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With 83% of the nation’s soybean crop in the ground and 56% emerged, growers need to research and prepare for common soybean diseases that could affect their crops throughout the busy growing season. It’s never too early to get ahead of these potentially yield-robbing threats to your soybean acres.

“Growers need to be prepared for the possibility of losing soybean yield to diseases,” says Tom Larson, Stine’s director of agronomy. “Last year, for example, 4.4% of the potential estimated soybean production was lost due to diseases. From stem and root rots to leaf blights, it’s important to be proactive throughout the growing season to get ahead of these common problems in soybean production.”

WHAT ARE THE MAJOR DISEASES OF SOYBEANS?

Sclerotinia stem rot (white mold), sudden death syndrome (SDS), charcoal rot and Phytophthora leaf and stem rot are some of the most common soybean diseases. Combined, these four soybean stem diseases destroyed almost 45 million bushels in 2022. Other diseases (leaf and aboveground), such as Cercospora leaf blight, frogeye leaf spot and Septoria brown rot, damaged close to 13 million bushels last year. It’s critical to understand the environments these diseases thrive in and how you can prevent them, if not this year, then the next.   

SOYBEAN DISEASE IDENTIFICATION AND CONTROL

Soybean disease identification can help protect your soil and crops to produce maximum yield this growing season.   

Named the leading soybean stem disease in 2022, soybean sudden death syndrome symptoms can appear between R1 and R6 growing stages as random yellow spots between leaf veins. Other SDS symptoms include soft, rotten roots; stem discoloration; necrosis of the leaf tissue between the veins; yellowing of leaves; and leaf drop. While infection of roots may occur early in the season, symptoms usually don’t develop until late July or August. The disease prefers cool, wet soils. Planting SDS-tolerant varieties is an effective way to limit your crop from developing disease. Additionally, crop rotation, tillage and the staggering of planting dates can help limit the disease.

“SDS is one of the most destructive diseases in soybeans,” says Larson. “Experts from Iowa State University Extension and Outreach conducted a study and found that, in areas with severe infestation, SDS can cause up to a 40% yield loss, especially when symptoms develop early. In 2022 alone, SDS destroyed close to 19 million bushels.”

More common in cool, humid and wet growing conditions, white mold can cause significant yield loss. Known for its fluffy white, cotton-like appearance on soybean stems, initial symptoms appear from R3 to R6 as gray to white lesions on plant stems. White mold can eventually lead to leaf death, stem rot and flower wilt. White mold overwinters in the soil and can do so for several years. Experts note it can easily spread to new fields when improperly cleaned seed is used and by the movement of infested soil.

“White mold can cause significant yield loss upwards of 10% bushel per acre,” says Larson. “We’ve seen it devastate fields. It should be a top concern for growers always, but there are ways to mitigate white mold by planting soybean varieties that offer some resistance to the disease and through crop rotation to small grains.”

Phytophthora root and stem rot of soybeans occurs in cool, wet conditions. The disease typically appear between VE and R6. A dark brown lesion on the lower stem that extends up from the taproot of the plant is the most common characteristic of the disease. Other Phytophthora root and stem rot symptoms can include yellowing of leaves, soft/rotting stems and roots and wilted plants. The disease is more severe in no-till fields or in areas that are susceptible to flooding. Tillage, seed treatments and planting resistant varieties are suggested for healthy soybean growth.

Caused by the soilborne fungus Macrophomina phaseolina, charcoal rot of soybeans issues the most damage when weather conditions are hot and dry. Early signs of charcoal rot include red to brown lesions on the roots and lower stems, which then turn to black specks. To help battle charcoal rot, planting the right variety, crop rotation and residue management can produce top yield and keep the disease at bay.

Contact your local Stine® agronomist or sales rep for more information on common soybean diseases and how to treat and prevent them now and in the future. Stine offers a full line of the industry’s most sought-after traits to help growers produce the most yield on their soybean acres.

With 26% of the nation’s corn crop planted — twice the rate at this time a year ago — it’s not too early for growers to consider common corn diseases that might impact their crop this growing season. It’s important to understand what diseased corn looks like, when and why diseases occur, and how to stop or slow the spread once a field has been infected.

“Throughout the growing season, corn must fend off several diseases, such as northern corn leaf blight and tar spot, to thrive,” says Tom Larson, Stine’s director of agronomy. “Knowing what corn disease looks like, what type of disease it is and how to treat it is crucial to your corn crop’s survival and ability to reach its maximum yield potential.”

WHAT CAUSES CORN DISEASE?

