Fig. 1. Bipolaris infected bermudagrass. Moderate infection on bermudagrass leaves (1a) and in the stand (1b). Photo by Cheryl Mackowiak and Ann Blount
Cheryl Mackowiak, UF/IFAS Soil Fertility/Water Quality Specialist), Ann Blount, UF/IFAS Forage Breeding Specialist
With the hot, humid and rainy return of summer, livestock producers can expect forage leaf and root diseases outbreaks in pastures. Some of our most common forage diseases come from fungal organisms, but fungicides are rarely applied due to cost and label restrictions on livestock grazing. Grass forages can be attacked by foliar or soil-borne fungal diseases.
One of the most commonly identified foliar diseases in our summer pastures is leaf blight, also known as Bipolaris or Helminthosporium (Bipolaris cynodontis). It is often found in bermudagrass, star grass, and limpograsses, but not as much in bahiagrass. Early symptoms appear as dark brown specks that enlarge over time into irregular blotches or lesions as the disease progresses (Fig. 1 above). Grazing or mowing off the field (removes the fungal inoculant) helps to limit damage, but also reinforces the need to review your fertilizer practices. Low soil potassium and/or sulfur is quite often associated with these outbreaks.
Fig. 2. Rust in bahiagrass. Rust pustules on individual leaves (2a) and in the stand (2b). Photo by Cheryl Mackowiak and Ann Blount
Leaf rust (Puccinia cynodontis) is a foliar fungal disease that attacks bermudagrass, star grass, and limpograss. This disease is most often observed from mid to late summer. The disease begins as small, dark brown to orange specks (pustules), similar in appearance to Bipolaris when observed from a distance (Fig. 2). However, if observed with a magnifying glass, you may notice that the pustules are raised above the leaf surface (Fig. 2). Sometimes they will leave an orange-brown residue (spores) on your fingers when you rub the leaves. Alicia and Jiggs bermudagrass tend to be more prone to rust. Grazing or cutting off the inoculant and managing for adequate potassium and sulfur soil fertility sometimes helps to minimize damage.
Fig. 3. Dollar Spot in bahiagrass. Infection of leaves (3a) and in a thinning stand (3b). Photo by Cheryl Mackowiak and Ann Blount
A common foliar fungal disease in bahiagrass is Dollar Spot (Sclerotinia homoeocarpa), but it is much less prevalent in the Argentine (wider leaf) variety. Pensacola, Tifton-9, Tif-Quik, and UF-Riata are examples of more susceptible varieties. The disease begins with dead and dying leaf blade tips and tan lesions further down the leaf blade (Fig. 3). Dollar spot can spread quickly under ideal conditions and it is not uncommon to lose large swaths or entire fields to the disease over several weeks, if it is not managed. Disease expression is strongest under moderate to warm temperatures, high humidity, soils that have been periodically dry, with excessive thatch residue. Deferred grazing or hay cuttings leading to rank growth that can also lead to outbreaks. Grazing or cutting to remove the inoculum may reduce disease spread and helps with recovery. Balanced soil fertility also helps.
Fig. 4. Take-All disease in bahiagrass. Beginning of root die-back (Fig. 4a) and eventual stand loss (Fig. 4b). Photo by Cheryl Mackowiak and Ann Blount
There are several fungal root diseases that may infect our summer forage grasses. Early symptoms of an outbreak can appear as small to large circles of weak or dying forage (Fig. 4) or you might observe bright yellow leaves (looks like iron deficiency) in the case of bahiagrass (Fig. 5). Root fungal diseases identified by the UF-IFAS Plant Pathology Diagnostic lab in 2018 this far include Fusarium spp., Rhizoctonia spp., and Take-All (Gaeumannomyces graminis var. avenae), root rot type diseases. Take-All is particularly insidious because it may infect a field in the fall, near the time of plant dormancy and go unnoticed until the next spring or early summer, when the stand is already severely damaged. High pH soils (above 6.5) with low manganese fertility have sometimes been associated with Take-All outbreaks in turf grasses. Further study on the most damaging root rot diseases impacting forage grasses and management options to lessen their impact is needed.
