Though most soybean-producing parishes of Louisiana faced an unseasonably cool, wet spring in late March and April, soybean plantings did not fall behind the five-year average until the third week of April. Soon after the first of May, however, Louisiana began to dry out and plantings quickly caught up with and surpassed the five-year average by the end of the second week of May.
Even with this quick recovery by most producers, some 40 percent of our soybean acreage was or will be planted beyond the LSU AgCenter’s recommended planting window.
Extensive planting date research conducted across the state has shown that soybeans typically begin to lose yield potential as planting extends past the second week of May.
Late planting decisions
For acres that have yet to be planted, there are a few ways to maximize the yield potential of late plantings. When choosing a variety for these late plantings, consider longer-season varieties to increase the amount of time available for vegetative development.
Soybeans are a photosensitive crop, so the date of planting influences the number of days to flowering. The use of early-maturing varieties will cause soybeans to bloom before the plants have fully developed. This means they will lack the vegetative infrastructure necessary to produce the number of pods needed to reach the maximum yield potential.
Growers should choose late maturity group IV or early MG V varieties when planting after the second week of May. Should plantings extend into late May and early June, select mid- to late MG V varieties.
Cultural practices can also help ensure maximum yield potential is realized when planting late. Growers should increase seeding rates by 10 to 15 percent, and if possible, they can reduce row widths to 20 inches. Both of these practices increase the chances of canopy closure, improving the plants’ ability to intercept light while helping reduce weed pressure.
Even though the threat of seedling disease is considerably lower with late-planted soybeans, broad-spectrum fungicide and insecticide seed treatments should still be used with these plantings. Preventing stress in late-planted soybeans is critical, and seed treatments help prevent stand loss and early-season stresses such as seedling diseases and insects.
Managing late-planted soybeans
Early-season weed control is vital to eliminate competition with newly emerged soybean seedlings. Producers may need to make an additional burndown application prior to planting to ensure a clean seedbed. This is especially true considering the rainfall needed to activate many pre-emergence herbicides can become scarce in late May and June.
Producers will need to increase scouting for weed emergence and be especially timely with postemergence herbicide applications. Research by LSU AgCenter weed scientists has shown soybeans must be kept weed-free for five weeks after emergence to avoid yield loss due to weed competition.
Late-planted soybeans also have an increased probability of facing threshold-level foliar- and pod-feeding insects throughout the growing season. Late-maturing soybeans can also be inundated with late-season populations of stinkbugs as surrounding fields are desiccated. With little room for error, producers should intensively scout this crop and make timely insecticide applications when necessary. This could result in increased costs, but additional applications are vital to maximizing yield potential.
Soybean rust is often associated with late-planted soybeans in Louisiana. Although treatment for soybean rust in Louisiana is not usually economical, late plantings are more likely to need fungicide treatment, as they will be susceptible through the majority of reproductive development. Rust is easily controlled with fungicide applications. Producers should carefully scout these plantings and consult their local AgCenter agent for product recommendations if an application is warranted.
The longer soybean plantings are delayed, the greater the risk of drought stress-induced yield loss. For irrigated fields, this may mean increased irrigation applications throughout the reproductive development of the crop. Again, this increases the potential to incur additional costs of production.
Late plantings have less time to compensate for stresses in the growing season, particularly once soybeans transition into reproductive development. For producers with a late-planted crop, it is beneficial to anticipate these challenges. Knowing upfront the stresses that may be faced will help prepare for management of the crop to maximize the yield potential for late-planted soybeans.