For a corn disease to take place, three factors must coexist: a pathogen, a susceptible host and favorable environmental conditions — otherwise known as the disease triangle. Common corn diseases can include seed rots and seedling blights; later in the season, foliar diseases and stalk and ear rots can occur. Planting corn on corn can increase the risk of disease as many can overwinter in infested corn residual.

“There are a number of fungal and bacterial diseases of corn represented across the country,” says Larson. “Your corn crop is always vulnerable, so it’s important to research and understand the factors causing the disease in your field and how to move forward and mitigate it this season and into the next.”

WHAT ARE THE COMMON DISEASES OF CORN?

As a grower, you’re likely familiar with most corn diseases and how they can damage your production year after year, especially if not treated accordingly. The four most common types of corn disease are gray leaf spot, tar spot, northern corn leaf blight and common rust; however, it’s important to note there are still other less common diseases.

Gray leaf spot is caused by the fungus Cercospora zeae-maydis and occurs nearly every growing season. The gray leaf spot disease cycle begins when the fungus overwinters in corn residue and then spreads via rain and wind. It thrives in warm, wet environments and has symptoms similar to other foliar diseases. Spores germinate and infect leaves, causing lesions on the leaves that impact the lower part of the corn stalk and then move to the higher leaves as the disease progresses. Gray leaf spot can be detrimental to yield, and disease severity depends on hybrid susceptibility and environmental conditions. According to Purdue University Extension, the lesions on an infected plant can reduce the number of photosynthetic areas on leaves, which leads to fewer carbohydrates available to the developing grain. Scouting for gray leaf spot should take place a few weeks before and after tasseling around the V15 to R4 stage.

Like gray leaf spot, tar spot overwinters in corn residue. It is caused by the fungus Phyllachora maydis, and hot, wet conditions accelerate its spread. If left untreated, tar spot can cause leaf deterioration, poor grain fill, comprised stalks and even plant death. A severely impacted field can reach yield losses upwards of 60 bushels per acre. Tar spot symptoms include small, raised black spots that resemble fisheyes scattered on both sides of leaves. Scouting for the disease is recommended between the R3 and R6 growing stages.

Northern corn leaf blight is a common corn disease caused by the fungus Setosphaeria turcica. The disease thrives in cool, wet conditions and has a disease cycle similar to gray leaf spot and tar spot as it overwinters in the ground in corn residue. Northern corn leaf blight can be detected by tan streaks or lesions that are parallel to the leaf structure. Symptoms usually first appear on the lower leaves. The best time to scout for northern corn leaf blight is from V15 through R4.  

Common rust in corn is caused by the fungus Puccinia sorghi and occurs every growing season. It is environmental and prolific in cool, wet conditions. It is rarely harmful to yield compared to grey leaf spot, tar spot and northern corn leaf blight. Common rust symptoms occur between V12 and R4 and include sporadic rust-colored pustules, which can be detected on both sides of the leaves.

HOW TO CONTROL COMMON DISEASES OF CORN

Proper corn disease management involves selecting corn products with genetic resistance to these diseases, using best management practices, such as tillage and crop rotation, and timely application of seed fungicides. Planting corn after corn is discouraged due to diseases lurking in crop debris. Additionally, avoiding poorly drained soils can prevent some diseases from taking over your crops. Planting at the right time and when the weather outlook is favorable can help keep diseases at bay. Early planting is recommended unless soils are excessively cold and wet.

Stine offers high-performing seed corn with the industry’s most desirable trait packages to help combat disease and yield loss. Reach out to your local Stine agronomist or sales rep for more information on how to treat common corn diseases and prevent them from infecting your crops next year.

Growers in the Midwest considering another corn-on-corn year may wish to consult their local agronomist or university extension specialist before planting. According to the 2022 Regional Corn Rootworm Monitoring Network Summary issued by the Corn Rootworm IPM Regional Working Group, corn rootworm populations are anticipated to be high again in areas of Iowa, Wisconsin, Minnesota, Michigan, Nebraska, Illinois, North Dakota, South Dakota, Nebraska and Kansas. These states are at an elevated risk as they produce a lot of corn-on-corn acres, and findings show that rootworm is becoming more resistant to the Bt trait.  

The report highlights, “Western corn rootworm (WCR) and northern corn rootworm (NCR) continue to dominate as economic pests throughout the U.S. and Canada … Recently, high corn rootworm populations and the development of resistance to Bt corn hybrids in some areas has sparked greater interest in scouting and alternative management of corn rootworms.”

Stine^® agronomists are on heightened alert as they have monitored the rootworm crisis in their regions and continue to spread word of the potential for yield loss if not properly managed. According to the Crop Adviser Institute, rootworms cause more than $1 billion in damage and control costs annually in the U.S..

