Early Planted Soybeans Considerations

Jake Jones, Extension Agriculture Agent, Kent County; jgjones@udel.edu

Of the top 10 yields recorded in the Delaware Soybean Board 2021 Soybean Yield Contest, five were planted in April and five were planted in May. “Early planted” soybeans have become popular in recent years due to the upside potential for additional yield and earlier harvests possible in the damp fall season. The logic of a longer grower season and higher photosynthesis with flowering occurring at the summer solstice is sound. Yields can reflect this, but early planting does not come without substantial challenges from weather, diseases, insects, and weeds.

Check the weather forecast.
Between 2000 to 2021 the average last frost date in Georgetown, DE was April 7 but the latest was April 22. Be wary of false springs, which in 2020 led to very early planting of some soybeans that emerged and were subsequently killed by a late frost. Soil temperatures at two inches of 77°F are ideal for soybean germination with a minimum requirement of 50°F. Check the forecast before early planting and make sure cold and rainy days aren’t ahead that can stall germination. Also, remember that surface residue can limit the solar radiation needed to heat soils in no-till situations. At 50°F, germination will occur very slowly, allowing for diseases and insects to reduce stands.

Use seed treatments to protect the seed.
Diseases that infect and reduce emergence are caused by Pythium, Phytophthora, Fusarium, and Rhizoctonia. Pythium and Phytophthora can cause pre and post-emergence damping off. Fusarium causes root rot and wilt. Rhizoctonia causes pre-emergence damping off and root rot post-emergence. Symptoms can occur immediately in germinating seedlings or remain latent until stressors and weather conditions later in the season cause symptom development. Sudden Death Syndrome (SDS), caused by Fusarium virguliforme, is a great example of an infection that occurs in the cold and wet early spring but symptom development is delayed until late vegetative or early reproductive stages. Using seed treatments and choosing resistant varieties are two ways to reduce disease infection of germinating soybeans.

Maintain season-long weed control.
Weed control can be both a challenge and an opportunity in early planted soybeans. The first step is always to start clean. Early soybeans are slow to emerge and grow, taking more days to close the canopy than soybeans planted in the same row spacing later in the year. Residual herbicides will be important during the slow emergence and canopy filling stages. Consult herbicide labels to stay below the maximum yearly herbicide rate. But with canopies that close earlier on the calendar, early soybeans could provide a benefit by shading out more of the summer emerging palmer amaranth.

Use row cleaners and close the seed furrow.
Slugs are public enemy number one for soybeans in no-till situations. The ideal conditions for slug damage are no-till situations with high residue, high moisture, and open seed furrows. Correct these conditions by waiting to plant until soil moisture is drier, move the residue with row cleaners, and use tillage, which is a very effective cultural tool in fields with a history of slugs. On the other hand, tillage of heavy residue into the soil could lead to the proliferation of a different insect pest, seedcorn maggot. Seedcorn maggot feeds on decaying organic matter in the soil and can also cause damage to germinating and emerging soybeans. With no rescue treatments for seedcorn maggot, the best option is to avoid planting during peak fly emergence for the first generation. If your field is the earliest soybean field to emerge in your area, expect the insects and deer to know about it.

Scout but don’t stress.
With seeds in the ground for longer, seedlings growing slower, and plants growing for longer, early planted soybeans face many challenges throughout the extended growing season. It is important to scout and properly identify the weeds, insects, and diseases in order to manage them properly and plan for future success with early planted soybeans. Soybeans have an amazing capacity for compensating for stand loss and maintaining yields. 60,000 plants per acre can yield 90% that of a normal population, so don’t be too quick to give up on a damaged field.

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