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AgAlerts 2002 From Griggs County
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Issue # 12, August 6, 2002
Hail was received in scattered areas in
Griggs County on Wednesday, July 31st. Damages varied from a trace to
100%. The following pictures show how extensive the damage was to six foot
plus corn in eastern Foster county.
(click on picture to enlarge)
Corn: The first step in yield damage assessment is to establish
what stage the plant was in at the time of damage. Growth stages after
tasseling are identified according to development of the ear shoot and kernels
as follows:
Blister stage - kernels on cob appear as watery blisters; kernel is white and fluid colorless.
Milk stage - roasting ear stage; full yellow color; cob has reached maximum length.
Dent stage - kernels dented or denting and can be easily with finger.
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Estimated Corn Yield Reduction Due to Defoliation at Various Stages of Growth |
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Expected yield reduction when amount of defoliation is - |
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Stage of Growth |
10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 100% |
| Tassled | 3 | 7 | 13 | 21 | 31 | 42 | 55 | 68 | 100 |
| Blister | 2 | 5 | 10 | 16 | 22 | 30 | 39 | 50 | 73 |
| Milk | 1 | 3 | 7 | 12 | 18 | 24 | 32 | 41 | 59 |
| Dented | 0 | 0 | 1 | 3 | 7 | 10 | 14 | 17 | 24 |
Soybean: Accurate determination of stage of growth is necessary to determine yield loss due to hail. Vegetative growth stages (or V-stages) are identified by the number of nodes above the cotyledons. A node is counted when the attached leaf is completely unfurled. Reproductive states (R-stages) occur after the plant begins to flower and are defined by the development of flowers, pods, and seeds. The following tables are from Nebraska bulletin G85-762, Soybean Yield Loss Due to Hail Damage (1985). For more information on determining growth stages, goto the following link. Soybean Growth and Management.
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Percent yield loss of indeterminant soybean varieties as affected by degree of defoliation |
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| Growth |
Defoliation (% leaf area destroyed) |
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| Stage | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% | 100% |
| R1-R2 | 0 | 2 | 3 | 5 | 6 | 7 | 9 | 12 | 16 | 23 |
| R3 | 2 | 3 | 4 | 6 | 8 | 11 | 14 | 18 | 24 | 33 |
| R4 | 3 | 5 | 7 | 9 | 12 | 16 | 22 | 30 | 39 | 56 |
| R5 | 4 | 7 | 10 | 13 | 17 | 23 | 31 | 43 | 58 | 75 |
| R6 | 1 | 6 | 9 | 11 | 14 | 18 | 23 | 31 | 41 | 53 |
Reports of grasshoppers have been increasing due to the haying of CRP and the maturing of small grains. Monitor soybeans, corn and sunflowers to see if grasshoppers are moving into these crops. For thresholds goto the NDSU Field Crop Insect Management Guide for 2002. Corn, Soybean, Sunflower.
We have been getting a lot of questions concerning soybean aphids. At this time I have not seen populations that warrant treatment. But this is not to say we don't need to keep monitoring for this insect. Early flowering is the critical time period for making aphid treatment decisions. Plants in early flowering with aphid populations of 200 aphids/plant or leaves showing a glossy appearance, during this susceptible growth stage are candidates for an insecticidal treatment. Soybean aphid populations can increase rapidly, so keeping a close eye on fields at this time is important.
Please Contact Our Office For Additional Information
E-mail: griggs@ndsuext.nodak.edu
Go to the 2002 AgAlert Index Page