Fig. 5. Early symptoms of a root rot disease in bahiagrass in late summer. Sometimes the yellowing will not get worse and the stand will recover without further intervention. Photo by Cheryl Mackowiak and Ann Blount
There is good news! Forage producers can often lessen the occurrence and impact of pasture fungal diseases by managing for optimal soil fertility. Sampling soils every year or so and following the soil report fertilizer and liming recommendations is a good starting point. Additionally, by practicing good grazing management and not allowing hay fields to become overgrown will often limit fungal disease damage to tolerable levels. If you suspect a disease is behind your pasture or hay field decline, visit with your local county extension agent. They will help you determine where and how to sample for a disease diagnosis, if needed, and review your forage management to determine if there are other underlying factors resulting in poor stand health. Since some of these diseases can spread fast and kill your stand, you might not be able to wait for an extension visit. In those situations, take a few photos with your camera or phone (close-up of symptoms and field-scale), send them to your local county extension agent, and then cut or graze off the grass as soon as possible (within a day or two) to help reduce fungal inoculum and to lessen long-term impact.
Cheryl Mackowiak, UF/IFAS NFREC Soils Specialist
As producers near the end of cover crop and cool-season forage planting in the Southeastern U.S., it is time to focus on fertilization. Depending upon your state, extension professionals have establish guidelines for how much and when to apply nitrogen (N), phosphorus (P), and potassium (K) fertilizers to meet crop demands. For example, annual ryegrass and small grains (i.e., wheat, oat, rye, triticale) planted on tilled land often benefit from split N rates such as 30 lbs N/acre at or near planting and another 40 to 50 lbs N/acre after establishment. Overseeded pastures may get by with an initial 30 lbs N/acre, but often 50 lbs N/acre is applied once the cool-season grass has emerged with another 50 lbs N/ac applied after repeated grazing to help support regrowth in spring, when winter forage is the most productive. In comparison, P and K applications are based upon soil sampling and your soil report recommendations. These nutrients are typically applied only once in the fall (if needed), and combined with your first N application.
Frequently, a call comes in that a farmer’s winter grass forage does not seem to be responding to N fertilizer. They have met or exceeded the N fertilizer recommendations and yet, the plants remain faded looking and stunted. The first question I ask: “How much sulfur (S) was applied?” Sulfur deficiency can often be mistaken for N deficiency in both, summer and winter grasses. We typically see more problems in winter grasses, because of where the grasses are planted and the previous season land-use. If none of your N fertilizer was applied as ammonium sulfate, or your K fertilizer did not contain potassium sulfate, SolPoMag, or a similar sulfate fertilizer, your grass may be suffering from S deficiency. The good news is that many grass species respond quickly to S fertilization, and an application rate as low as 10 lbs S/acre is often all that is required for recovery. An application of 10 to 20 lbs S/acre will hardly be noticed in your fertilizer bill.
Fig. 1. Nitrogen deficiency due to a faulty fertilizer applicator. Areas of stunted growth are relatively large and plants in the deficient areas appear more uniform than under S deficiency. Credit: Cheryl Mackowiak
Fig. 2. Mechanically induced N deficiency (strips of ample growth alternating with growth suppression). Credit: Cheryl Mackowiak
Both, N and S nutrient deficiencies will result in stunted growth, and a yellow color. However, if it is N deficiency, it is more typical that the field canopy will appear uniformly yellow over large areas, or you will observe straight line streaks where the fertilizer truck may have overlapped with the previous pass (Figs. 1 and 2). Upon closer inspection, the lower (older) leaves of N deficient plants will be lighter green or even yellow (Fig. 3).
Fig. 3. Close-up of N deficiency, with older (lower) leaves lighter or sometimes yellow, compared to more recently emerged leaves. Credit: Cheryl Mackowiak
With Sulfur (S) deficiency, the field will have a splotchy or mottled appearance, and sometimes the affected plants are intermixed with healthy looking plants (Fig. 4). Upon closer inspection, the newer leaves on individual plants may be lighter green than the older, or more basal leaves (Fig. 5).
Fig. 4. A small grains study site displaying classic S deficiency symptoms. Credit: Cheryl Mackowiak
Fig. 5. Individually affected plants will appear uniformly lighter green, or younger leaves may be lighter colored than older leaves. A visually healthy plant may grow adjacent to an impacted plant. Credit: Cheryl Mackowiak
Conditions that may lead to S deficiencies include, the lack of at least 10 lbs S, in sulfate form, as part of your fertilizer blend (elemental S will not provide a quick enough response), planting on row crop land, or planting on new land that had been forest or pine plantation (often locations for wildlife food plots). Well-managed pastures are less likely to suffer from S deficiencies, since livestock excreta contributes S to the soil. Not all labs analyze for soil S, so the safe bet is to include a small amount (10 to 20 lbs S/acre) of sulfate S in your fertilizer blend. Check the fertilizer label if you purchase bags, or make the request when you hire custom fertilizer spreading. If you have to apply the S fertilizer yourself (small areas), you can purchase SulPoMag, potassium sulfate, calcium sulfate (i.e., gypsum), or magnesium sulfate at many feed and seed stores. Remember, cool-season legumes (clovers, vetch, peas, etc) benefit from 20 lbs S/acre fertilization, as well!
