Value of a Pre-emerge Herbicide

Dr. Aaron Hager, Weed Science – University of Illinois states, “The key to winning the battle of the weeds is not looking for another herbicide to spray on it after it’s emerged. We’ve lost that battle. We will continue to lose that battle. We need to focus all of our attention on targeting the weakest stage of the life cycle of plants. That’s the seed.”

Weed Competition to Yield

University of Minnesota trials in 2014 showed corn yields suffered by 40 bu./acre when weed control was delayed by just five days beyond the optimum time for removal. In 2015, trials at the University of Nebraska, a broad-spectrum, soil-applied herbicide pushed the post weed control timing in soybeans to V5, a gain of three to four leaf stages for effective post-emergence weed control. The pre-emerge herbicide bought 16 to 21 days.

Understanding weed physiology and timing of emergence is important to stage the proper pre-emerge herbicide. The following resource, Weed Emergence Sequences, indicates giant ragweed emerges several weeks before the average corn planting date. Field history of giant ragweed without a pre-emerge herbicide could reduce corn and soybean yields due to early competition. In Ohio, a single giant ragweed plant every 3 ft. caused approximately 65% yield loss in corn and an 80% yield loss in soybeans. A well-targeted pre-emerge herbicide cuts down the density and variety of weeds that have to be controlled later. They will also be smaller and more uniform in size, allowing them to be targeted at a vulnerable seedling stage. Without a pre-emerge, a wider range of weed sizes and species make it difficult to get consistent weed control. In fact, yield losses stemming from poorly-timed weed control can be largely invisible. To buy more days for profitable weed control, apply a pre-emerge residual herbicide.

Selecting Effective Pre-emerge Herbicides

Initial weed resistance began with individual populations becoming resistant to the frequent use of specific herbicides at the population level. Without changes in herbicide use patterns, weeds became resistant to multiple herbicide groups at the individual level. This is called stacked resistance. The challenge is, which herbicide is the most effective for my weed spectrum without knowing the state of my weed resistance? To identify herbicides with weed resistance, use the International Survey of Herbicide Resistant Weeds. The following easy steps will provide information for your region:

#1. Click on the link above.
#2. Click on the drop down menu to list your state
#3. Click on GO to generate a chronological list of cases validated by local weed scientists.

This list of individual cases of weed resistance is essential to narrow herbicide options to the most effective choices. Weeds have evolved resistance to 23 of the 26 known herbicide sites of action and to 163 different herbicides. The purpose of this survey is to monitor the evolution of herbicide-resistant weeds and assess their impact. The site is a global collaboration between weed scientists with a common goal of understanding, preventing, and managing the occurrence of herbicide-resistant weeds. There are currently 559 cases of herbicide resistant weeds in the United States.

Once weed resistance for specific herbicides is identified in your region, use the Herbicide Classification Chart, to select an effective pre-emerge herbicide for your weed spectrum for maximum return on investment. Always read the label and follow directions.

Summary

Profitable crop production begins with a pre-emergence herbicide to start clean and protect yield. While unsteady commodity prices may tempt your customers to lower their investment in weed control, allowing crops to compete with weeds will steal dollars at harvest. Once weeds rob yield, growers can’t get it back. Don’t delay weed control with a post only herbicide plan. Money spent on the highest-yielding varieties of corn and soybeans is essentially wasted if weed infestations can’t be controlled timely throughout the season.

Fungicides | Protecting Against Hidden Yield Losses

Fungicides have traditionally been one of the last inputs that go into a corn and soybean strategy, however, between 2009 – 2013, many growers were regularly applying fungicides to their crops as a preventive measure, even without any disease pressure. Today, economics challenges the value of all inputs. Even with more scrutiny on inputs, industry surveys show overall fungicide sales remained strong during 2017. The grower community acknowledges the increased awareness of plant disease and its impact on yield. Through University and Extension education programs, the benefits of fungicide use are becoming better understood.

Soybean Disease Management

Sudden Death Syndrome (SDS)
Select soybean varieties have partial resistance to SDS. Reducing soil compaction is important. You can also reduce risk by delaying planting by a week or two and planting into warmer soils. Populations of SCN are usually associated with SDS and may increase its severity. Rotating to corn is not effective. Crop residue such as corn kernels and corn roots harbor the SDS pathogen in the soil.

Frog Eye Leaf Spot
Early season infections from infected seed, result in stunted seedlings. This fungus survives in infested crop residue and infected seed. Resistant soybean varieties are available. Foliar fungicides applied during late flowering and early pod set to pod filling stages can reduce the incidence of frog-eye leaf spot.

Septoria Brown Spot
Septoria Brown Spot is a common leaf disease. Yield losses of 5 – 8 % may occur under severe conditions when significant defoliation occurs. It can develop on the first true leaves early in the season. Because the pathogen survives on soybean residue, minimum tillage and continuous soybeans may enhance this disease. Fungicide applications made during R3 through R5 growth stages can protect yield.

Soybean White Mold (SWM)
SWM is a stem rot. This fungus survives in the soil for several years as sclerotia. No soybean variety is completely resistant. Many common weeds found in soybean fields are hosts of SWM. High weed populations of any weed in a soybean field may also increase the density of the total plant canopy and promote a moist climate that favors disease development. Legume and Brassica cover crops can act as hosts of sclerotia and should be avoided if there is any concern of SWM. A fungicide applied at the R1 growth stage provides a higher level of control than applications made at the R3 growth stage. Efficacy of fungicides for SWM declines significantly after symptoms are visible on the plants.

Corn Disease Management

Northern Corn Leaf Blight
Identified as cigar-shaped lesions unrestricted by leaf veins. This fungus overwinters in corn residue. Fungal spores are dispersed by wind and splashing water. Early infection leading to diseased upper leaves can increase yield losses. If the disease is present on 50 percent of the plants in the field at tasseling (one or more lesions per plant), a fungicide application may be necessary to protect yield. Severe NCLB development during grain fill can result in yield losses of 30 percent or more.

Eye Spot
Eyespot is a residue-borne, fungal disease that can reach levels causing yield loss in susceptible hybrids. Higher risk of disease occurs under no-till conditions and when corn is planted sequentially for two or more years. The first visible symptoms of eyespot are small, circular spots, water-soaked with yellow halos on leaves. These can occur as early as the V3/4 stage. Eye spot favors cool temperatures, humid and wet conditions, continuous corn, conservation tillage, and susceptible corn hybrids. Fungicides are economically beneficial if applied early.

Gray Leaf Spot
Gray leaf spot can occur every growing season. The fungus survives in corn residue and is often more severe in corn following corn. Lesions always start in the lower canopy. GLS can result in high yield loss when the disease spreads to leaves above the ear after tasseling. High GLS severity may also increase the risk of stalk rot. Fungicides are effective at reducing disease and protecting yield.

Goss’s Wilt
Yield losses from Goss’s Wilt can exceed 30% for susceptible hybrids. Goss’s Wilt primarily infects leaves that have been wounded by circumstances such as hail, sand-blasting, rain, wind, and strong storms. The primary symptoms on leaves are elongated tan lesions with irregular margins extending parallel to the veins. Dark, water-soaked spots (‘freckles’) develop in the lesions. Goss’s Wilt is caused by bacteria, so we do not recommend applying fungicides. This disease can be managed using resistant hybrids, rotating away from corn production, using tillage that buries corn residue after harvest, and by controlling grassy weeds.

In summary, during the season it’s not uncommon to see corn and soybean diseases. Since conditions change from year to year, it’s important to be prepared by learning how to identify key diseases and take action to protect against hidden yield losses. With today’s economics, it’s about creating tomorrow’s success today.