I woke up this morning to see a little rain fell last night. I think I had 0.15” last night. Not too far north of me they had just a few sprinkles but further south it sounds like they got a pretty good shot of precipitation again last night.
I think most of us have been seeing quite a bit of Corn go in the ground the past 2 weeks. I have some corn in the western side of my territory that you can row and looks very good. I have dug quite a few plants in these fields and most everything so far looks normal. One thing that I have been observing is wireworms in about every place that I dig for corn.
Wireworm are an early season pest, they injure the corn seed and/or the seedlings. Adult wireworms are the “click beetle”, they are dark brown and .5-.75” long. When they get flipped on their back they can “click” and flip themselves back over. Wireworm damage to the seed consists of hollowed out corn seeds before or right after germination. Wireworms may also tunnel through or feed a little on the young seedlings stalk. Cool wet weather like we have been experiencing this spring is ideal for wireworm damage. If you notice areas in a field where there is patchy emergence dig around a little and see if you can find the seeds. I have attached some pictures of seed damage and wireworms.
So with the prices of Corn and Soybeans does anyone raise alfalfa anymore? With acres shifting from pasture and hay into row crop I think we will see roughages be worth quite a bit more this year. Maybe we better manage them a little better than we have in the past. Just this morning I was out scouting in some wet alfalfa fields. In SW Iowa once we get about 200 growing degree days we should start scouting for alfalfa weevils. Alfalfa weevil hatch was predicted to start about April 25 around our area. Alfalfa weevil larvae are light green with a black head and a white stripe on their back. After hatching they are small, light green to yellow and about 1/16” long, they can be almost undetectable in the leaves of the upper stem. When full grown they are considerably darker green and about 5/16” long. Alfalfa weevil larvae can be very destructive to the first cutting of alfalfa. They feed on the top of the plant on the new growth “skelotonizing” the leaves and move down the stem. This feeding decreases quality and quantity of the hay.
Ok, here is the method to use when scouting:
Use a sweep net if you have one to see if we need to start counting larvae. Sweep the alfalfa while walking through a few areas in a field. Make sure to start with the south facing slopes now, this will be where hatching has occurred first. If you do find some in the net we need to take this a step further. Gather about 30 stems of alfalfa carefully so you don’t shake out the larvae accidentally. Shake the stem inside a white 5 gal bucket so you knock them out of the stem’s leaves. Do this with all 30 so you can get a good, accurate larvae per stem count. With this # look at the threshold chart to see if we have reached a threshold. With current prices of hay I am not sure if the old threshold tables we have go high enough for $/ton. This is the latest alfalfa weevil threshold table I could find from Iowa State University’s Integrated Crop Management News.
Table 1. Economic thresholds based on alfalfa weevil larvae per stem (calculated from a 30-stem sample).
Plant
Height $40/ton $70/ton $100/ton Management
(Inches) Decision
4 1.8-2.8 0.8-1.3 0.6-0.8 Reevaluate in
4 days. If damage
and larval
6 2.0-3.0 0.8-1.5 0.6-1.0 numbers are
increasing a long
8 2.2-3.2 0.9-1.7 0.7-1.2 residual
insecticide is
recommended to
prevent severe
yield loss.
10 2.3-3.5 0.9-1.9 0.8-1.4 If alfalfa is in
vegetative stages,
12 2.4-3.8 1.0-2.2 0.9-1.6 a short
residual
14 2.5-4.2 1.2-2.5 1.0-1.8 insecticide should
be used
16 2.6-4.6 1.5-2.8 1.1-2.0 If >60 percent of
alfalfa is in the bud
18 2.7-5.0 1.7-3.1 1.2-2.3 stage, harvest is
recommended.
20 2.8-5.8 2.0-3.4 1.4-2.6 Evaluate stubble
after harvest. If not
>20 3.0-7.0 2.4-4.0 1.6-3.0 scheduled to be
cut within 7-10
days, a short
residual
insecticide is
recommended.
Use the smaller threshold if alfalfa is drought stressed or control costs are relatively low ($7-10 per acre). Use larger threshold if rainfall is abundant, diseased larvae are present, or control costs are relatively high ($11-14 per acre).
Well that is enough for this week, with any luck we should get some more acres planted. Go check your corn and go scout your alfalfa. If you would like to update me on what is going on in your area let me know. I can always use updates on planting this time of year, especially from Page and Fremont counties. Thanks again, have a great weekend.