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Earliest soybeans near completed pod-fill

The Mississippi soybean crop is somewhat varied but that is no different from years past. Planting dates range from mid-March to just finishing up the first of July. The long cool, dry April/May caused this crop to be shorter in height than normal but with a couple of timely rains this should not be a major detriment to yield.

A lot of information has been circulated regarding when to use a fungicide program and what program to use. It is unfortunate that supplies of a straight strobilurin (Quadris/Headline) were short. Without rust, either of the two products, Topsin-M or a combination is an excellent option.

Rust has been identified in three new locations — Florida, southwest Alabama, and southeast Mississippi. At the stage of this crop, the time of the year and weather conditions through late July, it is doubtful rust will have much of an effect this season.

For some reason it has not built up as most expected. This may be surprising, but every day that passes gets us closer to not having to worry about this crop. If we can make it to mid-August it will have little effect on the majority of the 2005 crop. However, we must keep things in perspective. 100-degree heat and the lack of significant rainfall are not helping — rust is not our only concern.

We feel very good about our earlier predictions and the opportunity our statewide sentinel system provided you. The sentinel plots proved to be beneficial. It is disappointing, however, that the earliness of this crop will be penalized by the lack of adequate moisture early.

The earliest-planted portion of this crop has almost completed pod-fill, with at least half of the crop finished by late July. Once this crop reaches full seed (R6), rust will have minimal impact. However, the crop can still be affected up through the R7 growth stage. R6 is full seed, when the seed are plump and squared off. The R7 growth stage is when plants are turning and at least 50 percent of the pods have turned color.

Even though the crop has reached full seed, it is not finished. Two things that impact the crop late are irrigation and stink bugs.

Physiologically the plant does not dry down immediately at R6. At this stage it begins a slow dry-down phase. The plant is still pumping water and nutrients and the impact of a dry soil profile is most evident at R6. You should attempt to have a soil profile with adequate moisture as the dry-down phase begins. Seed may be filled and squared off at R6, but the lack of adequate moisture can still impact seed size and weight. Any adverse condition — lack of moisture, insects or disease — will have less of an effect after R6 than prior, but it can have an impact.

Stink bugs are causing more damage than most care to admit. Damage can be worse on the earliest-maturing portion of the crop because things happen fast when the crop is maturing in August/September prior to nighttime temperatures cooling off. Stink bugs can damage a green pecan. With that in mind, you can see the concern regarding late-season damage. Once plants reach R6, needs of the crop are less but by no means shut down.

Alan Blaine is the Mississippi Extension soybean specialist. e-mail:

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