Tag: stress

Yield Impact on Heat and Drought-Stressed Soybeans

Andrew Kness, Agriculture Agent
University of Maryland Extension, Harford County

According to the latest Drought Monitor report, approximately 43% of Maryland is experiencing abnormally dry to moderate drought conditions, predominantly in the central, western and southern eastern shore parts of the state. Rainfall has been sporadic in areas and July 2020 went down as the hottest month on record in Maryland since 1872. Because soybeans flower over several weeks, they can compensate for periods of drought better than crops with a short pollination period, such as corn. As a result, yield impacts from heat and drought stresses can be variable in soybean and difficult to predict.

Soybeans require between 0.25-0.33 inches of water per day, and photosynthesis peaks around 85°F. Further, soybeans are less sensitive to high nighttime temperatures than corn. However, when temperatures peak into the 90s and soil moisture becomes limited, soybeans will become stressed. In an attempt to conserve water, stomata will close, which also inhibits CO2 exchange and thus slows photosynthesis, leading to reduced growth. Soybeans will also allocate more energy to growing roots rather than vegetative tissue.

If drought conditions persist, leaves will begin to invert, exposing their silvery underside (Figure 1). The underside of the leaves reflect more light and helps to reduce water loss in the plant. The middle trifoliate of the leaf will also move upwards or flop over to cover one of the other trifoliates to help shade the leaflets (Figure 1). Nodulation and nitrogen fixation will also be reduced if high temperatures and low moisture persist, further inhibiting growth.

close-up of soybean leaf
Figure 1. Drought-stressed soybeans exposing the undersides of their leaves.

If heat and drought occur during the reproductive phases, soybean plants will abort flowers and pods. Even under perfect growing conditions, soybeans do not have the genetic potential to turn every flower into a seeded pod, so depending on the amount of stress, they will abort between 20-80% of their flowers. Indeterminate varieties have a longer flowering period, therefore if moisture returns, the plant can fill new pods and the effect on yield may not be significant. Furthermore, if moisture returns around R5 (beginning seed), a loss in yield from reduced pod number can be compensated by increased seed size. If drought conditions are present during pod fill, seed size may be reduced. Make sure your combine is adjusted accordingly to ensure that small-seeded beans are not going out the back of the combine.

Overall, the greatest yield reductions in soybean from drought stress occurs between R4-R6. If soybeans have a reduced pod set from stresses during flowering, good yields can still be achieved if soil moisture is adequate between R4-R6. If you intend to gauge soybean yields in the field, it is best to wait until R6. Soybean yields can be difficult to estimate from a field assessment, but this article written by Kelly Nichols provides guidance: https://blog.umd.edu/agronomynews/2018/09/07/estimating-corn-and-soybean-yields/.

 

The Fungicide Conundrum When It’s Hot and Dry

Andrew Kness, Agriculture Agent
University of Maryland Extension, Harford County

As corn and soybeans begin to enter reproductive growth stages, foliar fungal diseases can have a serious impact on yield if growing conditions favor their development. However, with the hot and dry weather, disease pressure is low and will remain low if these weather patterns persist. Weather patterns in the Mid-Atlantic can switch rapidly and in general, fungicides need to be applied as a protectant, so spray decisions need to be made before the onset of disease. Coupled with the fact that many new fungicides on the market today are promoted to help plants cope with stresses, such as drought and heat, can complicate the decision.

I like to remind folks that fungicides are designed to do one thing—and that is to manage fungal diseases; they do this job very well. Hundreds of university trials have demonstrated that the most likely yield response and economic return occurs when fungicides are applied at the correct time and used when disease pressure is high. When disease pressure is low, yield responses sometimes occur, but are far more inconsistent than when disease is present.

There is also limited university data regarding fungicide utility to help plants manage drought stress. In the lab, strobilurin and triazole fungicides have been shown to regulate stomatal conductance and photosynthesis intensity in some corn hybrids, which improves the plants response to drought. However, when conducted at the field level, results are inconsistent and do not occur predictably. More research is needed to determine if fungicides can improve yields in drought conditions, and if so, when the application should be made. Existing studies indicate that the fungicide needs to be applied before drought stress occurs in order to stimulate the appropriate response in the plant; which again, makes spray decisions difficult without a crystal ball in hand to see into the future.

Another consideration, and perhaps the most important, is economics. While a fungicide application may provide some measurable differences in appearance and/or yield, is it enough to cover the application cost? Again, this is a tricky question to answer, but the body of research indicates that a single fungicide application in corn around VT-R1 and R1-R3 in soybean is the most likely to provide an economic return on investment when disease is present. In the absence of disease, the probability of an economic return is very low. Here are some additional factors that you should account for when considering a fungicide:

  • Crop history and tillage: Many fungal pathogens of corn and soybean are residue-borne. If growing corn-on-corn or soybeans after soybeans, those fields will be prone to higher disease risk. Conservation tillage fields are also at higher risk.
  • Irrigation: In dry years, fields that are overhead irrigated will be at higher risk of developing fungal diseases than dryland fields.
  • Disease progression: Scout your fields and see if and where fungal lesions are present on the plants. Many of the most important diseases of corn and soybean start low in the canopy and progress up the plant if environmental conditions are conducive (Fig. 1). For soybean it is critical to keep the top ⅓ of the plant clean of disease from flowering to pod fill; and for corn, it is critical to keep the ear leaf clean. If you notice fungal pathogens encroaching on these upper plant parts as they begin to flower and tassel, a fungicide application may be beneficial to protect yield.