“With each passing year, we see the rootworm population increasing throughout the Corn Belt,” says Tom Larson, Stine’s director of agronomy. “Unfortunately, as we know well, these pests can devastate a crop. If you haven’t started planting yet, it’s not too late to consider a switch to soybeans on fields that experienced high rootworm pressure last year. If you’ve already planted corn-on-corn this year, talk to your local agronomist or extension expert to discuss what can be done in-season to slow the spread.”

2022 Findings
According to the 2022 results, 38% of sites tested exceeded the trapping threshold. The report notes, “For corn, the trapping threshold is 2 beetles/trap/day, regardless of species. For soybean, the trapping threshold is 1.5 western corn rootworm/trap/day; no soybean sites exceeded the threshold. These trapping thresholds indicate that the grower should consider switching up management practices the following year, because adult populations indicate that egg-laying in the field will likely result in severe larval injury the following year if corn is planted.”

Other report findings concluded western corn rootworm is the most dominant species throughout the Corn Belt but populations of northern rootworm are increasing, and fields with a history of corn rootworm are likely to have continuous issues with populations in the future. Of the sites that exceeded the trapping threshold, at least 59% were in continuous corn.

The most common issues reported in infected fields included goosenecking/lodging, high beetle populations or a combination of the two. Another reported issue was resistance to the Bt trait, which is problematic as growers have relied on the trait to suppress populations in difficult fields for  several years.  

“These findings align with what experts have been warning growers about,” says Larson. “Corn rootworms are not to be taken lightly. If it’s a problem one year, it will be a problem the next.”

Scouting tips
There are two types of corn rootworm prevalent in the Midwest — Western and Northern. Both are capable of laying eggs that can overwinter in the soil, so early-season scouting should include digging below the soil to check the roots of the plant. Later in the season, as they transition from larvae to adult rootworm beetles, they can be found directly on the plant as they feed off the leaves and silks as adults. This can greatly affect pollination during silking. 

“Early in the planting season, you’ll want to scout for the rootworm larvae by digging the soil around the corn plant,” says Larson. “Iowa State University Extension and Outreach has some great guidance for sampling, including the ‘float test,’ which involves filling a bucket of water and placing the soil and roots directly into the bucket so the larvae float to the top. This can help you detect any root damage to the plant.”

Iowa State also has an interactive node injury scale, which can help growers decipher the level of damage caused by corn rootworm larvae.

Later in the growing season as plants near silking and pollination, growers should be on the lookout for adult rootworm beetles. Western corn rootworms — the most commonly reported — are typically yellow or green and have black striping on their wings. Northern corn rootworms are light green or brown with no distinguishable marks. There are also Southern corn rootworm beetles that aren’t as common in the Midwest. These are yellow and green and have black spots on their backs.

“If you’re scouting for adult beetles, you’ll want to consider the time of day,” says Larson. “Research shows beetles are more active in the morning or late afternoon as they feed on silks and leaves, so it’s best to scout during their most active times.”

In addition to scouting, growers can employ sticky traps, which can help determine the amount of infestation. Sticky traps were one of the methods used by the Corn Rootworm IPM Regional Working Group for their 2022 findings report.  

Mitigation
“It’s clear that back-to-back corn-on-corn is an instigator when it comes to adding to the corn rootworm problem,” says Larson. “Crop rotation will continue to be critical in controlling populations.”

If crop rotation isn’t a viable strategy this year, growers need to prioritize scouting throughout the growing season. If rootworm larvae or beetles are detected, the next step would be to examine the level of infestation. From there, having a conversation with an agronomist or local extension expert can help determine next steps. One in-season strategy they might recommend is a soil- or foliar-applied insecticide. While it’s not the end-all strategy, it can help control the population throughout the important pollination stage.

“The biggest action growers can take is to plan ahead,” says Larson. “What you can do in season is minimal, so growers need to spend time discussing crop rotation and what traits make the most sense to plant next year. We know Bt traits are showing some signs of resistance, but there are likely other options growers haven’t discussed with their salesperson. Stine has an entire lineup of  Agrisure Duracade^® brand corn, for example, which has proven effective in mitigating corn rootworm. It’s definitely worth the conversation.”

One consideration to keep top of mind when discussing future strategies, according to the 2022 report, “Extension professionals do not recommend using multiple tactics to manage corn rootworm as research demonstrates no yield benefit, no reduction of larval feeding injury, and no reduction in adult emergence when both a Bt-rootworm hybrid and soil-applied insecticide are used. Furthermore, multiple management tactics could hasten resistance development.”

For more tips on preparing your fields for corn rootworm infestation this year and next, contact your local sales rep. Stine can help you maximize the potential of each and every acre by keeping corn rootworms at bay.