August 16-18 rainfall totals ranged from 2 to 5 inches across the Dodge and Washington Counties bringing a likely end to the irrigation season for many. Rainfall totals were lowest around Fremont and highest around Scribner.
Most corn is between the dough (R4) and dent (R5) stages. Disease pressure from southern rust, gray leaf spot, and northern corn leaf blight caused many producers to spray fields during the milk and dough growth stages the last two weeks. There has also been several reports of higher than normal northern corn rootworms beetle populations (likely extended diapause) in corn after soybean fields this month. Many growers across northern Dodge County only irrigated 1 to 2 inches this season and some fields were not irrigated at all. Overall, most of the corn crop is in good to excellent condition. Rainfed corn yields of 220 bu/ac will likely be obtained in portions of northern Dodge and Washington Counties.
Most soybeans are in beginning seed (R5) growth stage. More incidences of white mold (Figure 1), Phytophthora stem rot, and frogeye leaf spot have occurred this year compared to last year. Foliar symptoms of sudden death syndrome just started to appear this past week on compacted end rows. Soybean aphid populations (Figure 2) have been gradually climbing over the past 3 weeks, with some hot spots within fields over 250 aphids per plant. However, soybean aphid pressure across most fields has not justified insecticide applications so far. Many farmers were worried about how tall the soybeans grew this season and risk of lodging. Unfortunately, heavy rains and strong winds from storms this week caused many soybean plants to lodge. Some yield loss will be attributed to this lodging. Overall, soybeans are in good to excellent condition. I have been finding more 4-seed pods (Figure 3) this year than normal, so yield potential looks good.
Agronomic concerns for the coming week:
- Scout for soybean aphids, remember 250-80-6, which means the economic threshold is 250 aphids per plant on greater than 80% of the plants in a field with an increasing population prior to the full seed (R6) growth stage.
- Scout and take notes on your soybean fields to help prioritize variety selection for disease resistance (white mold, Phytophthora, and sudden death syndrome) when planting back into these fields next time.
- Scout and take notes on fields or portions of fields with waterhemp and marestail escapes to make adjustments next spring for increased pressure.
- Attend upcoming seed industry plot tours to learn how certain corn hybrids handled this year’s disease pressure (gray leaf spot and northern corn leaf blight). Ask!
Figure 1. White mold more common this year due to wet weather during flowering.
Figure 2. Soybean aphid populations only increased slightly from one week ago, many fields still below economic thresholds.
Figure 3. More 4-seed pods this year than normal.
