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Issue No. 13, Article 6/July 1, 2011

Wheat Harvest and Soybean Progress

As we wait for the corn crop to enter its critical pollination stage, the main problem continues to be saturated soils and issues related to the saturation. Over 90% of the state received above-normal rainfall in June, with parts of western Illinois getting more than double the normal amounts. But warm temperatures, a lot of sunshine, and a pause in rainfall this week will should help the crop to recover some.

Wheat harvest in Illinois is well underway following the interruption from heavy rainfall, especially in southwestern Illinois, where the wheat crop is concentrated. Fortunately, the quality, as measured by test weight, does not seem to have suffered much as a result of wet weather. This is probably because the grain was not completely dry when the rains came, so it didn't rehydrate and then dry down, at least more than once. While the crop did have some grain threshed out of the head by hail and heavy rain, reports are that test weights are high, yields are good to very good, and--now that we have some dry weather--harvest is proceeding quickly. After 2010, it's good to see the wheat crop make a nice comeback.

Soil moisture following wheat harvest is adequate, and in some places excessive, for getting double-crop soybean planted. Good soil moisture at planting is critical to getting double-crop soybeans off to a good start, and we expect fields to be planted quickly to take advantage of the soil moisture. As a reminder, double-crop soybean varieties should not be earlier in maturity than full-season soybeans. It's better to plant double-crop soybean in rows 20 inches apart or less, and seeding rates should be on the high side. Soybeans planted this late do not typically grow very large, so they often benefit from having plants somewhat closer together.

With fewer weather interruptions, wheat harvest is proceeding earlier than normal in central Illinois--we harvested the Urbana variety trial on June 28. This along with good soil moisture (and perhaps some push from the fact that many soybean fields were planted or replanted only recently) has some people thinking about trying double-crop soybeans farther north than usual this year.

We have little data on planting soybeans this late in central Illinois, but with the good soybean price, it should take less than 10 bushels per acre to pay the cost of planting soybeans after wheat. We think that the chances of yields of 10 bushels or more are good, but there's no certainty. The biggest dangers to double-crop soybeans are hot, dry spells in August or September and early frost, which would end seed-filling well before it's complete. But if the crop can get off to a quick start, it should begin seed-filling by mid-August and should be able, weather permitting, to fill a reasonable crop by late September.

One advantage with double-crop soybeans is the ability to wait to apply herbicide or to make other expenditures until you know something about crop prospects; if prospects are poor, you can cut your losses. As is the practice in southern Illinois, narrow rows and slightly higher seeding rates should be used farther north. Varietal maturity should be similar to what would be used for full-season soybeans; do not increase it as is sometimes done in southern Illinois, given the greater danger of frost coming before maturity farther north.

Like corn, the soybean crop has benefited from warm temperatures, with much of what was planted by mid-May now at V5 to V6 and starting to develop its canopy rapidly. Some earlier-planted fields showed a few flowers by the long┬Čest day of the summer last week, but the combination of shorter and cooler nights brought a halt to most flowering activity.

A crop is not considered to be in the flowering stage (R1) until at least half the plants have a flower; most fields are not yet there. The largest factor in soybean flowering time at this stage and date is night temperature; flowers will appear much faster with warm nights than with night temperatures in the 50s or low 60s. The substance in the plant that triggers flowering converts from an inactive form to its active form during the night; if the conversion isn't complete by the next morning, the plant won't flower. Both longer nights (night length increases after June 21) and warmer nights speed this process and help bring on flowering. Later varieties need longer (or warmer) nights to trigger flowering.

If temperatures stay about average, we expect that most earlier-planted fields will reach R1 in the second week of July. Remember, though, that when flowering starts is less important than how long it continues and how many flowers produce pods. So while an early start to flowering can be an advantage, setting a lot of pods will require favorable conditions through July and into August.--Emerson Nafziger

Emerson Nafziger

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