Delaware Agronomy Blog

University of Delaware Cooperative Extension

Author: Jarrod Miller (page 2 of 16)

July Temperatures and Pollination

According to data from the last two years (, silking and pollination (R1) has occurred between 1320 and 1594 growing degree days, while VT (tasseling) occurs between 1200-1300. In many of our research fields, VT also began to occur in this range last week, followed quickly by silking. Stress during pollination can determine initial pollination and kernel set, so temperature becomes very important. Planting date is an important part of this, as corn growth will follow heat accumulation, so cooler springs will take longer to reach R1 and vice versa. Continue reading

Checking Vegetative Growth Stages

Corn at our research station is at V4, which means we will probably be sidedressing several fields next week. Anyone who planted prior to April 25th may be one leaf ahead, and plans for sidedressing should be done. If you are unsure of which stage you are at, one common method is to count leaves based on the presence of the collar (Figure 1a). While many leaves can be emerged from the whorl, only those with collars are considered fully developed. Continue reading

A Warmer 2021 is Boosting Emergence

Emerging corn in a rye cover crop

Emerging corn in a rye cover crop

While it may not seem much warmer than it was in 2020, having steady days above 50°F had provided much faster emergence than last year. In 2019 we were getting about 10 growing degree days (GDD) per day, while now we are seeing 15-20. The threshold for emergence is about 100-120 GDD, which we have reached for most fields planted between April 15 and April 22nd (Table 1). In 2020, we had only reached half of that (60-90 statewide) over the same time period.

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Cover Crops May Protect Corn from Cooler Temperatures

The weather outlook in Georgetown includes no air temperatures (currently) in the 30s through April 21st. With that outlook, soybean and corn planting can probably start late next week. Although there can still be a random late freeze, the probability really drops after April 15th in our region.

The preferred soil temperature for corn germination is 50°F, which allows the seed to begin root and shoot growth.  Many of the weather stations on DEOS ( have soil temperature as an option, so you can track current conditions. Since April 1st, soil temperatures have ranged from 47-53°F in Newark and 47-55°F in Georgetown. Soil temperature does not change as rapidly as air temperature, so we would expect the daytime temperatures over the next week to keep soils above 50°F, even when nighttime temperatures dip into the 40s.

Figure 1: Corn on the left was planted in bare plots while corn a few inches away in a rye cover crop appears unaffected.

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Cover Crop Termination for 2021

Jamie Taraila,  Jarrod Miller,  and Amy Shober

With April and warmer temperatures finally here, it is time to think about cover crop termination. This spring, we expect lower cover crop biomass at burndown due to the cool, wet winter conditions that delayed growth, particularly small grains. Therefore, termination timing decisions are very important this year. We must recognize that there are pros and cons of early and late cover crop termination and make decisions that maximize benefits.

Figure 1: Vetch cover crop before spring corn planting.

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