    Grey leaf spot lesions on a corn leaf and froyeye leafspot lesions on a soybean leaf
    Figure 1. Two economically significant diseases of corn and soybeans: grey leaf spot lesions on corn (left) and frogeye leaf spot lesions on soybean (right).
  • Hybrid and variety resistance: Pay attention to your corn hybrid and soybean variety foliar disease ratings (resistance ratings are disease-specific); those that are more susceptible will have the greatest chance of an economic return on investment to a fungicide application than resistant varieties. Planting resistant varieties and hybrids is one of the most effective disease management tools.
  • Resistance management: It is generally considered bad practice to spray a fungicide when disease potential is low, as you are exposing pathogens to unnecessary chemistry, and with each exposure you drive the population towards resisting that chemical. This is why it is important to rotate modes of action and use full label rates, as cut rates can accelerate the development of resistance. The Take Action website (https://iwilltakeaction.com/) can help you choose products with differing modes of action.

The take-home message is to realize that you have the greatest chance for an economic return on your investment with a fungicide application when disease actually develops. Applying a fungicide to help plants cope with drought stress will likely not help to a degree that covers the cost of the application; as replicated field trials have yielded inconsistent and unpredictable results.

 

 

How will this hot, dry weather impact corn yield?

Nicole Fiorellino, Assistant Professor & Extension Agronomist
University of Maryland, Dept. of Plant Science and Landscape Architecture

The conditions this growing season have been a major improvement over the conditions we experienced during the 2018 growing season. Generally, the spring weather was favorable for timely planting of corn on the upper and mid-shore, southern Maryland, and northern Maryland regions, with other regions not lagging far behind. The 2019 growing season has generally been good to us, there was early optimism in the monthly crop reports, but by the end of June, warm and dry weather began around the state. Some areas may have received some spotty thunderstorms throughout July, but the July crop reports indicated droughty conditions throughout the state. As we enter into a new month with minimal precipitation thus far, farmers are concerned about the effects from the prolonged dry and warm conditions on corn yield.

Drought-stressed corn in vegetative growth stage
Drought-stressed corn in vegetative growth stage. Image: A. Kness, University of Maryland.

Warm temperatures and low rainfall cause stress to growing crops and this weather stress can be a major problem prior to pollination, as stress during this stage will impact the potential number of kernels per row. Warm temperatures, specifically, can cause corn plants to utilize more energy to carry out normal functions. Low rainfall can cause corn ear tips to lose kernels. Poor root development, from poor planting conditions and soil compaction early in the season, can amplify the effects of weather stress observed later in the season. But generally, the potential impact on corn yield from warm, dry weather will depend on the maturity of the corn crop when it experiences the weather stress.

Corn is particularly sensitive to weather stress during the late vegetative growth stages when the number of kernels is determined. Four days of weather stress between V12 and V14 could reduce yields 5 to 10%. Even into tassel emergence, total number of kernels can be affected, with yield reduction from 10 to 25% with four days of weather stress at this stage. Silk emergence and pollination is a critical period of moisture use in corn, with weather stress affecting pollination and leading to kernel abortion – four days of stress during silking could reduce yields up to 50%. Generally after pollination, reduced kernel fill can be expected during weather stress, with four days of weather stress post-pollination possibly reducing yields 30 to 40%. During blister and milk stages, kernel abortion is a concern during weather stress, while shallow or unfilled kernels can occur with stress during the dough stage, and reduced kernel weight is a concern during dent.

In summary, there is potential for reduction in corn yield due to the hot, dry weather but the impacts differ based on the maturity of the corn when it experiences the stress. Weather stress during silking and pollination can have the most severe impact on yield potential, with impacts from weather stress decreasing as corn moves further into reproductive maturity.

University of Maryland Extension Releases Farm Stress Management Online Resources

The University of Maryland Extension (UME) announces the release of a new web page devoted to assisting farm families in dealing with stress management through difficult economic times.
“Farm Stress Management,” released in conjunction with National Suicide Prevention week Sept. 9-15, is a set interdisciplinary resources to help farmers navigate the numerous publications online and provide timely, science-based education and information to support prosperous farms and healthy farm families.

Farm families are feeling the stress of an inconsistent and unreliable economy; declining incomes, several years of low commodity prices, and increasing costs have all led to worsening debt issues. Farmers have been forced to parcel off their land, file for bankruptcy, and take secondary jobs off the farm to provide supplemental income. Access to affordable and effective health insurance and care is one of the top concerns among farmers who are often self-employed. Providing health insurance, disability coverage, and planning for retirement and long-term future care have also proven problematic. In fact, in a USDA-funded study, 45 percent of farmers were concerned that they would have to sell some or all of their farm to address health-related costs.

The new web pages offer resources to manage farm stress through a variety of subject areas including financial management, legal aid, mediation, stress and health management, and crisis resources for families dealing with depression substance abuse, mental health concerns. Farms have a special role in American society and are critical to our national and local economies. With world populations expected to increase to a predicted 9 billion by 2050, farmers become even more crucial for feeding our communities. Healthy farms and healthy farm families promote
rural community growth, environmental stewardship and cultural legacies.

The new UME online resources can be found at:
https://extension.umd.edu/FarmStressManagement.
For more information, please contact Laura Wormuth, UME Communications Coordinator, at 301-405-6869 or lwormuth@umd.edu.