For more information related to this subject, use the following UF/IFAS publication links:
Cheryl Mackowiak, Soils Specialist
Fig. 2. Argentine bahiagrass under different management. From left to right: Over-grazing (>80% forage removed weekly), recommended grazing (50% of forage removed weekly), and no grazing (forage not removed).
It is June and we are fast approaching the longest day of the year (June 21st). You may wonder what day length has to do with timing your fertilizer applications. In general, perennial pasture grasses are photoperiod sensitive. In other words, their growth and flowering (seed head formation) respond to day length. This is why you often cannot grow the same amount of grass in March or October as you can mid-summer, even under unseasonably warm temperatures (Figure 1). Can we use this information to better manage our summer pasture fertilization? Perhaps…
Fig. 1. Argentine bahiagrass grown as hay at three Florida locations in 2006 to test Potassium (K) fertilizers. The treatment receiving no nitrogen fertilizer (No fertilizer) also demonstrated a growth response to day length, even though it was comparatively less. Different lower case letters represent treatment differences at each location.
Nitrogen (N) is the fertilizer nutrient required in the largest amount by pasture grasses, and where we often see the largest forage yield gains with increasing application rates (up to a few hundred pounds of N per acre, per season). If more of the season’s N is applied when the grass has the genetic potential to grow more forage (June/July), then we should increase seasonal yield, but it will be concentrated during the height of the growing season. If there is not enough livestock to graze it, or an ability to hay it, then that additional forage growth will be wasted. In those cases, a higher proportion of N fertilizer applied mid-season may not benefit your operation. In fact, in the case of a well-managed bahiagrass pasture (has healthy rhizome/roots), N timing may have little measurable difference in forage yield.
There is some supporting evidence of this found in the works of Dr. W.G. Blue during the 1980s. He speculated the massive rhizome/root structure of a well-maintained bahiagrass pasture can effectively absorb soil N when it is available, whether applied in spring or early summer, and store it for later use, more so than many other perennial summer forage grasses. However, it also needs mention that the potential genetic limit of forage yield from bahiagrass grown under optimal conditions does not match the maximum forage yield of some other improved pasture grasses, such as bermudagrass, limpo grass, or star grass cultivars.
In general, it is often recommended that you make your first fertilizer applications around the time of pasture green-up, which may occur as early as February/ March in south Florida or as late as April for locations further north. A small flush of new root growth also occurs during this period to help deliver emerging shoots the water and essential nutrients they need to begin the new season’s growth. As the spring green-up proceeds, the grass will begin replacing that borrowed energy taken from the rhizomes via photosynthesis.
A well-managed bahiagrass pasture will have a massive amount of rhizomatous storage capacity. However, if you have low energy reserves in your roots/rhizomes because of a history of poor soil fertility and/or over-grazing, your grass will suffer from it the following growing season (Figure 2). Weak plants are much more susceptible to pests, diseases, and weed encroachment. They also cannot as easily escape brief periods of drought or low fertility by growing more and deeper roots to better mine soil resources.
Management Considerations and Recommendations:
Follow the soil fertilization recommendations given for pastures in your area, and in particular, recommendations given in your soil fertility report. For example, University of Florida IFAS has published recommendations for bahiagrass pastures and management scenarios that cover low, medium, and high degrees of management/inputs, as well as grazing mixed with periodic hay removal. Please refer to the following publication for additional information: UF/IFAS Standardized Fertilization Recommendations for Agronomic Crops
Your local county extension office have staff and contacts who can help you interpret your soil report (once you sample your soils!) and provide general fertilizer rate recommendations that were developed for your region. Keep in mind that haying actually exports, from the field, relatively large amounts of fertilizer (often 2% of nitrogen and potash and 0.3% phosphate) per pound of dry hay (0% moisture), while grazing recycles most of the plant nutrients via excreta (urine and manure).
