Mississippi County
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Mississippi County Agronomy News
Monitor for Late Season Pests
As corn harvest is rapidly approaching be on the lookout for pests moving into flowering to podding soybeans and maturing grain sorghum (milo). Midge and corn earworm are the primary pests of milo. The top two soybean pests are stink bugs and corn earworm a.k.a. soybean podworm. Both of these pests feed on soybean pods.
This is the time to scout for Sorghum Midge. After the bloom stage it is too late to control midge. Late-planted or sequentially-planted fields will be more at risk than early-planted ones. The best time to scout sorghum fields for the midge is during the morning when winds are calm and the adults are most active on the flowering heads. Sample 10 heads at each of 10 locations per field to determine the extent of midge infestations. The University of Missouri action threshold is one adult midge per seedhead. Economic threshold of corn earworm is reached when 75% of seed heads are infested with one or more larvae. It is difficult to see the worms in the heads. So, take a bucket or stiff cardboard to the field and slap the seed heads onto the surface and count the worms. Divide a field up into 4 or 5 sections to get a representative sample. The earworm are most damaging during bloom to milk stages.
Podworm threshold in soybeans is one per foot of row. Shake the plants and count the worms on the ground. Begin scouting during bloom and early pod formation. Only treat at threshold and pods show damage. Two stink bug species are becoming more of problem in soybeans for the state as a whole. These bugs reduce pod fill, seed size and quality. Threshold is two stink bugs (large nymphs and adults) per 3-row feet or 12 per 25 sweeps with a sweep net. The most common of the two is green stink bug, however, it is important to identify the dominant species (green or brown) because different insecticides are required. Also, keep in mind the harvest intervals of insecticides when planning an application.
Wheat Seed Quality
Wheat performance information is available on the Mississippi County Extension Agriculture website and at the Extension Center. When selecting a variety consider yield potential, test weight, disease and insect package, heading date and maturity date.
If you plan to use saved seed, consider the quality of the wheat seed. This season, temperatures and rain events coincided with flowering in many fields in Southeast Missouri and neighboring states. These environmental conditions helped raise the presence of Fusarium head blight (scab). I also noticed and had calls this year about the presence of loose smut. These diseases stay with the seed. Fusarium scab affects overall quality and affects germination. Loose smut (black heads) spores spread and reside on the seed for next season, resulting in an exponential increase of smut or black heads. Reports of low germination are coming in due to the incidence of scab this year. First, cleaning the seed will help remove small and/or shrunken kernels. Next, this year would be a good year to get a germination test done. MO Department of Ag State Seed Lab and MO Seed Improvement Association do germination tests. Next assess whether to apply a fungicide seed treatment to help improve germination. Fungicides help protect against fungal infection, they will not improve germ of injured seed or dead seed. Typically, wheat with a germination below 80% should be avoided. Seed quality also includes seed size based on thousand kernel weight (TKW). If possible select a seed with a TKW of 30 grams or higher because these seeds tend to have increased fall tiller number and seedling vigor.
Terminating Soybean and Grain Sorghum Irrigation
For soybeans, termination is at full seed or growth stage R6. R6 can be identified by checking the pods at the four uppermost nodes on the main stem with a fully developed leaf. In general if 2/3 of the pods have full-size “green beans” that are touching in the pods, then irrigation can be terminated. For clay loam soils termination should occur when 1/3 of the pods have touching beans, and for coarse sands when all the pods have touching beans. The Mississippi County website will have a link to more information on soybean water use.
For grain sorghum, termination is at the hard dough stage. Additional information on irrigation can be found at the University of Missouri Outreach & Extension Irrigation web site. http://agebb.missouri.edu/irrigate/index.htm.
Root Knot Nematodes
By the end of August, I usually start getting some calls about stunted soybeans in a sandy field. Many times that problem is root knot nematode. By August the galls are large enough to inhibit water flow which results in reduced growth. Managing and reducing root knot nematode can only feasibly be accomplished through resistant varieties. Although rotation is always an excellent way to help keep pests in check, RKN has multiple hosts and unlike soybean cyst nematode rotating to other crops will not eliminate or significantly reduce populations.
If you suspect RKN, one simple way to determine its presence is examining roots from late August through October. Dig roots up, in order not to break them, and look for large galls or knots. These galls will be bigger than nodules. Unfortunately timing is important because soybean roots deteriorate rapidly after the plant matures, and the system may be so decomposed a few weeks after harvest that galls will not be detectable. Look at roots to determine if RKN galls are present, but one month post harvest may be too late. A problem with many fields in the area is the presence of both SCN and RKN. The difficulty with this situation is the limited number of varieties which contain both types of resistance. If SCN varieties have been a standard practice and RKN is identified or suspected, a variety with both resistant traits will be necessary to decrease RKN populations as well as maintain tolerable SCN populations. On the Mississippi County Extension website you can find a list of tested varieties that have good tolerance to RKN and SCN.
WEBSITES OF INTEREST
Mississippi County Web: http://outreach.missouri.edu/mississippi
UOE Farm Management: http://outreach.missouri.edu/seregion/fmmkt.htm
MO Dept. Conservation: http://www.conservation.state.mo.us/landown/wild/quail/
Southeast Ag Extension: http://outreach.missouri.edu/seregion/ag/index.shtml
Delta Center Weed Control Page: http://www.psu.missouri.edu/deltaweeds/
Ag Electronic Bulletin Board (AgEbb): http://agebb.missouri.edu
Crop Performance: http://agebb.missouri.edu/cropperf/vartest
MO Irrigation: http://agebb.missouri.edu/irrigate/
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University of Missouri Extension Mississippi County mississippico@missouri.edu Updated 05/24/04 |
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