By Jonathan Kleinjan
Cooler and wetter-than-average weather conditions have been prevalent in parts of South Dakota this Spring, and the extended weather forecast shows unfavorable planting conditions extending well into the month of May. According to the U.S. Department of Agriculture National Agricultural Statistics Service (USDA NASS) progress report published May 1, 2022, only 48% of spring wheat has been planted in South Dakota, which is well behind 78% in 2021 and slightly behind the 5-year average of 51%. Due to these adverse planting conditions, farmers have begun to consider switching acres away from small grains and into later-planted row crops, such as corn or soybeans. A major question that producers have been asking is, “How late can wheat be planted in South Dakota without a significant reduction in yield potential?” That can be a difficult question to answer definitively, as weather variables play an important role in determining final grain yield. As a rule, however, wheat is planted early to ‘beat the heat.’
Hard-red spring wheat is one of the most-tolerant crops to cold temperatures and frost events. Germination and growth will begin when the soil temperature reaches 34° to 36°F. It should be planted as early as possible, since cooler weather from emergence to the early reproductive stages generally favors tiller formation and the development of larger heads. Increased growth during the early season typically results in higher yields.
Management Considerations for Late Planting
A study in North Dakota showed that spring wheat planted on May 1st had six fewer days of growth from emergence to the 6-leaf stage when compared to wheat planted on April 15th. The number of days was further reduced to eleven when planting was delayed until May 15th. Yield data from this research suggests that wheat loses 1.5% of its yield potential every day after the optimum planting date. However, this can vary greatly from season to season.
Optimum planting dates in South Dakota vary according to the location within the state. The range of dates for optimum planting and latest recommend planting dates are listed for nine South Dakota growing regions in Table 1.
TABLE 1. OPTIMUM AND LATE PLANTING DATES FOR SPRING WHEAT IN SOUTH DAKOTA.
Region | Optimum range | Latest Recommended |
|---|
NW | April 8-27 | May 19 |
NC | April 8-27 | May 12 |
NE | April 8-27 | May 15 |
WC | April 5-22 | May 13 |
C | April 5-22 | May 8 |
EC | April 5-22 | May 11 |
SW | April 1-18 | May 13 |
SC | March 25 - April 15 | May 9 |
SE | March 25 - April 10 | May 11 |
Source: Best Management Practices for Wheat Production
It is recommended to increase seeding rates if the planting date is delayed from the optimum date to compensate for the possible loss of tiller formation. The recommended minimum seeding rate for a normal planting date is 1.2 million pure live seeds per acre, although no-till producers may want to use a slightly higher seed rate. Seeding rates should be increased by 1% per day for each day that planting is delayed. For example, if the optimum planting date is April 15th, and planting does not occur until May 10th, the seeding rate should be increased by 25% (1.2 million seeds/acre × 1.25 = 1.5 million seeds/acre). South Dakota State University (SDSU) Extension does not recommend planting more than 1.8 million seeds/acre.
Planting Date Is Not the Entire Story
If conditions are right, late-planted spring wheat can still produce very good yields. In 2018, the South Dakota State University spring wheat variety trial plots were planted on May 14th in South Shore, South Dakota and, despite the late planting date, averaged 69 bu/acre with several varieties yielding above 75 bu/acre.
The wild card in this situation is the weather in June and July. Wheat is highly susceptible to heat during pollination and grain fill. Prolonged exposure to daytime temperatures above 85° to 90°F and especially nighttime temperatures above 70°F, during these growth stages, can drastically reduce yields, especially if soil moisture levels are low. At present, the National Weather Service is predicting slightly above normal temperatures in the May-July timeframe. Decisions on weather risk are ultimately up to each individual producer.
Source : sdstate.edu