Questions are often raised on whether to adjust fertilizer application timing in regards to wet versus dry periods. Commercial, soluble, mineral fertilizers are supplied as salts and these salts need to dissolve in water in order to release the nutrients in a form the plant roots can take up. Even organic fertilizer sources will first mineralize the nutrients into inorganic forms that the plant can take up. The soil microorganisms needed for mineralization also require water. If you foliar apply fertilizer, the plant still needs water to carry out its physiological processes with the applied nutrients. As a general rule, it is often better to wait until you have sufficient soil moisture to support plant growth prior to fertilizing. If you are applying fertilizers other than nitrogen, you will not lose your fertilizer during a dry period. Urea nitrogen, however, can volatilize if left on the soil surface, thereby losing fertilizer value. Do not forget that exceedingly high nitrate accumulation in pasture plants is more likely to occur when nitrogen fertilizer is applied during periods of plant stress, such as water stress.
The biggest concern when applying fertilizers during exceedingly wet periods is the chance for nutrient losses through run-off or leaching. This is particularly true with nitrogen, but also potassium, sulfur, and sometimes even phosphorus can be washed or leached away from the plant. Lost fertilizer is bad for both the producer and the environment.
If my pasture is weak because I have continually over-grazed (did not allow recovery periods), then I will likely gain much more yield this season by changing my grazing practices (permanent or temporary cross-fencing) than I will by increasing fertilizer applications or changing application timing. If my pasture is weak because I applied only nitrogen (no other nutrients) year after year, then my best course of action is to soil and tissue sample to assess and address potential soil fertility imbalances. A soil and forage tissue test often costs less than $20 apiece, while thousands of dollars can be lost each season by applying what is not required or through lost revenues via livestock gains or additional pasture treatments (herbicides, etc.). Considering the many environmental factors affecting perennial pastures, and adopting research-based recommendations and management will keep you in the green!
The exceptionally dry fall, followed by above average rainfall in December surprised many and it has been problematic for those trying to plant and manage winter cover or forage crops. Many might be wondering if their soils have enough moisture reserve to support a cover crop if you decide to try a late planting. This article provides some guidance on how to assess and track soil moisture without having to purchase expensive equipment. In fact, there are only two pieces of equipment required and the third is optional: 1) your fingers, 2) a rain gauge, and 3) internet access. You can roughly estimate soil moisture by the feel method and the rain gauge will help track future rain events. In addition, internet access will allow you to use some exciting and free AgroClimate tools related to rainfall and soil moisture.
Much of the surface soils (sandy to loamy sand textures) in the Florida Panhandle can hold from 0.6 to 1.2 inches of water per foot depth of soil. We call this the Available Water Capacity (AWC). In comparison, some of our heavier, sandy clay subsoils can hold up to 2 inches of water per foot depth of soil. Details on how to determine soil moisture by feel and appearance can be found in the following NRCS publication: Estimating Soil Moisture by Feel and Appearance
In Florida, you can conservatively assume that your top foot of soil will hold up to 1 inch of water. You also need an inexpensive manual-read rain gauge to track rainfall at your location. During the cold winter weeks ahead, your plants (at full canopy) may lose approximately 0.3 inches of water per week in North Florida and up to 0.5 inches of water, downstate. In comparison, these losses can triple during the summer months. For the sake of this discussion, if it does not rain over the next three weeks, you might lose all available water in the top foot of soil, because the plants had removed nearly an inch of water (0.3 inches x 3 weeks). Luckily, roots are often growing deeper than a foot. Well-managed, cool-season cover or forage crops will have roots reaching below 2 feet, so they likely can extract another inch or more of deeper soil moisture before succumbing to drought.
Remember, the soil drying front begins at the surface and works its way down the soil profile over time. Dry conditions hit plants hardest when you have seedlings with rooting depths of only a few inches, where soil drying initiates. As of late December, the Panhandle had begun to recover from the dry fall and you might find that seeds that did not germinate during the prolonged dry period, are now germinating and establishing (Fig. 1). If the seed had begun developing roots during the drought, then it likely died and will not come back. Remember that exceedingly late emerging plants will likely need a little start-up nitrogen (30 to 50 lbs per acre) to continue growing strong. They have to compete with weeds and the older crop.
Fig. 1. Cereal rye planting in October, as conditions turned dry. About half of the seeds did not germinate until rainfall returned in December. Photo taken December 10th, 2016. Photo: Cheryl Mackowiak
Soil moisture forecasting relies on expert knowledge of climate and weather, which is not what most of us are trained in. Luckily, we all have free access to AgroClimate Forecasting Tools. This site allows you to view maps of forecasted temperature and rainfall over short (day) through longer (months or seasonal) periods. After your first visit, you might become a real fan, like myself, and play with their other AgroClimate tools. I recommend the Lawn and Garden Moisture Index (LGMI). This provides a good estimate of current soil moisture conditions for plant growth in the southeast U.S. (Fig. 2).
