurred, harvest the field as soon as possible. The lodging will cause the lower leaves to drop reducing quality and the photosynthetic capacity is reduced. Even though the forage yield might be a little lower than normal, the improved quality and the earlier initiation of regrowth will more than compensate for the small yield loss.

Note also that hay can be harvested at quite mature growth stages if the plant height is 20 inches or less (Table 1). Typically alfalfa at Fargo during the growth following the second harvest rarely exceeds 20 to 22 inches. Therefore, alfalfa harvest can wait until the flowering stages of growth prior to harvest. Remember, the forage quality of alfalfa harvested during a warm growth period (July or August) will have a lower forage quality than one that is grown under a cooler temperature. I usually shoot for 25 to 30% bloom in the third harvest to allow for greater yield but still have prime hay in the bale.

Dwain Meyer
Plant Sciences
Dwain.Meyer@ndsu.edu


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