Fig. 2. Source: University of Alabama at Huntsville, Alabama state climatologist Lawn and Garden Moisture Index (LGMI). Values in green represent adequate to abundant moisture, while yellow to red represent increasing soil moisture deficit.
They even have a drought index, called ARID that you can tailor to your location by providing zip code and choosing among soil types. There has never been a better time to take advantage of what extension and research are reporting and providing in terms of information and personal online tools to help keep you growing!
Exposed perennial peanut forage roots at 5 ft soil depth. (C.L. Mackowiak)
Forages, as with all plants, require light, water and nutrients. Even if you cannot control water inputs because you are on non-irrigated land, you may find it useful to know the water status of your soils to help estimate yields. Water deficits can lead to slowed growth and stunted plants. The plants may also show symptoms of nutrient deficiency and become increasingly susceptible to pests and diseases.
Field Capacity (FC) is a term used for a well-watered soil that no longer drains after a day. Basically, the gravitational pull downwards is in equilibrium with the ability of the soil pore space to hold water. Field capacity has a suction pressure of −33 J/kg (−0.33 bar), regardless of soil type. Finer textured (heavier) soils can hold more water at FC than coarser, sandier soils, but the plant water requirement is not affected by soil type. In practical terms, planted soils that hold less water (coarse textured soils) can become water deficient more rapidly than finer textured (heavier) soils.
You may wonder how much water your crop is removing from the soil each week and if there is enough water to support optimal forage growth and yield. Many use rain gauges to track rainfall, but not many of us know how much of that rainfall is being taken up or removed by the crop. Evapotranspiration is the sum of evaporation and plant transpiration to the atmosphere. Transpiration is the process of water movement through a plant and its evaporation as water vapor from pores (stomata) in its leaves. When water inputs, via rainfall or irrigation, are less than plant demand (evapotranspirational losses) the soil will become increasingly dry. If this continues for a long enough period (this might be only a few days in Florida), water deficits may develop and the plant will suffer. The greater the deficit, and the longer the period, the worse the effect will be on the plant. If water increases soil suction pressure to -1,500 J/kg (-15 bar), the plant reaches permanent wilting point (PWP) and it will not recover with re-watering.
In Florida and several other states, there are free access, online, weather station sites. In Florida we have Florida Automated Weather Network (FAWN). This site congregates weather data, including rainfall and evapotranspiration (ET), from over 40 sites across the state.The FAWN site provides both rainfall and estimated evapotranspiration on a daily basis. There are also coefficients available that improve the water demand estimates to specific crops at different growth stages, but the ET values from weather stations such as FAWN, are adequate assessments in many cases.
To illustrate how one might use this information, daily ET water loss at Quincy last week was approximately 0.2 inches per day (1.4 inches for the week) but rainfall was only 0.6 inches for the week, so plants were removing more soil moisture than was being replaced through rainfall, which is typical for mid-summer in the southeast. Florida sandy soils at FC may hold about an acre-inch (<1 inch for coarse sand to ~1.2 inches for loamy sands) of plant available water per foot depth of soil. This means that your soil can supply about 4 inches of plant available water in the upper 4 ft of soil. A two week period without rainfall at this time of year might remove 2.8 inches of water through ET. If your roots have a maximum root depth of 2 feet (because of continuous grazing without rest), your forages can suffer significant drought stress during a two week dry spell.
A deeper root system can be achieved by grazing only 50% of standing biomass at a time – “take half leave half”, or by allowing ample recovery time after grazing (2-3 weeks) or haying events (4-5 weeks). Root systems that reach 4 feet or deeper are more likely to survive dry spells of a week or two because their roots can reach deeper soil moisture (4 inches of plant available water in the upper 4 ft of soil versus only 2 inches in the upper 2 ft of soil). Managing your forage crop to grow deeper roots is one of the best ways to survive short-term droughts when irrigation is not available. Those who irrigate forages can replace some of the difference when rainfall falls short of ET. In the above example, there was a 0.8 inch water deficit. It might be wise to irrigate, unless additional rainfall is expected in the coming days. When weekly rainfall exceeds weekly ET, irrigation is not usually necessary.